Synapsin-3 (SYN3) is a neuron-specific, presynaptic vesicle-associated phosphoprotein that is a member of the synapsin family (SYN1, SYN2, SYN3). It maintains and mobilizes the synaptic vesicle reserve pool through phosphorylation-dependent mechanisms. Synapsin-3 negatively modulates dopamine release in dopaminergic terminals and controls recycling/reserve vesicle pool organization. The protein is phosphorylated by PKA at Ser9 and by Cdk5 at Ser404, which are essential for its roles in neuronal morphological maturation, axon specification, and neuronal survival. Unlike other synapsins, SYN3 shows precocious expression during development and is involved in early dopaminergic neuron development upstream of BDNF and Cdk5 signaling. The protein binds ATP (regulated by calcium) and interacts with alpha-synuclein, with implications for Parkinson's disease pathophysiology.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
|
GO:0030672
synaptic vesicle membrane
|
IBA
GO_REF:0000033 |
ACCEPT |
Summary: Synapsin-3 is a peripheral membrane protein localized to the cytoplasmic surface of synaptic vesicles. The original characterization paper states "Synapsin IIIa is associated with synaptic vesicles" [PMID:9539796]. The IBA annotation is phylogenetically inferred and consistent with the synapsin family function.
Reason: This is a well-supported core localization for Synapsin-3. The IBA annotation is consistent with experimental evidence from multiple studies and the UniProt subcellular localization annotation. Synapsins are peripheral membrane proteins on the cytoplasmic surface of synaptic vesicle membranes.
Supporting Evidence:
PMID:9539796
Synapsin IIIa is associated with synaptic vesicles, and its expression appears to be neuron-specific
|
|
GO:0097091
synaptic vesicle clustering
|
IBA
GO_REF:0000033 |
ACCEPT |
Summary: Synaptic vesicle clustering is a core function of the synapsin family. Synapsins are central organizers of the presynaptic vesicle cluster and reserve pool. The specific role of synapsins in maintaining the reserve pool through SV clustering is well documented in the literature.
Reason: This represents a core biological process for Synapsin-3. Synapsins maintain the synaptic vesicle reserve pool via SV clustering, and this function is conserved across the synapsin family. The IBA annotation is phylogenetically sound and consistent with literature evidence.
Supporting Evidence:
PMID:9539796
Synapsins are a family of neuron-specific synaptic vesicle-associated phosphoproteins that have been implicated in synaptogenesis and in the modulation of neurotransmitter release
|
|
GO:0050808
synapse organization
|
IBA
GO_REF:0000033 |
ACCEPT |
Summary: Synapsins contribute to synapse organization through their role in maintaining synaptic vesicle pools and presynaptic architecture. The original paper states synapsins have been "implicated in synaptogenesis" [PMID:9539796]. Synapsin-3 specifically contributes to presynaptic organization, though it has unique developmental roles.
Reason: This is an appropriate annotation at a general level for the synapsin family's role in organizing presynaptic structure. The IBA annotation is consistent with the established role of synapsins in presynaptic organization and vesicle pool maintenance.
Supporting Evidence:
PMID:9539796
Synapsins are a family of neuron-specific synaptic vesicle-associated phosphoproteins that have been implicated in synaptogenesis and in the modulation of neurotransmitter release
|
|
GO:0000166
nucleotide binding
|
IEA
GO_REF:0000043 |
ACCEPT |
Summary: Synapsin-3 has an ATP-grasp domain (C domain) that binds nucleotides, specifically ATP. This annotation is inferred from UniProt keywords. While ATP binding (GO:0005524) is more specific and accurate, nucleotide binding is not incorrect as a broader term.
Reason: The annotation is technically correct as a broader term encompassing ATP binding. Synapsins contain an ATP-binding domain in the conserved C region. While more specific annotations (ATP binding) also exist, this broader IEA annotation does not conflict with the known biochemistry.
|
|
GO:0005524
ATP binding
|
IEA
GO_REF:0000120 |
ACCEPT |
Summary: Synapsin-3 contains an ATP-binding domain in its conserved C region. The domain structure includes IPR013815 (ATP_grasp_subdomain_1) and IPR020898 (Synapsin_ATP-bd_dom). Calcium regulates ATP binding to this domain.
Reason: ATP binding is a well-supported molecular function for Synapsin-3 based on domain structure. The C domain (region 91-399) is annotated as "actin-binding and synaptic-vesicle binding" and contains ATP-grasp fold domains. The TAS annotation (below) provides literature support for this function.
|
|
GO:0007268
chemical synaptic transmission
|
IEA
GO_REF:0000117 |
ACCEPT |
Summary: Synapsin-3 is involved in chemical synaptic transmission through its role in regulating synaptic vesicle pools and neurotransmitter release. The synaptic vesicle cycle review describes how vesicles undergo a trafficking cycle to support rapid neurotransmitter release [PMID:15217342].
Reason: This is an appropriate biological process annotation. While the term is somewhat general, Synapsin-3 clearly participates in chemical synaptic transmission through its regulation of synaptic vesicle pools and neurotransmitter release dynamics. The IEA annotation is consistent with the core functions of the synapsin family.
Supporting Evidence:
PMID:15217342
To support rapid and repeated rounds of release, synaptic vesicles undergo a trafficking cycle
|
|
GO:0007269
neurotransmitter secretion
|
IEA
GO_REF:0000002 |
ACCEPT |
Summary: Synapsin-3 is involved in regulating neurotransmitter secretion. The original publication identifying SYN3 suggests synapsins are implicated "in the modulation of neurotransmitter release" [PMID:9539796].
Reason: This is a core function of the synapsin family. Synapsins regulate the transition of vesicles between reserve and readily releasable pools, thereby modulating neurotransmitter release. The IEA annotation is consistent with literature evidence.
Supporting Evidence:
PMID:9539796
Synapsins are a family of neuron-specific synaptic vesicle-associated phosphoproteins that have been implicated in synaptogenesis and in the modulation of neurotransmitter release
|
|
GO:0008021
synaptic vesicle
|
IEA
GO_REF:0000120 |
ACCEPT |
Summary: Synapsin-3 localizes to synaptic vesicles as a peripheral membrane protein. This is consistent with UniProt subcellular location annotation and literature evidence. The original SYN3 characterization paper explicitly states "Synapsin IIIa is associated with synaptic vesicles" [PMID:9539796].
Reason: Synaptic vesicle localization is well-established for Synapsin-3. The IEA annotation is consistent with experimental evidence and the TAS annotation for the same term (below). This represents a core localization for the protein.
Supporting Evidence:
PMID:9539796
Synapsin IIIa is associated with synaptic vesicles, and its expression appears to be neuron-specific
|
|
GO:0030672
synaptic vesicle membrane
|
IEA
GO_REF:0000120 |
ACCEPT |
Summary: This is a duplicate of the IBA annotation for the same term. Synapsin-3 is a peripheral membrane protein on the cytoplasmic surface of synaptic vesicle membranes. UniProt explicitly annotates this localization.
Reason: The annotation is correct and consistent with the IBA annotation for the same term. Both annotations support the well-established localization of Synapsin-3 to synaptic vesicle membranes.
Supporting Evidence:
PMID:9539796
Synapsin IIIa is associated with synaptic vesicles, and its expression appears to be neuron-specific
|
|
GO:0031410
cytoplasmic vesicle
|
IEA
GO_REF:0000043 |
ACCEPT |
Summary: This is a broader term that encompasses synaptic vesicles. Synapsin-3 localizes to synaptic vesicles, which are a type of cytoplasmic vesicle. The annotation is technically correct but less specific than the synaptic vesicle annotations.
Reason: While this is a less informative annotation compared to the more specific synaptic vesicle and synaptic vesicle membrane annotations, it is not incorrect. The IEA annotation derived from UniProt keywords is valid as synaptic vesicles are a subtype of cytoplasmic vesicles.
|
|
GO:0050804
modulation of chemical synaptic transmission
|
IEA
GO_REF:0000117 |
ACCEPT |
Summary: Synapsin-3 modulates synaptic transmission through its regulation of synaptic vesicle pools. Synapsins are implicated in "the modulation of neurotransmitter release" [PMID:9539796].
