LAUSR

Abstract Reproductive efficiency is one of the most critical factors affecting the productivity and profitability of the sheep industry. Therefore, the goal of this study is to identify candidate genes and/or loci that could be used for improving prolificacy in Egyptian sheep breeds. We selected four genes (GDF9, BMP15, BMP6 and BMPR1B), because of their previously reported contributions to sheep prolificacy and ovulation rate, to explore the effects of their variants on Egyptian sheep breeds as well as the effect of their expression level on follicular maturation. Sequence analysis of the four genes in Rahmani rams revealed seven SNPs, three of them are novel. The detected SNPs were genotyped in both Rahmani and Ossimi breeds. Association analysis showed that two SNPs located in GDF9 and BMPR1B are in association with litter size. Analysis of the mRNA transcripts in different ovarian cells and tissues showed that GDF9 and BMP15 transcripts are expressed exclusively by oocytes, however, their levels are significantly reduced in poor qualities oocytes, which underlines their importance in oocyte ovulation. The most interesting findings are the expression of BMPR1B mRNA in oocytes, granulosa, cumulus cells and corpora lutea along with BMP6 mRNA. This observation suggests that BMP6 would be the most likely ligand regulating follicular maturation and ovulation rate through BMPR1B. Also the presence of their transcripts in corpora lutea suggests the role these two genes in controlling luteolysis. However further studies are required to confirm these suggestions. To the best of our knowledge, this is the first report about the expression of BMP6 and BMPR1B in sheep cumulus cells and corpora lutea.