module: dmel_activin_signaling
title: Activin signaling pathway in Drosophila melanogaster
label: Activin signaling
module_type: SIGNALING_PATHWAY
description: >-
  The Drosophila activin branch of TGF-beta signaling is triggered by the
  activin-like ligands Activin-beta, Dawdle and Myoglianin. These ligands bind
  a receptor complex of the type I serine/threonine kinase Baboon and a type II
  receptor kinase (Punt, or Wishful thinking). The activated type I receptor
  phosphorylates the receptor-regulated SMAD Smox (dSmad2), which partners with
  the co-SMAD Medea and enters the nucleus to regulate target genes. The pathway
  acts in neuronal remodeling, cell and tissue growth, and metabolic homeostasis.
summary: >-
  Activin-like ligands signal through Baboon and type II receptors to
  phosphorylate Smox, which acts with Medea to regulate transcription.
concepts:
  - {id: GO:0032924, label: activin receptor signaling pathway}
parts:
  - id: activin_ligands
    label: Activin-like ligands
    role: secreted ligands
    description: TGF-beta superfamily ligands of the activin branch.
    genes: [Actbeta, daw, myo]
    complex: false
    function: {id: GO:0005125, label: cytokine activity}
  - id: activin_receptors
    label: Activin receptor kinases
    role: transmembrane receptor serine/threonine kinases
    description: >-
      Baboon is the type I receptor of the activin branch; Punt and Wishful
      thinking are type II receptor kinases that FlyBase places in the core
      pathway.
    genes: [babo, put, wit]
    complex: false
    unit_functions:
      babo: {id: GO:0016361, label: "activin receptor activity, type I"}
      put: {id: GO:0016362, label: "activin receptor activity, type II"}
      wit: null
  - id: activin_smads
    label: Smox-Medea SMAD complex
    role: signal transducers and transcriptional regulators
    description: >-
      Phosphorylated Smox (receptor-regulated SMAD) forms a complex with the
      co-SMAD Medea that regulates target gene transcription.
    genes: [Smox, Med]
    complex: true
    complex_term: {id: GO:0071144, label: heteromeric SMAD protein complex}
    function: {id: GO:0000981, label: "DNA-binding transcription factor activity, RNA polymerase II-specific"}
connections:
  - {source: activin_ligands, target: activin_receptors, connection_type: POSITIVELY_REGULATES,
     description: "Ligand binding assembles and activates the type I/type II receptor complex."}
  - {source: activin_receptors, target: activin_smads, connection_type: POSITIVELY_REGULATES,
     description: "Baboon phosphorylates Smox, which then associates with Medea and enters the nucleus."}
notes: >-
  Boundary. Core components only (FlyBase ACT-C). Medea is shared with the BMP
  pathway and Punt and Wishful thinking also act as BMP type II receptors. The
  role of Wishful thinking in activin signaling is less well defined than that
  of Punt, so no receptor activity is asserted for it here. Extracellular
  modulators (Follistatin, the tolloid proteases) are regulators, not parts.
group: ACT-C