vwc2 (brorin; ZFIN ZDB-GENE-090313-315, chromosome 13) is the zebrafish ortholog of vertebrate VWC2/Brorin, supported by conserved exon-intron structure and by synteny: ikzf1 and fignl1 are its neighbours in zebrafish, mouse and gar. PANTHER pairs it with the divergent si:dkey-283b1.7 as a teleost genome duplication paralog, but synteny and other gene trees do not confirm that pairing. It encodes a 309-residue secreted protein. The signal peptide is followed by a divergent N-terminal region and a conserved core of two chordin-like von Willebrand factor C (VWFC) cysteine-rich domains. Like mouse Brorin, it acts as a secreted antagonist of BMP signalling. Injected brorin mRNA suppresses Smad1/5/8 phosphorylation and dorsalizes embryos, while knockdown raises phospho-Smad1/5/8 in the dorsal brain without activating Wnt signalling. The gene is expressed predominantly in the developing nervous system (diencephalon primordium from 16 hpf; later ventral telencephalon, prethalamus/alar hypothalamus, hindbrain, spinal cord, olfactory placode and pituitary). Morphants rescued by brorin mRNA show loss of subpallial (ventral telencephalic) identity, fewer GABAergic interneurons and oligodendrocytes, more astroglia, and failure of forebrain commissures. In mammals, Brorin is also an extracellular constituent of AMPA receptor complexes.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005576 extracellular region | IBA GO_REF:0000033 | ACCEPT | Summary: Extracellular region (IBA, brorin family node). Reason: vwc2 encodes a signal-peptide-bearing secreted protein, and mouse Brorin is secreted. PANTHER node PTN002921765 covers both VWC2 and VWC2L (MGI donors Vwc2 and Vwc2l), so the property is ancestral to the brorin family. Supporting Evidence: PMID:28448525 Zebrafish Brorin is presumed to be a secreted protein composed of 309 amino acids with a putative 22-amino acid signaling sequence at its amino-terminus (Fig 1A). PMID:17400546 Mouse Brorin protein produced in cultured cells was efficiently secreted into the culture medium. |
| GO:0005576 extracellular region | IEA GO_REF:0000044 | ACCEPT | Summary: Extracellular region from the UniProt 'Secreted' keyword. Reason: Consistent with the predicted signal peptide and the secretion of mouse Brorin. Supporting Evidence: PMID:28448525 Zebrafish Brorin is presumed to be a secreted protein composed of 309 amino acids with a putative 22-amino acid signaling sequence at its amino-terminus (Fig 1A). |
| GO:0007399 nervous system development | IMP PMID:19852960 A novel neural-specific BMP antagonist, Brorin-like, of the ... | UNDECIDED | Summary: IMP from the Brorin-like (vwc2l) paper, Miwa et al. 2009. Reason: The cached record is abstract-only. The abstract describes knockdown of Brorin-like, which is vwc2l, not brorin/vwc2. The authors' 2017 full-text paper says that their earlier work reported the brorin-like knockdown, and that the role of brorin itself in early neural development had not been elucidated. ZFIN lists no morpholino for this vwc2 row, while vwc2l carries two morpholinos from the same paper. This row may therefore reflect vwc2l data. Without the full text I cannot exclude a vwc2 experiment, so I do not remove it. The term itself is supported for vwc2 by PMID:28448525. Supporting Evidence: PMID:19852960 The inhibition of Brorin-like functions in zebrafish resulted in the impairment of neural development. PMID:28448525 The amino acid sequence of Brorin is similar to that of Brorin-like/vwc2l, and we previously reported the expression of brorin-like and phenotype of brorin-like knockdown [17]. PMID:28448525 However, the role of Brorin in early neural development has not yet been elucidated. |
