Gene Expression Profiling of Corpus luteum Reveals Important Insights about Early Pregnancy in Domestic Sheep

Abstract

The majority of pregnancy loss in ruminants occurs during the preimplantation stage, which is thus the most critical period determining reproductive success. Here, we performed a comparative transcriptome study by sequencing total mRNA from corpus luteum (CL) collected during the preimplantation stage of pregnancy in Finnsheep, Texel and F1 crosses. A total of 21,287 genes were expressed in our data. Highly expressed autosomal genes in the CL were associated with biological processes such as progesterone formation (STAR, CYP11A1, and HSD3B1) and embryo implantation (e.g., TIMP1, TIMP2 and TCTP). Among the list of differentially expressed genes, sialic acid-binding immunoglobulin (Ig)-like lectins (SIGLEC3, SIGLEC14, SIGLEC8), ribosomal proteins (RPL17, RPL34, RPS3A, MRPS33) and chemokines (CCL5, CCL24, CXCL13, CXCL9) were upregulated in Finnsheep, while four multidrug resistance-associated proteins (MRPs) were upregulated in Texel ewes. A total of 17 known genes and two uncharacterized non-coding RNAs (ncRNAs) were differentially expressed in breed-wise comparisons owing to the flushing diet effect. The significantly upregulated TXNL1 gene indicated potential for embryonic diapause in Finnsheep and F1. Moreover, we report, for the first time in any species, several genes that are active in the CL during early pregnancy (including TXNL1, SIGLEC14, SIGLEC8, MRP4, and CA5A).

Functional profiling of the endometrium transcriptome during preimplantation development in Finnsheep, Texel and their F1 crosses

“…Several studies have reported that MGP is highly expressed in the bovine endometrium (Spencer et al 1999, Mamo et al 2012. The high level of MGP expression in our current and previous (Pokharel et al 2020) studies is consistent with earlier reports where this gene was found to be elevated during the preimplantation stage in sheep (Spencer et al 1999, Gray et al 2006) and cattle (Mamo et al 2012). Similarly, Casey et al (2005) reported that MGP was significantly upregulated in nonregressed compared to regressed bovine CLs.…”

“…be induced by the progesterone and are critical for conceptus elongation (Brooks et al 2014). We observed high abundance of key genes involved in progesterone production in the CL of the studied animals (Pokharel et al 2020) which complements findings from this data. This is consistent with maximal production of IFNT which causes massive changes in the endometrial gene expression starting Day 13 of pregnancy (Gray et al 2006, Forde and Lonergan 2017.…”

“…RNA-seq libraries of 18 ewes representing Finnsheep (n = 6), Texel (n = 6) and F1-crosses of purebreds (n = 6) were sequenced in the Illumina HiSeq 2000 system following paired-end (2 x 100 bp) strategy. Library preparation and sequencing was done in Finnish Microarray and Sequencing Center, Turku, Finland and have been described previously (Pokharel et al 2020).…”

“…Several tissue biopsies were collected at the slaughterhouse of which ovarian CL (Pokharel et al 2020) and the endometrium were employed for RNA-seq. Based on the visual inspection, we observed hatching on Day 7.…”

Identification and characterization of miRNAs during early pregnancy in domestic sheep

“…After 2–3 weeks of pregnancy, the ewes were slaughtered to collect the tissue biopsies of corpus luteum (CL) and endometrium for inclusion in this study. Procedures for RNA extraction, sample quality control measurements and sequence library preparation have been described previously (Hu et al, 2015; Pokharel et al, 2020). High‐quality libraries of miRNA were sequenced with an Illumina HiSeq 2000 system using single‐end (1 × 50) sequencing strategy.…”