module: dmel_salivary_glue_secretion
title: Larval salivary glue proteins and puparial adhesion in Drosophila melanogaster
label: Salivary glue and puparial adhesion
module_type: BIOLOGICAL_PROCESS
description: >-
  At the end of the third larval instar, the larval salivary glands make large
  amounts of glue glycoproteins in response to the ecdysone pulse, store them
  in secretory granules and release them into the gland lumen. At
  pupariation the larva expectorates the glue, which spreads over the body and
  hardens, fixing the puparium to the substrate for metamorphosis. The glue is
  a mixture of unrelated proteins: long, repeat-rich, heavily glycosylated
  mucin-like proteins (Sgs1, Sgs3, Sgs4 and the mucin Eig71Ee/gp150), small
  cysteine-rich proteins (Sgs7, Sgs8) and Sgs5 and Sgs5bis, whose role in the
  glue is not known.
summary: >-
  Salivary glue proteins expectorated at pupariation that attach the puparium
  to the substrate.
concepts:
  - {id: GO:0007594, label: puparial adhesion}
anatomical_locations: []
parts:
  - id: mucin_like_glue_proteins
    label: Repeat-rich glycosylated glue proteins
    role: mucin-like glue components
    description: >-
      Long glue proteins with internal repeats and heavy O-glycosylation. Eig71Ee
      (gp150) is also expressed in hemocytes and takes part in hemolymph clotting.
    genes: [Sgs1, Sgs3, Sgs4, Eig71Ee]
    function: {id: GO:0140073, label: bioadhesive activity}
    unit_functions:
      Eig71Ee: null
  - id: small_cysteine_rich_glue_proteins
    label: Small cysteine-rich glue proteins
    role: small glue components
    description: Short cysteine-rich glue proteins encoded by the paired Sgs7 and Sgs8 genes.
    genes: [Sgs7, Sgs8]
    function: {id: GO:0140073, label: bioadhesive activity}
  - id: sgs5_family_glue_proteins
    label: Sgs5 and Sgs5bis
    role: glue components of unknown role
    description: >-
      Sgs5 and its paralog Sgs5bis lack the long glycosylated repeats of
      Sgs1, Sgs3 and Sgs4; their contribution to adhesion is untested.
    genes: [Sgs5, Sgs5bis]
knowledge_gaps:
  - gap_statement: >-
      Which glue proteins provide adhesion, and what Sgs5, Sgs5bis and the small
      cysteine-rich proteins contribute (adhesion, cross-linking or setting of
      the glue), has not been tested gene by gene.
    boundary: >-
      Adhesive function of individual glue components; the glue secretion
      machinery (granule biogenesis and exocytosis) is outside this module.
    gap_kind: [BIOLOGY]
notes: >-
  Boundary. The module contains the glue proteins themselves. Glue granule
  biogenesis and exocytosis (for example Swip-1, which promotes glue granule
  exocytosis) and the ecdysone-triggered transcriptional program are upstream
  context, not parts. Most bioadhesive activity annotations rest on the 1976
  biochemical characterization of the glue (PMID:825230).
evidence:
  - source_id: PMID:825230
    title: "Differentiation in the salivary glands of Drosophila melanogaster: characterization of the glue proteins and their developmental appearance."
    statement: Identifies the major glue proteins and their developmental timing.
    supporting_text: >-
      These glands synthesize and secrete massive amounts of a glue which
      attaches the pupae to the substrate during metamorphosis.
group: GLUE