Morphology and mechanics of daughter cells "delaminating" from the ventricular zone of the developing neocortex

During the development of the murine neocortex, time-lapse imaging and microsurgical experiments demonstrate that distinct mechanical forces may be acting on the migration of delaminating daughter cells. Bipolar daughter cells transform into a unipolar morphology as they detach from the inner ventricular surface along the embryonic cerebral wall. Twisting and stretching of their distally remaining pial process establishes a spring-like mechanism that efficiently pulls the soma of these transforming cells to the outer pial surface. The significance of this physical contraction observed in transforming bipolar cells is highlighted when compared to the migration of pin-like daughter cells that lack a pial process. While bipolar and pin-like cells each initially appear epithelial with a ventricular process integrated into the adherence junction meshwork at the ventricular surface, the pin-like cells instead show a transient adventricular somal movement. Consequently, pin-like cells exit from the ventricular zone much more slowly than bipolar cells. Thus, these contrasting movements of daughter cells suggest that differential pulling forces may act separately on their pial and ventricular processes as they delaminate from the telencephalic germinal zone.