Dll3 (mouse) review notes

UniProt O88516 (DLL3_MOUSE), Delta-like protein 3, 592 aa, type I membrane protein.
PANTHER PTHR24044 (NOTCH LIGAND FAMILY MEMBER), subfamily PTHR24044:SF420. MGI:1096877.
Notch-module role: divergent DSL ligand acting as a cell-autonomous (cis) inhibitor of Notch;
does not activate Notch in trans.

Divergent structure

• Most divergent Delta homologue PMID:9272948
  UniProt/InterPro: Notch_ligand_N (MNNL) domain and EGF repeats; its DSL domain is degenerate
  (InterPro lists no DSL domain IPR001774 for Dll3, unlike Dll1). Lacks the intracellular
  PDZ-binding/ubiquitination motif architecture of Dll1 (not independently verified here).

Does not activate Notch; cis-inhibitor

• PMID:16144902
• PMID:16144902
• PMID:16144902
• As a Notch antagonist, Dll3 promoted Xenopus neurogenesis and inhibited glial differentiation of mouse
  neural progenitors PMID:16144902. This contradicts the earlier interpretation that ectopic Dll3
  inhibits primary neurogenesis as an activating ligand PMID:9272948.
• Knock-in replacing Dll1 by Dll3 does not rescue; DLL3 does not activate Notch in Drosophila wing
  PMID:17664336
  Geffers et al. did not detect DLL3 antagonism of DLL1 in mouse PSM (point of disagreement with Ladi/Chapman).

Subcellular localisation

• Endogenous DLL3 predominantly in the Golgi, not at the PSM cell surface
  PMID:17664336
• Interacts with Notch1 in late endocytic compartment, targeting Notch1 for lysosomal degradation
  PMID:21147753
• In oocytes, DLL3 is detected at the membrane close to MIB2; co-IP with Notch2 and Gm364; Gm364 KO reduces
  DLL3 ubiquitination PMID:34635817
• Mib1 interacts with all Notch ligands including Dll3 PMID:16000382

Somitogenesis / disease

• pudgy (Dll3 pu) and targeted null (Dll3 neo) cause vertebral/rib malformations; disrupted segmentation clock
  PMID:11923214
• PMID:9662403
• Human DLL3 mutation causes spondylocostal dysostosis type 1 (SCDO1) PMID:21147753.
• No overt neural phenotype is reported for Dll3 mutants in the cached literature; neural annotations rest on
  expression and overexpression assays.

Pathway-variant relevance

• Vertebrate-specific divergent DSL ligand; functions in cis (cis-inhibition), intracellular (Golgi /
  late endosome) rather than as a trans signal-sending ligand. Contrast with Dll1 (canonical activating
  ligand, cell surface, Mib1-dependent endocytosis).

Deep research

Falcon deep research completed on a second run with a 2400 s timeout (Dll3-deep-research-falcon.md).
Key points consistent with primary literature: cis-inhibitor, Golgi-retained, intracellular domain lacks
lysines and the PDZ-binding motif
[file:mouse/Dll3/Dll3-deep-research-falcon.md "Dll3 serves primarily as a cell-autonomous cis-inhibitor of Notch signaling"].
Primary support for the lysine-less intracellular region: PMID:18676613.
Note tension: Chen et al. 2021 report MIB2-dependent DLL3 ubiquitination in oocytes PMID:34635817, so
lysine-independent (or ectodomain) ubiquitination, or a context-specific mechanism, remains unresolved.

2026-10-12 Ortholog/family audit (Dll1, Dll3, Hes7, Rbpj)

• GOA refreshed: no new rows; coverage is complete and there are no stale entries. No human DLL3 review exists in the repo for comparison.
• DSL-family IBAs are shared with Dll1 (nodes PTN001170801 and PTN002371879). Each is judged against Dll3-specific divergence evidence, not donor count:
• Notch binding is ACCEPTed because it rests on cis binding PMID:16144902.
• Notch signaling pathway is MODIFIED to negative regulation of Notch signaling pathway (PROPAGATION_BAD, FUNCTIONAL_DIVERGENCE).
• Plasma membrane is KEEP_AS_NON_CORE. Dll1 ACCEPTs plasma membrane and keeps GO:0045746 as non-core; Dll3 ACCEPTs GO:0045746 as core. This is consistent with Dll3 being a cis-inhibitor that does not activate Notch in trans.
• REMOVE of negative regulation of neurogenesis (IDA, PMID:9272948) retained. The later full-text study directly contradicts it PMID:16144902.
• No action changes in this audit. Status set to COMPLETE.