boss (P22815) notes

Provenance of this review (2026-11-07)

• No deep-research provider key was available in the session, and FlyBase has no hand-written
  gene description for boss (just mod-description-deep-research DROME boss returned no curated text).
  The literature was searched directly: PubMed ("bride of sevenless"[Title/Abstract] OR boss[Title]) AND Drosophila
  (42 hits, sorted by date), keeping the papers on BOSS biology and caching them with fetch-pmid.
• Reviewed as the positive control for curated rule CR-0006 (projects/RAR_MISANNOTATION.md).

Key points

• BOSS is the R8-presented ligand of the Sevenless RTK PMID:3167983;
  PMID:7680109.
• Binding epitope: C-terminal peptide of the BOSS ectodomain and Sev FNIII-3 PMID:39827240.
  Membrane anchoring, not the 7TM bundle as such, is what activation needs
  PMID:39510067.
• Localization: apical plasma membrane of R8 PMID:42043338.
• Glucose response, metabolic and lifespan phenotypes come from one lab
  (PMID:18832180, PMID:26193363, PMID:28045997); the G-protein mechanism is open
  PMID:18832180.
• Evolution: PMID:42043338
  Outside Diptera the BOSS cognate is recognized by its transmembrane stack
  PMID:18392882;
  the authors attribute this to fast co-evolution with Sevenless and raise the possibility of conserved
  Sevenless signaling in endopterygote insects, which is in tension with the statement above. The CR-0006
  Diptera scope therefore rests on ectodomain detectability and on the absence of functional evidence
  outside Drosophila, not on absence of the gene.

Consequence for CR-0006

The 2026-11-06 version of CR-0006 used Arthropoda. 135 of its 211 matches are non-dipteran
(bees, wasps, beetles, true bugs, thrips and others), none with evidence of a Sevenless-binding
ectodomain. The rule was narrowed to Diptera (NCBITaxon:7147): 76 matches, including P22815.
UniProt queries: xref:interpro-IPR002956 AND xref:interpro-IPR050726 AND taxonomy_id:7147 (76)
and the same with taxonomy_id:6656 (211), 2026-11-07.

Open points

• GO:0035997 rhabdomere microvillus membrane (FlyBase IDA, PMID:1857416) is left UNDECIDED: abstract only;
  the documented location in the eye disc is the apical R8 membrane, before rhabdomeres form.
• The PTN001173582 IBA for glutamate-activated, cyclase-inhibiting receptor activity is marked over-annotated.