Differential expression of CART in ewes with differing ovulation rates

Abstract

We hypothesised that cocaine- and amphetamine-regulated transcript (CARTPT) would be differentially expressed in ewes with differing ovulation rates. Expression of mRNA forCARTPT, as well asLHCGR,FSHR,CYP19A1andCYP17A1was determined in antral follicles ≥1 mm in diameter collected during the follicular phase in ewes heterozygous for the Booroola and Inverdale genes (I+B+; average ovulation rate 4) and ++ contemporaries (++; average ovulation rate 1.8). In ++ ewes (n = 6),CARTPTwas expressed in small follicles (1 to <3 mm diameter), where 18.8 ± 2.5% follicles expressedCARTPT. CART peptide was also detected in follicular fluid of some follicles of ++ ewes. In I+B+ ewes, 5/6 ewes did not have any follicles that expressedCARTPT, and no CART peptide was detected in any follicle examined. Expression pattern ofCYP19A1differed between I+B+ and ++ ewes with an increased percentage of small and medium follicles (3 to <4.5 mm diameter) but decreased percentage of large follicles (≥4.5 mm diameter) expressingCYP19A1in the I+B+ ewes. Many of the large follicles from the I+B+ ewes appeared non-functional and expression ofLHCGR,FSHR,CYP17A1andCYP19A1was less than that observed in ++ ewes. Expression ofFSHRandCYP17A1was not different between groups in small and medium follicles, butLHCGRexpression was approximately double in I+B+ ewes compared to that in ++ ewes. Thus, ewes with high ovulation rates had a distinct pattern of expression ofCARTPTmRNA and protein compared to ewes with normal ovulation rates, providing evidence for CART being important in the regulation of ovulation rate.