Requirement of the MEK5-ERK5 pathway for neural differentiation in Xenopus embryonic development

Although previous studies have identified several key transcription factors in the generation process of the vertebrate nervous system, the intracellular signalling pathways that function in this process have remained unclear. Here we identify the evolutionarily conserved mitogen-activated protein kinase kinase 5 (MEK5)- extracellular signal-regulated kinase 5 (ERK5) pathway as an essential regulator in neural differentiation. Knockdown of Xenopus ERK5 or Xenopus MEK5 with antisense morpholino oligonucleotides results in the reduced head structure and inhibition of neural differentiation. Moreover, forced activation of the MEK5 - ERK5 module on its own induces neural differentiation. In addition, we show that the MEK5 - ERK5 pathway is necessary for the neuralizing activity of SoxD, a regulator of neural differentiation, and is sufficient for the expression of Xngnr1, a proneural gene. These results show that the MEK5 ERK5 pathway has an essential role in the regulation of neural differentiation downstream of SoxD and upstream of Xngnr1.