PSVI-11 Role of differentially expressed and imprinted genes in high and low fertility produced cattle pregnancies.

Abstract Pregnancy loss is considered one of the main causes of reproductive inefficiency in beef cattle. Most research focuses on female contribution to pregnancy success leaving the role of the sire in pregnancy loss largely understudied. The objective was to determine the differentially expressed genes (DEGs) and imprinted genes 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, on the TE 29 DEGs and 42 imprinted genes were identified. In the CAR, 16 DEGs and 43 imprinted genes were observed. On day 36 in the TE, 73 DEGs and 46 imprinted were identified. In CAR, there were 40 DEGs and 33 imprinted genes. Gene ontology analysis reported DEGs in the LF compared to the HF were associated with immunology and reproduction. Downregulated DEGs of particular interest: BoLA NC-1 known to be expressed by the trophoblast cells to inhibit the activation of uterine leukocytes and to protect the conceptus from immune-mediated rejection. The APOB 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. Imprinted genes of interest included OOEP known for embryonic pattern specification, establishment of apical/basal cell polarity. MEAK7 involved in TOR signaling; positive regulation of protein localization to lysosome; and response to insulin. Lastly, PHLDA2 known for its role in placental development, regulation of gene expression and embryonic development. 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 variation 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.