201 USING THE TRANSCRIPTOME SIGNATURE TO PREDICT PREGNANCY SUCCESS IN BEEF COWS AT 6 DAYS AFTER ARTIFICIAL INSEMINATION

Abstract

Pregnancy success is critical to the profitability of cattle operations. Attempts to reduce high rates of early embryonic loss mainly focus on the critical phase of embryo recognition by maternal tissue. However, the molecular events driving the uterine tissue toward a favourable stage, facilitating the maternal receptivity, are poorly understood. This study aimed to characterise the endometrial transcriptome profiles of pregnant versus nonpregnant beef cows during early pregnancy and attempted to define a potential set of marker genes that can be valuable for predicting pregnancy outcome. Therefore, pluriparous, cyclic Nellore (Bos indicus) cows were synchronized (n = 51) and artificially inseminated (n = 36) at detected oestrus using semen from a single high-fertility bull. Six days after AI (Day 6), jugular blood samples and an endometrial biopsy from the uterine horn contralateral to the ovary containing the CL were collected. Pregnancy diagnosis was performed by ultrasonography on Days 22 and 30. Based on pregnancy outcome, samples were retrospectively allocated to the following groups: pregnant (P; n = 6) and nonpregnant (NP; n = 5). Both groups had similar plasma progesterone concentrations on Day 6 (less than 1 ng mL^–1 between lowest and greatest concentrations). Endometrial biopsies were submitted to RNA-Seq analysis in an Illumina single flow cell line (Illumina Inc., San Diego, CA). The 272 685 768 million filtered reads were mapped to the Bos taurus UMD3.1 reference genome and 14 654 genes were effectively analysed for differential expression between groups. Transcriptome data showed that 216 genes are differently expressed when comparing P v. NP endometrial tissue (adjusted P < 0.1). More specifically, 36 genes showed a significantly up-regulated expression for pregnant cows and 180 are up-regulated for non-pregant cows. Functional enrichment and pathway analyses revealed enriched expression of genes associated with extracellular matrix remodelling in NP cows and nucleotide binding, microsome, and vesicular fraction in P cows. From the 40 top-ranked genes, six that were down- and three that were up-regulated in pregnant cows were further analysed by qRT–PCR in an additional 26 cows. Subsequent quantitative expression data were evaluated using multivariate statistics. Both principal component analysis (PCA; R2 = 0.82 and Q2 = 0.40) and orthogonal projections to latent structures analysis (OPLS), using pregnancy as the dependent variable (R2Y = 0.95 and Q2 = 0.86), efficiently separated P from NP animals. In conclusion, this study characterizes a unique set of genes, expressed in the endometrium as early as 6 days after AI, that indicate a receptive state leading to pregnancy success. Furthermore, expression of such genes can be used as potential markers to efficiently predict pregnancy success.