Expression of enzymes involved in the synthesis of prostaglandin E in early- and late-cleaved bovine embryos at different stages of preimplantation development.

Prostaglandin (PG) E plays a role in numerous aspects of mammalian reproduction, such as oviductal transport of gametes, hatching from the zona pellucida in blastocysts and early embryonic development. Despite the evident role of PGE in the regulation of female reproductive processes, in the literature, there is very little information concerning the expression of PGE synthesizing enzymes and the exact amount of PGE produced by bovine embryos in vitro. In the present study, we aimed to determine the mRNA levels and immunolocalization of the enzymes responsible for PGE synthesis (PTGS2, mPGES1, mPGES2 and cPGES) in embryos at the 2-cell, 4-cell, 8-cell, 16-cell, morula, early blastocyst, blastocyst, expanded blastocyst and hatched blastocyst stages, using a well-defined bovine model of oocyte developmental competence based on the time of first cleavage. PTGS2, mPGES2 and cPGES transcripts and proteins were detected in all stages of embryos, whereas the mPGES1 transcript and protein were not detected in embryos from the 2- to 16-cell stage. The results showed different transcription profiles of the enzymes involved in PGE synthesis in early- and late-cleaved embryos during the early stages of their in vitro preimplantation development. We also found that all the analysed stages of bovine preimplantation embryos released PGE, with the highest concentration on Day 7 of culture in both the early- and late-cleaved groups. The present study is the first to demonstrate PGE synthesis and production by bovine early- and late-cleaved embryos at different stages of preimplantation development. Bovine embryos can produce PGE, which may exert paracrine regulation during development. The transcription levels of PGE synthases were affected by the embryonic stage of development and quality. Our results indicate that the different transcription profiles of PTGS2, mPGES1, mPGES2 and cPGES, as well as PGE concentration, in early-versus late-cleaved embryos are dependent on the quality of the oocytes from which the embryos were obtained, which could reveal the association of PGE production during bovine preimplantation development with more advanced stages of embryo development.