Embryo-maternal communication

Understanding embryo-maternal interaction that regulates implantation

Tom Stout and his colleague collecting oocytes from a mare
Tom Stout and his colleague collecting oocytes from a mare

In horses and cattle, fertilisation rates are very high (>90%), but many pregnancies fail in the period leading up to implantation and the establishment of a stable placental attachment. Similarly in man, early embryonic death is a significant contributor to sub-fertility, and an important factor limiting the success of IVF programmes. While embryonic, and specifically chromosomal, abnormalities are undoubtedly a major contributor to these early losses, communication between the embryo and the maternal reproductive tract and, in particular, the ‘receptivity’ of the uterus for implantation appears to be an equally important contributor.

The uterus is prepared for its role in implantation and the support of pregnancy by two major factors, the maternal ovarian steroid hormone environment and biochemical signals released by the trophectoderm of the developing embryo. Moreover, reciprocal communication must be established to ensure that the conceptus and its uterine environment develop synchronously and harmoniously.

Supporting embryonic development

Our research focuses on the maternal steroid hormone cues and embryonic signals that fine tune the uterine transcriptome and proteome in a manner that helps support embryonic development and implantation. We do this using a mix of in vitro systems, large animal models and both data and samples recovered from clinical cases, in particular our large commercial equine assisted reproduction programme.

Microscopic image of a horse embryo in the shape of a heart
Microscopic image of a horse embryo by Marta de Ruijter-Villani

Experimental models that help unravel the interactions between the uterus and developing embryo include asynchronous embryo transfer, to examine the effects of exposing an embryo to an inappropriate uterine environment, the effects of dietary manipulation or ovarian steroid hormone priming (estrogens and progestogens), and the interaction between in vitro produced embryos and the uterus of a recipient mare.

Preventing early embryonic death

One of the advantages of studying early pregnancy in horses is that implantation is non-invasive and not completed until unusually late in gestation (day 40-45). Moreover, the developing conceptus can be identified, and its growth and development monitored, ultrasonographically from as early as day ten after ovulation. Finally, both conceptuses and endometrium can be recovered non-surgically, and without cross-contamination throughout the preimplantation period. These materials can be used for epigenomic, transcriptomic, proteomic or further in vitro studies to help understand vital components of embryo-maternal communication with ultimate aim of developing treatments or strategies to prevent early embryonic death.