Sox8 is a SoxE-group HMG-box transcription factor of Xenopus laevis, paralogous to Sox9 and Sox10. It has an N-terminal dimerisation region, a central HMG box that binds and bends DNA in the minor groove, and middle (TAM) and C-terminal (TAC) transactivation domains, and it acts in the nucleus as an RNA polymerase II sequence-specific transcription factor. Low-level transcripts are present in the blastula but disappear by the onset of gastrulation. Zygotic expression then begins at mid-gastrula at the lateral edges of the neural plate, in the prospective neural crest, before Sox9 and Sox10, which makes Sox8 the first SoxE factor deployed in the frog crest. Sox8 is induced there by the neural plate border specifiers Pax3 and Zic1 as part of the first wave of neural crest specifier genes (with snail1 and myc). Expression persists in migrating cranial crest populating the pharyngeal arches and in trunk crest, and later in the otic vesicle. Knockdown of Sox8 delays the induction of neural crest progenitors and impairs their migration into the periphery, so that multiple crest-derived lineages develop abnormally; the neural crest of Sox8 morphants can be rescued by any SoxE factor. Sox8 therefore acts as an early, partly redundant neural crest specifier downstream of the border module. The prominence of Sox8 is species-specific: in chick and mouse Sox9 is the first SoxE in the crest and Sox8 is largely dispensable, and zebrafish sox8 is not expressed in neural crest. Gnathostome Sox8/9/10 and lamprey SoxE1-3 arose by independent duplications, and amphioxus SoxE lacks neural crest enhancers. The crest-specifier role thus belongs to the vertebrate SoxE group, recruited into the crest by cis-regulatory change, and is allocated differently among paralogs in different lineages.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0000122 negative regulation of transcription by RNA polymerase II | IBA GO_REF:0000033 | KEEP AS NON CORE | Summary: Phylogenetic inference of transcriptional repression, seeded from human SOX9. Reason: SoxE proteins are primarily transcriptional activators (TAM/TAC transactivation domains and a 9aaTAD motif are annotated on Sox8). Repression of some targets is documented for mammalian SOX9, the donor for this node, and the SoxE group is functionally interchangeable in Xenopus, so the inference is plausible at the family level. There is no Xenopus Sox8-specific evidence for repression, and it does not describe the neural crest specifier role. Kept as non-core, consistent with the sox9-a and sox10 reviews. Supporting Evidence: file:XENLA/sox8/sox8-uniprot.txt The transactivation domains TAM and TAC (for transactivation PMID:16256735 the activities of individual SoxE factors are well conserved |
| GO:0000122 negative regulation of transcription by RNA polymerase II | IEA GO_REF:0000118 | KEEP AS NON CORE | Summary: TreeGrafter transfer of the IBA negative regulation of transcription annotation. Reason: Same basis as the IBA row; family-level SoxE property without Sox8-specific support in frog. Kept as non-core. Supporting Evidence: file:XENLA/sox8/sox8-uniprot.txt The transactivation domains TAM and TAC (for transactivation |
| GO:0000978 RNA polymerase II cis-regulatory region sequence-specific DNA binding | IBA GO_REF:0000033 | ACCEPT | Summary: Sequence-specific cis-regulatory DNA binding through the HMG box, inferred for the Sox family. Reason: Xenopus Sox8 has an intact SoxE HMG box (residues 98-166). Sequence-specific minor-groove binding and DNA bending by the HMG domain is the defining Sox activity and is conserved across the family. No Sox8-specific binding assay exists in frog, but the PAINT node placement is sound and nothing suggests loss of DNA binding. Supporting Evidence: PMID:39936824 binds to the DNA in the minor groove causing 70-85° bending toward the major groove file:XENLA/sox8/sox8-uniprot.txt DNA_BIND 98..166 |
| GO:0000978 RNA polymerase II cis-regulatory region sequence-specific DNA binding | IEA GO_REF:0000118 | ACCEPT | Summary: TreeGrafter transfer of HMG-box cis-regulatory DNA binding. Reason: Consistent with the IBA and the conserved HMG box. Supporting Evidence: PMID:39936824 binds to the DNA in the minor groove causing 70-85° bending toward the major groove |
