FOLLICULAR DOMINANCE IN CATTLE IS ASSOCIATED WITH DIVERGENT PATTERNS OF OVARIAN GENE-EXPRESSION FOR INSULIN-LIKE-GROWTH-FACTOR (IGF)-I, IGF-II, AND IGF BINDING PROTEIN-2 IN DOMINANT AND SUBORDINATE FOLLICLES

A decrease in insulin-like growth factor (IGF) binding protein (BP) am ount occurs within the follicular fluid of dominant ovarian follicles. At the same time, concentrations of follicular fluid IGF-I do not cha nge. The mRNA for IGF-I, IGF-II, IGFBP-2, and IGFBP-3 in dominant and subordinate follicles were measured to determine if changes in IGF or IGFBP gene expression are associated with follicular dominance. Heifer s were ovariectomized during a follicular wave, either during early-do minance (emerging dominant follicle, 9 mm diameter) or mid-dominance ( established dominant follicle, 14-16 mm diameter). Follicles were clas sified as either dominant (DF), subordinate (SF), or not-recruited (NR F; small antral follicles). mRNA was localized by in situ hybridizatio n and measured by image analyses. The IGF-I mRNA (granulosa cells) was greatest in DF and increased in DF, SF, and NRF from early-to mid-dom inance. Likewise, IGF-II mRNA (theca cells) was greatest in DF compare d with SF or NRF. The IGFBP-2 mRNA (granulosa cells), however, was nea rly undetectable in DF, whereas adjacent SF expressed abundant IGFBP-2 mRNA. The NRF were not uniform in their IGFBP-2 expression because on ly 5 of 13 NRF had IGFBP-2 mRNA. The IGFBP-3 mRNA (granulosa cells) wa s found only in two NRF, suggesting that local synthesis is not a pred ominant source of follicular fluid IGFBP-3. These data show that chang es in gene expression for IGFBP-2 are opposite to those for IGF-I or I GF-II. Increased IGF-I and IGF-II mRNA and decreased IGFBP-2 mRNA with in the DF may be one mechanism leading to follicular dominance. The op posite pattern of IGFBP-2 gene expression in SF and some NRF may lead to follicular atresia. (C) Elsevier Science Inc. 1998.