222 Maternal Recognition of Pregnancy in the Mare: What is Needed to Make Progress in our Understanding of This Complex Issue

Abstract

Abstract Maternal recognition of pregnancy (MRP) resulting in prolonged luteal lifespan is crucial to maintenance of pregnancy. Mechanisms underlying MRP differ in between species, whereat the precise mechanism by which luteolysis is prevented has yet to be described for equine pregnancy. Transcriptional profiling studies entailing analysis of endometrial and embryonic tissues have shed light into the wider context of maternal recognition of pregnancy. Our own studies revealed the secretion of fibrinogen by preimplantation equine embryos, which is a peculiar finding as fibrinogen synthesis almost exclusively occurs in the liver. Conceptus-derived fibrinogen likely contributes to cell adhesion during fixation and underlines the helpfulness of transcriptome studies in identifying species-specific aspects of early pregnancy. Despite all our advances, we yet have to decipher the signaling pathways leading to reduced endometrial production of prostaglandin F2alpha during MRP. We recently analyzed samples from mares undergoing spontaneous pregnancy loss in the face of high progesterone in comparison to samples collected from mares at Day 20 of intact pregnancy. No differentially expressed transcripts could be detected. It appears that after maternal recognition of pregnancy and consequent suppression of luteolysis, progesterone, not the presence of a viable conceptus, is the driving force of gene expression. This finding underlines the importance of understanding the events surrounding luteostasis. We propose that a standardized approach in vitro cell culture model is needed to address mechanistic questions pertaining to MRP. Approaches currently underway such as CRISPR/Cas9-mediated targeted integration of TERT and TERC to immortalize equine endometrial stromal fibroblasts will be discussed.