Forkhead box protein D3-A (FoxD3, XFD-6) is the L-homeolog copy of Xenopus laevis foxd3, a nuclear forkhead/winged-helix transcription factor that acts as a sequence-specific transcriptional repressor. Repression requires DNA binding by the forkhead domain and a C-terminal eh1/GEH motif that recruits Groucho/TLE corepressors (Grg4/tle4). foxd3 is expressed in pluripotent blastula animal cells, in the Spemann organizer at gastrula stages, and then in the presumptive and premigratory neural crest, where it is downregulated as crest cells migrate and differentiate. In the gastrula organizer it maintains Nodal-related gene expression required for dorsal mesoderm formation. At the neural plate border it acts as a neural crest specifier downstream of Zic/Wnt inputs and is required for Slug induction and neural crest determination; it also represses its own transcription. In other vertebrates Foxd3 maintains pluripotent epiblast cells and multipotent neural crest progenitors, and in zebrafish it first acts as a pioneer factor before switching to repression. FoxD3 recruitment to the neural crest is a vertebrate innovation: amphioxus FoxD is not expressed at the neural plate border, and a vertebrate-specific N-terminal motif confers the neural-crest-inducing activity that the ancestral FoxD repressor lacks.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0000978 RNA polymerase II cis-regulatory region sequence-specific DNA binding | IBA GO_REF:0000033 | ACCEPT | Summary: Phylogenetic inference that FoxD3-A binds RNA polymerase II cis-regulatory DNA sequence-specifically via its forkhead (winged-helix) domain. Reason: FoxD3 transcriptional repression and its developmental activities depend on sequence-specific DNA binding by the forkhead domain (DNA-contact mutant N140A/H144A is inactive), and Xenopus FoxD3 binds DNA sequences in vitro similar to amphioxus FoxD. Forkhead DNA binding is ancestral to the FoxD subfamily, so the PAINT node placement is sound. Endogenous Xenopus target enhancers remain undefined. Supporting Evidence: PMID:17138566 Structure-function analyses indicate that the transcriptional repression and mesoderm induction activities of FoxD3 are dependent on a C-terminal domain, as well as specific DNA-binding activity conferred by the forkhead domain. PMID:24252777 Amphioxus and vertebrate (Xenopus) FoxD proteins both exhibited transcriptional repressor activity in Gal4 transactivation assays and bound to similar DNA sequences in vitro. |
| GO:0000978 RNA polymerase II cis-regulatory region sequence-specific DNA binding | IEA GO_REF:0000118 | ACCEPT | Summary: TreeGrafter (PANTHER) electronic transfer of Pol II cis-regulatory sequence-specific DNA binding. Reason: Same conclusion as the IBA row: forkhead-domain sequence-specific DNA binding is experimentally supported for Xenopus FoxD3 and conserved across FoxD proteins. Supporting Evidence: PMID:17138566 Structure-function analyses indicate that the transcriptional repression and mesoderm induction activities of FoxD3 are dependent on a C-terminal domain, as well as specific DNA-binding activity conferred by the forkhead domain. PMID:24252777 Amphioxus and vertebrate (Xenopus) FoxD proteins both exhibited transcriptional repressor activity in Gal4 transactivation assays and bound to similar DNA sequences in vitro. |
| GO:0000981 DNA-binding transcription factor activity, RNA polymerase II-specific | IBA GO_REF:0000033 | ACCEPT | Summary: Phylogenetic inference of RNA polymerase II-specific DNA-binding transcription factor activity. Reason: Correct parent-level activity. Experimental evidence specifies the direction: FoxD3 acts as a repressor (Engrailed fusion mimics, VP16 fusion antagonises; Groucho recruitment via the eh1/GEH motif; no activation domain detected in Xenopus). The more precise child term GO:0001227 is proposed as a NEW annotation; this IBA stands as the correct inherited general activity. Zebrafish data indicating an early pioneer/activator phase argue against replacing the general term outright. Supporting Evidence: PMID:17138566 The results indicate that FoxD3 recruitment of Groucho corepressors is essential for the transcriptional repression of target genes and induction of mesoderm in Xenopus. PMID:17138566 No domains of FoxD3 were identified that were capable of activating reporter transcription PMID:30513303 foxd3 then gradually switches from an activator to its well-described role as a transcriptional repressor and potentially uses differential partners for each role. |
