module: dmel_epithelial_polarity_complexes
title: Apical-basal polarity complexes (Par, Crumbs, Scribble) in Drosophila melanogaster
label: Epithelial polarity complexes
module_type: BIOLOGICAL_PROCESS
description: >-
  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.
summary: >-
  Par, Crumbs and Scribble polarity complexes that set apical and basolateral
  membrane domains by mutual antagonism.
concepts:
  - {id: GO:0045197, label: establishment or maintenance of epithelial cell apical/basal polarity}
parts:
  - id: par_complex
    label: Par complex
    role: apical polarity kinase complex
    group: PAR
    complex: true
    complex_term: {id: GO:0120157, label: PAR polarity complex}
    unit_functions:
      aPKC: {id: GO:0004674, label: protein serine/threonine kinase activity}
  - id: crumbs_complex
    label: Crumbs complex
    role: apical membrane determinant
    group: CRBC
    complex: true
    locations:
      - {id: GO:0016324, label: apical plasma membrane}
  - id: scribble_module
    label: Scribble module
    role: basolateral polarity determinants
    description: >-
      Scribble, Dlg1 and Lgl act together genetically and localize basolaterally,
      but are not known to form a single stable complex.
    group: SCRIBC
    complex: false
connections:
  - source: par_complex
    target: scribble_module
    connection_type: NEGATIVELY_REGULATES
    description: >-
      aPKC phosphorylates Lgl, which removes Lgl from the apical cortex.
  - source: scribble_module
    target: par_complex
    connection_type: NEGATIVELY_REGULATES
    description: >-
      The Scribble module restricts the activity and extent of apical Par complex
      proteins.
  - source: crumbs_complex
    target: par_complex
    connection_type: POSITIVELY_REGULATES
    description: >-
      Crumbs recruits and stabilizes Par-6 and aPKC at the apical membrane.
notes: >-
  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.
groups: [PAR, SCRIBC, CRBC]