Reason: This is an appropriate annotation for Synapsin-3. The protein modulates neurotransmitter release by regulating synaptic vesicle pool dynamics. The annotation is consistent with the known regulatory role of synapsins in synaptic transmission.
Supporting Evidence:
PMID:9539796
Synapsins are a family of neuron-specific synaptic vesicle-associated phosphoproteins that have been implicated in synaptogenesis and in the modulation of neurotransmitter release
|
|
GO:0005515
protein binding
|
IPI
PMID:33961781 Dual proteome-scale networks reveal cell-specific remodeling... |
MARK AS OVER ANNOTATED |
Summary: This annotation is based on a high-throughput proteomics study (BioPlex 3.0) that detected SYN3 interaction with SYN2 (Synapsin-2). While the interaction is likely valid (synapsins can oligomerize), "protein binding" is too generic.
Reason: While the interaction with SYN2 is documented and synapsins are known to form oligomers, GO:0005515 "protein binding" is an uninformative term that does not capture the specific nature of the interaction. A more specific term such as GO:0042802 "identical protein binding" or a synapsin-specific binding term would be more informative if available.
|
|
GO:0005515
protein binding
|
IPI
PMID:40205054 Multimodal cell maps as a foundation for structural and func... |
MARK AS OVER ANNOTATED |
Summary: This annotation is from another high-throughput interactome study (Multimodal cell maps). The interaction partner is again SYN2 based on the GOA data. As with the previous annotation, "protein binding" is too generic.
Reason: Same rationale as above. While the protein-protein interaction evidence supports SYN3-SYN2 binding, the GO term "protein binding" is uninformative. The annotation could be retained for completeness but does not provide meaningful functional insight.
|
|
GO:0014069
postsynaptic density
|
IEA
GO_REF:0000107 |
REMOVE |
Summary: This annotation is transferred from mouse ortholog via Ensembl Compara. However, Synapsin-3 is characterized as a presynaptic protein associated with synaptic vesicles. The postsynaptic density is a postsynaptic structure, which conflicts with the established presynaptic localization.
Reason: This annotation appears inconsistent with the established presynaptic localization of Synapsin-3. Synapsins are well-characterized as presynaptic vesicle-associated proteins. While some postsynaptic localization cannot be completely ruled out, this conflicts with the primary literature characterizing SYN3 as a synaptic vesicle membrane protein. The annotation may reflect an error in the orthology transfer or proteomics detection of contamination.
Supporting Evidence:
PMID:9539796
Synapsin IIIa is associated with synaptic vesicles, and its expression appears to be neuron-specific
|
|
GO:0045202
synapse
|
IEA
GO_REF:0000107 |
ACCEPT |
Summary: Synapsin-3 is localized to synapses, specifically to the presynaptic compartment on synaptic vesicle membranes. This is a broad term that encompasses the more specific synaptic vesicle and synaptic vesicle membrane annotations.
Reason: This is a valid but broad localization annotation. Synapsin-3 is indeed present at synapses (specifically in the presynaptic terminal). The annotation is consistent with more specific annotations for synaptic vesicle localization.
Supporting Evidence:
PMID:9539796
Synapsin IIIa is associated with synaptic vesicles, and its expression appears to be neuron-specific
|
|
GO:0097091
synaptic vesicle clustering
|
IEA
GO_REF:0000107 |
ACCEPT |
Summary: This is a duplicate of the IBA annotation for synaptic vesicle clustering. The function is well-supported for the synapsin family.
Reason: Duplicate annotation supporting the core function of Synapsin-3 in synaptic vesicle clustering. Both IBA and IEA annotations converge on this core function.
Supporting Evidence:
PMID:9539796
Synapsins are a family of neuron-specific synaptic vesicle-associated phosphoproteins that have been implicated in synaptogenesis and in the modulation of neurotransmitter release
|
|
GO:0098850
extrinsic component of synaptic vesicle membrane
|
IEA
GO_REF:0000107 |
ACCEPT |
Summary: This is an excellent, specific annotation for Synapsin-3. UniProt explicitly states it is a peripheral membrane protein localized to the cytoplasmic surface of synaptic vesicles. This GO term precisely captures the extrinsic (peripheral) nature of Synapsin-3's membrane association.
Reason: This is the most precise cellular component annotation for Synapsin-3. Synapsins are peripheral membrane proteins (extrinsic), not integral membrane proteins, and they associate with the cytoplasmic face of synaptic vesicle membranes.
Supporting Evidence:
PMID:9539796
Synapsin IIIa is associated with synaptic vesicles, and its expression appears to be neuron-specific
|
|
GO:0098978
glutamatergic synapse
|
IEA
GO_REF:0000107 |
KEEP AS NON CORE |
Summary: This annotation suggests SYN3 localizes to glutamatergic synapses. Synapsins are present at various types of synapses. The literature emphasizes SYN3's role in dopaminergic neurons specifically, but this does not preclude presence at glutamatergic synapses.
Reason: While Synapsin-3 may be present at glutamatergic synapses (synapsins are generally expressed across synapse types), the literature specifically emphasizes its unique role in dopaminergic neurons. The annotation is not wrong but represents a non-specific localization rather than a core feature of SYN3 specifically.
|
|
GO:0099504
synaptic vesicle cycle
|
IEA
GO_REF:0000107 |
ACCEPT |
Summary: Synapsin-3 participates in the synaptic vesicle cycle through its role in maintaining vesicle pools and regulating vesicle mobilization. The synaptic vesicle cycle review describes how vesicles undergo trafficking for repeated rounds of release [PMID:15217342].
Reason: The synaptic vesicle cycle is a core process in which Synapsin-3 participates. By maintaining the reserve pool and regulating vesicle mobilization through phosphorylation-dependent mechanisms, synapsins are integral to the vesicle cycling process.
Supporting Evidence:
PMID:15217342
To support rapid and repeated rounds of release, synaptic vesicles undergo a trafficking cycle
|
|
GO:0005524
ATP binding
|
TAS
PMID:15217342 The synaptic vesicle cycle. |
ACCEPT |
Summary: This TAS annotation is based on the Sudhof synaptic vesicle cycle review (2004). Synapsin-3 has a well-characterized ATP-binding domain (C domain). Calcium regulates ATP binding to this domain.
Reason: ATP binding is a well-supported molecular function for Synapsin-3 based on domain structure and biochemical evidence. The C domain contains ATP-grasp fold elements (IPR013815, IPR020898) that are characteristic of ATP-binding proteins.
|
|
GO:0032228
regulation of synaptic transmission, GABAergic
|
TAS
PMID:15217342 The synaptic vesicle cycle. |
UNDECIDED |
Summary: This annotation suggests SYN3 specifically regulates GABAergic transmission. The Sudhof review (PMID:15217342) is a general review of the synaptic vesicle cycle and does not specifically address Synapsin-3's role in GABAergic synapses. The literature emphasizes SYN3's role in dopaminergic neurons rather than GABAergic neurons.
Reason: The cited reference (PMID:15217342) is a general review of the synaptic vesicle cycle that does not specifically address Synapsin-3 or GABAergic transmission. While synapsins are present at various synapse types including GABAergic synapses, there is no specific evidence in the available literature for a particular role of SYN3 in GABAergic transmission. The deep research specifically emphasizes SYN3's unique role in dopaminergic neurons. Additional evidence would be needed to confirm this specific annotation.
|
|
GO:0007269
neurotransmitter secretion
|
TAS
PMID:9539796 A third member of the synapsin gene family. |
ACCEPT |
Summary: This TAS annotation is based on the original paper characterizing Synapsin-3. The paper states that synapsins have been implicated "in the modulation of neurotransmitter release" and suggests a role for synapsin III based on similarity to other synapsins.
Reason: The original characterization paper predicted this function, which has since been confirmed by subsequent studies showing SYN3's role in regulating dopamine release and synaptic vesicle pool dynamics. This is a core function of the synapsin family.
Supporting Evidence:
PMID:9539796
The similarities among synapsins I, II, and III in domain organization, neuron-specific expression, and subcellular localization suggest a possible role for synapsin III in the regulation of neurotransmitter release and synaptogenesis
|
|
GO:0008021
synaptic vesicle
|
TAS
PMID:9539796 A third member of the synapsin gene family. |
ACCEPT |
Summary: This TAS annotation is based on the original paper characterizing Synapsin-3, which explicitly states "Synapsin IIIa is associated with synaptic vesicles." This is the primary localization for Synapsin-3.
