Septin5 (Sep5) is a Drosophila SEPT6-class septin that arose as a retrogene copy of Septin2. It assembles with Septin4 and Peanut into the Sep4-Sep5-Pnut hetero-oligomer, which overlaps the actomyosin ring at cell wounds and bends actin bundles; Sep5 mutants show delayed actomyosin ring disassembly during wound repair. Sep5 binds and bundles actin filaments and acts redundantly with Sep2 in imaginal cell proliferation, although the two paralogs have partly diverged in function. Like Sep2, it is expected to bind GTP but its hydrolytic activity has not been demonstrated.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0003924 GTPase activity | ISS GO_REF:0000024 | MARK AS OVER ANNOTATED | Summary: GTPase activity transferred to Sep5 by sequence similarity to Pnut. Reason: The ISS donor is Pnut (FBgn0013726), a SEPT7-class septin. Sep5 is a SEPT6-class retrogene copy of Sep2 (PMID:24433211, PMID:38728140), and recombinant Sep2 has no detectable GTPase activity (PMID:25355953). Sep5 hydrolytic activity has not been measured; GTP binding is well supported but hydrolysis is likely an over-transfer from a catalytically active paralog class. Supporting Evidence: PMID:38728140 Drosophila has 5 Septins that are grouped into three classes: Sep2 and Sep5 (SEPT6 class), Sep1 and Sep4 (SEPT2 class), and Pnut (SEPT7 class) PMID:25355953 Sep2 protein, on the other hand, did not possess any noticeable GTPase activity (Table 1). |
| GO:0005525 GTP binding | IEA GO_REF:0000120 | ACCEPT | Summary: GTP binding predicted from the septin-type G domain. Reason: Septins bind guanine nucleotide stably; the purified Drosophila complex copurifies with one bound guanine nucleotide per subunit. This holds even for the SEPT6-class subunits (Sep2/Sep5), which bind but do not exchange or hydrolyse GTP. Supporting Evidence: PMID:8636235 The complex copurifies with one molecule of bound guanine nucleotide per septin polypeptide. |
| GO:0005856 cytoskeleton | IEA GO_REF:0000044 | MODIFY | Summary: Septins are components of the cytoskeleton. Reason: Correct but general; septin hetero-oligomers form the septin cytoskeleton, and the gene already carries the more specific term GO:0031105 septin complex (a descendant of cytoskeleton). Proposed replacements: septin complex Supporting Evidence: file:DROME/Septin5/Septin5-uniprot.txt SUBCELLULAR LOCATION: Cytoplasm, cytoskeleton PMID:38728140 Taken together, our findings further suggest that Sep1/Sep2/Pnut and Sep4/Sep5/Pnut are functioning as distinct complexes within the context of cell wound repair. |
| GO:0007444 imaginal disc development | IGI PMID:24433211 The Drosophila melanogaster septin gene Sep2 has a redundant... | KEEP AS NON CORE | Summary: Sep2 and Sep5 act redundantly for imaginal disc formation. Reason: IGI: Sep2 Sep5 double mutants lack imaginal discs, attributed to failed imaginal cell proliferation, most likely reflecting the septin role in cytokinesis. Developmental consequence; non-core. Supporting Evidence: PMID:24433211 Sep2 Sep5 double mutants have an early pupal lethal phenotype and lack imaginal discs, suggesting that these genes have redundant functions during imaginal cell proliferation |
| GO:0007476 imaginal disc-derived wing morphogenesis | IMP PMID:34496252 Atypical laminin spots and pull-generated microtubule-actin ... | KEEP AS NON CORE | Summary: Septins required for microtubule-actin cables that mediate wing surface adhesion. Reason: IMP from a study of wing adhesion during metamorphosis, in which septins are needed to form pressure-resistant microtubule-actin projections. Tissue-level morphogenesis that likely reflects the general septin role in cortical cytoskeletal organisation; non-core. Supporting Evidence: PMID:34496252 Formation of cables resistant to pressure requires spectraplakin, Patronin, septins, and Sdb |
| GO:0031105 septin complex | IEA GO_REF:0000104 | ACCEPT | Summary: Septin complex membership predicted by UniRule. Reason: Consistent with experimental data: this subunit assembles with Pnut and a SEPT2-/SEPT6-class partner into the Sep4/Sep5/Pnut complex. Supporting Evidence: PMID:38728140 Taken together, our findings further suggest that Sep1/Sep2/Pnut and Sep4/Sep5/Pnut are functioning as distinct complexes within the context of cell wound repair. |
