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EXTRAOVARIAN AND INTRAOVARIAN REGULATION OF FOLLICULAR SELECTION IN THE OVARY.
Hernandez, Alvaro1, Bahr, Janice1, 1
ABSTRACT- Follicular selection is the basis for regular ovulation. In the chicken ovary, one small yellow follicle (SYF) is selected daily from a pool of similar size follicles and becomes a preovulatory follicle. Follicle stimulating hormone (FSH) and luteinizing hormone (LH) are primary regulators of follicular growth and differentiation. Epidermal growth factor (EGF), an intraovarian hormone, suppresses granulosa cell differentiation. However, the precise regulation and interactions of these hormones on follicular selection have not been determined. The objectives of this study were to investigate if FSH, LH and EGF alone or in combination regulate: 1) the abundance of FSH, LH and EGF receptor (FSHr, LHr and EGFr, respectively) mRNA in granulosa cells from SYF and 2) the expression of P450 side chain cleavage (P450scc) mRNA and production of progesterone (P4), the markers of follicular selection. Granulosa cells from SYF were cultured for 18 h in the presence of porcine FSH (0, 4, 20, 50, 100, 250 ng/ml), ovine LH or human EGF (0, 4, 10, 20, 50 and 100 ng/ml), alone or in combination. After culture, FSHr, LHr and EGFr and P450scc mRNA abundance and P4 production were determined by polymerase chain reaction and radioimmunoassay, respectively. FSH at near physiological doses increased P450scc mRNA and P4 secretion and decreased FSHr mRNA abundance. LH had a moderate effect on the abundance of P450scc mRNA and P4 production and decreased FSHr mRNA. EGF completely suppressed the expression of P450scc mRNA and decreased FSHr and LHr mRNA abundance. None of the hormones influenced the levels of EGFr mRNA. When used in combination, EGF overrode the positive effect of FSH and LH on expression of P450scc mRNA and production of P4 in a dose-dependent manner. Our results suggest that: 1) FSH induces selection by increasing P450scc mRNA and P4 secretion in granulosa cells of SYF, whereas LH has little impact at this stage of development, and 2) EGF counteracts the positive effects of FSH and LH on granulosa cell differentiation by reducing the abundance of FSH and LHr mRNA and by suppressing the expression of P450scc mRNA and production of P4. Our working model implies that the SYF that is more responsive to FSH overcomes the suppressive effect of EGF on granulosa cell differentiation and is selected. Funded in part by NSF-IBN-96-30957 and Hatch Funds.
KEY WORDS: Follicle, Selection, Chicken
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