The cellular kinetics of the developing mouse cerebellum. II. The function of the external granular layer in the process of gyrification.

Abstract The postnatal cerebellar gyrification in mice is associated with the intensive germinative activity of the external granular layer (EGL). The average proliferation rate of the EGL localized in the fissures is higher than that at the superficial (convex) parts of gyri. The difference (as measured by colcemide blockage) amounts to 38% in 2-day-old animals and to 13% in 7-day-old mice. The higher proliferation rate of the EGL is fissures results partly from the shorter generation cycle; it lasts 14.6 and 17.6 h in 2- and 7-day-old mice respectively. The corresponding values for the superficial convexity of gyri amounts to 16.2 and 19.3 h. In 2-day-old animals the difference in the ‘growth fraction’ probably also contributes to the different proliferation rate in both localities. The higher proliferation rate of the EGL in the region of fissures is assumed to be one of the reasons for faster growth of the cerebellar furrows. The causal relationship between the proliferation activity of the EGL and the primary origin of fissures, however, has not yet been proved.