Fig. 4. 12.5 dpc XY Fgf9 null gonads express markers of ovarian development. In situ hybridization using markers of ovarian fate Bmp2 (A,C,E,G) and follistatin (B,D,F,H) on 12.5 dpc XX (A-D) and XY (E-H) gonads of either Fgf9^+/– (A,B,E,F) or Fgf9^–/– (C,D,G,H) genotypes. All XX gonads express Bmp2 and follistatin normally (A-D). XY Fgf9^+/– samples do not express either of these ovarian markers (E,F). At 12.5 dpc, XY Fgf9^–/– gonads express both Bmp2 and follistatin (G,H) in a pattern similar to XX gonads. Sections of 14.5 dpc XX and XY gonads containing germ cells immunostained for PECAM (green) and phosphorylated H2AX (red) (I-K). Virtually all XX Fgf9^+/– germ cells are positive for phosphorylated H2AX staining, as expected (I), whereas XY Fgf9^+/– germ cells are not (J). Forty-seven percent of the germ cells that survive to this stage in XY Fgf9^–/– gonads are positive for phosphorylated H2AX (arrowhead in K), but some are not (arrow in K). Figures representative of three independent experiments of n5 (A-H) each and n=5 (I-K) each. Scale bar: 250 µm in A-H; 25 µm in I,K.