The scaffold protein JSAP1 regulates proliferation and differentiation of cerebellar granule cell precursors by modulating JNK signaling

Mol Cell Neurosci. 2008 Dec;39(4):569-78. doi: 10.1016/j.mcn.2008.08.003. Epub 2008 Aug 30.


Cerebellar granule cell precursors (GCPs) proliferate in the outer part of the external granular layer (EGL). They begin their differentiation by exiting the cell cycle and migrating into the inner part of the EGL. Here we report that JSAP1, a scaffold protein for JNK signaling pathways, is expressed predominantly in the post-mitotic GCPs of the inner EGL. JSAP1 knockdown or treatment with a JNK inhibitor enhances the proliferation of cultured GCPs, but the overexpression of wild-type JSAP1 leads to increased proportions of p27(Kip1)- and NeuN-positive cells, even with saturating concentrations of Sonic hedgehog (Shh), a potent GCP mitogen. However, these differentiation-promoting effects on GCPs are attenuated significantly in cells overexpressing a mutant JSAP1 that lacks the JNK-binding domain. Together, these data suggest that JSAP1 antagonizes the mitogenic effect of Shh on GCPs and promotes their exit from the cell cycle and differentiation, by modulating JNK activity.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adaptor Proteins, Signal Transducing / genetics
  • Adaptor Proteins, Signal Transducing / metabolism*
  • Animals
  • Cell Cycle / physiology
  • Cell Differentiation / physiology*
  • Cell Proliferation*
  • Cells, Cultured
  • Cerebellum / cytology*
  • Cyclin-Dependent Kinase Inhibitor p27 / metabolism
  • Hedgehog Proteins / genetics
  • Hedgehog Proteins / metabolism
  • Humans
  • JNK Mitogen-Activated Protein Kinases / antagonists & inhibitors
  • JNK Mitogen-Activated Protein Kinases / genetics
  • JNK Mitogen-Activated Protein Kinases / metabolism*
  • Ki-67 Antigen / metabolism
  • Mice
  • Nerve Tissue Proteins / genetics
  • Nerve Tissue Proteins / metabolism*
  • Recombinant Fusion Proteins / genetics
  • Recombinant Fusion Proteins / metabolism
  • Signal Transduction / physiology*
  • Stem Cells / cytology
  • Stem Cells / metabolism*


  • Adaptor Proteins, Signal Transducing
  • Cdkn1b protein, mouse
  • Hedgehog Proteins
  • Ki-67 Antigen
  • Mapk8ip3 protein, mouse
  • Nerve Tissue Proteins
  • Recombinant Fusion Proteins
  • Shh protein, mouse
  • Cyclin-Dependent Kinase Inhibitor p27
  • JNK Mitogen-Activated Protein Kinases