19 zyxwvutsrq Cell Differentiation and Development, 21 (1989) 19-28 Elsevier Scientific Publishers Ireland, Ltd. CDF 00589 Mouse gonadal differentiation in vitro in the presence of fetal calf serum Sarah Mackay and Robert A. Smith Department of Anatomy, University of Glasgow, Scotland (Accepted 6 March 1989) zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONML Other workers have shown that feud calf serum (F.C.S.) inhibits the differentiation of the rat testis, and disrupts established testicular cords, in vitro. To investigate the possibility of a serum effect in the mouse, indifferent urogenital complexes and differentiated gonads were removed from sexed fetuses and cultured for 7 days in medium with or without the addition of fetal calf serum. Cultures were assessed by light and electron microscopy. Testicular and ovarian differentiation occurred in the presence of fetal calf serum. Serum did not prevent basal lamina development in testicular cords of explants cultured to the equivalent of day-17 control testes. Ovarian differentiation; Testicular differentiation; Serum effect; Mouse; Ultrastructure Introduction The mouse gonad forms from the indifferent blastema in two main stages, a stage of differenti- ation when the two sexes first become dis- tinguishable, with the establishment of testicular or ovigerous cords, followed by a stage of develop- ment during which the differentiated gonad be- comes organised, with the appearance of struc- tures characteristic of the mature ovary or testis (for review see Byskov, 1986). Both these critical periods have been investigated by culture in vitro, which allows the examination of such problems as the origin of the gonadal blastema, the mecha- nisms of cell differentiation within it, the role of the mesonephros and the regulation of meiosis. Previous studies of the first stage of differentiation Correspondence address: Dr. S. Mackay, Department of Anat- omy, University of Glasgow, Glasgow G12 SQQ, Scotland. include those of Byskov and Sax& (1976) and Taketo and Koide (1981) while other workers have examined the second stage (Odor and Blandau, 1971; Baker and Neal, 1973; Evans et al., 1982). In all cases fetal calf or horse serum was used as a component of the culture medium. Recently attention has been drawn to possible detrimental effects of serum in vitro. Agelopoulou et al. (1984) have shown an inhibitory action of fetal calf serum on the differentiation of the rat testis: serum prevented the formation of testicular cords and also disrupted newly formed cords. However, the authors also reported that serum improved the general appearance, growth and number of mitoses seen in cultures. If cultured mouse gonads could be shown to benefit from these advantages of serum without suffering any inhibitory effects, then the mouse would be the more favourable species to use in studies of gonadal morphogenesis in vitro. Agelopoulou and co-workers point out that previous results from 0922-3371/89/$03.50 0 1989 Elsevier Scientific Publishers Ireland, Ltd.