Endocrine Abstracts

The factors responsible for regulating primordial follicle activation and early preantral follicle growth remain poorly understood, despite their importance in determining a female’s reproductive lifespan. The essential role of the epidermal growth factor (EGF) family of receptors (ErbBs) during ovulation is well established; however there is emerging evidence that ErbBs may also be important regulators of early follicle development. This study aimed to investigate the role of EGF and ErbBs during preantral follicle development in the mouse. Previous work has shown high mRNA levels of ErbB subtypes, ErbB1 (EGFR) and ErbB2, in PND16 mouse ovaries and preantral follicles, ErbB3 is present but at low levels (Atess, unpublished). EGFR and ERBB2 protein can be detected in preantral follicles by western blotting, with ERBB2 immunolocalised at the cell surface of granulosa cells (GCs) from the transitional stage onward. Preantral follicles isolated from PND16 mouse ovaries (C57BL/6) were cultured for 72 hours with EGF (10 ng/ml). EGF significantly increased follicle growth by inducing GC proliferation (P<0.01), as demonstrated by increased Ki67 immunostaining (P<0.001). The addition of AG1478 (10 μM), an EGFR inhibitor, reversed the stimulatory effect of EGF on follicle growth (P<0.01), and showed no inhibitory effects when added to culture alone. Inhibition of ErbB2 had no effect on baseline or EGF stimulated follicle growth. The addition of the MEK inhibitor U0126 (10 μM) also reduced EGF stimulated growth (P<0.05). EGF treatment altered mRNA levels of key genes involved in follicle growth. At 24 hours EGF significantly increased Bcl2 and Egr1 mRNA levels and decreased Fshr, Esr1, Esr2, Bmp15, Gdf9, Amh, Amhr2, Egfr, Erbb2 mRNA levels in cultured follicles. In conclusion, preantral follicles express EGFR and ErbB2 and are responsive to EGF, signalling primarily through the EGFR and MAPK pathway. This suggests a role for ErbBs in regulating early follicle development in the mouse.