Submitted to: Society for the Study of Reproduction Annual Meeting
Publication Type: Abstract only
Publication Acceptance Date: 4/24/2006
Publication Date: 7/1/2006
Citation: Aad, P.Y., Echternkamp, S.E., Spicer, L.J. 2006. IGF type II receptor gene expression in granulosa and theca cells of cattle selected for twin ovulations and births. Biology of Reproduction. (Supplement):173. (Abstract #454) Interpretive Summary:
Technical Abstract: Regulation of multiple ovulations in monotocous species such as cattle is not well understood. Therefore, gene expression of the IGF type II receptor (IGF2R) and LH receptor (LHR) in granulosa (GC) and theca (TC) cells as well as estradiol (E2) and progesterone (P4) levels in follicular fluid (FF) were quantitated in cows selected (Twinner) and unselected (Control) for twin births and multiple ovulations. Cows were slaughtered between day 3 and 6 of an estrous cycle, and ovaries collected. Individual follicles were snap frozen in liquid nitrogen, and FF, GC and TC separated and collected. Total RNA from GC and TC was extracted, and levels of LHR and IGF2R mRNA were quantified using multiplex real-time RT-PCR and expressed as relative mRNA abundance normalized to constitutively expressed 18S ribosomal RNA. Follicles were classified two ways: healthy (E2:P4 ratio >1; n = 63) or atretic (E2:P4 ratio <1; n = 99), and medium (4-8 mm; n = 84) or large (8-22 mm; n = 78). Healthy follicles had greater E2 (120.1 ± 15.6 vs 6.0 ± 10.6 ng/mL) and lower P4 levels (24.6 ± 19.9 vs 133.6 ± 13.5 ng/mL) than atretic follicles, and expression of LHR mRNA was greater (P<0.05) in GC of healthy versus atretic large follicles. Levels of LHR mRNA were 2.5-fold greater in TC of large versus medium follicles. However, FF E2 and P4 concentrations and levels of LHR mRNA in the GC or TC of medium and large follicles did not differ between Twinner and Control cows. In contrast, levels of IGF2R mRNA were 2.4-fold greater in TC, but not GC, of both medium and large follicles of Control versus Twinner cows. Levels of IGF2R mRNA in TC did not differ (P > 0.10) between healthy and atretic follicles. Because IGF2R sequesters free IGF-II and, thus, reduces its binding to the IGF type I receptor, we hypothesize that reduced thecal IGF2R levels in follicles of Twinner cows may increase the amount of free or bioavailable IGF-II, which may act in an autocrine or paracrine fashion to regulate follicular development.