Reproduction Abstracts

Introduction: The WNT signaling pathway plays important roles in sex determination and embryonic development. Previous results indicated that WNT4 is required for normal ovarian follicle development and fertility and that WNT4 and WNT5a play redundant roles in regulating oocyte entry into meiosis during embryogenesis, suggesting potential redundant roles of WNT4 and WNT5a in the ovary. The objective of this study was to determine the effect of granulosa cell-conditional knock-out of Wnt5a on follicle development.

Methods: Fertility was determined in 6-month mating trials with Wnt5a(flox/−); Amhr2(cre/+) and control mice. Ovaries were obtained at six and 32 weeks of age, and every fifth section used to count the number of follicles. TUNEL was used to assess apoptosis in adult ovaries. Microarray and RT-PCR were used to determine the effect of WNT5a on granulosa cell function.

Results: Wnt5a(flox/−);Amhr2(cre/+) mice had reduced fertility (P<0.05), reduced numbers of healthy follicles (P<0.05) and increased apoptosis in adult ovaries. Wnt5a(flox/−);Amhr2(cre/+) mice also had a decreased ovulation rate (P<0.05). To determine the mechanism of action of WNT5a, primary granulosa cells were treated in vitro with WNT5a, which decreased the expression of genes associated with granulosa cell differentiation (Cyp19a1, Lhcgr, Prlr, and Fshr). Consistent with this, the expression of these same genes in granulosa cells was higher in Wnt5a(flox/−);Amhr2(cre/+) mice compared to controls in vivo. Together, these results indicate that Wnt5a is required for normal female fertility and may act by regulating genes critical for granulosa cell differentiation and follicle development.