FMRFamide-related neuropeptides precursor protein in Sepia officinalis. This 331 amino acid precursor is proteolytically processed into at least 11 bioactive FMRFamide tetrapeptides plus three additional FaRP variants (FIRF-amide, FLRF-amide, ALSGDAFLRF-amide). The mature peptides function as excitatory neurotransmitters at the chromatophore neuromuscular junction, where they act as slow-onset, long-lasting excitors of chromatophore muscles to produce chromatophore expansion. FaRPs are expressed in the posterior chromatophore lobes of the brain and in peripheral nerves around chromatophores, consistent with their role in body patterning and pigmentation control in cephalopods.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005576 extracellular region | IEA GO_REF:0000044 | ACCEPT | Summary: The extracellular region annotation is based on UniProtKB subcellular location mapping. UniProt annotates this protein as "Secreted" based on experimental evidence from PMID:10805923. The mature FMRFamide peptides are released from neurons into the extracellular space at the chromatophore neuromuscular junction, where they act directly on chromatophore muscles (PMID:10805923, PMID:9319020). This is an appropriate cellular component annotation. Reason: The protein is a secreted neuropeptide precursor. After signal peptide cleavage and proteolytic processing, the bioactive peptides are released into the extracellular space at synapses. UniProt annotates this as "Secreted" with experimental evidence from PMID:10805923. The IEA mapping from the subcellular location annotation is correct. Supporting Evidence: PMID:10805923 Evidence is also presented suggesting that FMRFamide-related peptides (FaRPs) also function as neurotransmitters at the Sepia chromatophore NMJ. FMRFamide application causes contraction of chromatophore muscles PMID:9319020 FMRFamide-like immunoreactivity was also seen in the periphery, in the nerves around the chromatophores and in close apposition to the muscles in the chromatophore layer of the fin. |
| GO:0007218 neuropeptide signaling pathway | IEA GO_REF:0000120 | ACCEPT | Summary: The neuropeptide signaling pathway annotation is derived from InterPro2GO mapping via the FMRFamide-related peptide domain (IPR002544). This is well supported by the literature: the FMRFa precursor encodes multiple neuropeptides that function in peptidergic signaling at the chromatophore neuromuscular junction (PMID:9192498, PMID:9319020, PMID:10805923). Reason: This is the core biological process for this gene product. The FMRFa precursor is processed into multiple bioactive neuropeptides that function in neuropeptide signaling at the chromatophore NMJ. All four classes of FaRPs encoded by this precursor (FMRF, FLRF, FIRF, ALSGDAFLRF) cause chromatophore expansion when assayed in bioassays (PMID:9192498). The InterPro2GO mapping is appropriate and well supported. Supporting Evidence: PMID:9192498 Each of the four FaRPs encoded by this cDNA causes chromatophore expansion when assayed in an in vitro chromatophore bioassay. Thus, it is likely that one or more of the FaRPs identified in this study are involved in controlling chromatophore activity in cuttlefish. PMID:9319020 We present data demonstrating that the chromatophore muscles in the European cuttlefish Sepia officinalis are also regulated by the FMRFamide family of neuropeptides. Using an in vitro chromatophore bioassay, it has been determined that several FMRFamide-related peptides (FaRPs) are potent excitors of the chromatophore muscles, causing chromatophore expansion. |
| GO:0160041 neuropeptide activity | IDA PMID:9192498 Molecular analysis of FMRFamide- and FMRFamide-related pepti... | NEW | Summary: NEW annotation. The mature FMRFamide peptides function as neuropeptide ligands that activate receptors on chromatophore muscles. GO:0160041 (neuropeptide activity) is defined as "the receptor ligand activity of any polypeptide expressed in, and secreted from a neuron." FMRFa gene products are expressed in chromatophore motoneurons in the posterior chromatophore lobe and act directly on chromatophore muscles as excitatory neurotransmitters (PMID:10805923, PMID:9192498, PMID:9319020). Reason: This is the most appropriate molecular function term for this gene product. The FMRFamide peptides are neuropeptides secreted from neurons that act as receptor ligands on target muscle cells. This is directly supported by bioassay data showing chromatophore muscle excitation (PMID:9192498), pharmacological evidence of direct action on muscle receptors (PMID:10805923), and immunocytochemical localization in neurons (PMID:10805923, PMID:9319020). Supporting Evidence: PMID:10805923 FMRFamide application causes contraction of chromatophore muscles; however, the FMRFamide effect is slower and longer lasting than that of glutamate. Pharmacological data show that FMRFamide acts directly on the chromatophore muscles. PMID:9192498 The cDNA encodes a precursor protein containing four FaRPs: ALSGDAFLRF, FIRF, FLRF and FMRF. |
| GO:0007268 chemical synaptic transmission | IDA PMID:10805923 Roles of glutamate and FMRFamide-related peptides at the chr... | NEW | Summary: NEW annotation. FMRFamide peptides function as neurotransmitters at the chromatophore neuromuscular junction. Loi and Tublitz (2000) demonstrated that FaRPs function as slow transmitters at the chromatophore NMJ, acting alongside glutamate (the fast transmitter). FMRFamide-immunopositive neurons are found in the posterior chromatophore lobe, and some chromatophore motoneurons co-express both FaRP-like immunoreactivity and an FaRP-coding mRNA transcript. Reason: Chemical synaptic transmission is directly supported by multiple lines of evidence: (1) FaRPs cause chromatophore muscle contraction when applied exogenously (PMID:9319020, PMID:10805923); (2) pharmacological data show direct action on chromatophore muscles (PMID:10805923); (3) FMRFamide-immunopositive cells are present in the posterior chromatophore lobe where chromatophore motoneuron somata are located (PMID:10805923); (4) in situ hybridization confirms FaRP mRNA in putative chromatophore motoneurons (PMID:10805923). The peptides function as the slow component of dual neurotransmitter signaling at this synapse. Supporting Evidence: PMID:10805923 A combination of immunocytochemistry and in situ hybridization shows that some putative chromatophore motoneurons express FaRP-like immunoreactivity and an FaRP-coding mRNA transcript. Many FMRFamide-immunopositive cells in the posterior chromatophore lobes also express glutamate-like immunoreactivity. We conclude that glutamate and FaRPs likely function as fast and slow transmitters, respectively, at the Sepia chromatophore NMJ. PMID:9319020 Immunocytochemical analyses of the central nervous system using an FMRFamide antibody revealed the presence of FMRFamide-like immunoreactive cell bodies in the posterior chromatophore lobes, the region of the brain containing the chromatophore motoneurons of the fin and mantle. |
