Nemo-like kinase-myocyte enhancer factor 2A signaling regulates anterior formation in Xenopus development

Development of anterior neural structure in Xenopus requires the inhibition of BMP and Wnt signaling. We previously reported that NLK negatively regulates Wnt signaling via phosphorylation of TCF/LEF. However, the molecular events lying downstream of NLK pathways in early neural development remain unclear. In the present study, we identified the transcription factor MEF2A as a novel substrate for NLK. NLK regulates the function of xMEF2A via phosphorylation, and this modification can be abrogated by depletion of endogenous NLK. In Xenopus embryos, depletion of either NLK or MEF2A results in a severe defect in anterior development. Endogenous expression of anterior markers was blocked by depletion of endogenous xNLK or xMEF2A, but notably not by depletion of other xMEF2 family genes, xMEF2C or xMEF2D. Defects in head formation or expression of the anterior marker genes caused by depletion of endogenous xMEF2A could be rescued by expression of wild-type xMEF2A, but not xMEF2A containing mutated xNLK phosphorylation sites. Furthermore, the expression of xNLK-induced anterior markers was efficiently blocked by the depletion of endogenous xMEF2A in animal pole explants. These results show that NLK specifically regulates MEF2A activity required for the anterior formation in Xenopus development.