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.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0006887 exocytosis | IBA GO_REF:0000033 | KEEP AS NON CORE | Summary: Exocytosis is retained as an inferred SCAMP-family role, secondary to the directly demonstrated requirement for spore stability. Reason: The current PTHR10687 PAINT table places exocytosis at PTN000074638, separate from the localization ancestor PTN000074637. The existing OpenScientist report supports SCAMP membership and recommends non-core retention of trafficking annotations, while finding no direct SpiA trafficking assay. Its observation that NPF-less mammalian SCAMP4/5 still traffic prevents treating the absent NPF motifs as proof of functional loss. The spore-coat phenotype establishes the best-characterized role but does not exclude inherited trafficking activity. Supporting Evidence: PMID:1592257 Dd31 is associated with the inner face of spore coat fragments in a detergent-resistant manner. file:DICDI/spiA/spiA-hypotheses/spia-scamp-trafficking/openscientist.md Treat the vesicular-trafficking GO terms as **non-core, homology-only annotations** that do not represent the gene product's primary function. |
| GO:0032588 trans-Golgi network membrane | IBA GO_REF:0000033 | KEEP AS NON CORE | Summary: The trans-Golgi network membrane localization is a credible SCAMP-family inference that remains secondary to the experimentally demonstrated spore-wall localization. Reason: PTHR10687-paint.tsv places this localization at the eukaryotic ancestral node PTN000074637. Its experimental descendants include human SCAMP5 (Q8TAC9), itself an NPF-less SCAMP, so absence of NPF repeats in SpiA cannot establish loss of the inherited compartment. The existing OpenScientist report confirms SCAMP membership and explicitly acknowledges that NPF-less SCAMP4/5 still traffic; its recommendation is to retain trafficking terms as non-core. Localization at the inner spore coat also does not exclude earlier trafficking compartments. Restore the inference as non-core without presenting it as directly imaged in SpiA. Supporting Evidence: PMID:1592257 Dd31 is associated with the inner face of spore coat fragments in a detergent-resistant manner. file:DICDI/spiA/spiA-hypotheses/spia-scamp-trafficking/openscientist.md the short human SCAMP4/SCAMP5 (229/235 aa) are also NPF-less yet still traffic, so NPF absence is suggestive rather than decisive. |
| GO:0055038 recycling endosome membrane | IBA GO_REF:0000033 | KEEP AS NON CORE | Summary: The recycling endosome membrane localization is a credible SCAMP-family inference that remains secondary to the experimentally demonstrated spore-wall localization. Reason: PTHR10687-paint.tsv places this localization at the eukaryotic ancestral node PTN000074637. Its experimental descendants include human SCAMP5 (Q8TAC9), itself an NPF-less SCAMP, so absence of NPF repeats in SpiA cannot establish loss of the inherited compartment. The existing OpenScientist report confirms SCAMP membership and explicitly acknowledges that NPF-less SCAMP4/5 still traffic; its recommendation is to retain trafficking terms as non-core. Localization at the inner spore coat also does not exclude earlier trafficking compartments. Restore the inference as non-core without presenting it as directly imaged in SpiA. Supporting Evidence: PMID:1592257 Dd31 is associated with the inner face of spore coat fragments in a detergent-resistant manner. file:DICDI/spiA/spiA-hypotheses/spia-scamp-trafficking/openscientist.md the short human SCAMP4/SCAMP5 (229/235 aa) are also NPF-less yet still traffic, so NPF absence is suggestive rather than decisive. |
| 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. |
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