Abstract: 1

GERMINAL DISC-DERIVED EPIDERMAL GROWTH FACTOR: A POTENTIAL CONTRIBUTOR TO FORMATION OF A PROLIFERATION GRADIENT IN CHICKEN GRANULOSA LAYER.

Humphrey Hung-Chang Yao^{1 *}, Janice Bahr^{1 *}
Department of Animal Sciences, University of Illinois, Urbana, Il 61801 ¹

Granulosa cells in the chicken follicle express different phenotypes dependent upon their location relative to the germinal disc (GD). Granulosa cells close to the GD have a greater rate of proliferation than their distal counterparts. This observation led us to hypothesize that the GD produces a factor(s) that causes a regional difference in granulosa cell phenotypes. A previous immunocytochemical study showed that epidermal growth factor (EGF) was present in the GD. We then used Northern analysis to confirm that the GD synthesized EGF mRNA. Germinal disc conditioned medium (CM) contained a detectable amount of EGF (42± 3 pM, n=5) suggesting EGF is a paracrine factor produced by the GD. The biological activity of CM was examined by treating the CM with either EGF antibody or normal serum and then culturing it with granulosa cells (n=5). The germinal disc CM significantly stimulated proliferation of granulosa cells, whereas pretreatment with EGF antibody abolished the proliferation-stimulating effect of the CM. Next we verified that granulosa cells are the target cells for EGF. We found granulosa cells contained EGF receptor (EGFR) mRNA and protein as examined by RT-PCR and Western analysis, respectively. Furthermore, a semi-quantitative RT-PCR assay using chicken EGFR specific primers revealed that granulosa cells near the GD had more EGFR mRNA than granulosa cells distal to the GD. We conclude that the germinal disc-derived EGF is one of the contributing factors to the formation of a proliferation gradient in the granulosa layer. Granulosa cells proximal to the germinal disc express a proliferative phenotype possibly because they are exposed to a greater amount of EGF and are more responsive to the germinal disc-derived EGF.

    This abstract is being presented on Saturday, July 31 at 1:30 PM at Todd 116.