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 ewes.
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 (P450(scc)) 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 P450(scc) 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.
Monniaux
D
D
Physiologie de la Reproduction et des Comportements, UMR1291 INRA-CNRS-Université F. Rabelais de Tours, INRA 37380 Nouzilly, France. monniaux@tours.inra.fr
Monget
P
P
Pisselet
C
C
Fontaine
J
J
Elsen
J M
JM
D000818:Animals; D002478:Cells, Cultured; D005260:Female; D005640:Follicle Stimulating Hormone / Q000494:pharmacology; D018969:Insulin-Like Growth Factor Binding Proteins / Q000378:metabolism; D007334:Insulin-Like Growth Factor I / Q000378:metabolism* / Q000494:pharmacology; D006080:Ovarian Follicle / Q000187:drug effects / Q000502:physiology*; D010053:Ovary / Q000502:physiology; D017526:Receptor, IGF Type 1 / Q000378:metabolism*; D012756:Sheep / Q000235:genetics*
D018969:Insulin-Like Growth Factor Binding Proteins; D007334:Insulin-Like Growth Factor I; D005640:Follicle Stimulating Hormone; D017526:Receptor, IGF Type 1