RESEARCH ARTICLE Molecular Effects of Polymorphism in the 3’UTR of Unc-5 homolog C Associated with Conception Rate in Holsteins

Conception rates among dairy cows in Japan have declined in recent decades. To enhance our understanding of the genes involved in conception rates, we conducted a genome-wide association study (GWAS) using 822 Holsteins and identified a single-nucleotide polymor-phism (SNP) associated with conception rate: A+169G in the 3 ’ untranslated region (UTR) of unc-5 homolog C (UNC5C). Cows with higher conception rates carried the A polymor-phism in the UNC5C 3’UTR. Luciferase assays and quantitative analysis of allele ratios revealed that UNC5C transcripts with the A polymorphism were expressed at higher levels than those carrying the G polymorphism. UNC5C transmits either pro- or anti-apoptotic sig-nals depending on the availability of its ligand, Netrin-1. UNC5C expression is negatively regulated by reproductive homeobox X-linked 5 (Rhox5), and the Rhox5 locus is methylated by G9a methyltransferase. G9a-knockout mice have previously been demonstrated to be subfertile, and we found that UNC5C, G9a, and Netrin-1 expression levels increased from the 4-cell stage to the blastocyst stage in fertilized murine embryos, whereas Rhox5 expres-sion decreased. Repression of UNC5C, G9a, or Netrin-1 or forced expression of Rhox5 in the anterior nucleus stage inhibited development to the blastocyst stage, suggesting that cows carrying the G polymorphism in UNC5Cmight have lower conception rates because of the poor development of preimplantation embryos. This study provides novel insights into the role of UNC5C during embryonic development