| GO:0000981 DNA-binding transcription factor activity, RNA polymerase II-specific | IBA GO_REF:0000033 | ACCEPT | Summary: RNA polymerase II-specific DNA-binding transcription factor activity, the core molecular function. Reason: Sox8 combines an HMG box with TAM/TAC transactivation domains and regulates the onset of neural crest gene expression in frog. SoxE proteins are interchangeable in Xenopus neural crest assays (any SoxE rescues the Sox8 morphant), so the conserved transcription factor activity is the right core MF. The more specific activator term is likely correct but has no Sox8-specific frog assay (see suggested questions). Supporting Evidence: file:XENLA/sox8/sox8-uniprot.txt Regulates the onset of file:XENLA/sox8/sox8-deep-research-falcon.md Sox8 is not an enzyme or transporter: its relevant molecular activity is regulation of DNA-dependent transcription. |
| GO:0000981 DNA-binding transcription factor activity, RNA polymerase II-specific | IEA GO_REF:0000118 | ACCEPT | Summary: TreeGrafter transfer of RNA polymerase II-specific transcription factor activity. Reason: Consistent with the IBA; core MF. Supporting Evidence: file:XENLA/sox8/sox8-deep-research-falcon.md Sox8 is not an enzyme or transporter: its relevant molecular activity is regulation of DNA-dependent transcription. |
| GO:0002009 morphogenesis of an epithelium | IBA GO_REF:0000033 | KEEP AS NON CORE | Summary: Broad SoxE-family process inferred from epithelial morphogenesis roles of SoxE genes (otic, gonad, glandular epithelia). Reason: The node is seeded from several SoxE genes across vertebrates, and frog SoxE factors act equivalently in inner ear development. Xenopus Sox8 is expressed in the otic vesicle from around stage 30, so a contribution is plausible, but there is no Sox8-specific frog evidence and the term says nothing about its neural crest role. Kept as non-core, consistent with the paralog reviews. Supporting Evidence: PMID:16256735 SoxE factors function equivalently during neural crest and inner ear development file:XENLA/sox8/sox8-uniprot.txt otic expression only |
| GO:0002009 morphogenesis of an epithelium | IEA GO_REF:0000118 | KEEP AS NON CORE | Summary: TreeGrafter transfer of epithelium morphogenesis. Reason: Same basis as the IBA row; plausible family-level role without Sox8-specific frog support. Supporting Evidence: PMID:16256735 SoxE factors function equivalently during neural crest and inner ear development |
| GO:0005634 nucleus | IBA GO_REF:0000033 | ACCEPT | Summary: Nuclear site of action of a sequence-specific transcription factor. Reason: Sox8 acts on chromatin as a transcription factor; the HMG box carries the conserved nuclear localisation signals of the Sox family. The nucleus is the correct location of activity. Supporting Evidence: file:XENLA/sox8/sox8-uniprot.txt SUBCELLULAR LOCATION: Nucleus |
| GO:0005634 nucleus | IEA GO_REF:0000120 | ACCEPT | Summary: Nuclear localisation from UniProt subcellular location and TreeGrafter. Reason: Consistent with transcription factor function and the IBA. Supporting Evidence: file:XENLA/sox8/sox8-uniprot.txt SUBCELLULAR LOCATION: Nucleus |
| GO:0006357 regulation of transcription by RNA polymerase II | IEA GO_REF:0000118 | ACCEPT | Summary: General regulation of RNA polymerase II transcription. Reason: Correct and appropriately general for a sequence-specific RNA polymerase II transcription factor; the direction of regulation is not established for frog Sox8. Supporting Evidence: file:XENLA/sox8/sox8-uniprot.txt Regulates the onset of |
| GO:0007422 peripheral nervous system development | IBA GO_REF:0000033 | KEEP AS NON CORE | Summary: Peripheral nervous system development inferred from a SoxE subclade node. Reason: The peripheral nervous system is a neural crest derivative, and Sox8 knockdown disrupts several crest lineages in frog, so a contribution is plausible. Frog evidence attributes the lineage defects to failed crest migration rather than to a later PNS-specific requirement, and mammalian Sox8 is largely redundant with Sox10 in glial development. This is a downstream consequence of the crest-specifier role, not a core function. Supporting Evidence: PMID:16943273 This delay in neural crest specification had dramatic consequences on the development of multiple lineages of the neural crest PMID:39936824 Sox8 is not essential for the proper development of any of the involved systems, as it functions redundantly with Sox9 or Sox10 |
