exoc3l2a (exocyst complex component 3-like 2a) is one of two zebrafish co-orthologs of vertebrate EXOC3L2, retained from the teleost-specific genome duplication; its paralog is exoc3l2b. It encodes a 932-aa member of the EXOC3/Sec6 family with an N-terminal region and a C-terminal Sec6 helical-bundle domain. By sequence it is much closer to EXOC3L2 than to EXOC3, EXOC3L1, EXOC3L4 or TNFAIP2 (M-Sec). Mammalian EXOC3L2 is expressed in endothelial cells and co-precipitates with the exocyst subunit EXOC4. In cultured human endothelial cells it is needed for VEGFA-induced VEGFR2 phosphorylation and for directional migration. Mouse Exoc3l2 knockouts die in utero with hemorrhage and heart and brain defects, and human biallelic EXOC3L2 mutations cause a hindbrain, kidney and bone-marrow syndrome. In zebrafish, exoc3l2a is expressed in an endothelial-specific pattern at 24 hpf and belongs to the endothelial gene signature of the caudal hematopoietic tissue niche. No zebrafish loss-of-function or biochemical study of exoc3l2a has been published.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0000145 exocyst | IBA GO_REF:0000033 | ACCEPT | Summary: Exocyst (IBA) from the EXOC3/Sec6 family node PTN000480155, seeded by Sec6/EXOC3 orthologs from budding and fission yeast, Arabidopsis, Dictyostelium, fly and mouse. Reason: exoc3l2a keeps a complete Sec6 domain and is an EXOC3L2 co-ortholog. Mammalian EXOC3L2 is the only member of this subfamily studied biochemically. A tagged EXOC3L2 co-precipitates with EXOC4 and colocalises with EXOC4 and EXOC7, which supports association with the exocyst, the claim the propagated term makes. Whether EXOC3L2 is a stoichiometric subunit that replaces EXOC3, or a separate partner, has not been settled, so the term is kept at the complex level. Supporting Evidence: PMID:21566143 Myc-tagged EXOC3L2 co-precipitates with the exocyst protein EXOC4, and immunofluorescence detection of EXOC3L2 shows partial subcellular colocalization with EXOC4 and EXOC7. PMID:30086153 Therefore, it will be relevant to determine whether EXOC3 paralogs, particularly M-Sec and EXOC3L2, are interchangeable subunits that are selectively assembled into different functional variants of the exocyst complex, or independent operators. file:DANRE/exoc3l2a/exoc3l2a-bioinformatics/RESULTS.md Both copies keep a full-length Sec6 domain and the N-terminal region; neither is truncated. |
| GO:0000145 exocyst | IEA GO_REF:0000002 | ACCEPT | Summary: Exocyst from the InterPro EXOC3/Sec6 entry (IPR010326) mapping. Reason: Same claim as the IBA row. The Sec6 domain is intact, and the mammalian ortholog associates with the exocyst. Supporting Evidence: PMID:21566143 The subcellular localization and the colocalization with EXOC4 indicate an association between EXOC3l2 and the exocyst complex. |
| GO:0000149 SNARE binding | IBA GO_REF:0000033 | MARK AS OVER ANNOTATED | Summary: SNARE binding (IBA) from node PTN000480155, with budding-yeast Sec6 as the only experimental donor. Reason: SNARE binding has been shown only for yeast Sec6. The node spans the whole EXOC3/Sec6 family, including the vertebrate EXOC3-like paralogs (EXOC3L1, EXOC3L2, EXOC3L4, TNFAIP2), and none of these paralogs has been tested for SNARE binding. exoc3l2a is only 19.7% identical to human EXOC3 and is the faster-evolving copy of its pair. The one EXOC3L2 interaction studied is with the exocyst core subunit EXOC4. The function could have been inherited from Sec6, but no data support it for the EXOC3L2 lineage. exoc3l2b carries no IBA rows, because the accession in the PANTHER tree (A0A8M3B147) has since been deleted