Negative uterine asynchrony retards early equine conceptus development and upregulation of placental imprinted genes.

The study investigates how negative uterine asynchrony after embryo transfer affects the early development of horse embryos and the expression of certain placental imprinted genes and DNA methyltransferases. The researchers found that embryos developed in an asynchronous uterus had slower physical development and upregulation of these genes, but they are able to adapt and ‘reset’ their development to the uterine stage, highlighting the inherent resilience of horse embryos to asynchrony post-embryo transfer.

Objective and Methodology of the Study

• The study’s main aim was to understand the impact of negative uterine asynchrony, a situation where the embryo transfer takes place prematurely (on day 3 rather than day 8 post-ovulation, in this case), on the early development of horse embryos and the expression of placental imprinted genes and DNA methyltransferases.
• Placental imprinted genes are important as they are seemingly sensitive indicators of an unsuitable pre-implantation environment.
• To carry out this research, the scientists transferred Day 8 embryos into recipient mares either on Day 8 (synchronous) or Day 3 (asynchronous) after ovulation. They then recovered the conceptuses 6 or 11 days later (on Day 14 or 19 of the development).

Findings of the Research

• In the asynchronous conditions, Day 14 conceptuses had visibly smaller embryonic discs and slower developing primitive streaks compared to their synchronous counterparts.
• Similarly, asynchronous Day 19 embryos showed retardation in length, somite number, and organogenesis compared to synchronous Day 19 embryos.
• Various maternal and paternal imprinted genes, as well as DNA methyltransferases (DNMT1, 3A, and 3B), saw higher up-regulation (increase in response to an external stimulus) between Day 14 and Day 19 of pregnancy. This was predominantly higher in synchronous Day 19 yolk sac membrane than in its asynchronous counterpart.

Implications of the Results

• Interestingly, the researchers also found an ability to ‘reset’ conceptus development to the uterine stage. Even though their development is initially delayed in asynchronously implanted embryos, the embryos can adjust their development process to match the stage of the uterus into which they are implanted. This adaptation might explain why horse embryos are unusually tolerant of asynchrony after an embryo transfer.