Existing Annotations Review

GO Term	Evidence	Action	Reason
GO:0006887 exocytosis	IBA GO_REF:0000033	KEEP AS NON CORE	Summary: Phylogenetic (IBA) inference of an exocytosis role transferred from the broader SCAMP family, whose canonical members function in post-Golgi membrane trafficking and regulated exocytosis. For spiA/Dd31 there is no direct evidence of an exocytic function; the experimentally established role is in maintaining spore stability, and the demonstrated location is the inner face of the spore coat. Reason: A membrane-trafficking/exocytic role is plausible for a SCAMP-family protein and could relate to delivery of spore coat material during encapsulation, but it has not been demonstrated for this divergent spore-specific paralog and is not the core, experimentally supported function. Supporting Evidence: PMID:1592257 Dd31 is associated with the inner face of spore coat fragments in a detergent-resistant manner.
GO:0032588 trans-Golgi network membrane	IBA GO_REF:0000033	MARK AS OVER ANNOTATED	Summary: IBA localization transferred from canonical SCAMP proteins, which cycle through the trans-Golgi network. The only experimentally determined location for Dd31 is the inner face of the spore coat, not the TGN, and spiA is a highly divergent, spore-specific family member. Reason: This is a generic family-level localization not supported by any direct evidence for spiA. The demonstrated site of action is the spore coat, so assigning an active TGN-membrane location over-annotates this divergent paralog. Propagation Review Root cause: PROPAGATION BAD Failure modes: COMPARTMENT OR COMPLEX MISMATCH Sources checked: PANTHER:PTN000074637 · PANTHER node for SCAMP secretory-carrier membrane proteins SUPPORTS SOURCE BUT NOT TARGET trans-Golgi-network-membrane localization is a canonical SCAMP property; SpiA is a spore-coat protein and the family compartment is not demonstrated for it UniProtKB:O15127 · human SCAMP2 SUPPORTS SOURCE BUT NOT TARGET Canonical SCAMP cycles through the TGN; SpiA localizes to the spore coat, so the compartment does not transfer Supporting Evidence: PMID:1592257 Dd31 is associated with the inner face of spore coat fragments in a detergent-resistant manner.
GO:0055038 recycling endosome membrane	IBA GO_REF:0000033	MARK AS OVER ANNOTATED	Summary: IBA localization transferred from canonical SCAMP proteins that reside on recycling endosomes. As with the TGN annotation, there is no direct evidence placing Dd31 on recycling endosomes; the demonstrated location is the spore coat. Reason: Family-level localization inference not supported for this spore-specific SCAMP. The experimentally shown location is the inner face of the spore coat, so an active recycling-endosome-membrane location over-annotates the gene. Propagation Review Root cause: PROPAGATION BAD Failure modes: COMPARTMENT OR COMPLEX MISMATCH Sources checked: PANTHER:PTN000074637 · PANTHER node for SCAMP secretory-carrier membrane proteins SUPPORTS SOURCE BUT NOT TARGET Recycling-endosome-membrane localization is a canonical SCAMP property not supported for the spore-specific SpiA UniProtKB:O15127 · human SCAMP2 SUPPORTS SOURCE BUT NOT TARGET Canonical SCAMP resides on recycling endosomes; SpiA is a spore-coat protein Supporting Evidence: PMID:1592257 Dd31 is associated with the inner face of spore coat fragments in a detergent-resistant manner.
GO:0015031 protein transport	IEA GO_REF:0000002	KEEP AS NON CORE	Summary: InterPro2GO (IEA) annotation derived from the SCAMP domain (IPR007273). Protein transport is a broad process associated with the SCAMP family but has not been demonstrated for spiA, whose characterized role is in spore maintenance. Reason: A membrane-trafficking/protein-transport role is consistent with SCAMP family membership and cannot be excluded, but it is a domain-based inference rather than an experimentally established core function for this gene. Supporting Evidence: PMID:1592257 Dd31 is associated with the inner face of spore coat fragments in a detergent-resistant manner.
GO:0016020 membrane	IEA GO_REF:0000120	ACCEPT	Summary: Dd31 is a multi-pass membrane protein with four predicted transmembrane helices, consistent with SCAMP family topology. Membrane localization is well supported. Reason: The protein sequence contains four hydrophobic transmembrane segments and UniProt annotates it as a multi-pass membrane protein; a generic membrane location is correct, though more specific locations (spore coat) are better captured elsewhere. Supporting Evidence: PMID:1592257 Dd31 is associated with the inner face of spore coat fragments in a detergent-resistant manner.
GO:0003674 molecular_function	ND GO_REF:0000015	ACCEPT	Summary: Root molecular_function placeholder (ND) reflecting that no specific molecular activity has been assigned to Dd31. This accurately represents the current state of knowledge. Reason: The molecular function of spiA/Dd31 is genuinely unknown; beyond SCAMP family membership and membrane topology, no biochemical activity has been demonstrated. The ND annotation is appropriate and should be retained until a specific activity is established.
GO:0030587 sorocarp development	IMP PMID:1592257 Disruption of the sporulation-specific gene spiA in Dictyost...	ACCEPT	Summary: Gene disruption (IMP) shows that spiA is required for normal spore properties during fruiting body (sorocarp) development. spiA-null strains develop and form morphologically normal spores, but the spores lose viability abnormally rapidly with age, a defect rescued by reintroducing the gene. Reason: This is the core, experimentally supported developmental role of the gene, established by a clean knockout-and-rescue experiment showing a specific spore-stability phenotype within sorocarp development. Supporting Evidence: PMID:1592257 Mutant spores have normal viability when assayed soon after the completion of development, but, as the spiA- spores age, they lose viability more rapidly than those of the spiA+ parent. PMID:1592257 Reinserting an intact copy of the spiA gene into a spiA- strain restores the stability of its spores.
GO:0031160 spore wall	IDA PMID:1592257 Disruption of the sporulation-specific gene spiA in Dictyost...	ACCEPT	Summary: Direct evidence (IDA) localizes Dd31 to the spore coat/wall, specifically to the inner face of spore coat fragments in a detergent-resistant manner. This is the core, experimentally established subcellular location of the protein. Reason: An antibody against Dd31 showed the protein is stably associated with the inner face of the spore coat, directly supporting a spore-wall location that is consistent with its role in spore stability. Supporting Evidence: PMID:1592257 Dd31 is associated with the inner face of spore coat fragments in a detergent-resistant manner. PMID:1592257 This location is consistent with its observed role in maintaining stability of the spores.
GO:0031154 culmination involved in sorocarp development	IEP PMID:25887420 Leaps and lulls in the developmental transcriptome of Dictyo...	KEEP AS NON CORE	Summary: Expression-based (IEP) annotation reflecting that spiA transcript is sharply up-regulated during culmination (18-24 h of development) and is used as a sporulation marker. Expression timing indicates involvement in this stage but does not by itself demonstrate a causal function in culmination. Reason: The IEP evidence establishes that spiA is expressed specifically during culmination, consistent with its spore-maturation role, but expression pattern alone is weaker than the knockout evidence and marks stage-specific expression rather than a demonstrated driver of culmination; retain as a non-core process annotation. Supporting Evidence: PMID:25887420 spiA was up-regulated between 18 h and 20 h, and accumulated rapidly through 24 h. PMID:1592257 The spiA gene of Dictyostelium is expressed specifically in prespore cells and spores during culmination, the final stage of development during which prespore and prestalk cells undergo terminal differentiation to form spores and stalk.