| GO:0030514 negative regulation of BMP signaling pathway | IBA GO_REF:0000033 | ACCEPT | Summary: Negative regulation of BMP signaling pathway (IBA, brorin family node). Reason: Directly supported in zebrafish for this gene. Injected brorin mRNA abolishes Smad1/5/8 phosphorylation, and knockdown raises it in the dorsal brain, without affecting canonical Wnt targets. Mouse Brorin inhibits BMP2/BMP6 activity in cells. This is the core function. PANTHER node PTN002921765 covers both VWC2 and VWC2L (MGI donors Vwc2 and Vwc2l), so the property is ancestral to the brorin family. Supporting Evidence: PMID:28448525 These results indicate that the overexpression of brorin leads to the inactivation of Bmp signaling. PMID:28448525 In brorin morphants, pSmad was increased in the dorsal region of the brain (MO1, n = 11/11 and MO2, n = 18/18) PMID:28448525 These results indicate that Brorin inhibits Bmp signaling, but not canonical Wnt signaling. PMID:17400546 The protein inhibited the activity of bone morphogenetic protein 2 (BMP2) and BMP6 in mouse preosteoblastic MC3T3-E1 cells. |
| GO:0030900 forebrain development | IMP PMID:28448525 Brorin is required for neurogenesis, gliogenesis, and commis... | ACCEPT | Summary: brorin morphants (two splice-blocking MOs, mRNA-rescued) lose subpallial identity and forebrain commissures. Reason: Two non-overlapping splice morpholinos with verified mis-splicing give the same phenotype, and it is rescued by brorin mRNA. The phenotype is explained by raised BMP signalling in the dorsal brain. The MOs are specific for vwc2 over the paralogs (RESULTS.md). There is no mutant yet, so the result carries the usual morpholino caveat. Supporting Evidence: PMID:28448525 These results indicate that brorin is required for the development of the subpallial telencephalon. PMID:28448525 We found that the co-injection of brorin RNA with brorin MO1 prevented the development of brain defects caused by brorin MO1 (n = 11/12) (Fig 3G). PMID:28448525 In brorin morphants, pSmad was increased in the dorsal region of the brain (MO1, n = 11/11 and MO2, n = 18/18) file:DANRE/si_dkey-283b1.7/si_dkey-283b1.7-bioinformatics/RESULTS.md The brorin morpholinos of PMID:28448525 match vwc2 perfectly and have 9 or more mismatches to si:dkey-283b1.7 |
| GO:0032281 AMPA glutamate receptor complex | IBA GO_REF:0000033 | KEEP AS NON CORE | Summary: AMPA glutamate receptor complex (IBA from mouse Vwc2/Vwc2l proteomics). Reason: Mouse Brorin and Brorin-like co-purify with native AMPA receptors as peripheral extracellular constituents, recruited by Noelins. The PAINT inference is sound for the family, but there is no zebrafish test, and the zebrafish functional data concern early BMP antagonism in forebrain development. Kept as a plausible, non-core location. Supporting Evidence: PMID:37591201 Brorin and Brorin-like have been consistently retrieved in previous anti-GluA APs PMID:37591201 were entirely deprived of both Nrn1 and Brorin (Figure 1D) |
| GO:0045202 synapse | IEA GO_REF:0000044 | KEEP AS NON CORE | Summary: Synapse from the UniProt ARBA subcellular location rule. Reason: Follows from the AMPA receptor association of mammalian Brorin. It is plausible in the adult zebrafish brain but untested. Supporting Evidence: PMID:37591201 Brorin and Brorin-like have been consistently retrieved in previous anti-GluA APs |
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Download this section (compressed HTML)Q: Does Brorin bind BMP ligands directly (and which), or act through another component? No binding assay has been reported for any Brorin family member.
Q: Do stable vwc2 mutants reproduce the morphant forebrain phenotypes, and do vwc2 and vwc2l act redundantly in the prethalamus, where both are expressed?
Q: Is the IMP to nervous system development from PMID:19852960 based on a vwc2 experiment, or is it vwc2l data attached to vwc2?
Experiment: Generate vwc2 mutants (including an RNA-less allele), score pSmad1/5/8, dlx2a, gad1 and commissures, and test suppression with a BMP receptor inhibitor (e.g. dorsomorphin, DMH1).
Hypothesis: vwc2 loss-of-function phenotypes reflect raised BMP signalling.
Type: mutant analysis with pharmacological suppression
Experiment: Compare expression (in situ, retina and brain) and test whether si:dkey-283b1.7 mRNA can rescue vwc2 mutants or dorsalize embryos like brorin mRNA.
Hypothesis: si:dkey-283b1.7 does not share the vwc2 forebrain role.
Type: cross-rescue / overexpression
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