| GO:0000981 DNA-binding transcription factor activity, RNA polymerase II-specific | IEA GO_REF:0000118 | ACCEPT | Summary: TreeGrafter electronic transfer of Pol II-specific DNA-binding transcription factor activity. Reason: Consistent with the IBA and experimental data; repressor-specific child term is added separately as NEW. Supporting Evidence: PMID:17138566 The results indicate that FoxD3 recruitment of Groucho corepressors is essential for the transcriptional repression of target genes and induction of mesoderm in Xenopus. |
| GO:0001707 mesoderm formation | IMP PMID:17138566 FoxD3 and Grg4 physically interact to repress transcription ... | KEEP AS NON CORE | Summary: FoxD3 knockdown/antagonism and gain-of-function in the Xenopus gastrula show that FoxD3, acting as a Groucho-dependent repressor in the Spemann organizer, maintains Nodal-related gene expression needed for dorsal mesoderm formation. Reason: The organizer/mesoderm function is well supported in Xenopus (FoxD3 morpholino blocks axis formation and organizer Nodal expression; FoxD3 induces mesoderm non-cell-autonomously via Nodal). The mechanism is indirect (a repressor maintaining Nodal expression, likely through derepression of an unidentified inhibitor), but FoxD3 is a genuine transcriptional regulator in the organizer, so the process annotation is acceptable. It is an early, separate deployment from the neural crest role and is not conserved as an organizer function in the outgroup sense (amphioxus FoxD is in mesoderm/notochord, which is consistent with an ancestral mesodermal deployment). Kept as non-core. Supporting Evidence: PMID:17138566 In the gastrula, FoxD3 functions as a transcriptional repressor in the Spemann organizer to maintain the expression of Nodal-related members of the transforming growth factor-beta superfamily that induce dorsal mesoderm formation. PMID:17092955 Therefore, FoxD3 is required for Nodal expression in the Spemann organizer and this function is essential for dorsal mesoderm formation. PMID:17092955 Engrailed-FoxD3, but not VP16-FoxD3, was identical to native FoxD3 in mesoderm-inducing activity, indicating that FoxD3 functions as a transcriptional repressor to induce mesoderm. file:XENLA/foxd3-a/foxd3-a-deep-research-falcon.md The relevant endogenous inhibitor and any direct FoxD3-bound regulatory element were **not identified** in these experiments. |
| GO:0003677 DNA binding | IDA PMID:11335115 Overexpression of the transcriptional repressor FoxD3 preven... | ACCEPT | Summary: DNA binding by Xenopus FoxD3 (Pohl and Knochel 2001). Reason: Correct but general; the repression activity requires the winged-helix DNA-binding domain. More specific sequence-specific/cis-regulatory binding is captured by GO:0000978 (IBA/IEA). Abstract-only cache; deferring to curator on assay details. Supporting Evidence: PMID:11335115 By injections of VP16 and engrailed fusions we can demonstrate that FoxD3 acts as a negative transcriptional regulator; this repressive function strictly requires the presence of the winged helix domain. PMID:24252777 Amphioxus and vertebrate (Xenopus) FoxD proteins both exhibited transcriptional repressor activity in Gal4 transactivation assays and bound to similar DNA sequences in vitro. |
