Fig. 4. Expression of Pdgf-B in 12.5 dpc male urogenital ridge. The in situ hybridization (a,a') shows that the growth factor is mainly expressed by cells in the interstitial compartment of the developing testis, as indicated by arrowheads; b, phase contrast. c, hybridization with sense probe and, d, its phase contrast. Bar, 100 µm.