Transcriptome changes in the equine conceptus during maternal recognition of pregnancy

During the period of initial maternal recognition of pregnancy (MRP), the equine conceptus shows a series of unique events characterized by rapid blastocyst expansion, secretion of a variety of molecules, and constant migration during the entire uterus driven by uterine contractions. So far, the specific transcriptome changes of the conceptus underlying these events are not well characterized. Thus, the objective of this study was to perform an integrative transcriptomic (including mRNA, miRNAs, and other small non-coding RNAs) analysis of embryos collected from days 10 to 13 of pregnancy. The results revealed a very dynamic transcriptome profile with a total of 1311 RNAs identified as differentially expressed across days of pregnancy, including 18 microRNAs (miRNAs). Interestingly, two main RNA profiles for mRNAs and miRNAs were identified, one with higher expression in conceptuses smaller than 5 mm and the second with higher expression in conceptuses larger than 5 mm. Overall, our data showed a fine-tuned transcriptomic regulation of the developing conceptus depending more on the size, rather than day of pregnancy. The identification of specific mRNAs and miRNAs, particularly on days 12 and 13 of pregnancy, pointed to key players in equine conceptus development. Moreover, it provided potential conceptus-derived signal(s) for MRP and prevention of luteolytic endometrial prostaglandin F2alpha release. These data revealed new insights on prostaglandin synthesis by the equine conceptus, potential miRNAs involved in modulation of the maternal immune response, regulation of endometrial receptivity, and association with regulation of late implantation in the mare.