Abstract
During maternal recognition of pregnancy (MRP), a conceptus-derived signal leads to the persistence of the corpus luteum and the maintenance of gestation. In the horse, the nature of this signal remains to be elucidated. Several studies have focused on the changes in gene expression during MRP, but little information exists at the protein level. The aim of this study was to identify the proteins at the embryo-maternal interface around signalling of MRP in the horse (day 13) by means of mass spectrometry. A distinct influence of pregnancy was established, with 119 proteins differentially expressed in the uterine fluid of pregnant mares compared to cyclic mares and with upregulation of several inhibitors of the prostaglandin synthesis during pregnancy. By creating an overview of the proteins at the embryo-maternal interface in the horse, this study provides a solid foundation for further targeted studies of proteins potentially involved in embryo-maternal interactions, MRP and pregnancy loss in the horse.
Highlights
During maternal recognition of pregnancy (MRP), a conceptus-derived signal leads to the persistence of the corpus luteum and the maintenance of gestation
A line of fluid was noticed by ultrasound of the uterus 1 day after artificial insemination (AI) and she was treated by intramuscular administration of oxytocin
Maternal recognition of pregnancy is an intriguing subject in the horse and extensive research on the molecular processes involved has been performed in the field of transcriptomics[7,18]
Summary
During maternal recognition of pregnancy (MRP), a conceptus-derived signal leads to the persistence of the corpus luteum and the maintenance of gestation. Potential embryonic signal targets involved in the luteostatic mechanism in the horse are prostaglandin-endoperoxide synthase 2 (PTGS2), an enzyme in the biosynthesis of PGF2α, and oxytocin, which stimulates endometrial PGF2α secretion through a positive feedback loop[8]. Both PTGS2 and oxytocin receptor expression (OXTR) are repressed during early pregnancy compared to cycling mares, with downregulation of PTGS2 at the RNA level and of OXTR at the protein level[9,10,11,12,13]. The authors detected prostaglandin F2 receptor inhibitor (PTGFRN) and a progesterone potentiating protein, FK506 binding protein 4 (FKBP4), in the blastocoel fluid, but it remained to be determined whether these proteins were actively secreted into the uterine lumen
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