|Aad, Pauline -|
|Spicer, Leon -|
Submitted to: Domestic Animal Endocrinology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 10, 2013
Publication Date: November 1, 2013
Citation: Aad, P.Y., Echternkamp, S.E., Spicer, L.J. 2013. Possible role of IGF2 receptors in regulating selection of 2 dominant follicles in cattle selected for twin ovulations and births. Domestic Animal Endocrinology. 45(4):187-195. Interpretive Summary: Reproductive rate of beef cows is low relative to females from other meat-producing species, producing only one calf/year. Conversely, embryo transfer studies indicate that beef cows are capable of producing twin calves. The main factor controlling the production of twin calves is the generation of two eggs (oocytes) from the ovary. Insulin-like growth factor (IGF) -1 is a hormone that stimulates the development of eggs from the ovary, and cattle selected for two or more ovulations and multiple births have greater IGF-1. Like IGF-1, IGF-2 is a similar hormone produced within the ovary that stimulates development of oocytes. However, IGF-2 preferentially binds to an IGF-2 receptor protein (IGF2R), which renders it inactive. Our results indicate that IGF-2 receptor is less in ovaries of cows that routinely deliver multiple calves, suggesting that this reduction in IGF-2 receptor may free IGF-2 to stimulate oocyte development and contribute to the ability to shed multiple eggs.
Technical Abstract: Abundance of IGF-2 receptor (IGF2R), FSH receptor (FSHR), and LH receptor (LHCGR) mRNA in granulosa cells (GCs) or theca cells (TCs) or both cells as well as estradiol (E2), progesterone (P4), and androstenedione concentrations in follicular fluid were compared in cows genetically selected (Twinner) or not selected (control) for multiple ovulations and twin births. Cows were slaughtered at day 3 to 4 (day 3) and day 5 to 6 (day 5) of an estrous cycle, and ovaries, follicular fluid, GCs, and TCs were collected. The two largest (F1 and F2) E2-active (EA) and E2-inactive (EI) follicles were selected according to their E2-to-P4 ratio and diameter. Androstenedione levels in EA F1 and F2 follicles were 5-fold greater (P < 0.05) in Twinner cows than in control cows on day 3 but did not differ on day 5. Twinner cows also had greater (P < 0.05) E2 and P4 concentrations, whereas steroid levels in EI follicles did not differ (P > 0.10) between genotypes. In EA F2 follicles, IGF2R levels in GCs were greater (P < 0.05) in control cows than in Twinner cows on day 3 and day 5, whereas IGF2R mRNA in TCs did not differ (P > 0.10). On day 3, FSHR mRNA levels were greater (P < 0.05) in GCs of EA F1 and EI F2 follicles of control cows than of Twinner cows. LH receptor mRNA expression was less in GCs and greater in TCs of EA F2 follicles in control cows than in Twinner cows (P < 0.05). We hypothesize that reduced GC IGF2R expression in F2 follicles of Twinner cows may play a role in the development of 2 or more dominant follicles.