Amino acid transporter expression in the endometrium and conceptus membranes during early equine pregnancy.

The research investigates the expression of amino acid transporters in horses during early pregnancy, in both normal circumstances and when there’s a timing mismatch between the embryo and uterus. The study revealed unique expression patterns of amino acid transporters in the early membranes of equine pregnancies and suggests that these transporters play a crucial role in nourishing the embryo during its long preimplantation period.

Descriptions of Experiments and Procedures

• In this study, scientists extracted the conceptuses, or early embryos, and the lining of the uterus, known as endometrium, from horses at different time intervals (Days 7, 14, 21, and 28) after ovulation.
• They also carried out a procedure to cause asynchrony between the embryo and uterus. This was conducted by transferring Day 8 embryos to recipient mares on Day 8 or Day 3, with embryos retrieved 6 or 11 days later.
• They then evaluated and compared the expression of various amino acid transporters at these different times in both normal and asynchronous conditions.

Findings of the Study

• Examining the endometrium, the researchers found that the expression of several amino acid transporters (SLC38A2, SLC1A4, and SLC1A5) increased during early pregnancy, while others (SLC7A8, SLC43A2, and SLC7A1) decreased. Meanwhile, SLC1A1 and SLC7A2 expression remained unaffected.
• In the conceptus membranes, most of the transporters studied were upregulated or increased after day 14 (SLC7A5, SLC38A2, SLC1A4, SLC1A5, and SLC7A1) or day 21 (SLC43A2 and SLC7A2).
• The asynchronous embryo transfer procedures indicated that the expression of some transporters in the endometrium (SLC1A5, SLC1A1 and SLC7A8) is primarily regulated by factors related to the conceptus itself and/or the duration of progesterone exposure.

Conclusions and Speculations

• The study concludes by noting that amino acid transporters are expressed in specific spatiotemporal patterns in the early membranes and endometrium during equine pregnancy.
• Because conceptuses express a wider range of transporters than the endometrium, the authors speculate that the equine yolk sac, which nourishes the embryo, may recognize and use these transporters to ensure adequate nutrient provision during a typically long preimplantation period.