BTBD3 (BTB/POZ domain-containing protein 3) is a 520-residue cytoplasmic protein of the BTBD1/2/3/6 family, built from an N-terminal BTB/POZ dimerization domain, a BACK domain and a C-terminal PHR domain. Its function is known only from mammals: in the developing mouse somatosensory (barrel) cortex, Btbd3 is expressed in layer 4 spiny stellate neurons, moves from the cytosol into the nucleus in response to neuronal activity, and orients their primary dendrites toward active thalamocortical axon terminals; it does the same in ferret visual cortex. Mouse knockouts show compulsive-like behaviour and reduced exploration that track hippocampal expression. Its molecular activity is not established; BTB-domain proteins of this kind commonly self-associate and act as adaptors. Chicken BTBD3 is an unreviewed, ortholog-predicted entry with no direct experimental characterisation; its role is inferred from the conserved vertebrate BTBD3 orthologue group, and in birds it would act in the pallium, which lacks the layered neocortex in which the mammalian function was described.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005737 cytoplasm | IEA GO_REF:0000044 | MODIFY | Summary: Cytoplasm comes from the UniProt subcellular-location keyword, which on this TrEMBL entry rests only on an ARBA rule. The location is correct (mouse Btbd3 is cytosolic and moves to the nucleus with activity), but the gene already carries the more specific cytosol term from the IBA row. Reason: True but general. The mouse orthologue was localised to the cytosol directly (PMID:24179155, curated in Swiss-Prot P58545), and this gene already carries GO:0005829 cytosol by IBA, so the specific term is preferred. Proposed replacements: cytosol Supporting Evidence: PMID:24179155 endogenous Btbd3 translocated to the cell nucleus in response to neuronal activity |
| GO:0005829 cytosol | IBA GO_REF:0000033 | ACCEPT | Summary: Cytosolic localisation inherited from the BTBD1/2/3/6 family node, with mouse Btbd3 (IDA, PMID:24179155) and human BTBD1 among the donors. Mouse Btbd3 resides in the cytosol at rest and enters the nucleus upon neuronal activity. Reason: The family is cytoplasmic throughout, the mouse orthologue has direct evidence, and nothing about the chicken protein suggests divergence. The activity-induced nuclear pool is a second location that GOA does not carry for chicken; it is recorded in core_functions rather than proposed as a NEW row because no chicken data exist. Supporting Evidence: PMID:24179155 endogenous Btbd3 translocated to the cell nucleus in response to neuronal activity |
| GO:0021987 cerebral cortex development | IBA GO_REF:0000033 | MODIFY | Summary: Inherited from the vertebrate BTBD3 orthology node PTN002908884 (lamprey, fishes, frog, reptiles, birds, mammals), whose only experimental donor is mouse Btbd3 (IMP, PMID:24179155: dendrite orientation of barrel-cortex layer 4 neurons). This is the row flagged for Gallus gallus by Wei et al. 2020 (PMID:32470107). GO defines the cerebral cortex as "the outer layered region of the telencephalon"; birds lack a layered neocortex, and their candidate layer 4 homologues are organised as pallial nuclei. GO:0021987 is part_of GO:0021543 pallium development, which applies to all vertebrates. Reason: The node placement is reasonable for the gene's function: BTBD3 is a single conserved vertebrate orthologue, and there is no sign of loss or divergence in birds. What does not transfer cleanly is the anatomy. The avian pallium is mostly nuclear rather than layered, and whether its sectors are homologous to neocortex is disputed. Dugas-Ford et al. (PMID:23027930) argue that layer 4 input and layer 5 output cell types are conserved but form nuclei in birds; Rueda-Alana et al. (PMID:39946453) find that chick sensory-circuit neurons have divergent developmental origins and argue for convergence. The claim that survives this dispute is the pallium-level one, so the row is generalised to GO:0021543 pallium development, the part_of parent. The GO taxon constraint (only_in_taxon Bilateria) does not forbid the original term in birds, and about 1,759 bird rows to GO:0021987 exist, almost all TreeGrafter or Ensembl IEA. The issue is therefore systemic and is raised in suggested_questions. It is not treated as a wrong-function error, so REMOVE is not appropriate. Propagation Review Root cause: TERM SCOPING PROBLEM Failure modes: LINEAGE OR TAXON MISMATCH GRANULARITY MISMATCH Sources checked: MGI:MGI:2385155 · Btbd3 (mouse) SUPPORTS SOURCE BUT NOT TARGET Mouse IMP/IDA (PMID:24179155) for dendrite orientation in barrel-cortex layer 4 is sound for a mammal with a layered neocortex; the cortex-specific anatomy does not carry over to the nuclear avian pallium. PANTHER:PTN002908884 · PTN002908884 SUPPORTS SOURCE BUT NOT TARGET Vertebrate BTBD3 orthology node (lamprey, fishes, frog, reptiles, birds, mammals). Placement is right for the gene function but propagates a mammal-anatomy term to taxa without a layered cortex. Proposed replacements: pallium development Supporting Evidence: PMID:24179155 during the development of the sensory cortex, dendritic field orientation is controlled by the BTB/POZ domain-containing 3 (BTBD3) PMID:23027930 Our findings establish that the layer 4 input and the layer 5 output cell types are conserved across the amniotes, but are organized into very different architectures, forming nuclei in birds, cortical areas in reptiles, and cortical layers in mammals. PMID:26154980 The neocortex is found only in mammals PMID:39946453 suggesting the convergence of high-order sensory processing across amniote lineages PMID:33574185 Birds display advanced behaviors, including vocal learning and problem-solving, yet lack a layered neocortex file:CHICK/BTBD3/BTBD3-notes.md GO:0021543 pallium development, Aves: 0 annotations. |
