Epidermal growth factor in the germinal disc and its potential role in follicular development in the chicken

The germinal disc region (GDR; germinal disc + overlying granulosa cells) of the hen's ovarian follicle secretes one or more factors that stimulate proliferation of, and decrease progesterone (P4) production by, granulosa cells. Destruction of the GDR results in apoptosis and atresia of the follicle. These data suggested that the GDR produces a growth factor(s) to sustain the development of the follicle. These findings prompted us to investigate two questions: 1) Is epidermal growth factor (EGF) or transforming growth factor alpha (TGFalpha), which binds to the EGF receptor, present in the GDR? 2) Does EGF regulate granulosa cell functions in the hen? Immunocytochemistry revealed that EGF, but not TGFalpha, was present in the germinal disc of the four largest preovulatory follicles of the hen. TGFalpha was found only in the theca interna. To determine whether EGF regulates granulosa cell functions, granulosa layer explants (13 mm in diameter) from the second-largest preovulatory follicle were cultured for 36 h with 0,0.017, or 0.17 microM EGF. Proliferation, apoptosis, and P4 production of granulosa layer explants were then measured by using a colorimetric method for determining viable cell number, gel electrophoresis, and RIA, respectively. EGF regulates several functions of granulosa layer explants by stimulating proliferation, inhibiting apoptosis, and decreasing basal P4 production. These data indicate that EGF is present in the germinal disc and may be one of the factors that regulate follicular development in the hen.