Chicken granulosa cells show differential expression of epidermal growth factor (EGF) and luteinizing hormone (LH) receptor messenger RNA and differential responsiveness to EGF and LH dependent upon location of granulosa cells to the germinal disc

Granulosa cells in the chicken follicle exhibit different phenotypes accord ing to their location relative to the germinal disc (GD), Granulosa cells p roximal to the GD (referred to as proximal granulosa cells) are more prolif erative, whereas granulosa cells distal to the GD (referred to as distal gr anulosa cells) are more differentiated, We have shown that epidermal growth factor (EGF) derived from the CD stimulated proliferation of granulosa cel ls proximal to the CD, whereas extraovarian LH promoted differentiation. We tested the hypothesis that phenotypic differences of granulosa cells are t he result of differential responsiveness of granulosa cells to EGF and LH, We found that both granulosa and theca layers of chicken preovulatory folli cles expressed mRNA for EGF receptor (EGFr) by polymerase chain reaction (P CR) analysis. However, only the granulosa layer showed differential express ion of EGFr and LH receptor (LHr) mRNA. Competitive reverse transcription-P CR revealed that proximal granulosa cells expressed more EGFr mRNA but less LHr mRNA than distal granulosa cells. In addition, proximal granulosa cell s proliferated more in response to EGF than their distal counterparts. We f urther demonstrated that FGF decreased LHr mRNA expression by granulosa cel ls in a dose-dependent manner,whereas EGF and LH had no effect on FGFr mRNA expression except at one dose of LH (15 ng/ml) that stimulated EGFr mRNA e xpression. Our findings suggest that EGF derived from the CD influences the phenotypes of granulosa cells. Granulosa cells proximal to the CD exhibit a proliferative phenotype possibly because they are exposed to and are more responsive to GD-derived EGF, Furthermore, CD-derived EGF decreases LHr mR NA expression by proximal granulosa cells and therefore results in less dif ferentiated granulosa cell phenotype, In contrast, granulosa cells distal t o the GD are not under the influence of EGF and exhibit a more differentiat ed phenotype.