Initiation of vertical migration and formation of a T-shaped axon. A, At the beginning, a granule cell (asterisks) located near the EGL–ML border (dotted line), had vertically oriented soma with two horizontal and one vertical process. The cell remained stationary for the first 30 min before its soma quickly moved radially toward the bottom of the ML. As a result, the granule cell developed a trailing process (small arrow) and a T-shaped axon. Time interval (in minutes) is indicated on the bottom right of each photograph. Open arrows represent rapid extension of the horizontal process of other granule cells. Scale bar, 10 μm. The total distance traversed by the granule cell soma (B), the direction and distance traveled by the soma during each 10 min of the testing period (C), and the length/width ratio of the soma (D) were plotted as a function of elapsed time.