Inhibited neurogenesis in JNK1-deficient embryonic stem cells

The JNKs are components of stress signaling pathways but also regulate morphogenesis and differentiation. Previously, we invoked a role for the JNKs in nerve growth factor (NGF)-stimulated PC12 cell neural differentiation (L. Marek et al., J. Cell. Physiol. 201:459-469, 2004; E. Zentrich et al., J. Biol. Chem. 277:4110-4118, 2002). Herein, the role for JNKs in neural differentiation and transcriptional regulation of the marker gene, NFLC, modeled in mouse embryonic stem (ES) cells was studied. NFLC-luciferase reporters revealed the requirement for NFLC promoter sequences encompassing base pairs -128 to -98 relative to the transcriptional start site as well as a proximal cyclic AMP response element-activating transcription factor binding site at -45 to -38 base pairs for transcriptional induction in NGF-treated PC12 cells and neurally differentiated ES cells. The findings reveal common promoter sequences that integrate conserved signal pathways in both PC12 cell and ES cell systems. To test the requirement for the JNK pathway in ES cell neurogenesis, ES cell lines bearing homozygous disruptions of the jnk1, jnk2, or jnk3 genes were derived and submitted to an embryoid body (EB) differentiation protocol. Neural differentiation was observed in wild-type, JNK2(-/-), and JNK3(-/-) cultures but not in JNK1(-/-) EBs. Rather, an outgrowth of cells with epithelial morphology and enhanced E-cadherin expression but low NFLC mRNA and protein was observed in JNK1(-/-) cultures. The expression of wnt-4 and wnt-6, identified inhibitors of ES cell neurogenesis, was significantly elevated in JNK1(-/-) cultures relative to wild-type, JNK2(-/-), and JNK3(-/-) cultures. Moreover, the Wnt antagonist, sFRP-2, partially rescued neural differentiation in JNK1(-/-) cultures. Thus, a genetic approach using JNK-deficient ES cells reveals a novel role for JNK1 involving repression of Wnt expression in neural differentiation modeled in murine ES cells.