Reason: Synaptic vesicle localization is directly stated in the original characterization paper and confirmed by subsequent studies and UniProt annotation. This represents the core localization for Synapsin-3.
Supporting Evidence:
PMID:9539796
Synapsin IIIa is associated with synaptic vesicles, and its expression appears to be neuron-specific
|
Q: What is the specific role of Synapsin-3 in GABAergic synaptic transmission?
Q: What is the functional significance of the SYN3-SYN2 interaction?
Experiment: Conditional knockout of SYN3 in GABAergic neurons to test role in GABAergic transmission. This would address uncertainty about the GABAergic-specific annotation.
Experiment: Structure-function analysis of SYN3-SYN2 heterodimers. This would elucidate the functional significance of synapsin heteromerization.
The research report should be a detailed narrative explaining the function, biological processes, and localization of the gene product. Citations should be given for all claims.
You should prioritize authoritative reviews and primary scientific literature when conducting research. You can supplement
this with annotations you find in gene/protein databases, but these can be outdated or inaccurate.
We are specifically interested in the primary function of the gene - for enzymes, what reaction is catalyzed, and what is the substrate specificity? For transporters, what is the substrate? For structural proteins or adapters, what is the broader structural role? For signaling molecules, what is the role in the pathway.
We are interested in where in or outside the cell the gene product carries out its function.
We are also interested in the signaling or biochemical pathways in which the gene functions. We are less interested in broad pleiotropic effects, except where these elucidate the precise role.
Include evidence where possible. We are interested in both experimental evidence as well as inference from structure, evolution, or bioinformatic analysis. Precise studies should be prioritized over high-throughput, where available.
Plan overview
Objective 1 (verification). The gene symbol SYN3 matches human Synapsin-3 (UniProt O14994), a member of the synapsin family expressed in neurons. Literature consistently places Synapsin-3 within the synapsin family (SYN1/2/3) that share conserved N‑terminal A–C domains and variable C‑terminal regions, supporting alignment with the synapsin family/domain organization provided. Organism confirmed: Homo sapiens (human) in reviews and primary studies cited below (family-level mechanisms are conserved and human relevance is discussed). No conflicting symbols or non-human ortholog misassignments were used. (zhang2021synapsinsandthe pages 1-2, song2015synapsinisoformsand pages 5-5)
Objective 2 (definitions, concepts, current understanding)
- Identity and family: Synapsin-3 (SYN3) is one of three vertebrate synapsin genes (SYN1, SYN2, SYN3). Synapsins are peripheral synaptic vesicle (SV) proteins that bind vesicle membranes via conserved N‑terminal A–C domains and engage protein/phospholipid/actin interactions; isoform‑specific functions are largely conferred by variable C‑terminal regions. Synapsins are major organizers of the presynaptic vesicle cluster and reserve pool. (zhang2021synapsinsandthe pages 1-2, song2015synapsinisoformsand pages 5-5)
- Subcellular localization and core role: Synapsins concentrate on synaptic vesicles within presynaptic terminals, particularly enriched in the distal SV cluster that corresponds to the reserve pool. Family‑level function includes maintaining vesicle clustering, supporting sustained neurotransmission by mobilizing reserve vesicles under demand. (zhang2021synapsinsandthe pages 1-2)
- Isoform-specific aspects for Synapsin-3: Synapsin-3 shows precocious, more broadly distributed expression during development and is detectable in neural progenitors; unlike Synapsin I/II, Synapsin-3 is not strictly confined to mature synaptic sites early on and contributes to early neuronal polarization and survival. (piccini2015phosphorylationbypka pages 1-2)
Objective 3 (mechanism, pathways, localization, and regulation)
- Presynaptic vesicle pools and reserve-pool maintenance: Synapsins maintain the reserve pool and regulate transitions among pool states underlying short-term plasticity. Reviews summarize three operational pools—readily releasable (RRP), recycling, and reserve—where synapsins anchor/cluster vesicles to preserve a large RP and modulate mobilization by phosphorylation-state changes. (zhang2021synapsinsandthe pages 1-2, song2015synapsinisoformsand pages 5-5)
- Synapsin-3 in dopamine terminals: In dopaminergic neurons, Synapsin-3 negatively modulates dopamine release and governs the size/organization of recycling/reserve vesicle pools. Evidence indicates Synapsin-3 uniquely regulates VMAT2-positive vesicle pools in striatum, pointing to isoform specificity for monoaminergic terminals. (zaltieri2015αsynucleinandsynapsin pages 1-1)
- Phosphorylation control of Synapsin-3: PKA and Cdk5 phosphorylate Synapsin-3 at functionally critical sites—conserved PKA site Ser9 and a Cdk5 site Ser404. Genetic/mutational rescue experiments show that Synapsin-3’s promotion of neurite/axon outgrowth, neuronal maturation, and survival requires these phosphorylation events; nonphosphorylatable mutants fail to rescue Syn3 knockout phenotypes, whereas a Cdk5 phosphomimetic rescues maturation/axon elongation. (piccini2015phosphorylationbypka pages 2-3, piccini2015phosphorylationbypka pages 1-2)
- Developmental roles and upstream signaling: Synapsin-3 governs early phases of dopaminergic neuron development across vertebrates and acts upstream of BDNF- and Cdk5-dependent dendritic development. Loss of Syn3 in zebrafish, mouse, and human iPSC-derived neurons reduces early dopaminergic differentiation/TH+ neurons and perturbs dendritogenesis, with developmental timing and partial recovery patterns documented in mice. (faustini2022synapsiniiiregulates pages 22-23, faustini2021synapsiniiicontrols pages 25-28)
- Interaction with alpha-synuclein and implications for PD: Alpha-synuclein (α-syn) interacts with and modulates Synapsin-3; perturbations in α-syn (absence/aggregation) alter Synapsin-3 distribution in dopaminergic neurons, reorganize vesicle pools, and Synapsin-3 accumulates in the caudate/putamen of Parkinson’s disease patients. Functionally, Synapsin-3 constrains dopamine overflow yet α-syn loss decreases basal/evoked striatal dopamine release amid altered Synapsin-3 organization, implicating the α-syn–Syn3 axis in presynaptic pathophysiology. (zaltieri2015αsynucleinandsynapsin pages 1-1)
Objective 4 (recent developments, 2021–2024 emphasis)
- Reserve-pool mechanism updates and condensate/cross-linking models: A 2021 synthesis evaluates whether synapsins maintain vesicle clusters by cross‑linking SVs versus liquid-like condensates, consolidating modern views of reserve-pool organization; this review explicitly covers isoform evidence relevant to Synapsin-3. (2021; Cells review) (zhang2021synapsinsandthe pages 1-2)
- Dopaminergic development across species: A 2022 primary study in Cells demonstrates conserved Syn3 roles in vertebrate dopaminergic neuron development across zebrafish/mouse/human iPSC neurons, acting upstream of BDNF and Cdk5, and connecting Syn3 genotype to ADHD-like behavioral/stimulant-response phenotypes. (2022; Cells) (faustini2022synapsiniiiregulates pages 22-23)
- Kinase regulation with neuron-morphogenesis readouts: 2015 primary studies established PKA/Cdk5 phospho‑control at Ser9/Ser404 for Syn3’s developmental functions (neurite/axon growth, survival) and placed Syn3 downstream of Semaphorin 3A/CDK5 for radial migration and orientation of pyramidal neurons in vivo; these mechanistic anchors remain the basis for current models that link Syn3 to Cdk5- and neurotrophin-signaling axes. (2015; J Neurosci and Cell Reports) (piccini2015phosphorylationbypka pages 2-3)
Objective 5 (current applications and real-world implementations)
- Model systems and disease modeling: The vertebrate Syn3 KD/KO/iPSC systems provide tractable models to interrogate dopamine neuron development, stimulant pharmacology, and BDNF/Cdk5 signaling dependencies relevant to ADHD neurobiology. Behavioral phenotyping (e.g., stimulant responses) and structural measures (TH+ counts, dendritic metrics) are applied outcomes. (faustini2022synapsiniiiregulates pages 22-23)
- Parkinson’s disease research: The α‑syn–Syn3 interaction is leveraged to study early presynaptic changes in dopaminergic systems, integrating mouse genetics and human tissue to connect vesicle‑pool reorganization with disease‑linked synaptic vulnerability. This offers targets for presynaptic therapeutic strategies (e.g., modulating kinases/phosphorylation state that impact Syn3’s vesicle-clustering function). (zaltieri2015αsynucleinandsynapsin pages 1-1)
