Ser (Serrate) — curation notes (DROME, P18168)

Session 2026-09-30 (Notch signaling module)

Deep research: Ser-deep-research-falcon.md (falcon) produced during the session (wrapper
reported a timeout but the client completed). It notes the Serrate/Jagged cysteine-rich domain,
strong Mib1 dependence and cis-inhibition; used for corroboration.

Key findings

• Serrate binds the same Notch EGF repeats (11-12) as Delta PMID:1657403.
• Ser-Notch affinity is similar to Dl-Notch PMID:10504334.
• Fringe inhibits responsiveness to Serrate and potentiates Delta PMID:9202123, restricting
  Ser-Notch signaling to the wing D/V boundary.
• Conserved intracellular motifs: one Mib1/Neur-interaction motif needed for trans-activation and
  endocytosis but not for cis-inhibition; cis-inhibition occurs at the cell surface
  PMID:17006545.
• Ser ectodomain binds glycosphingolipids via a conserved GSL-binding motif PMID:20176925.
• Serrate (not Delta) is the ligand for crystal cell specification in the lymph gland
  [PMID:12445385; PMID:12569125].
• A third, DSL-less Notch ligand, Weary (CG31665), acts in the adult heart PMID:20203305 — relevant
  to pathway variants.

Decisions

• Core MF: GO:0005112 Notch binding and GO:0048018 receptor ligand activity; process Notch
  signaling pathway; location plasma membrane / apical PM.
• REMOVE: GO:0005515 protein binding (Mib1). MODIFY: GO:0007166 -> GO:0007219.
• Axon/axolemma/neuron projection, endosomal compartments, apical cortex kept as non-core.

PANTHER

UniProt DR PANTHER: PTHR12916 ("CYTOCHROME C OXIDASE POLYPEPTIDE VIC-2") and PTHR12916:SF11
("MUCIN-4") — official PANTHER names, evidently not descriptive of Serrate. Note that Ser is not in
PTHR24049 with Dl/N. IBA GO:0005112 <- PANTHER:PTN002371879 (same node as Dl).