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 cel ls) of the hen's ovarian follicle secretes one or more factors that st imulate proliferation of, and decrease progesterone (P-4) production b y, granulosa cells. Destruction of the GDR results in apoptosis and at resia of the follicle. These data suggested that the GDR produces a gr owth factor(s) to sustain the development of the follicle. These findi ngs prompted us to investigate two questions: 1) Is epidermal growth f actor (EGF) or transforming growth factor alpha (TGF alpha), which bin ds to the EGF receptor, present in the GDR? 2) Does EGF regulate granu losa cell functions in the hen? Immunocytochemistry revealed that EGF, but not TGF alpha, was present in the germinal disc of the four large st preovulatory follicles of the hen. TGF alpha was found only in the theca interna. To determine whether EGF regulates granulosa cell funct ions, granulosa layer explants (13 mm in diameter) from the second-lar gest preovulatory follicle were cultured for 36 h with 0, 0.017, or 0. 17 mu M EGF. Proliferation, apoptosis, and P-4 production of granulosa layer explants were then measured by using a colorimetric method for determining viable cell number, gel electrophoresis, and RIA, respecti vely. EGF regulates several functions of granulosa layer explants by s timulating proliferation, inhibiting apoptosis, and decreasing basal P -4 production. These data indicate that EGF is present in the germinal disc and may be one of the factors that regulate follicular developme nt in the hen.