- Synaptic physiology frameworks: Family‑level synapsin pool models are widely used to interpret short‑term plasticity, fatigue resistance, and pool replenishment dynamics in physiological/optogenetic experiments. These frameworks contextualize Syn3’s contributions relative to other isoforms. (zhang2021synapsinsandthe pages 1-2, song2015synapsinisoformsand pages 5-5)
Objective 6 (expert opinions and authoritative synthesis)
- Consensus role of synapsins: Authoritative reviews conclude synapsins are central organizers of the presynaptic vesicle cluster and reserve pool, with phosphorylation-dependent tuning of SV mobilization. Isoform‑specific roles, including Syn3’s developmental prominence and monoaminergic specialization, are emphasized as key to presynaptic diversity. (zhang2021synapsinsandthe pages 1-2, song2015synapsinisoformsand pages 5-5)
- Dopaminergic specialization and disease: Primary experts link Syn3 to dopamine neuron function, highlighting negative modulation of dopamine overflow and α‑syn–Syn3 cooperation in vesicle‑pool organization; accumulation of Syn3 in PD striatum is proposed as a disease‑relevant hallmark. (zaltieri2015αsynucleinandsynapsin pages 1-1)
Objective 7 (relevant statistics and data excerpts)
- Developmental phenotypes: Syn3 knockdown in zebrafish reduces TH+ neuron counts and early neuronal markers; Syn3 KO mice exhibit reduced early development of midbrain dopaminergic neurons with partial recovery of TH+ cell counts by two months yet persistent projection deficits. Behavioral readouts show ADHD-like features and altered stimulant responses (e.g., attenuated cocaine response, methylphenidate effects modulated by Syn3 status). Quantitative values and timelines are detailed in the 2022 study. (faustini2022synapsiniiiregulates pages 22-23)
- Phosphorylation-site function: Rescue experiments show that wild-type Syn3 corrects neurite/axon growth and survival defects in Syn3 KO neurons; nonphosphorylatable PKA and Cdk5 mutants fail, whereas a Cdk5 pseudo‑phosphorylated mutant restores maturation/axon elongation, quantitatively linking phosphorylation state to morphological indices and survival (activated caspase‑3, TrkB isoform expression). (piccini2015phosphorylationbypka pages 2-3, piccini2015phosphorylationbypka pages 1-2)
- Vesicle-pool reorganization in dopamine neurons: In α‑syn-null or α‑syn-perturbed conditions, Syn3 levels/distribution and vesicle-pool metrics (recycling/reserve sizes, VMAT2+ pools) shift, correlating with reduced basal/evoked striatal dopamine release despite increased locomotor response to synapsin‑dependent dopamine overflow. Human PD striatum shows Syn3 accumulation in caudate/putamen. (zaltieri2015αsynucleinandsynapsin pages 1-1)
Key functional annotation (concise)
- Molecular function: Neuronal phosphoprotein that binds synaptic vesicles; modulates vesicle clustering/mobilization and negatively tunes dopaminergic neurotransmitter release; phosphorylation by PKA (Ser9) and Cdk5 (Ser404) is essential for Syn3‑dependent neurite/axon growth and neuronal survival. (zhang2021synapsinsandthe pages 1-2, zaltieri2015αsynucleinandsynapsin pages 1-1, piccini2015phosphorylationbypka pages 2-3)
- Biological processes: Presynaptic vesicle‑pool maintenance and mobilization; early neuronal development (axon specification, neurite outgrowth, radial migration); dopaminergic neuron development upstream of BDNF and Cdk5 signaling. (zhang2021synapsinsandthe pages 1-2, piccini2015phosphorylationbypka pages 1-2, faustini2022synapsiniiiregulates pages 22-23, piccini2015phosphorylationbypka pages 2-3)
- Cellular localization: Presynaptic terminals, enriched on synaptic vesicles, especially within the reserve pool; broader, transient early developmental distribution including neural progenitors. (zhang2021synapsinsandthe pages 1-2, piccini2015phosphorylationbypka pages 1-2)
- Pathway context: PKA/Cdk5 kinase pathways; neurotrophin (BDNF/TrkB) signaling; α‑synuclein–synapsin cooperation influencing presynaptic organization and dopamine release dynamics. (piccini2015phosphorylationbypka pages 2-3, piccini2015phosphorylationbypka pages 1-2, faustini2022synapsiniiiregulates pages 22-23, zaltieri2015αsynucleinandsynapsin pages 1-1)
| Aspect | Key finding/claim | Model/system | Year | Source (journal) | URL/DOI | Citation ID |
|---|---|---|---|---|---|---|
| Identity / family / domains | Synapsins (SYN1, SYN2, SYN3) share conserved N-terminal A–C domains and variable C-terminal tails; synapsins bind synaptic vesicles (SVs) and mediate SV–actin interactions. | Review / proteomic & biochemical analyses | 2021 | Cells (review) | https://doi.org/10.3390/cells10030658 | (zhang2021synapsinsandthe pages 1-2) |
| Early expression & non-synaptic localization | Synapsin-3 (SynIII) is expressed precociously in developing neurons and in nestin-positive neural progenitors; it shows broader, transient/localization not strictly confined to mature synaptic sites. | Mouse primary neurons, in vitro KO/rescue | 2015 | The Journal of Neuroscience | https://doi.org/10.1523/jneurosci.1379-15.2015 | (piccini2015phosphorylationbypka pages 1-2) |
| Presynaptic role; dopamine-specific effects | SynIII negatively modulates dopamine release and controls recycling/reserve vesicle pools in dopaminergic terminals; shows isoform-specific effects on VMAT2+ vesicle pools. | Dopamine neuron studies; mouse models | 2015 | Journal of Cell Science | https://doi.org/10.1242/jcs.157867 | (zaltieri2015αsynucleinandsynapsin pages 1-1) |
| Phosphoregulation (PKA Ser9; Cdk5 Ser404) | SynIII is phosphorylated by PKA (Ser9) and Cdk5 (Ser404); phosphorylation is required for SynIII-mediated neurite/axon outgrowth, neuronal survival, and rescue of KO phenotypes (nonphosphorylatable mutants fail to rescue). | Mouse neurons; mutagenesis and rescue experiments | 2015 | The Journal of Neuroscience | https://doi.org/10.1523/jneurosci.1379-15.2015 | (piccini2015phosphorylationbypka pages 2-3) |
| Developmental role upstream of BDNF & Cdk5 | SynIII governs early dopaminergic neuron development across vertebrates and acts upstream of BDNF- and Cdk5-dependent dendritic development; conserved in zebrafish, SynIII KO mice, and human iPSC-derived neurons. | Zebrafish KD, SynIII KO mice, human iPSC-derived neurons | 2021, 2022 | SSRN / Cells (primary studies) | https://doi.org/10.2139/ssrn.3902138 ; https://doi.org/10.3390/cells11233902 | (faustini2021synapsiniiicontrols pages 25-28, faustini2022synapsiniiiregulates pages 22-23) |
| Interaction with α-synuclein; PD relevance | α-Synuclein interacts with and modulates SynIII; α-syn perturbation/aggregation alters SynIII distribution, reorganizes SV pools in dopamine neurons, and SynIII accumulates in striatum of PD cases. | Mouse genetics, human PD tissue analyses | 2015 | Journal of Cell Science | https://doi.org/10.1242/jcs.157867 | (zaltieri2015αsynucleinandsynapsin pages 1-1) |
| Synapsin family: reserve-pool mechanism | Synapsins (family-level) maintain the synaptic vesicle reserve pool via SV clustering/phase behavior; phosphorylation state regulates SV mobilization from reserve to recycling pools. | Reviews and mechanistic studies | 2021 | Cells (review) | https://doi.org/10.3390/cells10030658 | (zhang2021synapsinsandthe pages 1-2) |
| Synaptic vesicle pool conceptual context | RRP / recycling / reserve pool organization underlies short-term plasticity; synapsins are central effectors linking phosphorylation signaling to pool sizes and release competence. | Conceptual reviews (SV cycle, pool models) | 2015 (review synthesis) | Molecules & Cells / Cells (reviews) | https://doi.org/10.14348/molcells.2015.0233 ; https://doi.org/10.3390/cells10030658 | (song2015synapsinisoformsand pages 5-5, zhang2021synapsinsandthe pages 1-2) |
| 2021+ review on synapsins & reserve pool | Modern synthesis (2021) evaluates synapsin mechanism models (cross-linking vs. condensate/liquid-phase) and summarizes isoform-specific evidence relevant to SynIII. | Literature review / synthesis | 2021 | Cells (review) | https://doi.org/10.3390/cells10030658 | (zhang2021synapsinsandthe pages 1-2) |
| Recent primary evidence (2022 Cells paper) | 2022 Cells study demonstrates SynIII’s role in dopaminergic neuron development and links SynIII genotype/KO to behavioral and dopaminergic signaling phenotypes (relevance to ADHD-like phenotypes and stimulant responses). | Zebrafish KD, SynIII KO mice, human iPSC neurons | 2022 | Cells (primary research) | https://doi.org/10.3390/cells11233902 | (faustini2022synapsiniiiregulates pages 22-23) |
Table: Concise table summarizing primary findings and reviews about human Synapsin‑3 (SYN3), including identity/domains, localization, presynaptic roles, phosphorylation regulation, developmental functions, α‑synuclein interaction, and recent primary/review sources (with citations).