Core Functions

spiA/Dd31 is a late spore-specific, multi-pass membrane protein of the SCAMP family that becomes stably associated with the inner face of the spore coat during culmination and is required to maintain long-term spore viability and dormancy. Its specific molecular activity is not established; loss of function does not block spore formation but accelerates the loss of spore viability with age.

Molecular Function:

molecular_function

Directly Involved In:

sorocarp development

Cellular Locations:

spore wall membrane

Supporting Evidence:

PMID:1592257
Dd31 is associated with the inner face of spore coat fragments in a detergent-resistant manner.
PMID:1592257
This location is consistent with its observed role in maintaining stability of the spores.
PMID:1592257
Mutant spores have normal viability when assayed soon after the completion of development, but, as the spiA- spores age, they lose viability more rapidly than those of the spiA+ parent.

References

GO_REF:0000002

Gene Ontology annotation through association of InterPro records with GO terms

GO_REF:0000015

Use of the ND evidence code for Gene Ontology (GO) terms

GO_REF:0000033

Annotation inferences using phylogenetic trees

GO_REF:0000120

Combined Automated Annotation using Multiple IEA Methods

PMID:1592257

Disruption of the sporulation-specific gene spiA in Dictyostelium discoideum leads to spore instability.

spiA is expressed specifically in prespore cells and spores during culmination, the terminal stage of development.

"The spiA gene of Dictyostelium is expressed specifically in prespore cells and spores during culmination, the final stage of development during which prespore and prestalk cells undergo terminal differentiation to form spores and stalk."
The Dd31 protein is associated with the inner face of the spore coat in a detergent-resistant manner.

"Dd31 is associated with the inner face of spore coat fragments in a detergent-resistant manner."
spiA-null spores develop and look normal but lose viability far more rapidly with age than wild-type spores, and reintroducing spiA restores spore stability.

"Mutant spores have normal viability when assayed soon after the completion of development, but, as the spiA- spores age, they lose viability more rapidly than those of the spiA+ parent."

PMID:25887420

Leaps and lulls in the developmental transcriptome of Dictyostelium discoideum.

spiA is a sporulation marker whose transcript is up-regulated during culmination between 18 and 24 h of development.

"spiA was up-regulated between 18 h and 20 h, and accumulated rapidly through 24 h."

file:DICDI/spiA/spiA-hypotheses/spia-scamp-trafficking/openscientist.md

OpenScientist function-assignment analysis of the SpiA SCAMP trafficking hypothesis

Deep Research

OpenScientist

(spiA-hypotheses/spia-scamp-trafficking/openscientist.md)

SpiA (Q02465) — SCAMP Family Membership vs. Vesicular Trafficking Function OpenScientist openscientist-autonomous 8 citations 2 artifacts 2026-07-12T12:17:45.464590 citations file

OpenScientist final report (text/html)

OpenScientist final report (application/pdf)

SpiA (Q02465) — SCAMP Family Membership vs. Vesicular Trafficking Function

Target gene: spiA (Q02465, DD31_DICDI), Dictyostelium discoideum (NCBITaxon:44689)
Seed hypothesis: SpiA is a secretory carrier membrane protein (SCAMP family) that functions in vesicular membrane trafficking.
Focus type: function_assignment

Summary

The seed hypothesis bundles two separable claims, and the evidence pulls them apart sharply. The family claim — that SpiA is a SCAMP (secretory carrier membrane protein) — is well supported by concordant, independent domain and sequence evidence: SpiA carries the SCAMP Pfam domain (PF04144), the InterPro SCAMP signature (IPR007273), and the PANTHER subfamily assignment (PTHR10687:SF2), plus a canonical four-transmembrane-helix membrane core and ~28% mean identity to the five human SCAMPs concentrated in that core. Critically, SpiA is the single SCAMP-family gene in the entire D. discoideum genome, so this is not a paralog-confused call.

