Consequences of the Presence of the Booroola F Gene on the Intraovarian Insulin-Like Growth Factor System and Terminal Follicular Maturation in Mérinos d’Arles Ewes1
Open Access
- 1 October 2000
- journal article
- Published by Oxford University Press (OUP) in Biology of Reproduction
- Vol. 63 (4), 1205-1213
- https://doi.org/10.1095/biolreprod63.4.1205
Abstract
In sheep, the presence of the Booroola F gene has several important consequences for ovarian function. This study investigated the consequences of the presence of the F gene for the insulin-like growth factor (IGF) system in the ewe ovary. Studies were undertaken in ovaries from F+ and ++ Mérinos d’Arles ewes to determine 1) the levels of type I IGF receptors and IGF binding proteins (IGFBPs) in follicular cells by quantitative autoradiography of [125]-IGF-I binding sites on ovarian sections; 2) the pattern of intrafollicular IGFBPs, by Western-ligand blotting on follicular fluids; and 3) the effects of IGF-I and FSH on proliferation and differentiation of granulosa cells in vitro, assessed by progesterone secretion and cytochrome P450 side-chain cleavage (P450scc) expression. The amounts of type I IGF receptors were similar in F+ and ++ follicular cells; however, at the same follicular size, F+ healthy follicles contained lower concentrations of IGFBPs smaller than 40 kDa (particularly IGFBP-2) than ++ healthy follicles. In vitro, in basal conditions as well as in IGF-I- or FSH-stimulated conditions (or both), granulosa cells from F+ follicles had a lower proliferative activity, secreted higher amounts of progesterone, and expressed higher levels of P450scc than granulosa cells from ++ follicles of the same size. When F+ and ++ preovulatory follicles were compared at the end of the follicular phase, IGFBPs <40 kDa concentrations were slightly higher, and responsiveness of granulosa cells to FSH in vitro was lower in F+ than in ++ follicles, suggesting that terminal maturation of F+ follicles, although precocious, was less complete than it was in ++ follicles. The early decrease in intrafollicular IGFBPs <40 kDa concentrations observed in F+ antral follicles, which likely leads to an early increase in IGF bioavailability, may at least partly account for the increased ovulation rate that characterizes F-carrier ewes.Keywords
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