Fig. 1. Fgf9^-/- XY gonads on the C57BL/6 background do not form testis cords. Testis cords are visible in wild-type XY gonads by 12.5 dpc (A,C) and consist of groups of germ cells (red, detected with an antibody against PECAM) surrounded by a layer of Sertoli cells and enclosed by a basal lamina (green, detected with an antibody against laminin). PECAM (red) also labels cells in the vasculature. Fgf9^-/- XY gonads on the C57BL/6 background did not form testis cords (B,D). In wild-type XY gonads, SF1 (green) is detected in the nuclei of Leydig precursors (ley) outside testis cords and, at a lower level, in the nuclei of Sertoli cells (s) within testis cords at 12.5 dpc (examples indicated in E). In Fgf9^-/- XY gonads, a smaller number of SF1-positive cells were detected, located near the surface of the gonad (F). Laminin (green) and germ cell (red) localization in Fgf9^-/- XX gonads at 12.5 dpc (H) were indistinguishable from Fgf9^+/- XX gonads (G). Scale bars: 50 µm.