The functional claim — that SpiA "functions in vesicular membrane trafficking" — is only weakly (homology-only) supported and is not the gene's demonstrated primary function. Every trafficking-flavored GO annotation on the protein (exocytosis, recycling endosome membrane, trans-Golgi network membrane, protein transport) carries a phylogenetic (IBA) or electronic (IEA) evidence code with no organism-specific experimental backing. The only directly demonstrated function of SpiA is a structural, spore-coat-associated role in maintaining spore viability during dormancy, established by targeted gene deletion (Richardson & Loomis 1992, PMID: 1592257). SpiA is also a divergent SCAMP that lacks the N-terminal NPF motif repeats that mechanistically drive canonical SCAMP–EH-domain trafficking interactions.

Bottom line for the curator: Retain the SCAMP-family molecular identity and the experimentally grounded spore/sorocarp terms as core. Treat the vesicular-trafficking GO terms as non-core, homology-only annotations that do not represent the gene product's primary function. The seed hypothesis should narrow the review — SpiA is a SCAMP, but its established biology is spore-coat maintenance, not general membrane trafficking. Verdict: partially supported / over-annotated on the trafficking claim.

Key Findings

Finding 1 — SpiA is confidently a SCAMP-family multi-pass membrane protein

SpiA (Q02465, DD31_DICDI) is unambiguously a SCAMP on structural and domain grounds. The UniProt entry describes a 269-amino-acid protein with four predicted transmembrane helices (approximately residues 111–131, 139–159, 177–197, and 225–245), matching the canonical SCAMP membrane core of four TM segments flanked by cytoplasmic N- and C-termini. Three independent classification resources converge: Pfam PF04144 (SCAMP), InterPro IPR007273 (SCAMP), and PANTHER PTHR10687:SF2 (Secretory carrier-associated membrane protein), and UniProt carries the SIMILARITY comment "Belongs to the SCAMP family" (ECO:0000305, curator inference). This is the robust half of the hypothesis — supported by multiple orthogonal signatures, with no competing family assignment. The caveat is that it is homology/domain-level evidence, not a direct biochemical demonstration.

Finding 2 — SpiA lacks canonical SCAMP NPF trafficking motifs and is structurally divergent

A direct sequence scan of Q02465 found zero NPF (Asn-Pro-Phe) motifs and zero NPY variants. This matters mechanistically: canonical mammalian SCAMP1–3 carry two to four N-terminal NPF repeats that bind EH-domain proteins (e.g., intersectin, EHD family) to recruit the machinery driving endocytic and exocytic vesicle trafficking. SpiA's N-terminal cytoplasmic region (~residues 1–110) is instead short, partly disordered (annotated disordered 1–35), and Ser/Ala/Pro-rich, not an NPF-repeat interaction module, and the protein is shorter (269 aa) than the long mammalian SCAMPs (~330 aa). The absence of the very motif that mechanistically links SCAMPs to vesicle traffic undermines the specific trafficking claim. Caveat: the short human SCAMP4/SCAMP5 (229/235 aa) are also NPF-less yet still traffic, so NPF absence is suggestive rather than decisive.

Finding 3 — The demonstrated function of SpiA is spore-coat-associated stability, not trafficking

The decisive evidence is the loss-of-function study of Richardson & Loomis 1992 (PMID: 1592257). Using homologous recombination to delete spiA, they found that spiA-null cells develop normally and produce morphologically normal spores (indistinguishable from wild type by transmission and scanning EM). The defect is one of durability, not formation: as spiA-null spores age, they lose viability far faster than the parent — after 11 days submerged in dilute buffer (conditions preventing germination), spiA-null spore viability dropped ~10⁵-fold versus only ~10-fold for the parent — a phenotype rescued by reinserting an intact spiA copy. The gene product Dd31 (30 kDa) associates with the inner face of the spore coat in a detergent-resistant manner, consistent with a structural role stabilizing the dormant spore. The experimental GO annotations mirror this biology: spore wall (GO:0031160, IDA), sorocarp development (GO:0030587, IMP), and culmination (GO:0031154, IEP) — while all trafficking terms remain IBA/IEA.

Finding 4 — SpiA is the ONLY SCAMP gene in D. discoideum, ruling out paralog confusion

UniProt searches restricted to organism 44689 return exactly one protein for Pfam PF04144, one for InterPro IPR007273, and one for PANTHER PTHR10687 — Q02465/spiA in all three cases. There is therefore no within-organism paralog-confusion risk. For comparison, humans carry five SCAMPs (SCAMP1 O15126 338 aa, SCAMP2 O15127 329 aa, SCAMP3 O14828 347 aa, SCAMP4 Q969E2 229 aa, SCAMP5 Q8TAC9 235 aa). SpiA (269 aa) is closest in size to the short SCAMP4/5 subgroup, which also lack NPF repeats yet still function in synaptic-vesicle trafficking — keeping the trafficking hypothesis alive as a possibility but not a fact. The single-copy status cuts both ways: it removes paralog confusion but implies Dictyostelium has repurposed its lone ancestral SCAMP toward a lineage-specific, developmentally restricted spore-coat role.

Finding 5 — Quantitative confirmation: ~28% identity to human SCAMPs, concentrated in the TM core

Global Needleman–Wunsch alignment of SpiA against the five human SCAMPs gave SCAMP1 30.6%, SCAMP3 30.6%, SCAMP2 28.9%, SCAMP4 26.6%, SCAMP5 23.8% (mean 28.1%). The highest identity is to the long SCAMP1/SCAMP3 rather than the size-matched short SCAMP4/5, indicating that conservation is concentrated in the transmembrane core rather than the cytoplasmic tails. This twilight-zone identity, combined with concordant Pfam/InterPro/PANTHER HMM hits, solidly confirms genuine but divergent SCAMP-family membership while explaining why the trafficking-associated N-terminal features are not conserved.