| GO:0045933 positive regulation of muscle contraction | IDA PMID:9319020 Peptidergic regulation of chromatophore function in the Euro... | NEW | Summary: NEW annotation. FMRFamide peptides are excitatory neurotransmitters that cause contraction of chromatophore muscles, resulting in chromatophore expansion. All four FaRP classes (FMRF, FLRF, FIRF, ALSGDAFLRF) were shown to be potent excitors of chromatophore muscles in in vitro bioassays (PMID:9319020, PMID:9192498). FMRFamide acts directly on the chromatophore muscles (PMID:10805923). Reason: This annotation captures the direct excitatory effect of FMRFamide peptides on chromatophore muscle contraction. The bioassay data from multiple publications consistently show that FaRPs cause chromatophore muscle contraction (leading to chromatophore expansion). This is a core function of the FMRFa gene product in Sepia officinalis. Note the unique biology: chromatophore expansion occurs via muscle contraction (the muscles radially pull the chromatophore sac open). Supporting Evidence: PMID:9319020 Using an in vitro chromatophore bioassay, it has been determined that several FMRFamide-related peptides (FaRPs) are potent excitors of the chromatophore muscles, causing chromatophore expansion. PMID:10805923 FMRFamide application causes contraction of chromatophore muscles; however, the FMRFamide effect is slower and longer lasting than that of glutamate. Pharmacological data show that FMRFamide acts directly on the chromatophore muscles. PMID:9192498 Each of the four FaRPs encoded by this cDNA causes chromatophore expansion when assayed in an in vitro chromatophore bioassay. |
| GO:0043473 pigmentation | IDA PMID:9319020 Peptidergic regulation of chromatophore function in the Euro... | NEW | Summary: NEW annotation. FMRFamide peptides regulate chromatophore expansion, which is the mechanism underlying body patterning and pigmentation in cephalopods. The FaRPs control chromatophore activity by directly activating chromatophore muscles, causing the pigment-filled sac to expand and display color (PMID:9319020, PMID:9192498). The SOFaRP2 gene is expressed in brain regions involved in chromatophore regulation (PMID:23465584). Reason: Pigmentation in cephalopods is achieved through chromatophore organ expansion/retraction, which is under neural control. FMRFamide peptides are excitatory neurotransmitters at the chromatophore NMJ that cause chromatophore expansion (color display). While the FMRFamide peptides do not regulate pigment synthesis, they regulate the display of pigment through chromatophore expansion, which is part of the pigmentation process in the broader sense. Supporting Evidence: PMID:9319020 these data suggest that the FaRPs are likely to be endogenous excitors of the chromatophore muscles in cephalopods. PMID:9192498 The display of complex color patterns of the cuttlefish Sepia officinalis is under the regulation of the FMRFamide-related peptide (FaRP) family. |
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Download this section (compressed HTML)Q: What are the specific receptors for FMRFamide peptides on Sepia chromatophore muscles? Identifying the receptor(s) would enable more precise annotation of the signaling pathway and could clarify whether FMRFamide acts via ionotropic or metabotropic mechanisms.
Q: Do different FaRP variants (FMRF vs FLRF vs FIRF vs ALSGDAFLRF) have distinct potencies or receptor specificities at the chromatophore NMJ? The precursor encodes 14 peptides of different sequences, suggesting possible functional diversification.
Q: Are there other functional roles for FMRFa gene products beyond chromatophore regulation (e.g., cardiovascular, feeding, reproductive functions)? The broad CNS expression pattern of the related SOFaRP2 gene suggests possible pleiotropic functions.
Q: What is the relationship between the two S. officinalis FaRP genes (FMRFa/SOFaRP1 and SOFaRP2) in terms of functional redundancy or specialization at the chromatophore NMJ?
Experiment: Dose-response curves comparing the four FaRP variants (FMRFamide, FLRFamide, FIRFamide, ALSGDAFLRFamide) for chromatophore expansion potency in the in vitro bioassay, to determine whether different peptides from the same precursor have distinct efficacies.
Hypothesis: Different FaRP variants encoded by the same precursor may have distinct potencies at the chromatophore NMJ, reflecting functional specialization within the peptide family.
Experiment: In vivo gene knockdown (e.g., morpholino injection into embryos) of FMRFa to assess effects on body patterning behavior and chromatophore function in developing cuttlefish.
Hypothesis: Loss of FMRFa expression will impair chromatophore-mediated body patterning behavior, confirming the essential role of FaRPs in this process.
Experiment: Electrophysiological recording of chromatophore muscle responses to individual FaRP peptides to characterize the receptor pharmacology and ion channel mechanisms underlying FMRFamide excitation at the chromatophore NMJ.
Hypothesis: FMRFamide peptides activate specific receptors on chromatophore muscles that produce slow depolarizing currents, distinct from the fast glutamate-mediated response.
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