Stage- and Cell-Specific Expression of FGF9 in Embryonic Gonads

<div><p>(A–F) Detection of FGF9 protein (red) at different stages of gonad development. FGF9 is up-regulated in XY gonads at 11.5 (B), 12.5 (D), and 13.5 dpc (F) while it is down-regulated in XX after 11.5 dpc (A, C, and E). No signal was detected in XY <i>Fgf9</i>^−/− gonads (unpublished data). </p> <p>(G–J) Serial sections of wild-type XX and compound heterozygous <i>Kit</i>^W/Wv XY gonads stained for alkaline phosphatase (purple; G and I) and FGF9 (red; H and J). Testis cords are formed in the absence of germ cells in XY <i>Kit</i>^W/Wv mutant gonads at 12.5 dpc (arrowhead in J). Expression of FGF9 is present in the mutant gonads where Sertoli cells are the only remaining cell type in the cords (J). Semitransparent dotted line indicates the boundary between gonad and mesonephroi. PECAM (green) marks germ cells and vascular endothelial cells (C–F, H, and J). The scale bars represent 25 μm. </p> <p>g, gonad; m, mesonephroi.</p>