Single-cell atlas of the pregnant equine endometrium before and after implantation.

This research article conveys an exploration into the transcriptome and subpopulations of endometrial cells in pregnant horses, with a specific focus on the period before and after embryo implantation. Single-cell RNA sequencing was utilized to study nearly 97,000 endometrial cells and highlight similarities and differences in the processes of horse versus human embryo implantation.

Objective of Study

• The aim of this research was to determine and compare the transcriptome and subpopulations of endometrial cells before and after embryo implantation in mares. Researchers wanted to investigate the regulation factors of late implantation in horses, and if horse implantation shares similarities with other species.

Methodology

• The researchers utilized single-cell RNA sequencing to study the endometrial cellular composition.
• Nearly 97,000 endometrial cells were collected from horse endometrium biopsies on day 33 (before implantation) and day 42 (after implantation) of gestation.

Findings

• The research identified 16 immune and 24 non-immune cell clusters. These clusters incorporated known major cell populations and potentially new subpopulations of horse immune cells such as resident innate lymphoid cells and mucosal-associated invariant T cells.
• Contrary to current knowledge, the study found endometrial natural killer (eNK) cells to be the most prevalent leukocyte population present during horse embryo implantation.
• The eNK cells expressed genes which may interact with fetal MHC I, such as LY49F, and also exerted immunoregulatory functions independent of MHC I expression, such as CD96/TIGIT.
• Similar to other species studied, an upregulation of CXCR4 was found in several immune cell subpopulations.

Conclusions

• The study concluded that despite differences in placentation timings as compared to humans, horses share some key similarities with humans concerning embryo implantation mechanisms.
• This knowledge can potentially aid in understanding the biology behind species-specific variations in the pregnancy process.