Annotated bibliography (URLs/dates)
- Zhang M, Augustine GJ. Synapsins and the synaptic vesicle reserve pool: Floats or Anchors? Cells. 2021 Mar;10:658. URL: https://doi.org/10.3390/cells10030658 (review on synapsin family, reserve pool, isoform considerations). (zhang2021synapsinsandthe pages 1-2)
- Song S‑H, Augustine GJ. Synapsin Isoforms and Synaptic Vesicle Trafficking. Molecules and Cells. 2015 Nov;38:936‑940. URL: https://doi.org/10.14348/molcells.2015.0233 (isoform‑level review; domain A–C functions; synapsin III features and disease links). (song2015synapsinisoformsand pages 5-5)
- Piccini A et al. Phosphorylation by PKA and Cdk5 Mediates the Early Effects of Synapsin III in Neuronal Morphological Maturation. J Neurosci. 2015 Sep;35(38):13148‑13159. URL: https://doi.org/10.1523/JNEUROSCI.1379-15.2015 (Ser9/Ser404 sites; rescue with phospho‑mutants; survival/axon metrics). (piccini2015phosphorylationbypka pages 2-3, piccini2015phosphorylationbypka pages 1-2)
- Zaltieri M et al. α‑synuclein and synapsin III cooperatively regulate synaptic function in dopamine neurons. J Cell Sci. 2015 Jul;128(13):2231‑2243. URL: https://doi.org/10.1242/jcs.157867 (α‑syn–Syn3 interaction; dopaminergic vesicle pools; human PD striatum accumulation). (zaltieri2015αsynucleinandsynapsin pages 1-1)
- Faustini G et al. Synapsin III Regulates Dopaminergic Neuron Development in Vertebrates. Cells. 2022 Dec;11:3902. URL: https://doi.org/10.3390/cells11233902 (zebrafish/mouse/human iPSC integration; upstream of BDNF/Cdk5; stimulant behaviors/ADHD‑like phenotypes). (faustini2022synapsiniiiregulates pages 22-23)
- Faustini G et al. Synapsin III Controls Early Phases of Dopaminergic Neurons Development in Fishes and Mammals by Acting Upstream of BDNF and Cdk5 Signaling. SSRN. 2021 Aug. URL: https://doi.org/10.2139/ssrn.3902138 (preprint precursor documenting conserved Syn3 developmental control). (faustini2021synapsiniiicontrols pages 25-28)
Notes and limitations on 2023–2024 evidence
- We prioritized 2021–2022 peer‑reviewed/primary sources directly addressing Synapsin‑3’s unique functions. While several 2023–2024 preprints and system-level studies mention SYN3 expression/regulation, high‑confidence, isoform‑specific, mechanistic updates centered on Syn3 remain sparse in the curated evidence used here. The 2022 Cells paper represents the most recent vertebrate‑integrative primary study with direct mechanistic data on Syn3. (faustini2022synapsiniiiregulates pages 22-23)
Conclusions
- Verified identity: Human SYN3 encodes Synapsin‑3, a synapsin family member with conserved A–C domains and specialized C‑terminal features consistent with the synapsin superfamily and presynaptic SV binding. (zhang2021synapsinsandthe pages 1-2, song2015synapsinisoformsand pages 5-5)
- Primary function and localization: Synapsin‑3 is a presynaptic vesicle‑associated phosphoprotein that maintains and mobilizes the reserve pool and negatively modulates dopamine release; it localizes to SV clusters in terminals, with distinct early developmental distribution. (zhang2021synapsinsandthe pages 1-2, zaltieri2015αsynucleinandsynapsin pages 1-1, piccini2015phosphorylationbypka pages 1-2)
- Regulation and pathways: PKA (Ser9) and Cdk5 (Ser404) phosphorylation are required for Syn3’s actions in neuronal morphogenesis and survival; Syn3 acts upstream of BDNF/Cdk5 in dopaminergic neuron development. (piccini2015phosphorylationbypka pages 2-3, piccini2015phosphorylationbypka pages 1-2, faustini2022synapsiniiiregulates pages 22-23)
- Disease relevance and applications: α‑syn–Syn3 interaction shapes dopaminergic vesicle‑pool organization and associates with PD pathology in human striatum; Syn3 loss perturbs dopaminergic development/behavior with ADHD‑like phenotypes, offering tractable in vivo and iPSC models for translational studies. (zaltieri2015αsynucleinandsynapsin pages 1-1, faustini2022synapsiniiiregulates pages 22-23)
Overall, Synapsin‑3 emerges as a phospho‑regulated organizer of presynaptic vesicle architecture with distinctive roles in early neuronal and dopaminergic development and a mechanistic interface with α‑synuclein relevant to Parkinson’s disease.
References
(zhang2021synapsinsandthe pages 1-2): Minchuan Zhang and George J. Augustine. Synapsins and the synaptic vesicle reserve pool: floats or anchors? Cells, 10:658, Mar 2021. URL: https://doi.org/10.3390/cells10030658, doi:10.3390/cells10030658. This article has 80 citations and is from a poor quality or predatory journal.
(song2015synapsinisoformsand pages 5-5): Sang-Ho Song and George J. Augustine. Synapsin isoforms and synaptic vesicle trafficking. Molecules and Cells, 38:936-940, Nov 2015. URL: https://doi.org/10.14348/molcells.2015.0233, doi:10.14348/molcells.2015.0233. This article has 130 citations and is from a peer-reviewed journal.
(piccini2015phosphorylationbypka pages 1-2): Alessandra Piccini, Laura E. Perlini, Laura Cancedda, Fabio Benfenati, and Silvia Giovedì. Phosphorylation by pka and cdk5 mediates the early effects of synapsin iii in neuronal morphological maturation. The Journal of Neuroscience, 35:13148-13159, Sep 2015. URL: https://doi.org/10.1523/jneurosci.1379-15.2015, doi:10.1523/jneurosci.1379-15.2015. This article has 35 citations.
(zaltieri2015αsynucleinandsynapsin pages 1-1): Michela Zaltieri, Jessica Grigoletto, Francesca Longhena, Laura Navarria, Gaia Favero, Stefania Castrezzati, Maria Alessandra Colivicchi, Laura Della Corte, Rita Rezzani, Marina Pizzi, Fabio Benfenati, Maria Grazia Spillantini, Cristina Missale, PierFranco Spano, and Arianna Bellucci. Α-synuclein and synapsin iii cooperatively regulate synaptic function in dopamine neurons. Journal of Cell Science, 128:2231-2243, Jul 2015. URL: https://doi.org/10.1242/jcs.157867, doi:10.1242/jcs.157867. This article has 175 citations and is from a domain leading peer-reviewed journal.
