Functional analysis of the scaffold protein JSAP1 in the developing mouse cerebellum

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Scaffold proteins of the mammalian MAP kinase (MAPK) cascades are thought to function in the spatio-temporal regulation of these pathways by organizing the signaling components into functional modules. We have examined the functions of c-Jun NH,-terminal kinase (JNK)/stress-activated protein kinase-associated protein 1 (JSAP1), a scaffold protein that are involved in INK MAPK cascades. Our findings are summarized as follows:1) We first generated genetically engineered mice carrying a lox-P-flanked (foxed) Jsap 1 gene, and introduced the foxed Jsap 1 deletion mutant specifically into the neural lineage. The Jsap 1 conditional knockout mice showed essentially the same phenotypes as the JSAP1-null mice, suggesting that the neonatal death of Jsap 1-deficient mice is caused by defects in the nervous system (Neurosci. Lett., 2007).2) We showed that JSAP1 scaffold regulates cell-cell interactions in PC12h cells specifically in the NGF-induced signaling pathway, and does so by modulating N-cad … More herin (Biochem. Biophys. Res. Commun., 2007) through the knock down experiments in PC12h cells.3) We also studied JSAP1 and JNK expression in mouse brains. Our results obtained by in situ hybridization and immunohistochemical analyses strongly suggested that JSAP1-JNK signaling plays important roles in developing and adult mouse brains (J. Neurothem., 2006).4) During the development of the cerebellum, massive clonal expansion of granule cell precursors (GCPs) occurs in the outer part of the external granular layer (EGL). We have provided evidence that JSAP1 and active JNK were expressed preferentially in the post-mitotic inner EGL progenitors in the developing cerebellum. Moreover, Jsap 1 deficiency resulted in increasing numbers of proliferating GCPs in mouse embryos. Besides, overexpression of JSAP1 in cultured GCPs led to increased numbers of NeuN-positive cells together with the activation of JNK. Together, these data strongly indicated that JSAP1 promotes the cell-cycle exit and differentiation of GCPs by modulating JNK activity in cerebellar development (in preparation). Less