Mechanistic Model / Interpretation

    SEED HYPOTHESIS
    "SpiA is a SCAMP that functions in vesicular trafficking"
          |
 +----------------+----------------+
 |                                 |
   CLAIM A: family                  CLAIM B: function
   "is a SCAMP"                     "vesicular trafficking"
 |                                 |
   SUPPORTED (strong)              WEAK / homology-only
   - PF04144, IPR007273,           - all trafficking GO = IBA/IEA
     PTHR10687:SF2                  - NO NPF motifs (canonical SCAMP
   - 4-TM core                        trafficking motif absent)
   - 28.1% id to human SCAMPs      - divergent, short disordered N-term
   - single-copy (no paralog       - NO organism-specific trafficking assay
     confusion)                          |
                   DEMONSTRATED FUNCTION instead:
                   - spiA-null: normal spores that lose
                     viability 10^5-fold on aging
                   - Dd31 on INNER spore coat,
                     detergent-resistant
                   - GO: spore wall (IDA), sorocarp
                     dev (IMP), culmination (IEP)

The most parsimonious model is that Dictyostelium possesses a single, ancestral SCAMP that has been evolutionarily specialized as a structural component of the dormant spore's inner coat. Its SCAMP membrane architecture (4-TM core) is retained and likely inserts into spore-coat/plasma membranes, but the trafficking-adaptor module (N-terminal NPF repeats) that defines canonical SCAMP trafficking has been lost or never elaborated in this lineage. Developmental regulation (PKA → SrfA → spiA) places SpiA firmly in a terminal-differentiation/sporulation program, not a constitutive membrane-traffic pathway.

An important caveat preserves a minimal trafficking possibility: the spore coat itself is assembled from secreted prespore-vesicle contents, and clathrin-mediated traffic is required for spore differentiation (PMID: 9053320). So SpiA operates within a trafficking-dependent developmental context, but the data localize SpiA to the product (the inner coat) rather than the machinery (vesicles/adaptors). Being embedded in a trafficking-dependent process is not the same as being a trafficking effector — indeed, the clathrin data place spiA expression downstream of the trafficking machinery.

Evidence Matrix

Citation	Evidence type	Direction	Claim tested	Key finding	Context	Confidence / limitations
UniProt Q02465 (PF04144, IPR007273, PTHR10687:SF2)	Structural/evolutionary + computational	Supports	SpiA is a SCAMP-family protein	SCAMP domain + 4 TM helices = canonical SCAMP core	D. discoideum record	High for family; homology-based (ECO:0000305/IEA)
Sequence scan of Q02465 (this work)	Computational	Qualifies/refutes trafficking	Does SpiA have canonical SCAMP trafficking motifs?	Zero NPF/NPY motifs; short, disordered, Ser/Ala/Pro-rich N-terminus; 269 aa vs ~330 aa	In-silico	Weakened caveat: short human SCAMP4/5 also NPF-less yet traffic
Needleman–Wunsch alignment (this work)	Structural/evolutionary + computational	Supports family; qualifies trafficking	Quantitative SCAMP identity	28.1% mean identity to 5 human SCAMPs, concentrated in TM core	Sequence	High; conservation in core not termini
UniProt taxon-44689 search (this work)	Computational	Qualifies	Paralog confusion?	Exactly one SCAMP gene in D. discoideum (=spiA); human has 5	Genome-wide	High; rules out within-organism paralog cross-annotation
Richardson & Loomis 1992, PMID: 1592257	Mutant phenotype + localization	Refutes trafficking as core; supports spore role	What does SpiA do?	spiA-null → normal spores lose viability 10⁵-fold on aging; Dd31 on inner spore coat, detergent-resistant; rescued by re-insertion	D. discoideum spores	High; decisive functional study. No trafficking assay done
Escalante & Sastre 1998, PMID: 9729488	Expression/regulation	Qualifies (context)	When/where is spiA expressed	Late prespore/spore maturation marker; mRNA reduced in srfA-null	Sporulation	Medium-high; spore-specific, not vegetative-trafficking context
SrfA/PKA study, PMID: 12204259	Expression/regulation	Qualifies (context)	Regulation of spiA	spiA induced via PKA→SrfA at culmination	Sporulation	Medium; regulatory context
Niswonger & O'Halloran 1997, PMID: 9053320	Mutant phenotype (clathrin)	Competing/context	Is spiA downstream of trafficking machinery?	Clathrin-minus cells fail to express spiA and make no spores	Development	Medium; places spiA downstream of, not as, trafficking effector
stkA/stalky, PMID: 11100898; PMID: 8898200	Mutant phenotype/expression	Qualifies (context)	spiA as spore-pathway marker	spiA fails to express in stalky mutants; spore-specific transcript	Cell-fate	Medium; confirms spore-specificity
yelA, PMID: 9254905	Mutant phenotype/expression	Qualifies (context)	spiA as sporulation marker	spiA precociously expressed in yelA-null	Development	Low-medium; regulatory context only

GO Curation Implications

Likely curation action (leads requiring curator verification):

Retain (direct evidence): GO:0031160 spore wall (IDA), GO:0030587 sorocarp development (IMP), GO:0031154 culmination involved in sorocarp development (IEP). Consider adding GO:0016021 integral component of membrane (4 TM helices) and a spore-coat CC consistent with the detergent-resistant inner-coat localization.
Keep but flag as non-core / homology-only: GO:0006887 exocytosis (IBA), GO:0055038 recycling endosome membrane (IBA), GO:0032588 trans-Golgi network membrane (IBA), GO:0015031 protein transport (IEA). Do not upgrade to experimental; the divergent, NPF-less sequence weakens automatic SCAMP propagation, and no Dictyostelium trafficking assay exists.
Family/MF term: the SCAMP-family membrane-protein assignment is justified from PF04144/IPR007273; avoid asserting a specific vesicular-transport MF beyond family membership, and avoid "protein binding" as a final recommendation.
Seed-hypothesis-as-core-function: Do not record "vesicular membrane trafficking" as SpiA's primary function; the supported core function is spore-coat-associated maintenance of spore viability within sorocarp development.

