(A,B) AMH-expressing cells (red) are found in excess of SOX9-expressing cells (green) in 17.5 dpc Rspo1-/- mutant ovaries. (C,D) Immunolabeling of germ cells with SCP3 (blue) shows that XX Rspo1-/- mutants have many meiotic germ cells at 17.5 dpc. Contrary to wild type ovaries, Rspo1-/- ovaries show anteriorly restricted AMH expression (red). (E,F) p27 expression (green) is downregulated in the anterior end of Rspo1-/- ovaries, coinciding with regions of AMH upregulation (red). (G,H) Following busulfan treatment at 11.5 dpc, 17.5 dpc Rspo1-/-ovaries have fewer AMH-expressing cells. The dotted line in (H) marks the location of the ectopic vasculature. Samples were whole mount immunostained and oriented with the anterior end to the left. Scale bars represent 50 μm in main panels and 11.5 μm in the inset (D).