Serotonergic neurons migrate radially through the neuroepithelium by dynamin-mediated somal translocation

Embryonic CNS neurons can migrate from the ventricular zone to their final destination by radial glial-guided locomotion. Another less appreciated mechanism is somal translocation, where the young neuron maintains its primitive ventricular and pial processes, through which the cell body moves. A major problem in studying translocation has been the identification of neuronal-specific markers that appear in primitive, radially shaped cells. We used enhanced yellow fluorescent protein under control of the Pet-1 enhancer/promoter region (ePet-EYFP), a specific marker of early differentiated serotonergic neurons, to study their migration via immunohistology and time-lapse imaging of living slice cultures. As early as E10.0, ePet-EYFP-expressing neurons were axonless, radially oriented, and spanned the entire neuroepithelium. The soma translocated within the pial process toward the pial surface and could also translocate through its neurites, which sprouted from the pial process. The dynamin inhibitor dynasore significantly reduced translocation velocity, while the nonmuscle myosin II inhibitor blebbistatin and the kinesin inhibitor AMP-PNP had no significant effect. Here we show for the first time that serotonergic neurons migrate by somal translocation mediated, in part, by dynamin.