Oviductal transcriptional profiling of a bovine fertility model by next-generation sequencing

In cattle, the oviduct plays a fundamental role in the reproductive process. Oviductal functions are controlled by the ovarian sex steroids: estradiol and progesterone. Here, we tested the hypothesis that the exposure to contrasting sex steroid milieus differentially impacts the oviductal transcriptional profile. We manipulated growth of the pre-ovulatory follicle to obtain cows that ovulated a larger (LF group) or a smaller (SF group) follicle. The LF group presented greater proestrus/estrus concentrations of estradiol and metaestrus concentrations of progesterone (Gonella-Diaza et al. 2015 [1], Mesquita et al. 2014 [2]). Also, the LF group was associated with greater fertility in timed-artificial insemination programs (Pugliesi et al. 2016 [3]). Cows were slaughtered on day 4 of the estrous cycle and total RNA was extracted from ampulla and isthmus fragments and analyzed by RNAseq. The resulting reads were mapped to the bovine genome (Bos taurus UMD 3.1, NCBI). The differential expression analyses revealed that 325 and 367 genes in ampulla and 274 and 316 genes in the isthmus were up-regulated and down-regulated in LF samples, respectively. To validate the RNAseq results, transcript abundance of 23 genes was assessed by qPCR and expression patterns were consistent between the two techniques. A functional enrichment analysis was performed using Database for Annotation, Visualization and Integrated Discovery (DAVID) software. Processes enriched in the LF group included tissue morphology changes (extracellular matrix remodeling), cellular changes (proliferation), and secretion changes (growth factors, ions and metal transporters). An overview of the gene expression data was deposited in the NCBI's Gene Expression Omnibus (GEO) and is accessible through the accession number GSE65681. In conclusion, differences in the peri-ovulatory sex steroid milieu modify the oviductal gene expression profiles. Such differences may be associated with the greater fertility of the LF cows. This dataset is useful for further investigations of the oviductal biology and the impact of sex-steroid on the female reproductive tract.

Size of the Ovulatory Follicle Dictates Spatial Differences in the Oviductal Transcriptome in Cattle

In cattle, molecular control of oviduct receptivity to the embryo is poorly understood. Here, we used a bovine model for receptivity based on size of the pre-ovulatory follicle to compare oviductal global and candidate gene transcript abundance on day 4 of the estrous cycle. Growth of the pre-ovulatory follicle (POF) of Nelore (Bos indicus) cows was manipulated to produce two groups: large POF large corpus luteum (CL) group (LF-LCL; greater receptivity) and small POF-small CL group (SF-SCL). Oviductal samples were collected four days after GnRH-induced ovulation. Ampulla and isthmus transcriptome was obtained by RNA-seq, regional gene expression was assessed by qPCR, and PGR and ERa protein distribution was evaluated by immunohistochemistry. There was a greater abundance of PGR and ERa in the oviduct of LF-LCL animals thus indicating a greater availability of receptors and possibly sex steroids stimulated signaling in both regions. Transcriptomic profiles indicated a series of genes associated with functional characteristics of the oviduct that are regulated by the periovulatory sex steroid milieu and that potentially affect oviductal receptivity and early embryo development. They include tissue morphology changes (extra cellular matrix remodeling), cellular changes (proliferation), and secretion changes (growth factors, ions and metal transporters), and were enriched for the genes with increased expression in the LF-LCL group. In conclusion, differences in the periovulatory sex steroid milieu lead to different oviductal gene expression profiles that could modify the oviductal environment to affect embryo survival and development.

The transcriptome signature of the receptive bovine uterus determined at early gestation

Pregnancy success is critical to the profitability of cattle operations. However, the molecular events driving the uterine tissue towards embryo receptivity are poorly understood. This study aimed to characterize the uterine transcriptome profiles of pregnant (P) versus non-pregnant (NP) cows during early pregnancy and attempted to define a potential set of marker genes that can be valuable for predicting pregnancy outcome. Therefore, beef cows were synchronized (n=51) and artificially inseminated (n=36) at detected estrus. Six days after AI (D6), jugular blood samples and a biopsy from the uterine horn contralateral to the ovary containing the corpus luteum were collected. Based on pregnancy outcome on D30, samples were retrospectively allocated to the following groups: P (n=6) and NP (n=5). Both groups had similar plasma progesterone concentrations on D6. Uterine biopsies were submitted to RNA-Seq analysis in a Illumina platform. The 272,685,768 million filtered reads were mapped to the Bos Taurus reference genome and 14,654 genes were analyzed for differential expression between groups. Transcriptome data showed that 216 genes are differently expressed when comparing NP versus P uterine tissue (Padj ≤ 0.1). More specifically, 36 genes were up-regulated in P cows and 180 are up-regulated in NP cows. Functional enrichment and pathway analyses revealed enriched expression of genes associated with extracellular matrix remodeling in the NP cows and nucleotide binding, microsome and vesicular fraction in the P cows. From the 40 top-ranked genes, the transcript levels of nine genes were re-evaluated using qRT-PCR. In conclusion, this study characterized a unique set of genes, expressed in the uterus 6 days after insemination, 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.