Abstract
Equine maternal recognition of pregnancy (MRP) is a process whose signal remains unknown. During MRP the conceptus and endometrium communicate to attenuate prostaglandin F2α (PGF) secretion, sparing the corpus luteum and maintaining progesterone production. Recognition of a mobile conceptus by the endometrium is critical by days 14–16 post-ovulation (PO), when endometrium produces PGF, initiating luteolysis. The objective of this study was to evaluate endometrial gene expression changes based upon pregnancy status via RNA sequencing. This experiment utilized a cross-over design with each mare serving as both a pregnant and non-mated control on days nine, 11, and 13 PO (n = 3/status/day). Mares were randomly assigned to collection day and pregnancy confirmed by terminal uterine lavage at the time of endometrial biopsy. Total RNA was isolated and libraries prepared using Illumina TruSeq RNA sample preparation kit. Reads were mapped and annotated using HISAT2 and Stringtie. Expression values were evaluated with DESEQ2 (P ≤ 0.05 indicated significance). On day nine, 11, and 13 there were 1435, 1435 and 916 significant transcripts, respectively. Multiple genes with splice variants had different expression patterns within the same day. These are the first data to evaluate the endometrial transcriptome during MRP on days nine, 11, and 13.
Highlights
Maternal recognition of pregnancy (MRP) in the horse is a complex process that involves communication between the conceptus and maternal endometrium
Oxytocin binds to endometrial receptors, which causes release of more oxytocin and subsequently, prostaglandin F2α (PGF2α) [4]
Fertilization occurs in the oviduct, but the embryo does not enter the uterus until day six
Summary
Maternal recognition of pregnancy (MRP) in the horse is a complex process that involves communication between the conceptus and maternal endometrium. The equine conceptus does not attach to the endometrium until approximately day 35 post-ovulation (PO), so communication is occurring without attachment to prevent the endometrium from secreting prostaglandin F2α (PGF2α ), which causes luteal regression of the corpus luteum, eliminating the source of progesterone [1,2]. In both pregnant and non-pregnant mares, the hormonal profile stays the same until day 14 PO [3]. Fertilization occurs in the oviduct, but the embryo does not enter the uterus until day six. At this time the embryo is surrounded by the zona pellucida. At approximately day seven, the embryo remains covered by an acellular, glycoprotein capsule [5]
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