GO Decision Table (computed — lead requiring curator verification)

GO_ID	term	aspect	evidence code	curation lead	rationale
GO:0031160	spore wall	CC	IDA (dictyBase)	RETAIN	Direct: Dd31 on inner face of spore coat (PMID 1592257)
GO:0030587	sorocarp development	BP	IMP (dictyBase)	RETAIN	Direct: spiA-null spore-instability phenotype (PMID 1592257)
GO:0031154	culmination in sorocarp development	BP	IEP (dictyBase)	RETAIN	Spore/prespore-specific expression at culmination
GO:0016021	integral component of membrane	CC	(add) ISS/IEA	ADD-LEAD	4 predicted TM helices; supported by topology
GO:0006887	exocytosis	BP	IBA (GO_Central)	KEEP-NONCORE	Homology-only; no Dictyostelium assay
GO:0055038	recycling endosome membrane	CC	IBA (GO_Central)	KEEP-NONCORE	Homology-only; conflicts with spore-coat localization
GO:0032588	trans-Golgi network membrane	CC	IBA (GO_Central)	KEEP-NONCORE	Homology-only; no organism-specific data
GO:0015031	protein transport	BP	IEA (InterPro)	KEEP-NONCORE	Electronic family propagation only

Mechanistic Scope

The immediate molecular identity tested is an integral, multi-pass (4-TM) SCAMP-family membrane protein. The direct cellular function demonstrated is association with the inner face of the spore coat and maintenance of spore structural integrity/viability during dormancy. The proposed "vesicular membrane trafficking" is a family-level inference, not a measured activity; the spore-instability phenotype is the demonstrated loss-of-function outcome and is developmental/structural, not a generic trafficking defect. Distinctions to keep clear:

Direct activity (demonstrated): membrane-embedded, inner-spore-coat protein required to maintain spore viability during dormancy.
Direct activity (hypothesized, homology-only): SCAMP-type vesicular carrier — not shown in Dictyostelium, and weakened by NPF-motif absence.
Downstream/context phenotype: the spore-viability decay on aging is the readout of losing a structural protein, not evidence of a trafficking defect.
Pathway context: spore-coat assembly overall depends on vesicular secretion and clathrin (PMID: 9053320), but those functions belong to other genes; SpiA is a cargo/product component, not the machinery.

Conflicts and Alternatives

Divergent-paralog / over-propagation risk: SpiA lacks canonical SCAMP NPF EH-binding repeats, so IBA transfer of exocytosis/recycling-endosome/TGN terms from long metazoan/plant SCAMPs may over-annotate this specialized ortholog. Caveat: short human SCAMP4/5 are also NPF-less yet still traffic, so NPF absence is suggestive, not decisive.
Single-SCAMP genome: D. discoideum encodes exactly one SCAMP-family gene — spiA itself. This removes classic paralog confusion (no separate housekeeping SCAMP to mis-map), but implies the lone ancestral SCAMP was co-opted/neofunctionalized for a terminal spore-coat role, so uncritically propagating generic SCAMP trafficking terms is risky.
Developmental specialization: SpiA is expressed only at terminal spore differentiation, unlike housekeeping SCAMPs that operate constitutively.
Downstream vs. effector: clathrin-minus data (PMID: 9053320) place spiA expression downstream of the trafficking machinery, arguing SpiA is a differentiation product rather than a trafficking effector.

Limitations and Knowledge Gaps

Direct trafficking assay in Dictyostelium — none exists. Checked PubMed; no Dictyostelium SCAMP/exocytosis study found. Resolving this would determine whether the IBA terms are real.
Membrane topology/orientation — predicted (4 TM) but not experimentally mapped; matters for whether cytoplasmic loops could engage trafficking partners.
Interaction partners — no known EH-domain or SNARE partners; NPF absence predicts none. An interactome would test the trafficking mechanism.
N-terminal function unknown — the Ser/Ala/Pro-rich disordered N-terminus is uncharacterized and may mediate a Dictyostelium-specific interaction (e.g., with coat proteins such as SP85/PsB, PMID: 12455962).
Structure not experimentally solved — only predicted TM topology is available; an AlphaFold model exists but was not parsed here.
Single functional study — the definitive phenotype rests largely on one 1992 deletion study; modern reproduction with quantitative trafficking assays would strengthen the negative-for-trafficking case.

Overall, conclusions about trafficking are conservative because they hinge on absence of evidence plus motif divergence rather than a direct negative assay.

Discriminating Tests

GFP-SpiA live imaging across vegetative and developing cells: does it traffic through endosomes/TGN/plasma membrane, or only deposit at the forming spore coat?
Endocytosis/exocytosis assays in spiA-null vegetative cells (fluid-phase uptake, lysosomal-enzyme secretion, contractile-vacuole dynamics) to test for a generic trafficking phenotype.
Interaction proteomics (BioID/AP-MS) for EH-domain proteins/SNAREs (trafficking) vs. spore-coat proteins such as SP85/PsB, SP60, cotB (structural).
Domain-swap/rescue: can a mammalian SCAMP rescue spiA-null spore instability, and can SpiA rescue a SCAMP-trafficking defect? Tests functional equivalence.
Comparative genomics across Amoebozoa to determine whether the single-SCAMP, spore-specialized configuration is lineage-conserved.