| GO:0003700 DNA-binding transcription factor activity | IEA GO_REF:0000002 | ACCEPT | Summary: InterPro2GO mapping of DNA-binding transcription factor activity from the forkhead domain. Reason: Correct, general; more specific Pol II and repressor terms are captured elsewhere. Supporting Evidence: PMID:17138566 Structure-function analyses indicate that the transcriptional repression and mesoderm induction activities of FoxD3 are dependent on a C-terminal domain, as well as specific DNA-binding activity conferred by the forkhead domain. |
| GO:0005515 protein binding | IPI PMID:17138566 FoxD3 and Grg4 physically interact to repress transcription ... | MODIFY | Summary: Direct interaction of FoxD3 (C-terminal eh1/GEH motif) with the Groucho corepressor Grg4/tle4 (O42478), shown by GST pull-down in Xenopus embryo lysates; the interaction is needed for repression. Reason: Generic protein binding is uninformative. The cited paper shows that the partner is a transcriptional corepressor (Grg4/TLE4), that binding requires the eh1/GEH motif, and that Grg4 enhances and dominant-negative Grg5 reduces FoxD3 repression. This supports the more informative GO:0001222 transcription corepressor binding. Proposed replacements: transcription corepressor binding Supporting Evidence: PMID:17138566 Deletion and point mutagenesis demonstrated that the FoxD3 eh1/GEH motif is required for both repression of transcription and induction of mesoderm, as well as the direct physical interaction of FoxD3 and Grg4 (Groucho-related gene-4). PMID:17138566 Consistent with a functional interaction of FoxD3 and Grg4, the transcriptional repression activity of FoxD3 is enhanced by Grg4, and reduced by Grg5, a dominant inhibitory Groucho protein. |
| GO:0005634 nucleus | IBA GO_REF:0000033 | ACCEPT | Summary: Phylogenetic inference of nuclear localization (is_active_in nucleus). Reason: FoxD3 is a nuclear forkhead transcription factor; nuclear localization of Xenopus FoxD3 has been shown directly. Supporting Evidence: PMID:17138566 Therefore, exogenous FoxD3 is localized to the nucleus of cells competent to form mesoderm in response to FoxD3. |
| GO:0005634 nucleus | IDA PMID:17138566 FoxD3 and Grg4 physically interact to repress transcription ... | ACCEPT | Summary: Exogenous FoxD3 protein localized to nuclei in Xenopus explant cells. Reason: Direct observation consistent with transcription-factor function. Supporting Evidence: PMID:17138566 Therefore, exogenous FoxD3 is localized to the nucleus of cells competent to form mesoderm in response to FoxD3. |
| GO:0005634 nucleus | IEA GO_REF:0000044 | ACCEPT | Summary: UniProt subcellular location mapping to nucleus. Reason: Consistent with experimental data. Supporting Evidence: PMID:17138566 Therefore, exogenous FoxD3 is localized to the nucleus of cells competent to form mesoderm in response to FoxD3. |
| GO:0006355 regulation of DNA-templated transcription | IEA GO_REF:0000002 | ACCEPT | Summary: InterPro2GO mapping to regulation of DNA-templated transcription. Reason: Correct, general; more specific Pol II and negative-regulation terms are supported experimentally. Supporting Evidence: PMID:17138566 The results indicate that FoxD3 recruitment of Groucho corepressors is essential for the transcriptional repression of target genes and induction of mesoderm in Xenopus. |
| GO:0006357 regulation of transcription by RNA polymerase II | IBA GO_REF:0000033 | ACCEPT | Summary: Phylogenetic inference of involvement in regulation of transcription by RNA polymerase II. Reason: Correct general process; experimentally FoxD3 represses Pol II reporter transcription (Gal4-UAS-Goosecoid minimal promoter) via Groucho recruitment. Supporting Evidence: PMID:17138566 The results indicate that FoxD3 recruitment of Groucho corepressors is essential for the transcriptional repression of target genes and induction of mesoderm in Xenopus. |
| GO:0006357 regulation of transcription by RNA polymerase II | IEA GO_REF:0000118 | ACCEPT | Summary: TreeGrafter electronic transfer of regulation of transcription by RNA polymerase II. Reason: As for the IBA row. Supporting Evidence: PMID:17138566 The results indicate that FoxD3 recruitment of Groucho corepressors is essential for the transcriptional repression of target genes and induction of mesoderm in Xenopus. |
