Gene expression profiling of corpus luteum reveals the importance of immune system during 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. While ovulation rate is the major determinant of litter size in sheep, interactions among the conceptus, corpus luteum and endometrium are essential for pregnancy 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, and mapping the RNA-Seq reads to the latest Rambouillet reference genome. A total of 21,287 genes were expressed in our dataset. Highly expressed autosomal genes in the CL were associated with biological processes such as progesterone formation (STAR, CYP11A1, and HSD3B1) and embryo implantation (eg. TIMP1, TIMP2 and TCTP). Among the list of differentially expressed genes, a group of sialic acid-binding immunoglobulin (Ig)-like lectins (Siglecs), solute carriers (SLC13A5, SLC15A2, SLC44A5) and chemokines (CCL5, CXCL13, CXCL9) were upregulated in Finnsheep, while four multidrug resistance-associated proteins (MRPs) were upregulated in Texel ewes. A total of 17 genes and two non-coding RNAs (ncRNA) were differentially expressed in breed-wise comparisons owing to flushing diet effect. Moreover, we report, for the first time in any species, several genes that are active in the CL during early pregnancy (including SIGLEC13, SIGLEC14, SIGLEC6, MRP4, and CA5A). Importantly, functional analysis of differentially expressed genes suggested that Finnsheep have a better immune system than Texel and that high prolificacy in Finnsheep might be governed by immune system regulation.