Curation Leads (require curator verification)

Reference to verify: PMID: 1592257 (Richardson & Loomis 1992) — snippet: "Dd31 is associated with the inner face of spore coat fragments in a detergent-resistant manner. This location is consistent with its observed role in maintaining stability of the spores." Supports spore-coat CC + spore-stability BP as the core function.
Reference to verify: PMID: 9729488 (Escalante & Sastre 1998) — spiA as srfA-dependent spore maturation marker.
Reference to verify: PMID: 9053320 — clathrin (not SpiA) is the trafficking component required upstream of spiA expression.
Candidate action changes: retain direct spore terms; add GO:0016021 integral component of membrane; keep trafficking terms with IBA/IEA codes but do not treat as core; add a curator note that SpiA is a divergent, NPF-less SCAMP with no organism-specific trafficking evidence.
Suggested questions for curator: Should IBA exocytosis/recycling-endosome/TGN terms be retained for a lineage-specific, motif-divergent SCAMP with a demonstrated non-trafficking phenotype? Is a spore-coat structural-constituent term warranted?
Suggested experiments: GFP-SpiA localization time-course; endo/exocytosis assays in spiA-null; interaction proteomics — as detailed under Discriminating Tests.

Evidence Base (Literature Summary)

PMID	Title (abbrev.)	Role in this evaluation
1592257	Disruption of spiA leads to spore instability	Decisive. Establishes spore-coat structural role; refutes trafficking as primary function
9729488	SRF homolog required for spore differentiation	Regulatory context; spiA as spore maturation marker
12204259	SrfA mediates PKA activation during sporulation	PKA→SrfA→spiA regulatory axis
9053320	Clathrin required for spore differentiation	Trafficking machinery is upstream of, and separate from, SpiA
11100898	STKA-dependent genes	spiA is a spore-pathway transcript
8898200	Cell fate gene stalky	spiA fails in stalky mutants
9254905	yelA null precocious sporulation	spiA as precocious-sporulation marker
12455962	Outside-in signaling by spore coat protein SP85	Spore-coat assembly context (potential SpiA partners)
10556070	Adenylyl cyclase acrA in late development	Sporulation regulatory context

Conclusion

The seed hypothesis is half right and half over-reaching. SpiA is genuinely a SCAMP-family, four-transmembrane membrane protein — a call supported by concordant domain assignments, quantitative sequence identity (~28% to human SCAMPs, concentrated in the TM core), and single-copy status that rules out paralog confusion. But "functions in vesicular membrane trafficking" is an inference from mammalian homology that is (a) mechanistically weakened by SpiA's loss of the canonical NPF trafficking motifs, and (b) not the gene product's demonstrated primary function. The one direct functional study shows SpiA is a detergent-resistant inner-spore-coat protein whose loss causes accelerated spore-viability decay — a structural, developmentally restricted role. For curation, keep the SCAMP identity and the experimentally grounded spore/sorocarp terms as core, and treat the trafficking GO terms as non-core, homology-only annotations that must not be presented as SpiA's primary function.