| GO:0022008 neurogenesis | IBA GO_REF:0000033 | TOO GENERAL | Summary: Family-level IBA from the deep BTBD1/2/3/6 node PTN001229949, with a Drosophila family member and mouse Btbd3 as donors. For BTBD3 the only supporting biology is the dendrite-orientation role, and dendrite morphogenesis is an is_a descendant of neurogenesis (via neuron differentiation). Reason: True of the gene, but entailed by GO:0048813 dendrite morphogenesis, which is accepted below. There is no evidence that BTBD3 contributes to generating neurons (proliferation or fate specification), as opposed to shaping their dendrites, so the broad term adds nothing. Supporting Evidence: PMID:24179155 oriented primary dendrites toward active axons in the barrel hollow |
| GO:0042802 identical protein binding | IEA GO_REF:0000107 | KEEP AS NON CORE | Summary: Ensembl Compara transfer of the human BTBD3 self-interaction detected in the HuRI yeast two-hybrid interactome (IntAct IPI, PMID:32296183). BTB/POZ domains typically mediate homodimerization, so self-association of the chicken orthologue is plausible. Reason: Plausible and consistent with the BTB fold, but it comes from a high-throughput binary screen of the human protein and says nothing about the protein's biological activity. It is retained as a non-core structural property. Supporting Evidence: PMID:32296183 yeast two-hybrid (Y2H) represents the only binary PPI assay that can be operated at sufficient throughput to systematically screen the human proteome for binary PPIs file:CHICK/BTBD3/BTBD3-uniprot.txt IPR000210; BTB/POZ_dom. |
| GO:0048813 dendrite morphogenesis | IBA GO_REF:0000033 | ACCEPT | Summary: Inherited from the vertebrate BTBD3 orthology node, donor mouse Btbd3 (IDA, PMID:24179155). Mouse Btbd3 orients primary dendrites of layer 4 neurons toward active axons, and the effect is reproduced in ferret visual cortex and by ectopic expression in mouse visual cortex. This is the best-characterised function of the gene. Reason: This is the core biological process of BTBD3, and it is anatomy-neutral, so it transfers to birds without the homology problem that affects the cerebral cortex term. The orthology group is single-copy in amniotes and the function is conserved across mammalian species and cortical areas. No chicken experiment exists, but there is no evidence of divergence. Supporting Evidence: PMID:24179155 Btbd3 also directed dendrites toward active axon terminals when ectopically expressed in mouse visual cortex or normally expressed in ferret visual cortex. PMID:24179155 BTBD3 regulation of dendrite orientation is conserved across species and cortical areas |
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Download this section (compressed HTML)Q: Should GO:0021987 cerebral cortex development, defined as development of "the outer layered region of the telencephalon", carry a taxon constraint (for example only_in_taxon Mammalia, or an explicit treatment of reptile and bird pallial cortices)? At present it is constrained only to Bilateria, and about 1,759 bird annotations exist, almost all TreeGrafter or Ensembl IEA, while GO:0021543 pallium development has none. A constraint or a taxon-neutral grouping term would redirect these propagations to the pallium level automatically.
Q: Is the PAINT node PTN002908884 the right place for cerebral cortex development? It sits at the vertebrate BTBD3 orthology node and so propagates the term to lampreys and teleosts, whose everted pallium has no layered cortex. Dendrite morphogenesis at the same node transfers cleanly; a pallium-level process term would be the anatomy-neutral equivalent.
Q: Does chicken BTBD3 mark the avian layer-4-like input neurons (entopallium, field L, nucleus basorostralis) that Dugas-Ford and colleagues identified by layer-marker expression? If it does, the cell-type homology argument would support a cortex-like role even though the anatomy is nuclear.
Experiment: In situ hybridisation or spatial transcriptomics for BTBD3 across embryonic and post-hatch chick pallium, co-registered with thalamorecipient markers (for example RORB) in the entopallium, field L and nucleus basorostralis.
Hypothesis: BTBD3 is expressed in avian thalamorecipient input neurons during the period when thalamic afferents arrive, as mouse Btbd3 is in barrel layer 4.
Type: expression mapping
Experiment: In ovo electroporation of BTBD3 shRNA or a dominant-negative construct into the chick dorsal telencephalon, followed by morphometry of dendrite orientation relative to labelled thalamic afferents.
Hypothesis: Chicken BTBD3 is required to bias dendrites of pallial input neurons toward active afferents, which would confirm that the function, not just the gene, is conserved in birds.
Type: loss of function with morphometry
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