Apical-basal polarity complexes (Par, Crumbs, Scribble) in Drosophila melanogaster

Epithelial cells divide their plasma membrane into apical and basolateral domains using three conserved groups of polarity proteins that act on each other. The Par complex, Bazooka (Par-3), Par-6 and atypical protein kinase C (aPKC), marks the apical side and the adherens junction; aPKC phosphorylates basolateral proteins to exclude them from the apical membrane. The Crumbs complex, the transmembrane protein Crumbs with Stardust (PALS1) and Patj, defines the apical membrane above the adherens junction. The Scribble module, Scribble, Discs large (Dlg1) and Lethal (2) giant larvae (Lgl), acts basolaterally and restricts apical determinants. Mutual antagonism between apical and basolateral proteins sets the boundary, and loss of the Scribble module causes neoplastic overgrowth.

MODULE:dmel_epithelial_polarity_complexesDRAFTCONCRETEBiological Processmodules/dmel_epithelial_polarity_complexes.yaml
establishment or maintenance of epithelial cell apical/basal polarityGO:0045197
FB:FBgg0001760
FlyBase gene group PAR: Par complex
FlyBase release FB2026_03 groups 3 D. melanogaster genes as par complex (PAR); this module models that group.
FB:FBgg0001762
FlyBase gene group SCRIBC: Scribble complex
FlyBase release FB2026_03 groups 3 D. melanogaster genes as scribble complex (SCRIBC); this module models that group.
FB:FBgg0001763
FlyBase gene group CRBC: Crumbs complex
FlyBase release FB2026_03 groups 3 D. melanogaster genes as crumbs complex (CRBC); this module models that group.
GO:0045197
establishment or maintenance of epithelial cell apical/basal polarity
GO term grounding the module as establishment or maintenance of epithelial cell apical/basal polarity.

The Par complex also acts in neuroblast asymmetric division and the Scribble module in neuromuscular junction organization; this module describes their shared core composition. Other polarity regulators (Cdc42, Yurt, Coracle group, Par-1) are context and not parts. FlyBase groups realized by this module: PAR (FBgg0001760), SCRIBC (FBgg0001762), CRBC (FBgg0001763). Participants were generated from the FlyBase gene-group membership and mapped to UniProtKB by projects/FLYBASE_GENE_GROUPS/generate_modules.py from module_specs/dmel_epithelial_polarity_complexes.yaml. None of the member genes has a gene review in this repository yet.

4Nodes
3Parts
0Variant Sets
0Variants
5Annotons
3Connections

Derived QC

Recommended-field compliance

100.0% recommended fields populated

All recommended fields populated.

Module deep research

✗ none found

No MODULE:dmel_epithelial_polarity_complexes deep-research report alongside the module YAML.

Leaf nodes lacking representative members

✓ every leaf node grounds to a representative protein.

Template conformance

✓ every declared conforms_to bundle matches its template motif.

Function consistency and core coverage

0 gene-function check(s) reflected in core functions · 0 conflict(s) · 1 evidence or coverage gap(s) (1 comparison(s))

Retained noncore functions are reported separately; they do not require promotion to core functions. Support from representative genes does not establish conservation across the whole family. Missing reviews or identifiers leave a claim unverified.

AnnotonParticipantFunctionAssessment
par_complex_complex/apkc aPKC
UniProtKB:A1Z9X0
Complex Unit
protein serine/threonine kinase activity
GO:0004674
Review Missing
No ai-review exists for this protein; its function and core-function coverage cannot yet be checked.

Feedback loops (advisory, prose-driven: a regulator counts as "feedback" when its own description says so)

✓ every negative regulator described as feedback has an upstream edge closing the loop.

  • par_complex ⊣ scribble_module [closed]
    par_complex is regulated by crumbs_complex: feedback loop closed
  • scribble_module ⊣ par_complex [input]
    scribble_module is a negative regulator with no upstream edge (not described as feedback)

Gene-review completeness (2/9 grounded genes reviewed)

1 complete review(s) · 2 with deep research · 7 missing review · 0 reviewed but lacking deep research

Gene Review Complete Deep research
aPKC A1Z9X0 ✗ — —
crb P10040 ✓ ✓ ✓
dlg1 P31007 ✓ 97/98 ✓
sdt E2QD98 ✗ — —
par-6 O97111 ✗ — —
l(2)gl P08111 ✗ — —
baz Q0KHR3 ✗ — —
scrib Q7KRY7 ✗ — —
Patj Q9NB04 ✗ — —

Details

Context
Drosophila melanogasterNCBITaxon:7227
Epithelial polarity complexesBiological Processdmel_epithelial_polarity_complexes

Par, Crumbs and Scribble polarity complexes that set apical and basolateral membrane domains by mutual antagonism.

establishment or maintenance of epithelial cell apical/basal polarityGO:0045197
Context
Drosophila melanogasterNCBITaxon:7227

Connections

par_complex -> scribble_module Negatively Regulates
aPKC phosphorylates Lgl, which removes Lgl from the apical cortex.
scribble_module -> par_complex Negatively Regulates
The Scribble module restricts the activity and extent of apical Par complex proteins.
crumbs_complex -> par_complex Positively Regulates
Crumbs recruits and stabilizes Par-6 and aPKC at the apical membrane.
Part 1: apical polarity kinase complex
Par complexBiological Processpar_complex

Annotons

Par complex
par_complex_complex
Participant: Protein Complex: Par complex
Protein Complex:
Par complexGO:0120157
Active units:
aPKC
Participant: Gene Product: aPKC
Gene Product:
Function:
protein serine/threonine kinase activityGO:0004674
baz
Participant: Gene Product: baz
Gene Product:
par-6
Participant: Gene Product: par-6
Gene Product:
Part 2: apical membrane determinant
Crumbs complexBiological Processcrumbs_complex

Annotons

Crumbs complex
crumbs_complex_complex
Participant: Protein Complex: Crumbs complex
Protein Complex:
Crumbs complex
Active units:
Patj
Participant: Gene Product: Patj
Gene Product:
crb
Participant: Gene Product: crb
Gene Product:
sdt
Participant: Gene Product: sdt
Gene Product:

Locations

apical plasma membraneGO:0016324
Part 3: basolateral polarity determinants
Scribble moduleBiological Processscribble_module

Scribble, Dlg1 and Lgl act together genetically and localize basolaterally, but are not known to form a single stable complex.

Annotons

dlg1 Scribble module
scribble_module_dlg1
Participant: Gene Product: dlg1
Gene Product:
l(2)gl Scribble module
scribble_module_l_2_gl
Participant: Gene Product: l(2)gl
Gene Product:
scrib Scribble module
scribble_module_scrib
Participant: Gene Product: scrib
Gene Product: