Conditional ablation of Insr and Igf1r using Esr2 -Cre leads to abnormal ovarian follicle development and infertility in mice

Conditional ablation of Igf1r in early folliculogenesis has demonstrated the necessity of insulin signaling to progress to the antral stage, whereas ablation of both Insr and Igfr1 in the periovulatory window allows the formation of the antrum but reduces the efficiency of ovulation and subsequent luteinization. For this study, we examined the independent and shared actions in single and double knockouts (DKO) for Insr and Ifg1r using Esr2-Cre. As this recombinase is active during neonatal ovarian development and the initial wave of folliculogenesis, we hypothesized that abnormalities in ovary formation and establishment of the initial follicle pool would occur, which could alter female reproductive lifespan. We found that ablation of both receptors led to a delay in puberty, altered mating frequency, and ultimately infertility for Igf1rd/d and DKO females. Quantitation of germ cell cyst breakdown, and formation of primordial and primary follicles were normal in the neonatal window and at puberty, suggesting insulin signaling was not essential for establishment of ovarian reserve. However, the loss of IGF1R signaling impaired transition from primary to secondary follicles, which was worsened when IGF ligand cross-reactivity from INSR signaling was lost in DKO mice. DKO mice also exhibited abnormal follicle activation in the absence of hormone stimulation, but no subsequent proliferation of granulosa cells or antrum formation occurred. In adult mice, loss of either receptor disrupted estrous cyclicity, with DKO mice rarely leaving metestrus indicating abnormal regulation of the HPG axis contributing to subfertility and infertility observed in single and double receptor knockouts.