(piccini2015phosphorylationbypka pages 2-3): Alessandra Piccini, Laura E. Perlini, Laura Cancedda, Fabio Benfenati, and Silvia Giovedì. Phosphorylation by pka and cdk5 mediates the early effects of synapsin iii in neuronal morphological maturation. The Journal of Neuroscience, 35:13148-13159, Sep 2015. URL: https://doi.org/10.1523/jneurosci.1379-15.2015, doi:10.1523/jneurosci.1379-15.2015. This article has 35 citations.
(faustini2022synapsiniiiregulates pages 22-23): Gaia Faustini, Francesca Longhena, Alessia Muscò, Federica Bono, Edoardo Parrella, Luca La Via, Alessandro Barbon, Marina Pizzi, Franco Onofri, Fabio Benfenati, Cristina Missale, Maurizio Memo, Daniela Zizioli, and Arianna Bellucci. Synapsin iii regulates dopaminergic neuron development in vertebrates. Cells, 11:3902, Dec 2022. URL: https://doi.org/10.3390/cells11233902, doi:10.3390/cells11233902. This article has 10 citations and is from a poor quality or predatory journal.
(faustini2021synapsiniiicontrols pages 25-28): Gaia Faustini, Francesca Longhena, Alessia Muscò, Federica Bono, Edoardo Parrella, Luca La Via, Alessandro Barbon, Marina Pizzi, Franco Onofri, Fabio Benfenati, Cristina Missale, Maurizio Memo, Daniela Zizioli, Arianna Bellucci, and Sneak Peek Administrator. Synapsin iii controls early phases of dopaminergic neurons development in fishes and mammals by acting upstream of bdnf and cdk5 signaling. SSRN Electronic Journal, Aug 2021. URL: https://doi.org/10.2139/ssrn.3902138, doi:10.2139/ssrn.3902138. This article has 0 citations.
id: O14994
gene_symbol: SYN3
product_type: PROTEIN
status: COMPLETE
taxon:
id: NCBITaxon:9606
label: Homo sapiens
description: >-
Synapsin-3 (SYN3) is a neuron-specific, presynaptic vesicle-associated phosphoprotein
that is a member of the synapsin family (SYN1, SYN2, SYN3). It maintains and mobilizes
the synaptic vesicle reserve pool through phosphorylation-dependent mechanisms.
Synapsin-3 negatively modulates dopamine release in dopaminergic terminals and
controls recycling/reserve vesicle pool organization. The protein is phosphorylated
by PKA at Ser9 and by Cdk5 at Ser404, which are essential for its roles in neuronal
morphological maturation, axon specification, and neuronal survival. Unlike other
synapsins, SYN3 shows precocious expression during development and is involved in
early dopaminergic neuron development upstream of BDNF and Cdk5 signaling. The
protein binds ATP (regulated by calcium) and interacts with alpha-synuclein, with
implications for Parkinson's disease pathophysiology.
existing_annotations:
- term:
id: GO:0030672
label: synaptic vesicle membrane
evidence_type: IBA
original_reference_id: GO_REF:0000033
review:
summary: >-
Synapsin-3 is a peripheral membrane protein localized to the cytoplasmic surface
of synaptic vesicles. The original characterization paper states "Synapsin IIIa
is associated with synaptic vesicles" [PMID:9539796]. The IBA annotation is
phylogenetically inferred and consistent with the synapsin family function.
action: ACCEPT
reason: >-
This is a well-supported core localization for Synapsin-3. The IBA annotation is
consistent with experimental evidence from multiple studies and the UniProt subcellular
localization annotation. Synapsins are peripheral membrane proteins on the cytoplasmic
surface of synaptic vesicle membranes.
supported_by:
- reference_id: PMID:9539796
supporting_text: "Synapsin IIIa is associated with synaptic vesicles, and its expression appears to be neuron-specific"
- term:
id: GO:0097091
label: synaptic vesicle clustering
evidence_type: IBA
original_reference_id: GO_REF:0000033
review:
summary: >-
Synaptic vesicle clustering is a core function of the synapsin family. Synapsins
are central organizers of the presynaptic vesicle cluster and reserve pool.
The specific role of synapsins in maintaining the reserve pool through SV clustering
is well documented in the literature.
action: ACCEPT
reason: >-
This represents a core biological process for Synapsin-3. Synapsins maintain the
synaptic vesicle reserve pool via SV clustering, and this function is conserved
across the synapsin family. The IBA annotation is phylogenetically sound and
consistent with literature evidence.
supported_by:
- reference_id: PMID:9539796
supporting_text: "Synapsins are a family of neuron-specific synaptic vesicle-associated phosphoproteins that have been implicated in synaptogenesis and in the modulation of neurotransmitter release"
- term:
id: GO:0050808
label: synapse organization
evidence_type: IBA
original_reference_id: GO_REF:0000033
review:
summary: >-
Synapsins contribute to synapse organization through their role in maintaining
synaptic vesicle pools and presynaptic architecture. The original paper states
synapsins have been "implicated in synaptogenesis" [PMID:9539796]. Synapsin-3
specifically contributes to presynaptic organization, though it has unique
developmental roles.
action: ACCEPT
reason: >-
This is an appropriate annotation at a general level for the synapsin family's role
in organizing presynaptic structure. The IBA annotation is consistent with the
established role of synapsins in presynaptic organization and vesicle pool maintenance.
supported_by:
- reference_id: PMID:9539796
supporting_text: "Synapsins are a family of neuron-specific synaptic vesicle-associated phosphoproteins that have been implicated in synaptogenesis and in the modulation of neurotransmitter release"
- term:
id: GO:0000166
label: nucleotide binding
evidence_type: IEA
original_reference_id: GO_REF:0000043
review:
summary: >-
Synapsin-3 has an ATP-grasp domain (C domain) that binds nucleotides, specifically
ATP. This annotation is inferred from UniProt keywords. While ATP binding (GO:0005524)
is more specific and accurate, nucleotide binding is not incorrect as a broader term.
action: ACCEPT
reason: >-
The annotation is technically correct as a broader term encompassing ATP binding.
Synapsins contain an ATP-binding domain in the conserved C region. While more specific
annotations (ATP binding) also exist, this broader IEA annotation does not conflict
with the known biochemistry.
- term:
id: GO:0005524
label: ATP binding
evidence_type: IEA
original_reference_id: GO_REF:0000120
review:
summary: >-
Synapsin-3 contains an ATP-binding domain in its conserved C region. The domain
structure includes IPR013815 (ATP_grasp_subdomain_1) and IPR020898
(Synapsin_ATP-bd_dom). Calcium regulates ATP binding to this domain.
action: ACCEPT
reason: >-
ATP binding is a well-supported molecular function for Synapsin-3 based on domain
structure. The C domain (region 91-399) is annotated as "actin-binding and synaptic-vesicle
binding" and contains ATP-grasp fold domains. The TAS annotation (below) provides
literature support for this function.
- term:
id: GO:0007268
label: chemical synaptic transmission
evidence_type: IEA
original_reference_id: GO_REF:0000117
review:
summary: >-
Synapsin-3 is involved in chemical synaptic transmission through its role in
regulating synaptic vesicle pools and neurotransmitter release. The synaptic
vesicle cycle review describes how vesicles undergo a trafficking cycle to
support rapid neurotransmitter release [PMID:15217342].
action: ACCEPT
reason: >-
This is an appropriate biological process annotation. While the term is somewhat
general, Synapsin-3 clearly participates in chemical synaptic transmission through
its regulation of synaptic vesicle pools and neurotransmitter release dynamics.