| GO:0009653 anatomical structure morphogenesis | IBA GO_REF:0000033 | KEEP AS NON CORE | Summary: Broad phylogenetic inference (FOX family) of anatomical structure morphogenesis. Reason: Not wrong for a developmental transcription factor whose activity shapes neural-crest-derived and axial structures, but very general and uninformative; the specific processes where FoxD3 does its work are neural crest cell fate commitment and (in the gastrula) mesoderm formation. Supporting Evidence: PMID:11493569 These data demonstrate that FoxD3 (or its closely related factor) is an essential upstream regulator of neural crest determination. PMID:17092955 Therefore, FoxD3 is required for Nodal expression in the Spemann organizer and this function is essential for dorsal mesoderm formation. |
| GO:0009653 anatomical structure morphogenesis | IEA GO_REF:0000118 | KEEP AS NON CORE | Summary: TreeGrafter electronic transfer of anatomical structure morphogenesis. Reason: As for the IBA row: very general, retained as non-core. Supporting Evidence: PMID:11493569 These data demonstrate that FoxD3 (or its closely related factor) is an essential upstream regulator of neural crest determination. |
| GO:0014034 neural crest cell fate commitment | IMP PMID:11493569 Requirement of FoxD3-class signaling for neural crest determ... | ACCEPT | Summary: Dominant-negative FoxD3 (FoxD3delN) blocks neural crest marker expression in vivo without affecting the CNS marker Sox2; FoxD3 overexpression induces neural crest markers in embryos and ectodermal explants; FoxD3 is required for Slug induction by Zic factors. Reason: This is the core developmental process and the correct network layer. Multiple lines of evidence converge: expression in presumptive neural crest from late gastrula (overlapping Zic-r1, similar to Slug); sufficiency (induces neural crest markers in explants; vertebrate FoxD3 including Xenopus induces ectopic neural crest in chick neural tube); loss-of-function (dominant-negative blocks crest, rescued by Slug); network position downstream of the border specifier Zic and upstream of Slug; and the mouse requirement for Foxd3 in neural crest progenitors. FoxD3 is therefore a neural crest specifier, not a neural plate border specifier. GO:0014034 (commitment) is appropriately pitched: the data cover both specification and the 'determination' language of the authors, so neither child term (GO:0014036 specification, GO:0014035 determination) is clearly preferable. Caveats: the dominant-negative construct may interfere with related FoxD factors, and assays do not distinguish the L/S homeologs. Supporting Evidence: PMID:11493569 Expression of FoxD3 in the presumptive neural crest region starts at the late gastrula stage in a manner similar to that of Slug, and overlaps with that of Zic-r1. PMID:11493569 When overexpressed in the embryo and in ectodermal explants, FoxD3 induces expression of neural crest markers. PMID:11493569 Attenuation of FoxD3-related signaling by a dominant-negative FoxD3 construct (FoxD3delN) inhibits neural crest differentiation in vivo without suppressing the CNS marker Sox2. PMID:11493569 Slug induction by Zic factors requires FoxD3-related signaling PMID:24252777 whereas vertebrate FoxD3 genes induced the differentiation of ectopic NCCs when overexpressed in chick neural tube, neither amphioxus FoxD nor any other vertebrate FoxD paralogs exhibited this activity. PMID:18367558 Here, we report that Foxd3 is required for maintenance of the multipotent mammalian neural crest. file:XENLA/foxd3-a/foxd3-a-deep-research-falcon.md The historical experiments generally studied “Xenopus FoxD3/XFD-6” and did not resolve modern *X. laevis* homeologs; they therefore cannot automatically be assigned uniquely to Q9DEN4. |
