Granule cell differentiation occurs simultaneously with the onset of cerebellar foliation. Math1-CreER; Tau-STOP-myrGFP-IRES-nLacZ animals were administered tamoxifen at E15.5. Permanent myrGFP and nuclear LacZ expression are initiated once cells become postmitotic. Gcps (DAPI positive) proliferate in the oEGL. (a, b) Coronal sections of E17.5 Cb show that fate mapped gcs (red) are located in the inner layer of the EGL (iEGL). (a) Marked gcs (arrowhead) have round cell bodies and have extended their axons (parallel fibers; green). (b) In the layers below the iEGL, a 90° elongated cell body rotation (arrow) of some granule cells can be visualized, in addition to a developing descending radial fiber. (c) Anti-Pax6 (green) and anti-βgal (red) double immunostaining confirms that the fate mapped cells are granule cells. (d) Anti-Calbindin (green) and anti-βgal (red) double immunostaining reveals that fate mapped cells are found below the Pc layer. (e-e3) At E17.5, fate mapped cells are positive for Sema6a, a marker for translobular migrating granule cells. Dotted line indicates the border between oEGL and iEGL. (f-f2) Double immunostaining for anti-BrdU and anti-βgal reveals that gcs differentiate at a slightly higher rate at the base of the fissure than at the crown of the folia. Yellow lines in (f) depict the area from which BrdU/βgal positive cells were counted. Arrows indicate BrdU/βgal positive gcs. (g) Bar graphs depict quantification of BrdU/βgal positive gcs at the base of fissure (blue bars) versus the crown of the folia (red bars). Bar height indicates the mean value of each data set, and error bars indicate standard error. An asterisk indicates statistically significant differences between the base of the fissure and the crown of the folia for each data set (p < 0.006 for βgal; p < 0.05 for BrdU/βgal). Scale bars: (a, b) 50 μm; (c, d, f) 100 μm; (e) 25 μm.