Figure 6. BrdU-positive mossy cell precursors are decreased in the hilus of developing Rac1^N/Rac3^KO mice.

Mice were injected twice with BrdU at E12.5–E13 as detailed in the Materials and Methods. BrdU-injected mice were then sacrificed at P8 or P13. (A) Sagittal sections of the dorsal hippocampus from P8 Rac3^KO (left panels) and Rac1^N/Rac3^KO (right panels) mice were immunostained with antibodies for BrdU (red) and for Prox1 (green); nuclei were visualized by DAPI (blue). GCL, granule cell layer; hi, hilus. Scale bar: 50 µm. (B) Enlargement of the hilar region from the control section shown in (A). Arrows point to putative mossy cell precursors identified as BrdU-positive, Prox1-negative cells with a large round nucleus. Arrowheads indicate Prox1-positive granule cells. Scale bar: 12.5 µm. (C) Hippocampus from a P8 control mouse stained for BrdU. The areas used for quantification are indicated: zone 1 (Z1) includes the ventricular and subventricular zones and the dentate migratory stream; zone 2 (Z2) includes the hilar region, from which the zone that may include pyramidal cells from the CA3 has been excluded. Scale bar: 50 µm. (D) Quantification of BrdU-labelled cells in zone 1 and zone 2 of the hippocampus of Rac3^KO and Rac1^N/Rac3^KO littermates at P8 and P13. Bars are means ± SEM of the number of BrdU-positive cells (zone 1), and of BrdU-positive, Prox1-negative cells with large round nuclei (zone 2). At each stage, BrdU-positive cells were counted from 24–27 sections taken from 3 different mice per genotype. **P<0.001.