| GO:0030154 cell differentiation | IBA GO_REF:0000033 | KEEP AS NON CORE | Summary: Broad phylogenetic inference of cell differentiation. Reason: Very general. FoxD3 contributes to the specification of neural crest fate, but in mouse its prominent role is to maintain multipotent progenitors and restrict premature mesenchymal differentiation, so 'cell differentiation' is a weak descriptor. Retained as non-core. Supporting Evidence: PMID:21228004 Foxd3 mediates a fate restriction choice for multipotent NC progenitors with loss of Foxd3 biasing NC toward a mesenchymal fate. PMID:11493569 These data demonstrate that FoxD3 (or its closely related factor) is an essential upstream regulator of neural crest determination. |
| GO:0030154 cell differentiation | IEA GO_REF:0000118 | KEEP AS NON CORE | Summary: TreeGrafter electronic transfer of cell differentiation. Reason: As for the IBA row. Supporting Evidence: PMID:21228004 Foxd3 mediates a fate restriction choice for multipotent NC progenitors with loss of Foxd3 biasing NC toward a mesenchymal fate. |
| GO:0043565 sequence-specific DNA binding | IEA GO_REF:0000002 | ACCEPT | Summary: InterPro2GO mapping to sequence-specific DNA binding. Reason: Correct; forkhead domain sequence-specific DNA binding is experimentally supported. Supporting Evidence: PMID:17138566 Structure-function analyses indicate that the transcriptional repression and mesoderm induction activities of FoxD3 are dependent on a C-terminal domain, as well as specific DNA-binding activity conferred by the forkhead domain. PMID:24252777 Amphioxus and vertebrate (Xenopus) FoxD proteins both exhibited transcriptional repressor activity in Gal4 transactivation assays and bound to similar DNA sequences in vitro. |
| GO:0045892 negative regulation of DNA-templated transcription | IDA PMID:11335115 Overexpression of the transcriptional repressor FoxD3 preven... | MODIFY | Summary: Engrailed- and VP16-FoxD3 fusions show that Xenopus FoxD3 acts as a negative transcriptional regulator dependent on the winged-helix domain; FoxD3 also represses its own expression. Reason: Correct in essence; FoxD3 is a transcriptional repressor. The genes it represses here (neural crest markers Xslug, Xtwist, Xcadherin-11 indirectly, and its own gene) are RNA polymerase II genes, and Pol II reporter repression is directly shown by Yaklichkin et al. 2007, so GO:0000122 is the more precise term (consistent with the other GO:0045892 rows). Proposed replacements: negative regulation of transcription by RNA polymerase II Supporting Evidence: PMID:11335115 By injections of VP16 and engrailed fusions we can demonstrate that FoxD3 acts as a negative transcriptional regulator; this repressive function strictly requires the presence of the winged helix domain. PMID:11335115 FoxD3 also inhibits its own expression, thereby acting in a negative autoregulatory loop. |
| GO:0045892 negative regulation of DNA-templated transcription | IDA PMID:11493569 Requirement of FoxD3-class signaling for neural crest determ... | MODIFY | Summary: Sasai et al. 2001 show FoxD3 acting as a transcriptional repressor in neural crest determination (abstract-only cache). Reason: Consistent with the repressor activity established by multiple independent studies (full text not available here; the transcriptional-repression claim itself is not disputed). As for the other GO:0045892 rows, the Pol II-specific child GO:0000122 is the more precise term, since FoxD3 targets are Pol II genes and repression of a Pol II promoter is directly demonstrated for Xenopus FoxD3. Proposed replacements: negative regulation of transcription by RNA polymerase II Supporting Evidence: PMID:11493569 These data demonstrate that FoxD3 (or its closely related factor) is an essential upstream regulator of neural crest determination. PMID:11335115 By injections of VP16 and engrailed fusions we can demonstrate that FoxD3 acts as a negative transcriptional regulator; this repressive function strictly requires the presence of the winged helix domain. |
