FGF-8 is expressed during specific phases of rodent oocyte and spermatogonium development

We have studied the localization of the expression of FGF-8 mRNA in adult and developing rat and mouse gonads by in situ hybridization. The expression of FGF-8 mRNA was high in oocytes of small and large antral follicles of adult mouse ovaries. No signal was observed in fetal ovaries, or in primordial and atretic follicles of adult ovary. In mouse testis, the FGF-8 mRNA signal could be demonstrated in prespermatogonia during a short period covering the fetal days 15 to 17, but not any more on day 19 of fetal life, or in adult testis. The time course of the expression of FGF-8 mRNA in mouse testis was confirmed by RT-PCR reaction. Corresponding in situ results were obtained by studying rat tissues. The observed germ cell-specific expression of FGF-8 mRNA in maturing oocytes and fetal prespermatogonia suggests that FGF-8, which is a secretory protein, has a paracrine function during the specific phases of the maturation of the follicle and fetal seminiferous epithelium.