The IEA annotation is consistent with the core functions of the synapsin family.
supported_by:
- reference_id: PMID:15217342
supporting_text: "To support rapid and repeated rounds of release, synaptic vesicles undergo a trafficking cycle"
- term:
id: GO:0007269
label: neurotransmitter secretion
evidence_type: IEA
original_reference_id: GO_REF:0000002
review:
summary: >-
Synapsin-3 is involved in regulating neurotransmitter secretion. The original
publication identifying SYN3 suggests synapsins are implicated "in the modulation
of neurotransmitter release" [PMID:9539796].
action: ACCEPT
reason: >-
This is a core function of the synapsin family. Synapsins regulate the transition
of vesicles between reserve and readily releasable pools, thereby modulating
neurotransmitter release. The IEA annotation is consistent with literature evidence.
supported_by:
- reference_id: PMID:9539796
supporting_text: "Synapsins are a family of neuron-specific synaptic vesicle-associated phosphoproteins that have been implicated in synaptogenesis and in the modulation of neurotransmitter release"
- term:
id: GO:0008021
label: synaptic vesicle
evidence_type: IEA
original_reference_id: GO_REF:0000120
review:
summary: >-
Synapsin-3 localizes to synaptic vesicles as a peripheral membrane protein.
This is consistent with UniProt subcellular location annotation and literature
evidence. The original SYN3 characterization paper explicitly states "Synapsin IIIa
is associated with synaptic vesicles" [PMID:9539796].
action: ACCEPT
reason: >-
Synaptic vesicle localization is well-established for Synapsin-3. The IEA annotation
is consistent with experimental evidence and the TAS annotation for the same term
(below). This represents a core localization for the protein.
supported_by:
- reference_id: PMID:9539796
supporting_text: "Synapsin IIIa is associated with synaptic vesicles, and its expression appears to be neuron-specific"
- term:
id: GO:0030672
label: synaptic vesicle membrane
evidence_type: IEA
original_reference_id: GO_REF:0000120
review:
summary: >-
This is a duplicate of the IBA annotation for the same term. Synapsin-3 is a
peripheral membrane protein on the cytoplasmic surface of synaptic vesicle membranes.
UniProt explicitly annotates this localization.
action: ACCEPT
reason: >-
The annotation is correct and consistent with the IBA annotation for the same term.
Both annotations support the well-established localization of Synapsin-3 to
synaptic vesicle membranes.
supported_by:
- reference_id: PMID:9539796
supporting_text: "Synapsin IIIa is associated with synaptic vesicles, and its expression appears to be neuron-specific"
- term:
id: GO:0031410
label: cytoplasmic vesicle
evidence_type: IEA
original_reference_id: GO_REF:0000043
review:
summary: >-
This is a broader term that encompasses synaptic vesicles. Synapsin-3 localizes
to synaptic vesicles, which are a type of cytoplasmic vesicle. The annotation
is technically correct but less specific than the synaptic vesicle annotations.
action: ACCEPT
reason: >-
While this is a less informative annotation compared to the more specific synaptic
vesicle and synaptic vesicle membrane annotations, it is not incorrect. The IEA
annotation derived from UniProt keywords is valid as synaptic vesicles are a
subtype of cytoplasmic vesicles.
- term:
id: GO:0050804
label: modulation of chemical synaptic transmission
evidence_type: IEA
original_reference_id: GO_REF:0000117
review:
summary: >-
Synapsin-3 modulates synaptic transmission through its regulation of synaptic
vesicle pools. Synapsins are implicated in "the modulation of neurotransmitter
release" [PMID:9539796].
action: ACCEPT
reason: >-
This is an appropriate annotation for Synapsin-3. The protein modulates
neurotransmitter release by regulating synaptic vesicle pool dynamics. The
annotation is consistent with the known regulatory role of synapsins in
synaptic transmission.
supported_by:
- reference_id: PMID:9539796
supporting_text: "Synapsins are a family of neuron-specific synaptic vesicle-associated phosphoproteins that have been implicated in synaptogenesis and in the modulation of neurotransmitter release"
- term:
id: GO:0005515
label: protein binding
evidence_type: IPI
original_reference_id: PMID:33961781
review:
summary: >-
This annotation is based on a high-throughput proteomics study (BioPlex 3.0) that
detected SYN3 interaction with SYN2 (Synapsin-2). While the interaction is likely
valid (synapsins can oligomerize), "protein binding" is too generic.
action: MARK_AS_OVER_ANNOTATED
reason: >-
While the interaction with SYN2 is documented and synapsins are known to form
oligomers, GO:0005515 "protein binding" is an uninformative term that does not
capture the specific nature of the interaction. A more specific term such as
GO:0042802 "identical protein binding" or a synapsin-specific binding term would
be more informative if available.
- term:
id: GO:0005515
label: protein binding
evidence_type: IPI
original_reference_id: PMID:40205054
review:
summary: >-
This annotation is from another high-throughput interactome study (Multimodal cell
maps). The interaction partner is again SYN2 based on the GOA data. As with the
previous annotation, "protein binding" is too generic.
action: MARK_AS_OVER_ANNOTATED
reason: >-
Same rationale as above. While the protein-protein interaction evidence supports
SYN3-SYN2 binding, the GO term "protein binding" is uninformative. The annotation
could be retained for completeness but does not provide meaningful functional insight.
- term:
id: GO:0014069
label: postsynaptic density
evidence_type: IEA
original_reference_id: GO_REF:0000107
review:
summary: >-
This annotation is transferred from mouse ortholog via Ensembl Compara. However,
Synapsin-3 is characterized as a presynaptic protein associated with synaptic
vesicles. The postsynaptic density is a postsynaptic structure, which conflicts
with the established presynaptic localization.
action: REMOVE
reason: >-
This annotation appears inconsistent with the established presynaptic localization
of Synapsin-3. Synapsins are well-characterized as presynaptic vesicle-associated
proteins. While some postsynaptic localization cannot be completely ruled out,
this conflicts with the primary literature characterizing SYN3 as a synaptic vesicle
membrane protein. The annotation may reflect an error in the orthology transfer
or proteomics detection of contamination.
supported_by:
- reference_id: PMID:9539796
supporting_text: "Synapsin IIIa is associated with synaptic vesicles, and its expression appears to be neuron-specific"
- term:
id: GO:0045202
label: synapse
evidence_type: IEA
original_reference_id: GO_REF:0000107
review:
summary: >-
Synapsin-3 is localized to synapses, specifically to the presynaptic compartment
on synaptic vesicle membranes. This is a broad term that encompasses the more
specific synaptic vesicle and synaptic vesicle membrane annotations.
action: ACCEPT
reason: >-
This is a valid but broad localization annotation. Synapsin-3 is indeed present
at synapses (specifically in the presynaptic terminal). The annotation is
consistent with more specific annotations for synaptic vesicle localization.
supported_by:
- reference_id: PMID:9539796
supporting_text: "Synapsin IIIa is associated with synaptic vesicles, and its expression appears to be neuron-specific"
- term:
id: GO:0097091
label: synaptic vesicle clustering
evidence_type: IEA
original_reference_id: GO_REF:0000107
review:
summary: >-
This is a duplicate of the IBA annotation for synaptic vesicle clustering. The
function is well-supported for the synapsin family.
action: ACCEPT
reason: >-
Duplicate annotation supporting the core function of Synapsin-3 in synaptic
vesicle clustering. Both IBA and IEA annotations converge on this core function.
supported_by:
- reference_id: PMID:9539796
supporting_text: "Synapsins are a family of neuron-specific synaptic vesicle-associated phosphoproteins that have been implicated in synaptogenesis and in the modulation of neurotransmitter release"
- term:
id: GO:0098850
label: extrinsic component of synaptic vesicle membrane
evidence_type: IEA
original_reference_id: GO_REF:0000107
review:
summary: >-
This is an excellent, specific annotation for Synapsin-3. UniProt explicitly states
it is a peripheral membrane protein localized to the cytoplasmic surface of synaptic
vesicles. This GO term precisely captures the extrinsic (peripheral) nature of
Synapsin-3's membrane association.
action: ACCEPT
reason: >-
This is the most precise cellular component annotation for Synapsin-3. Synapsins
are peripheral membrane proteins (extrinsic), not integral membrane proteins,
and they associate with the cytoplasmic face of synaptic vesicle membranes.
supported_by:
- reference_id: PMID:9539796
supporting_text: "Synapsin IIIa is associated with synaptic vesicles, and its expression appears to be neuron-specific"
- term:
id: GO:0098978
label: glutamatergic synapse
evidence_type: IEA
original_reference_id: GO_REF:0000107
review:
summary: >-
This annotation suggests SYN3 localizes to glutamatergic synapses. Synapsins are
present at various types of synapses. The literature emphasizes SYN3's role
in dopaminergic neurons specifically, but this does not preclude presence at
glutamatergic synapses.
action: KEEP_AS_NON_CORE
reason: >-
While Synapsin-3 may be present at glutamatergic synapses (synapsins are
generally expressed across synapse types), the literature specifically
emphasizes its unique role in dopaminergic neurons. The annotation is not
wrong but represents a non-specific localization rather than a core feature
of SYN3 specifically.
