fgf8b notes (DANRE, Q805B2)

2026-09-28 session log

• Deep research FAILED for this gene (Edison: 402 Payment Required; the OpenAI key is invalid).
  Not retried, per instructions. Literature research was done by hand with Europe PMC REST; the
  searches and newly cached PMIDs are listed in ../fgf8a/fgf8a-notes.md.
• Searches for fgf8b (or its old names fgf17 / fgf17a) morphants, mutants or CRISPR alleles found
  no published loss-of-function study of fgf8b. Full-text query BODY:"fgf8b morpholino" OR ...
  returned 0 hits; BODY:"fgf8b mutant" hits are dominated by the unrelated human FGF8b SPLICE
  ISOFORM. So every functional claim for fgf8b is expression, gain of function, or inference.

Identity and naming

• Originally described as zebrafish fgf17 (Reifers et al. 2000); UniProt synonyms fgf17, fgf17a
  [file:DANRE/fgf8b/fgf8b-uniprot.txt "Synonyms=fgf17"].
• Renamed as a TGD co-orthologue of FGF8
  PMID:17708537.
• Even at first description it was closer to Fgf8 in sequence
  PMID:11091072.
• Synteny: fgf8b on Dre1 with FGF8-flanking orthologues
  PMID:19562753.
• The fgf8b block lost fbxw4, whose introns carry fgf8 enhancers
  PMID:17387144.
• Protein: 212 aa, signal peptide 1-27, one N-glycosylation site; 70.8% identity to fgf8a
  (compare_pair.py). UniProt protein existence is "Evidence at transcript level".

Expression (UniProt / PMID:11091072 and PMID:19562753)

• Not expressed during gastrulation; first at 8 somites in ventral MHB and anterior somites;
  optic stalks; otic vesicle at 24 h; hyoid at 30 h; dorsal diencephalon at 36 h
  [file:DANRE/fgf8b/fgf8b-uniprot.txt "Not expressed during gastrulation."].
• Shared with fgf8a at mid-somitogenesis: MHB and somites
  PMID:19562753.
• fgf8a-only domains: dorsal diencephalon and tailbud at mid-segmentation; telencephalon,
  olfactory epithelium, pharyngeal arches and fin AER at long-pec; heart.
  PMID:19562753
• Ear, anterior sensory patch: zebrafish fgf8b weak, fgf8a strong; stickleback the reverse
  PMID:19562753.
• No fgf8b-unique expression domain in zebrafish is reported in the sources read.

Function

• Protein activity: mRNA injection shows it can act like fgf8
  PMID:11091072.
• Regulation: downstream of pax2a (dose-dependent) and of fgf8a (maintenance) at the MHB
  PMID:11091072.
• Redundancy with fgf8a: the only test (ace;noi double mutants lacking fgf8a function and fgf8b
  expression) showed no enhanced DA-neuron phenotype
  PMID:12843251.

Decisions

• 20 GOA rows reviewed.
• MF (growth factor activity, FGFR1/FGFR2 binding, FGFR binding NAS), FGFR signalling, MAPK
  cascade and extracellular region: ACCEPT. The protein keeps the FGF8 fold and signal peptide and
  acts like fgf8 in an injection assay, so the IBA MF/pathway terms apply to both paralogues.
• Cytoplasm IBA: MARK_AS_OVER_ANNOTATED (secreted ligand), same as fgf8a and human FGF8.
• D/V pattern formation IBA: MARK_AS_OVER_ANNOTATED. The protein could act in D/V patterning
  (injection assay), but the D/V axis is set in the blastula/gastrula, when fgf8b is not expressed.
  This is an expression-level loss of an ancestral subfunction, not a protein-level one.
• ARBA negative regulation of endodermal cell fate specification: REMOVE (gastrula-stage process;
  fgf8b not expressed then; no fgf8b evidence).
• ARBA mesoderm development and A/P pattern specification: MARK_AS_OVER_ANNOTATED (no
  fgf8b-specific evidence; the fgf8a evidence is gastrula-stage).
• NAS MHB development and pattern specification process: KEEP_AS_NON_CORE (expression and
  genetic-hierarchy evidence only; no loss-of-function).
• No NEW terms: no loss-of-function data exist for fgf8b.