Artifacts

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id: Q02465
gene_symbol: spiA
product_type: PROTEIN
status: COMPLETE
taxon:
  id: NCBITaxon:44689
  label: Dictyostelium discoideum
description: spiA encodes Dd31, a late spore-specific, multi-pass membrane protein
  of the SCAMP (secretory carrier-associated membrane protein) family in the social
  amoeba Dictyostelium discoideum. Its transcript is induced specifically in prespore
  cells and spores during culmination, the terminal stage of fruiting body
  (sorocarp) formation, making spiA a widely used sporulation marker. The Dd31
  protein (~30 kDa on Western blots) is associated with the inner face of the spore
  coat in a detergent-resistant manner. Loss of spiA does not detectably perturb
  development or spore morphology, but mutant spores lose viability far more rapidly
  than wild-type spores as they age, especially when submerged in dilute buffer,
  indicating a role in maintaining long-term spore stability and dormancy. The
  precise molecular activity of Dd31 is not established.
existing_annotations:
- term:
    id: GO:0006887
    label: exocytosis
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: involved_in
  review:
    summary: Phylogenetic (IBA) inference of an exocytosis role transferred from the
      broader SCAMP family, whose canonical members function in post-Golgi membrane
      trafficking and regulated exocytosis. For spiA/Dd31 there is no direct
      evidence of an exocytic function; the experimentally established role is in
      maintaining spore stability, and the demonstrated location is the inner face
      of the spore coat.
    action: KEEP_AS_NON_CORE
    reason: A membrane-trafficking/exocytic role is plausible for a SCAMP-family
      protein and could relate to delivery of spore coat material during
      encapsulation, but it has not been demonstrated for this divergent
      spore-specific paralog and is not the core, experimentally supported function.
    supported_by:
    - reference_id: PMID:1592257
      supporting_text: Dd31 is associated with the inner face of spore coat fragments
        in a detergent-resistant manner.
- term:
    id: GO:0032588
    label: trans-Golgi network membrane
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: is_active_in
  review:
    summary: IBA localization transferred from canonical SCAMP proteins, which cycle
      through the trans-Golgi network. The only experimentally determined location
      for Dd31 is the inner face of the spore coat, not the TGN, and spiA is a highly
      divergent, spore-specific family member.
    action: MARK_AS_OVER_ANNOTATED
    propagation_review:
      root_cause: PROPAGATION_BAD
      failure_modes:
      - COMPARTMENT_OR_COMPLEX_MISMATCH
      source_entities:
      - source_id: PANTHER:PTN000074637
        source_label: "PANTHER node for SCAMP secretory-carrier membrane proteins"
        source_status: SUPPORTS_SOURCE_BUT_NOT_TARGET
        comment: "trans-Golgi-network-membrane localization is a canonical SCAMP property; SpiA is a spore-coat protein and the family compartment is not demonstrated for it"
      - source_id: UniProtKB:O15127
        source_label: "human SCAMP2"
        source_status: SUPPORTS_SOURCE_BUT_NOT_TARGET
        comment: "Canonical SCAMP cycles through the TGN; SpiA localizes to the spore coat, so the compartment does not transfer"
    reason: This is a generic family-level localization not supported by any direct
      evidence for spiA. The demonstrated site of action is the spore coat, so
      assigning an active TGN-membrane location over-annotates this divergent
      paralog.
    supported_by:
    - reference_id: PMID:1592257
      supporting_text: Dd31 is associated with the inner face of spore coat fragments
        in a detergent-resistant manner.
- term:
    id: GO:0055038
    label: recycling endosome membrane
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: is_active_in
  review:
    summary: IBA localization transferred from canonical SCAMP proteins that reside
      on recycling endosomes. As with the TGN annotation, there is no direct
      evidence placing Dd31 on recycling endosomes; the demonstrated location is the
      spore coat.
    action: MARK_AS_OVER_ANNOTATED
    propagation_review:
      root_cause: PROPAGATION_BAD
      failure_modes:
      - COMPARTMENT_OR_COMPLEX_MISMATCH
      source_entities:
      - source_id: PANTHER:PTN000074637
        source_label: "PANTHER node for SCAMP secretory-carrier membrane proteins"
        source_status: SUPPORTS_SOURCE_BUT_NOT_TARGET
        comment: "Recycling-endosome-membrane localization is a canonical SCAMP property not supported for the spore-specific SpiA"
      - source_id: UniProtKB:O15127
        source_label: "human SCAMP2"
        source_status: SUPPORTS_SOURCE_BUT_NOT_TARGET
        comment: "Canonical SCAMP resides on recycling endosomes; SpiA is a spore-coat protein"
    reason: Family-level localization inference not supported for this spore-specific
      SCAMP. The experimentally shown location is the inner face of the spore coat,
      so an active recycling-endosome-membrane location over-annotates the gene.
    supported_by:
    - reference_id: PMID:1592257
      supporting_text: Dd31 is associated with the inner face of spore coat fragments
        in a detergent-resistant manner.
- term:
    id: GO:0015031
    label: protein transport
  evidence_type: IEA
  original_reference_id: GO_REF:0000002
  qualifier: involved_in
  review:
    summary: InterPro2GO (IEA) annotation derived from the SCAMP domain (IPR007273).
      Protein transport is a broad process associated with the SCAMP family but has
      not been demonstrated for spiA, whose characterized role is in spore
      maintenance.
    action: KEEP_AS_NON_CORE
    reason: A membrane-trafficking/protein-transport role is consistent with SCAMP
      family membership and cannot be excluded, but it is a domain-based inference
      rather than an experimentally established core function for this gene.
    supported_by:
    - reference_id: PMID:1592257
      supporting_text: Dd31 is associated with the inner face of spore coat fragments
        in a detergent-resistant manner.
- term:
    id: GO:0016020
    label: membrane
  evidence_type: IEA
  original_reference_id: GO_REF:0000120
  qualifier: located_in
  review:
    summary: Dd31 is a multi-pass membrane protein with four predicted transmembrane
      helices, consistent with SCAMP family topology. Membrane localization is well
      supported.
    action: ACCEPT
    reason: The protein sequence contains four hydrophobic transmembrane segments and
      UniProt annotates it as a multi-pass membrane protein; a generic membrane
      location is correct, though more specific locations (spore coat) are better
      captured elsewhere.
    supported_by:
    - reference_id: PMID:1592257
      supporting_text: Dd31 is associated with the inner face of spore coat fragments
        in a detergent-resistant manner.
- term:
    id: GO:0003674
    label: molecular_function
  evidence_type: ND
  original_reference_id: GO_REF:0000015
  qualifier: enables
  review:
    summary: Root molecular_function placeholder (ND) reflecting that no specific
      molecular activity has been assigned to Dd31. This accurately represents the
      current state of knowledge.
    action: ACCEPT
    reason: The molecular function of spiA/Dd31 is genuinely unknown; beyond SCAMP
      family membership and membrane topology, no biochemical activity has been
      demonstrated. The ND annotation is appropriate and should be retained until a
      specific activity is established.
- term:
    id: GO:0030587
    label: sorocarp development
  evidence_type: IMP
  original_reference_id: PMID:1592257
  qualifier: acts_upstream_of_or_within
  review:
    summary: Gene disruption (IMP) shows that spiA is required for normal spore
      properties during fruiting body (sorocarp) development. spiA-null strains
      develop and form morphologically normal spores, but the spores lose viability