- term:
id: GO:0099504
label: synaptic vesicle cycle
evidence_type: IEA
original_reference_id: GO_REF:0000107
review:
summary: >-
Synapsin-3 participates in the synaptic vesicle cycle through its role in
maintaining vesicle pools and regulating vesicle mobilization. The synaptic
vesicle cycle review describes how vesicles undergo trafficking for repeated
rounds of release [PMID:15217342].
action: ACCEPT
reason: >-
The synaptic vesicle cycle is a core process in which Synapsin-3 participates.
By maintaining the reserve pool and regulating vesicle mobilization through
phosphorylation-dependent mechanisms, synapsins are integral to the vesicle
cycling process.
supported_by:
- reference_id: PMID:15217342
supporting_text: "To support rapid and repeated rounds of release, synaptic vesicles undergo a trafficking cycle"
- term:
id: GO:0005524
label: ATP binding
evidence_type: TAS
original_reference_id: PMID:15217342
review:
summary: >-
This TAS annotation is based on the Sudhof synaptic vesicle cycle review (2004).
Synapsin-3 has a well-characterized ATP-binding domain (C domain). Calcium
regulates ATP binding to this domain.
action: ACCEPT
reason: >-
ATP binding is a well-supported molecular function for Synapsin-3 based on
domain structure and biochemical evidence. The C domain contains ATP-grasp
fold elements (IPR013815, IPR020898) that are characteristic of ATP-binding
proteins.
- term:
id: GO:0032228
label: regulation of synaptic transmission, GABAergic
evidence_type: TAS
original_reference_id: PMID:15217342
review:
summary: >-
This annotation suggests SYN3 specifically regulates GABAergic transmission. The
Sudhof review (PMID:15217342) is a general review of the synaptic vesicle cycle
and does not specifically address Synapsin-3's role in GABAergic synapses. The
literature emphasizes SYN3's role in dopaminergic neurons rather than GABAergic
neurons.
action: UNDECIDED
reason: >-
The cited reference (PMID:15217342) is a general review of the synaptic vesicle
cycle that does not specifically address Synapsin-3 or GABAergic transmission.
While synapsins are present at various synapse types including GABAergic synapses,
there is no specific evidence in the available literature for a particular role
of SYN3 in GABAergic transmission. The deep research specifically emphasizes
SYN3's unique role in dopaminergic neurons. Additional evidence would be needed
to confirm this specific annotation.
- term:
id: GO:0007269
label: neurotransmitter secretion
evidence_type: TAS
original_reference_id: PMID:9539796
review:
summary: >-
This TAS annotation is based on the original paper characterizing Synapsin-3. The
paper states that synapsins have been implicated "in the modulation of neurotransmitter
release" and suggests a role for synapsin III based on similarity to other synapsins.
action: ACCEPT
reason: >-
The original characterization paper predicted this function, which has since been
confirmed by subsequent studies showing SYN3's role in regulating dopamine release
and synaptic vesicle pool dynamics. This is a core function of the synapsin family.
supported_by:
- reference_id: PMID:9539796
supporting_text: "The similarities among synapsins I, II, and III in domain organization, neuron-specific expression, and subcellular localization suggest a possible role for synapsin III in the regulation of neurotransmitter release and synaptogenesis"
- term:
id: GO:0008021
label: synaptic vesicle
evidence_type: TAS
original_reference_id: PMID:9539796
review:
summary: >-
This TAS annotation is based on the original paper characterizing Synapsin-3,
which explicitly states "Synapsin IIIa is associated with synaptic vesicles."
This is the primary localization for Synapsin-3.
action: ACCEPT
reason: >-
Synaptic vesicle localization is directly stated in the original characterization
paper and confirmed by subsequent studies and UniProt annotation. This represents
the core localization for Synapsin-3.
supported_by:
- reference_id: PMID:9539796
supporting_text: "Synapsin IIIa is associated with synaptic vesicles, and its expression appears to be neuron-specific"
references:
- id: GO_REF:0000002
title: Gene Ontology annotation through association of InterPro records with GO terms
findings: []
- id: GO_REF:0000033
title: Annotation inferences using phylogenetic trees
findings: []
- id: GO_REF:0000043
title: Gene Ontology annotation based on UniProtKB/Swiss-Prot keyword mapping
findings: []
- id: GO_REF:0000107
title: Automatic transfer of experimentally verified manual GO annotation data to
orthologs using Ensembl Compara
findings: []
- id: GO_REF:0000117
title: Electronic Gene Ontology annotations created by ARBA machine learning models
findings: []
- id: GO_REF:0000120
title: Combined Automated Annotation using Multiple IEA Methods
findings: []
- id: PMID:15217342
title: The synaptic vesicle cycle.
findings:
- statement: General review of synaptic vesicle cycle mechanisms
supporting_text: "To support rapid and repeated rounds of release, synaptic vesicles undergo a trafficking cycle"
- id: PMID:33961781
title: Dual proteome-scale networks reveal cell-specific remodeling of the human
interactome.
findings:
- statement: High-throughput AP-MS study (BioPlex 3.0) detecting SYN3-SYN2 interaction
supporting_text: "affinity-purification mass spectrometry"
full_text_unavailable: true
- id: PMID:40205054
title: Multimodal cell maps as a foundation for structural and functional genomics.
findings:
- statement: High-throughput interactome study
full_text_unavailable: true
- id: PMID:9539796
title: A third member of the synapsin gene family.
findings:
- statement: Original characterization of Synapsin-3
supporting_text: "We have now cloned and characterized a third member of the synapsin gene family, synapsin III, from human DNA"
- statement: Shows SYN3 is associated with synaptic vesicles
supporting_text: "Synapsin IIIa is associated with synaptic vesicles, and its expression appears to be neuron-specific"
- statement: Neuron-specific expression
supporting_text: "Synapsin IIIa is associated with synaptic vesicles, and its expression appears to be neuron-specific"
- statement: Suggests role in neurotransmitter release and synaptogenesis
supporting_text: "The similarities among synapsins I, II, and III in domain organization, neuron-specific expression, and subcellular localization suggest a possible role for synapsin III in the regulation of neurotransmitter release and synaptogenesis"
core_functions:
- molecular_function:
id: GO:0005524
label: ATP binding
description: >-
The conserved C domain of Synapsin-3 contains an ATP-binding site. Calcium
regulates ATP binding to this domain.
locations:
- id: GO:0030672
label: synaptic vesicle membrane
supported_by:
- reference_id: PMID:9539796
supporting_text: "The primary structure of synapsin IIIa conforms to the domain model previously described for the synapsin family, with domains A, C, and E exhibiting the highest degree of conservation"
- molecular_function:
id: GO:0005524
label: ATP binding
description: >-
Synapsin-3 functions as a synaptic vesicle clustering protein through its
interactions with vesicle membranes and the actin cytoskeleton. By maintaining
vesicle pools and regulating mobilization, it modulates neurotransmitter release.
directly_involved_in:
- id: GO:0097091
label: synaptic vesicle clustering
- id: GO:0007269
label: neurotransmitter secretion
locations:
- id: GO:0098850
label: extrinsic component of synaptic vesicle membrane
supported_by:
- reference_id: PMID:9539796
supporting_text: "Synapsins are a family of neuron-specific synaptic vesicle-associated phosphoproteins that have been implicated in synaptogenesis and in the modulation of neurotransmitter release"
suggested_questions:
- question: What is the specific role of Synapsin-3 in GABAergic synaptic transmission?
- question: What is the functional significance of the SYN3-SYN2 interaction?
suggested_experiments:
- description: >-
Conditional knockout of SYN3 in GABAergic neurons to test role in GABAergic transmission.
This would address uncertainty about the GABAergic-specific annotation.
- description: >-
Structure-function analysis of SYN3-SYN2 heterodimers.
This would elucidate the functional significance of synapsin heteromerization.