| GO:0045892 negative regulation of DNA-templated transcription | IMP PMID:17138566 FoxD3 and Grg4 physically interact to repress transcription ... | MODIFY | Summary: Mutation of the eh1/GEH Groucho-interaction motif abolishes FoxD3 repression of a Gal4-UAS Goosecoid minimal-promoter reporter; Grg4 enhances and Grg5 inhibits FoxD3 repression. Reason: The repression is of an RNA polymerase II reporter promoter, and the biological targets (neural crest genes, organizer Nodal regulators) are Pol II genes. GO:0000122 negative regulation of transcription by RNA polymerase II is the more precise term. Proposed replacements: negative regulation of transcription by RNA polymerase II Supporting Evidence: PMID:17138566 The results indicate that FoxD3 recruitment of Groucho corepressors is essential for the transcriptional repression of target genes and induction of mesoderm in Xenopus. PMID:17138566 Consistent with a functional interaction of FoxD3 and Grg4, the transcriptional repression activity of FoxD3 is enhanced by Grg4, and reduced by Grg5, a dominant inhibitory Groucho protein. |
| GO:0050768 negative regulation of neurogenesis | IMP PMID:11335115 Overexpression of the transcriptional repressor FoxD3 preven... | MARK AS OVER ANNOTATED | Summary: Based on Pohl and Knochel 2001, where FoxD3 overexpression enlarges the neural plate, abolishes neural crest formation and blocks differentiation and migration of transplanted crest cells. Reason: The phenotype is an overexpression (gain-of-function) phenotype at high dose and an indirect consequence of disrupting neural crest progression; the abstract reports an enlarged neural plate, which does not obviously indicate reduced neurogenesis. A second Xenopus study (Sasai 2001) is annotated to the opposite-sign term (positive regulation of neurogenesis). FoxD3's work is done as a neural crest specifier/maintenance repressor; neurogenesis regulation is a downstream readout, not a process FoxD3 is known to execute. Full text not available, so not removed. Supporting Evidence: PMID:11335115 Ectopic overexpression of FoxD3 leads to an enlargement of the neural plate concomitant with a failure in neural crest formation PMID:11335115 Transplantation experiments show that FoxD3 overexpressing cells from the prospective neural crest do neither differentiate nor migrate. PMID:21228004 Foxd3 mediates a fate restriction choice for multipotent NC progenitors with loss of Foxd3 biasing NC toward a mesenchymal fate. |
| GO:0050769 positive regulation of neurogenesis | IMP PMID:11493569 Requirement of FoxD3-class signaling for neural crest determ... | MARK AS OVER ANNOTATED | Summary: Based on Sasai et al. 2001: dominant-negative FoxD3 inhibits neural crest differentiation; presumably neural-crest-derived neuronal/peripheral markers were reduced. Reason: The loss-of-function phenotype reflects failure of neural crest determination, from which neural derivatives secondarily fail; the CNS marker Sox2 was not suppressed. This is an indirect, downstream consequence of FoxD3's role in neural crest fate commitment (already annotated), and it conflicts in sign with the GO:0050768 annotation from overexpression. In mouse, Foxd3 maintains neural potential of crest progenitors, which is better captured by crest-progenitor terms than by generic neurogenesis. Full text not available, so not removed. Supporting Evidence: PMID:11493569 Attenuation of FoxD3-related signaling by a dominant-negative FoxD3 construct (FoxD3delN) inhibits neural crest differentiation in vivo without suppressing the CNS marker Sox2. PMID:11493569 These data demonstrate that FoxD3 (or its closely related factor) is an essential upstream regulator of neural crest determination. PMID:21228004 Foxd3 mediates a fate restriction choice for multipotent NC progenitors with loss of Foxd3 biasing NC toward a mesenchymal fate. |