| GO:0007422 peripheral nervous system development | IEA GO_REF:0000118 | KEEP AS NON CORE | Summary: TreeGrafter transfer of peripheral nervous system development. Reason: Same basis as the IBA row. Supporting Evidence: PMID:16943273 This delay in neural crest specification had dramatic consequences on the development of multiple lineages of the neural crest |
| GO:0014029 neural crest formation | IEA GO_REF:0000117 | MODIFY | Summary: ARBA machine-learning annotation to neural crest formation. Reason: The annotation is sound in substance, but GO:0014029 is defined as formation of the specialised ectodermal region between neural plate and non-neural ectoderm, which in the network sense is the job of the neural plate border specifiers (Pax3, Zic1, Msx1, Tfap2a). Sox8 is induced by Pax3/Zic1 inside the prospective crest and is the earliest SoxE specifier. The more specific descendant GO:0014036 neural crest cell fate specification (part_of neural crest formation) describes its layer. This matches the treatment of the sox9-a and sox10 paralogs. Proposed replacements: neural crest cell fate specification Supporting Evidence: PMID:23509273 these transcription factors cooperate to activate the NC specifiers snail2 ( snai2 ), soxE ( sox8, 9, 10 ), and foxd3 in the ectoderm PMID:16943273 in contrast to its mouse and chick orthologs, Sox8 expression precedes that of Sox9 and Sox10 in neural crest progenitors |
| GO:0014029 neural crest formation | IMP PMID:16943273 Functional analysis of Sox8 during neural crest development ... | MODIFY | Summary: Sox8 morpholino knockdown delays induction of neural crest progenitors and blocks crest migration into the periphery, disrupting multiple crest lineages. Reason: Combined evidence places Sox8 in the neural crest specifier layer. (1) Expression: Sox8 appears at the lateral edges of the neural plate at mid-gastrula, before Sox9 and Sox10. (2) Upstream regulation: it is induced by the border specifiers Pax3 and Zic1 among the earliest NC specifiers (with snail1 and myc). (3) Loss of function: knockdown delays, but does not abolish, progenitor induction; the authors attribute the later lineage defects to failed migration. (4) Redundancy: any SoxE rescues the morphant, and SoxE activities are conserved. Neural crest cell fate specification (GO:0014036) is the precise process for the specification phenotype. The authors explicitly conclude that the downstream lineage defects reflect a migration failure rather than a specification or survival deficit, so neural crest cell migration (GO:0001755) is also proposed. Whether this migration requirement is separate from delayed specification is unresolved (cache is abstract-only; see suggested questions), so migration is not treated as core. Proposed replacements: neural crest cell fate specification neural crest cell migration Supporting Evidence: PMID:16943273 Although morpholino-mediated knockdown of Sox8 protein did not prevent the formation of neural crest progenitors, the timing of their induction was severely affected PMID:16943273 We demonstrate that these defects are due to the inability of neural crest cells to migrate into the periphery, rather than to a deficiency in neural crest progenitors specification and survival PMID:23509273 a group of early genes ( snail1 , sox8 , and myc ) was activated during early neurulation (between stages 12 and 15) PMID:33424631 The neural crest can be rescued in Sox8 morphants by any of the SoxE factors suggesting there is functional redundancy between the SoxE factors |
