Fig. 1. A sex-dimorphic distribution of the glycogen deposits in the gonads at 11.5 dpc (18 ts stage). (A-D) Transverse sections of 11.5-dpc XX (A,C) and XY (B,D) embryos. Periodic acid Schiff (PAS) staining (red staining). In both XY and XX embryos, several tissues including notochord (nc), skeletal muscle (sm) and the area close to dorsal aorta (da) show positive PAS staining. However, in developing genital ridges, PAS reactions are observed only in the gonadal region of XY, but not XX, embryos. In the XY gonad, PAS-positive cells are located close to germ cells (asterisks) (D), whereas no positive cells are detected in XX gonad (C). Plates C and D show higher magnification images, indicated by the broken rectangle in plates A and B, respectively. asterisk, germ cell; ce, coelomic epithelium; da; dorsal aorta; ms, mesonephros; nc, notochord; nt, neural tube; sm, skeletal muscle. Bar, 50 µm. (E,F) Transmission electron micrographs showing an accumulation of glycogen granules (arrows; a massive glycogen deposit is indicated by `Gly') in the cytoplasm of gonadal somatic cells closely associated with germ cells in the XY (F), but not the XX, gonad (E). G, germ cell; Gly, glycogen granule. Bar, 1 µm. (G,H) Two serial sections of the 11.5-dpc XY gonad were pretreated with (H) or without -amylase (G) before PAS staining. -amylase digestion results in a complete loss of PAS reaction in the XY gonad. The insets show higher magnification of the cells indicated by arrows. asterisk, germ cell; ms, mesonephros. Bar, 50 µm.