| GO:0031105 septin complex | TAS PMID:38728140 Two Septin complexes mediate actin dynamics during cell woun... | ACCEPT | Summary: Subunit of the hetero-oligomeric septin complex. Reason: Direct biochemical evidence that this subunit assembles into a hetero-oligomeric septin complex (Sep1/Sep2/Pnut and/or Sep4/Sep5/Pnut). Core location. Supporting Evidence: PMID:38728140 Taken together, our findings further suggest that Sep1/Sep2/Pnut and Sep4/Sep5/Pnut are functioning as distinct complexes within the context of cell wound repair. |
| GO:0042060 wound healing | IMP PMID:38728140 Two Septin complexes mediate actin dynamics during cell woun... | ACCEPT | Summary: Septins are required for efficient cell wound repair. Reason: All five septins are required for efficient wound repair of the syncytial embryo; Sep1/Sep2 and Sep4/Sep5 loss give distinct actin-ring phenotypes. Direct IMP evidence; this is single-cell (plasma membrane/cortex) wound repair. Supporting Evidence: PMID:38728140 we show that all five Drosophila Septins are required for efficient cell wound repair PMID:38728140 Sep4 knockdown and Sep5 mutant embryos exhibit delayed actomyosin ring disassembly |
| GO:0044837 actomyosin contractile ring organization | IMP PMID:38728140 Two Septin complexes mediate actin dynamics during cell woun... | ACCEPT | Summary: Septins organise the actomyosin ring during single-cell wound repair. Reason: In the Drosophila embryo cell-wound model, knockdown or mutation of each septin perturbs actomyosin ring assembly, contraction or disassembly; the two complexes bend actin bundles to different curvatures. Core process for the septin complexes. Supporting Evidence: PMID:38728140 Sep4 knockdown and Sep5 mutant embryos exhibit delayed actomyosin ring disassembly PMID:38728140 Interestingly, we observe curved F-actin bundles induced by two separate Septin complexes, whereas individual Septins can only bind to and bundle F-actin. |
| GO:0051015 actin filament binding | IDA PMID:38728140 Two Septin complexes mediate actin dynamics during cell woun... | ACCEPT | Summary: Purified septin subunits and complexes bind and bundle actin filaments. Reason: Each of the five Drosophila septins, purified individually, binds and bundles F-actin in vitro, and the assembled Sep1/Sep2/Pnut and Sep4/Sep5/Pnut complexes additionally bend the bundles into rings. Direct F-actin binding is a core activity linking septins to the actomyosin cytoskeleton. Supporting Evidence: PMID:38728140 Strikingly, we find that all five Drosophila Septins can bind to and bundle actin filaments PMID:38728140 Interestingly, we observe curved F-actin bundles induced by two separate Septin complexes, whereas individual Septins can only bind to and bundle F-actin. |
| GO:0051726 regulation of cell cycle | IGI PMID:24433211 The Drosophila melanogaster septin gene Sep2 has a redundant... | MARK AS OVER ANNOTATED | Summary: Imaginal cell proliferation defect of Sep2 Sep5 double mutants. Reason: The double mutant lacks imaginal discs, which the authors attribute to failed imaginal cell proliferation. There is no evidence that Sep2 or Sep5 regulate cell-cycle progression as such; the proliferation defect is best explained by the septin requirement for cytokinesis. 'Regulation of cell cycle' over-interprets the phenotype. Supporting Evidence: PMID:24433211 Sep2 Sep5 double mutants have an early pupal lethal phenotype and lack imaginal discs, suggesting that these genes have redundant functions during imaginal cell proliferation |
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Download this section (compressed HTML)Septin 5 (Septin5) encodes a member of the septin family of GTP-binding proteins. Septins form hetero-oligomeric filaments and rings that have roles in cytokinesis, cell polarity and membrane rigidity. Septin5 is not essential for development, but mutants display a synthetic lethal pupal phenotype when combined with mutations in its paralog Septin2.
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