PSLBII-18 - Transcriptomic comparison of embryonic tissues between high and low fertility sired pregnancies

Abstract: Pregnancy loss is considered one of the main causes of reproductive inefficiency in beef cattle industry. The objective was to determine the differentially expressed genes (DEGs) between the conceptus and uterus of pregnancies produced by sires of known fertility. We hypothesized that the paternal genome would have a significant effect on transcript abundance between these tissues. The sires used have been previously reported to have significantly different levels of field fertility; however, they had passed all normal quality control standards for frozen thawed semen. Bos indicus heifers (n=45) were subjected to estrus synchronization and embryo transfer with IVP embryos from either a High Fertility (HF) or a Low Fertility sire (LF), pregnancies were confirmed at slaughter. Samples were collected from the trophectoderm (TE) and caruncle (CAR) on days 25 and 36 of gestation for transcriptome analysis. Total RNA was isolated from tissue samples using the RNeasy kit (QIAGEN; Hilden, Germany) per manufacturer’s instructions. Sequencing was conducted using an Illumina platform. Sequences were aligned to the reference genome ARS-UCD1.2. DEGs between sires and tissue were determined using edge-R package from R. False discovery rate was 0.1. On day 25, out of 15,755 genes expressed in the trophectoderm, 19 genes were downregulated and 9 genes were upregulated in the LF. In the CAR 9 genes were downregulated and 7 were upregulated. On day 36, in the TE the LF resulted in 53 downregulated genes and 20 upregulated genes. In CAR there were 18 downregulated genes for the LF whereas 22 genes were upregulated. Gene ontology analysis reported DEGs in the LF compared to the HF were associated with immunology and reproduction. Of particular interest BoLA NC-1APOB gene known for its involvement in embryonic development, spermatogenesis and flagellated sperm motility, as well as, FETUB known for its function of binding sperm to the zona pellucida. These data suggest that field fertility records might be inaccurate for bull selection to improve reproductive performance. The downregulation of these genes appears to be detrimental to pregnancy success and could be responsible for the amount of variety seen in conception rates. Results from this study could lead us to identify sub-fertile bulls. It is evident that the paternal genome seems to play a much bigger role in pregnancy establishment than originally thought.