| GO:0001227 DNA-binding transcription repressor activity, RNA polymerase II-specific | IDA PMID:17138566 FoxD3 and Grg4 physically interact to repress transcription ... | NEW | Summary: Xenopus FoxD3 represses Pol II reporter transcription through sequence-specific forkhead DNA binding plus a C-terminal eh1/GEH motif that recruits Groucho/TLE corepressors; no activation domain was found. Reason: Multiple independent Xenopus studies (VP16/Engrailed fusions; Gal4 fusion reporter assays; Groucho recruitment; amphioxus/Xenopus Gal4 assays) converge on repressor activity, and repression is what is required for both mesoderm induction and neural crest effects. The general GO:0000981 is correct but the repressor child is the informative molecular function. Zebrafish data suggest an earlier pioneer/activator phase in NC; this does not undermine the repressor annotation but is why GO:0000981 is retained. Supporting Evidence: PMID:17138566 The results indicate that FoxD3 recruitment of Groucho corepressors is essential for the transcriptional repression of target genes and induction of mesoderm in Xenopus. PMID:17138566 No domains of FoxD3 were identified that were capable of activating reporter transcription PMID:11335115 By injections of VP16 and engrailed fusions we can demonstrate that FoxD3 acts as a negative transcriptional regulator; this repressive function strictly requires the presence of the winged helix domain. PMID:17092955 Engrailed-FoxD3, but not VP16-FoxD3, was identical to native FoxD3 in mesoderm-inducing activity, indicating that FoxD3 functions as a transcriptional repressor to induce mesoderm. PMID:24252777 Amphioxus and vertebrate (Xenopus) FoxD proteins both exhibited transcriptional repressor activity in Gal4 transactivation assays and bound to similar DNA sequences in vitro. |
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Download this section (compressed HTML)Q: GO has no neural plate border specification/formation process term. FoxD3 sits downstream of the border specifiers (Zic, Pax3, Msx1, Tfap2a) and is not expressed at the amphioxus border; should a border term be created so that border specifiers and crest specifiers such as FoxD3 can be separated in annotation, rather than both being placed under neural crest fate commitment/formation?
Q: Should Xenopus FoxD3 carry a progenitor/potency maintenance process (e.g. stem cell population maintenance) given blastula expression and the mouse epiblast and neural crest progenitor requirements, or is that role not yet demonstrated by loss-of-function in frog?
Q: Do foxd3-a (L) and foxd3-b (S) differ in expression or activity, or should the experimental annotations currently attached only to foxd3-a also apply to foxd3-b (Q9DEN3)?
Q: Is the pioneer/chromatin-opening activity reported for zebrafish foxd3 in early neural crest conserved in Xenopus, and is there an appropriate GO molecular function term to capture pioneer activity distinct from repression?
Q: What does the vertebrate-specific FoxD3 N-terminal motif do biochemically (partner recruitment, activator function, chromatin access) to confer neural-crest-inducing activity absent from amphioxus FoxD?
Experiment: Homeolog-resolved CUT&RUN/ChIP-seq for FoxD3 and TLE4 in Xenopus neural crest explants (Wnt8+Chordin induced animal caps), combined with ATAC-seq after foxd3-a/foxd3-b morpholino or F0 CRISPR, to define direct targets and test for a pioneer-to-repressor switch.
Hypothesis: FoxD3 directly occupies and represses (and early on primes) neural crest specifier and mesenchymal-fate enhancers in Xenopus neural crest.
Experiment: Rescue foxd3 knockdown in Xenopus with wild-type FoxD3, N-terminal-motif-deleted FoxD3, amphioxus FoxD, and amphioxus FoxD carrying the vertebrate N-terminal segment; score neural crest markers (snai2, sox10, twist1) and identify motif-dependent interacting proteins by IP-MS.
Hypothesis: The vertebrate N-terminal motif is required for FoxD3 neural crest activity in Xenopus.
Experiment: Late (post-specification) inducible inhibition of FoxD3 (hormone-inducible dominant-negative or degron) in Xenopus neural crest, followed by lineage tracing and single-cell RNA-seq to test for premature mesenchymal differentiation and loss of neural/glial derivatives.
Hypothesis: FoxD3 maintains neural crest multipotency in Xenopus as in mouse.
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