Phactr4 regulates neural tube and optic fissure closure by controlling PP1-, Rb-, and E2F1-regulated cell-cycle progression

Dev Cell. 2007 Jul;13(1):87-102. doi: 10.1016/j.devcel.2007.04.018.


Here we identify the humpty dumpty (humdy) mouse mutant with failure to close the neural tube and optic fissure, causing exencephaly and retinal coloboma, common birth defects. The humdy mutation disrupts Phactr4, an uncharacterized protein phosphatase 1 (PP1) and actin regulator family member, and the missense mutation specifically disrupts binding to PP1. Phactr4 is initially expressed in the ventral cranial neural tube, a region of regulated proliferation, and after neural closure throughout the dorsoventral axis. humdy embryos display elevated proliferation and abnormally phosphorylated, inactive PP1, resulting in Rb hyperphosphorylation, derepression of E2F targets, and abnormal cell-cycle progression. Exencephaly, coloboma, and abnormal proliferation in humdy embryos are rescued by loss of E2f1, demonstrating the cell cycle is the key target controlled by Phactr4. Thus, Phactr4 is critical for the spatially and temporally regulated transition in proliferation through differential regulation of PP1 and the cell cycle during neurulation and eye development.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Actins / metabolism
  • Animals
  • Cell Differentiation / physiology
  • Cell Division / physiology
  • Coloboma / genetics*
  • Coloboma / metabolism
  • Coloboma / pathology
  • Cytoskeletal Proteins
  • E2F1 Transcription Factor / metabolism*
  • Gene Expression Regulation, Developmental
  • Mice
  • Mice, Inbred C3H
  • Mice, Mutant Strains
  • Neural Tube Defects / genetics*
  • Neural Tube Defects / metabolism
  • Neural Tube Defects / pathology
  • Nuclear Proteins / genetics*
  • Nuclear Proteins / metabolism*
  • Phenotype
  • Phosphoprotein Phosphatases / metabolism*
  • Phosphorylation
  • Protein Phosphatase 1
  • Retina / embryology
  • Retina / physiology
  • Retinoblastoma Protein / metabolism*


  • Actins
  • Cytoskeletal Proteins
  • E2F1 Transcription Factor
  • E2f1 protein, mouse
  • Nuclear Proteins
  • Phactr4 protein, mouse
  • Retinoblastoma Protein
  • Phosphoprotein Phosphatases
  • Protein Phosphatase 1