Deep sequencing of the porcine endometrial transcriptome on day 12 of pregnancy
The porcine conceptus undergoes rapid differentiation and expansion of its trophoblastic membranes between Days 11 and 12 of gestation. Concomitant with trophoblast elongation, production of conceptus estrogen, the porcine embryonic pregnancy recognition signal increases. Conceptus attachment to the uterine surface epithelium starts after Day 13 initiating epitheliochorial placentation. To analyze the transcriptome changes in the endometrium in the course of maternal recognition of pregnancy (MRP), deep sequencing of endometrial RNA samples of Day 12 pregnant animals (n=4) and corresponding non-pregnant controls (n=4) was performed using Illumina RNA-Seq. Between 30 and 35 million sequence reads per sample were produced and mapped to the porcine genome (Sscrofa10.2). Analysis of read counts revealed 2,593 differentially expressed genes (DEG). Expression of selected genes was validated by the use of quantitative real-time RT-PCR. Bioinformatics analysis identified several functional terms specifically overrepresented for up-regulated or down-regulated genes. Comparison of the RNA-Seq data from Days 12 and 14 of pregnancy was performed at the level of all expressed genes, of the DEG, and at the level of functional categories. This revealed specific gene expression patterns, reflecting the different functions of the endometrium during these stages, i.e. recognition of pregnancy and preparation for conceptus attachment. Genes related to mitosis, immune response, epithelial cell differentiation and development, proteolysis, and prostaglandin signaling and metabolism are discussed in detail. In conclusion, this study identified comprehensive transcriptome changes in porcine endometrium associated with MRP and initiation of implantation and a number of genes and pathways potentially involved in regulation of these processes. Overall design: In total, 8 samples were analyzed, 4 biological replicates for pregnant animals (samples from 4 different animals) and 4 biological replicates for cyclic controls (samples from 4 different animals)