The role of the subplate layer in radial neuronal migration and cortical


During the formation of mammalian six-layered neocortical structure, newborn neurons depart the ventricular zone and migrate toward the pial surface. At a middle stage of cortical development, newly differentiated postmitotic neurons show multipolar shape (MP), and move non-radially in the intermediate zone (multipolar migration). When these multipolar neurons pass through the subplate (SP) layer, they show dynamic morphological changes and adopt bipolar shape (BP). Then, they migrate toward the pial surface (locomotion). Many KO mice with radial migration defects show abnormal MP-BP conversion at the SP suggesting that the interaction between migrating neurons and SP layer plays critical roles in switching the migration mode. SP neurons are known to help thalamocortical innervation during early stage of neural circuit formation, but their roles in radial neuronal migration remain to be elucidated. Our present working hypothesis is that MP neurons receive certain signals from the SP to change their morphology and migration mode. To test our hypothesis, we are analyzing the interaction between migrating young neurons and SP in many aspects. In this context, we examined neuronal activity of SP neurons by Ca2+-imaging using GCaMP3, and observed that they exhibited calcium oscillations at E15. Moreover, we found that suppression of neuronal activities of SP neurons by electroporation of inward-rectifier potassium ion channel Kir2.1 led to the impairment of radial migration. This suggests that neuronal activity of SP neurons is critical for radial migration. I will also discuss the evolutionally aspect of this study.