from UniProt. Propagation Review Root cause: UNRESOLVED Sources checked: PANTHER:PTN000480155 UNRESOLVED Family-wide EXOC3/Sec6 node; its only SNARE-binding evidence is yeast Sec6, and it is unknown whether the vertebrate EXOC3-like paralogs kept this activity. SGD:S000001330 · SEC6 (budding yeast) SUPPORTS SOURCE BUT NOT TARGET Sec6 binding to SNAREs is sound for yeast Sec6, but the EXOC3L2 lineage diverged far from EXOC3/Sec6 (about 20% identity) and has not been tested. Supporting Evidence: file:DANRE/exoc3l2a/exoc3l2a-bioinformatics/RESULTS.md The two zebrafish proteins are 50.9% identical to each other, 35-36% identical to human EXOC3L2 and only 19.7-21.9% identical to human EXOC3 (the Sec6 ortholog), EXOC3L1, EXOC3L4 and TNFAIP2. file:DANRE/exoc3l2a/exoc3l2a-bioinformatics/RESULTS.md exoc3l2a is the faster-evolving copy. PMID:21566143 Myc-tagged EXOC3L2 co-precipitates with the exocyst protein EXOC4, and immunofluorescence detection of EXOC3L2 shows partial subcellular colocalization with EXOC4 and EXOC7. |
| GO:0006887 exocytosis | IBA GO_REF:0000033 | KEEP AS NON CORE | Summary: Exocytosis (IBA) from the EXOC3/Sec6 family node. Reason: An exocyst-associated protein is plausibly involved in exocytosis, and the proposed model for EXOC3L2 is exocyst-dependent delivery of VEGFR2 to the cell surface. But no secretion or exocytosis assay has been done for EXOC3L2 in any species; the measured effects are on VEGFR2 phosphorylation and directional migration. The term is kept as a plausible family-level process, not as a demonstrated core function. Supporting Evidence: PMID:21566143 We hypothesized that EXOC3L2 may be involved in the exocytosis of VEGFR2, and that a down-regulation of EXOC3L2 expression thus could have an effect on VEGFR2 phosphorylation. PMID:21566143 Finally, we show that exoc3l2 silencing inhibits VEGF receptor 2 phosphorylation and VEGFA-directed migration of cultured endothelial cells. |
| GO:0006887 exocytosis | IEA GO_REF:0000002 | KEEP AS NON CORE | Summary: Exocytosis from the InterPro EXOC3/Sec6 mapping. Reason: Same reasoning as the IBA row. The process is plausible for an exocyst-associated protein but has not been measured for EXOC3L2. Supporting Evidence: PMID:21566143 We hypothesized that EXOC3L2 may be involved in the exocytosis of VEGFR2, and that a down-regulation of EXOC3L2 expression thus could have an effect on VEGFR2 phosphorylation. |
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Download this section (compressed HTML)Q: Is exoc3l2a required for vascular development in zebrafish, as Exoc3l2 is in mouse? Do exoc3l2a mutants show hemorrhage, sprouting defects or an abnormal caudal hematopoietic tissue niche?
Q: Is exoc3l2b also expressed in endothelium, or is the endothelial domain carried by exoc3l2a alone?
Q: PANTHER lists EXOC3L4 as the human ortholog and places the gene in a TNFAIP2-named subfamily, while sequence identity, synteny and Ensembl Compara support EXOC3L2. Should the PANTHER tree for PTHR21292 be revisited?
Experiment: Make exoc3l2a, exoc3l2b and double mutants, including an RNA-less or promoter-deletion allele to avoid transcriptional adaptation. Score vascular patterning, hemorrhage and CHT hematopoiesis in kdrl and gata1 reporter backgrounds.
Experiment: Do two-colour in situ hybridization (HCR) for exoc3l2a and exoc3l2b with kdrl and sox10 at 12-48 hpf, to test whether the endothelial and neural-crest domains are split between the copies.
Experiment: Co-immunoprecipitate tagged Exoc3l2a with zebrafish exocyst subunits (Exoc4, Exoc7) and with RalA.
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