Sexual differentiation of germ cell deficient gonads in the medaka, Oryzias latipes

To determine whether germ cells perform any function in gonadal sexual diff erentiation, development of gonads in the medaka, Oryzias latipes, after ex posure to busulfan was investigated. Busulfan suppressed proliferation of e arly germ cells, thus significantly reducing the number of germ cells and g enerating regions without germ cells in the developing gonads. Globular str uctures were observed in the parenchyma in these regions. The structure was male specific, developed at the same time as acinus (seminiferous tubule p recursor), surrounded by the basal lamina, and contained characteristic des mosomes. These results strongly suggest that these globular structures are the precursors of seminiferous tubules devoid of germ cells. In the ovary, no follicles were observed but a well-developed ovarian cavity was evident. From these results we conclude that differentiation of gonadal parenchyma cells, except for follicular ones, is not germ cell dependent, though morph ological differentiation of the somatic cells seems to follow the different iation of germ cells. (C) 2001 Wiley-Liss, Inc.