| GO:0014032 neural crest cell development | IBA GO_REF:0000033 | ACCEPT | Summary: Neural crest cell development inferred for the SoxE clade. Reason: The term covers progression of neural crest cells from commitment to differentiated derivatives. Sox8 is expressed in premigratory and migrating crest, and its knockdown impairs crest migration and several crest lineages in frog. The term is broad but correct at the SoxE clade level, and it subsumes the migration phenotype. Supporting Evidence: PMID:16943273 Sox8 expression persists in migrating cranial crest cells as they populate the pharyngeal arches and in trunk neural crest cells PMID:16943273 This delay in neural crest specification had dramatic consequences on the development of multiple lineages of the neural crest |
| GO:0014032 neural crest cell development | IEA GO_REF:0000118 | ACCEPT | Summary: TreeGrafter transfer of neural crest cell development. Reason: Consistent with the IBA and with frog loss-of-function data. Supporting Evidence: PMID:16943273 This delay in neural crest specification had dramatic consequences on the development of multiple lineages of the neural crest |
| GO:0048484 enteric nervous system development | IBA GO_REF:0000033 | KEEP AS NON CORE | Summary: Enteric nervous system development inferred from a SoxE subclade node. Reason: The enteric nervous system derives from vagal and sacral neural crest, and SoxE factors (especially Sox10) are required for it in mammals. No frog Sox8 enteric data exist, and mammalian Sox8 is largely redundant. Plausible as a downstream consequence of crest specification and migration; non-core. Supporting Evidence: PMID:39936824 Sox8 is not essential for the proper development of any of the involved systems, as it functions redundantly with Sox9 or Sox10 |
| GO:0048484 enteric nervous system development | IEA GO_REF:0000118 | KEEP AS NON CORE | Summary: TreeGrafter transfer of enteric nervous system development. Reason: Same basis as the IBA row. Supporting Evidence: PMID:39936824 Sox8 is not essential for the proper development of any of the involved systems, as it functions redundantly with Sox9 or Sox10 |
Loading supporting content…
Download this section (compressed HTML)Q: GO has no neural plate border formation/specification term. Sox8 is the clearest example of an NC specifier induced by the border module, and frog Sox8 expression defines the border/presumptive crest domain most clearly. Without a border term, border specifiers and early NC specifiers can only be separated by GO:0014029 versus GO:0014036; the project now proposes a neural plate border formation term and the obsoletion of GO:0014029. Does Sox8's early border-domain expression put any of its activity in the border layer, or is it purely a specifier?
Q: Is the migration defect of Sox8 morphants a separate requirement for Sox8 in migrating crest, or a consequence of delayed specification (premigratory programme not yet complete when neighbouring tissues move)? This decides whether neural crest cell migration (GO:0001755) is a direct Sox8 process.
Q: Does frog Sox8 act as an activator (GO:0001228) on specific NC enhancers (e.g. sox10, snai2, foxd3), and which targets are direct?
Q: The early crest-specifier role is carried by different SoxE paralogs in different lineages (Sox8 in frog, Sox9 in chick/mouse, sox9a/b in zebrafish, SoxE1/2 in lamprey, which duplicated independently). Should orthology-based transfer of the frog Sox8 specifier role to other species' sox8 genes (e.g. zebrafish, where sox8 is not expressed in crest) be avoided, with the role annotated on whichever paralog carries it?
Experiment: CUT&RUN for tagged Sox8 in Pax3-GR/Zic1-GR-induced animal caps and dissected neural folds, integrated with ATAC-seq and RNA-seq of sox8 F0 CRISPR mutants or morphants.
Hypothesis: Sox8 directly binds enhancers of later NC specifier genes (sox10, snai2, foxd3) at stages 11.5-13 in Xenopus.
Type: genomic binding assay
Experiment: Deplete Sox8 only after specification (e.g. inducible dominant-negative Sox8 or degron activated at stage 17-19) and assay crest emigration in vivo and in cranial crest explant migration assays.
Hypothesis: Sox8 is required in migrating crest independently of its early specification role.
Type: genetic perturbation
Loading supporting content…
Download this section (compressed HTML)Loading supporting content…
Download this section (compressed HTML)Loading supporting content…
Download this section (compressed HTML)