Analysis of the role of MAP kinase in the formation of neural connection

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Mitogen-activated protein kinases(MAPKs) are involved in the central pathways that respond to various extracellular signals. Extracellular signal-regulated kinase(ERK) is a member of MAPKs and has various functions in the neural development. Here, we investigated the expression of p-ERK in the spinal cord and dorsal root ganglion(DRG) of chick embryos using a specific antibody. In the spinal cord, p-ERK positive cells appeared in the ventral ventricular zone on embryonic day 4 (E4). From E6 onward, they migrated radially toward the ventral horn to be localized abundantly in the white matter. Double staining method revealed that these p-ERK positive cells included oligodendrocyte precursors. In the dorsal horn, p-ERK positive small cells appeared on E6. Subsequently, the positive cells in the dorsal horn increased transiently in number and disappeared by E10. In vitro study revealed that p-ERK expression was induced in the dorsal horn of the spinal cord slices co-cultured with DRG. Furthermore, p-ERK was also induced in the dorsal horn of the spinal cord slices by acute treatment of brain-derived neurotrophic factor(BDNF). Motoneurons also expressed p-ERK transiently on E7. In DRG, weak p-ERK immunoreaction appeared in the ventrolateral part on E5. From E6, the immunoreactivity became stronger and intense p-ERK positive cells were observed throughout the DRG by E9. The strong expression of p-ERK in DRG was maintained until E15, and then reduced greatly on E18. The present study provides a structural basis to examine in vivo roles of ERK in the neural development.