      abnormally rapidly with age, a defect rescued by reintroducing the gene.
    action: ACCEPT
    reason: This is the core, experimentally supported developmental role of the
      gene, established by a clean knockout-and-rescue experiment showing a specific
      spore-stability phenotype within sorocarp development.
    supported_by:
    - reference_id: PMID:1592257
      supporting_text: Mutant spores have normal viability when assayed soon after
        the completion of development, but, as the spiA- spores age, they lose
        viability more rapidly than those of the spiA+ parent.
    - reference_id: PMID:1592257
      supporting_text: Reinserting an intact copy of the spiA gene into a spiA-
        strain restores the stability of its spores.
- term:
    id: GO:0031160
    label: spore wall
  evidence_type: IDA
  original_reference_id: PMID:1592257
  qualifier: located_in
  review:
    summary: Direct evidence (IDA) localizes Dd31 to the spore coat/wall, specifically
      to the inner face of spore coat fragments in a detergent-resistant manner. This
      is the core, experimentally established subcellular location of the protein.
    action: ACCEPT
    reason: An antibody against Dd31 showed the protein is stably associated with the
      inner face of the spore coat, directly supporting a spore-wall location that is
      consistent with its role in spore stability.
    supported_by:
    - reference_id: PMID:1592257
      supporting_text: Dd31 is associated with the inner face of spore coat fragments
        in a detergent-resistant manner.
    - reference_id: PMID:1592257
      supporting_text: This location is consistent with its observed role in
        maintaining stability of the spores.
- term:
    id: GO:0031154
    label: culmination involved in sorocarp development
  evidence_type: IEP
  original_reference_id: PMID:25887420
  qualifier: acts_upstream_of_or_within
  review:
    summary: Expression-based (IEP) annotation reflecting that spiA transcript is
      sharply up-regulated during culmination (18-24 h of development) and is used as
      a sporulation marker. Expression timing indicates involvement in this stage but
      does not by itself demonstrate a causal function in culmination.
    action: KEEP_AS_NON_CORE
    reason: The IEP evidence establishes that spiA is expressed specifically during
      culmination, consistent with its spore-maturation role, but expression pattern
      alone is weaker than the knockout evidence and marks stage-specific expression
      rather than a demonstrated driver of culmination; retain as a non-core process
      annotation.
    supported_by:
    - reference_id: PMID:25887420
      supporting_text: spiA was up-regulated between 18 h and 20 h, and accumulated
        rapidly through 24 h.
    - reference_id: PMID:1592257
      supporting_text: The spiA gene of Dictyostelium is expressed specifically in
        prespore cells and spores during culmination, the final stage of development
        during which prespore and prestalk cells undergo terminal differentiation to
        form spores and stalk.
references:
- id: GO_REF:0000002
  title: Gene Ontology annotation through association of InterPro records with GO
    terms
  findings: []
- id: GO_REF:0000015
  title: Use of the ND evidence code for Gene Ontology (GO) terms
  findings: []
- id: GO_REF:0000033
  title: Annotation inferences using phylogenetic trees
  findings: []
- id: GO_REF:0000120
  title: Combined Automated Annotation using Multiple IEA Methods
  findings: []
- id: PMID:1592257
  title: Disruption of the sporulation-specific gene spiA in Dictyostelium discoideum
    leads to spore instability.
  findings:
  - statement: spiA is expressed specifically in prespore cells and spores during
      culmination, the terminal stage of development.
    supporting_text: The spiA gene of Dictyostelium is expressed specifically in
      prespore cells and spores during culmination, the final stage of development
      during which prespore and prestalk cells undergo terminal differentiation to
      form spores and stalk.
  - statement: The Dd31 protein is associated with the inner face of the spore coat
      in a detergent-resistant manner.
    supporting_text: Dd31 is associated with the inner face of spore coat fragments
      in a detergent-resistant manner.
  - statement: spiA-null spores develop and look normal but lose viability far more
      rapidly with age than wild-type spores, and reintroducing spiA restores spore
      stability.
    supporting_text: Mutant spores have normal viability when assayed soon after the
      completion of development, but, as the spiA- spores age, they lose viability
      more rapidly than those of the spiA+ parent.
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: Primary knockout-and-rescue study establishing the spore-coat
      localization and spore-stability role of Dd31/spiA. Cached record is
      abstract-only (full_text_available false); all quotes are verbatim from the
      abstract.
- id: PMID:25887420
  title: Leaps and lulls in the developmental transcriptome of Dictyostelium discoideum.
  findings:
  - statement: spiA is a sporulation marker whose transcript is up-regulated during
      culmination between 18 and 24 h of development.
    supporting_text: spiA was up-regulated between 18 h and 20 h, and accumulated
      rapidly through 24 h.
  reference_review:
    relevance: MEDIUM
    correctness: VERIFIED
    review_notes: Developmental transcriptome study; supports the culmination-stage,
      sporulation-marker expression of spiA. Full text available and quote is
      verbatim.
- id: file:DICDI/spiA/spiA-hypotheses/spia-scamp-trafficking/openscientist.md
  title: OpenScientist function-assignment analysis of the SpiA SCAMP trafficking hypothesis
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: >-
      Independent OpenScientist function-assignment run (3 iterations). Verdict
      PARTIALLY SUPPORTED / over-annotated on the trafficking claim. SCAMP
      family membership is strongly supported by concordant orthogonal
      signatures (Pfam PF04144, InterPro IPR007273, PANTHER PTHR10687:SF2, a
      canonical four-transmembrane core, ~28 percent identity to the five human
      SCAMPs), and SpiA is the single SCAMP gene in the D. discoideum genome, so
      the family call is not paralog-confused. However the vesicular-trafficking
      function is homology-only (all trafficking GO terms are IBA/IEA), SpiA
      lacks the N-terminal NPF motifs that drive canonical SCAMP trafficking,
      and the only experimentally demonstrated role is the structural
      spore-coat / spore-viability function. Concordant with this review keeping
      the trafficking terms non-core and the spore-coat role core.
core_functions:
- description: spiA/Dd31 is a late spore-specific, multi-pass membrane protein of the
    SCAMP family that becomes stably associated with the inner face of the spore coat
    during culmination and is required to maintain long-term spore viability and
    dormancy. Its specific molecular activity is not established; loss of function
    does not block spore formation but accelerates the loss of spore viability with
    age.
  molecular_function:
    id: GO:0003674
    label: molecular_function
  directly_involved_in:
  - id: GO:0030587
    label: sorocarp development
  locations:
  - id: GO:0031160
    label: spore wall
  - id: GO:0016020
    label: membrane
  supported_by:
  - reference_id: PMID:1592257
    supporting_text: Dd31 is associated with the inner face of spore coat fragments
      in a detergent-resistant manner.
  - reference_id: PMID:1592257
    supporting_text: This location is consistent with its observed role in
      maintaining stability of the spores.
  - reference_id: PMID:1592257
    supporting_text: Mutant spores have normal viability when assayed soon after the
      completion of development, but, as the spiA- spores age, they lose viability
      more rapidly than those of the spiA+ parent.

spiA

Gene Description