Fig. 4. Fgf9 expression. (A) Using in situ hybridization, Fgf9 was expressed in both XY and XX gonads (g) during early stages of gonad development (11.5 dpc). By 12.5 dpc, Fgf9 was specific to testis cords in XY gonads and not detected in XX gonads. In the neighboring mesonephros (m), Fgf9 was expressed within the mesonephric duct and tubules (mt, arrows) of both sexes. (B) RT-PCR showed that FGF9 transcript was present in both XX and XY gonads at 11.5 dpc, but was specific to XY gonads by 12.5 dpc. Reactions without reverse transcriptase served as a control. Hprt and Fgf9 were amplified together in each tube, with expected sizes of 325 bp and 400 bp, respectively.