Transcriptome Analysis Reveals Equine Endometrium's Gene Expression Profile Around Embryo Fixation

The success or failure of embryo fixation is crucial for embryo attachment and later development. As an epithelial chorioallantoic placenta-type animal, the horse has a special process of embryo implantation, and the mechanism of embryo fixation in horses is still unclear.

In this study, the structural and transcriptomic characteristics of endometrial tissue from the fixed and nonfixed sides of 20-day gestation embryos in Mongolian horses were investigated to search for important genes and potential molecular markers associated with the fixation phase of equine embryos.

A comparison of the structures of the endometrial tissues of the two sides revealed that the endometrium on the fixed side presented distinctive features, which were characterized mainly by the development of glands on the fixed side compared with those on the nonfixed side. A total of 3987 differentially expressed genes were identified in the transcriptome, among which 1931 genes were highly expressed on the fixed side of the embryo, including CDH1, DRA, DQB, CLND2, BOLA-DQB, CLDN10, PTGER2, and PTGFR. The differentially expressed genes were enriched in biological processes such as cell adhesion, morphogenesis, NOD signaling, and vitamin uptake, as well as prostatic hormones.

These results suggest that equine embryo fixation may depend at least on the regulation of prostaglandins and the establishment of cellular connections. This provides a foundation for exploring the molecular mechanisms of key genes and pathways related to equine embryo fixation and offers new insights into feeding management and the monitoring of mares in the early stages of pregnancy.