Rspo1 promotes XX germ cells proliferation. A- Reduction of germ cell proliferation in XX Rspo1 mutant gonads. Immunodetection of the proliferating germ cells with green (BrdU), surface red (MVH), nuclei blue (DAPI) (upper panel). The apoptotic germ cells with TUNEL (green) and MVH (red) (lower panel) Mouse XX gonad at E12.5.