Expression of enzymes involved in the synthesis of prostaglandin E-2 in bovine in vitro-produced embryos
Résumé
Prostaglandin E-2 (PGE(2)) may play a major role in embryo development and the establishment of pregnancy in cattle. The biosynthesis of PGE(2) implies the sequential transformation of arachidonic acid to PGH(2) by cyclooxygenases (COXs), then the conversion of PGH(2) to PGE(2) by prostaglandin E synthases (PGESs). Quantitative RT-PCR was used to examine the expression of COX-1, COX-2, microsomal PGES-1 (mPGES-1), microsomal PGES-2 (mPGES-2) and cytosolic PGES (cPGES) mRNAs in day 7 in vitro-produced (IVP) embryos from oocytes collected by ovum pick-up in Holstein heifers. Transcripts for COX-2 and mPGES-1 were detected in all embryos, whereas transcripts for COX-1 and mPGES-2 were not detected and cPGESs were at the limit of detection in 40% of embryos. Levels of COX-2 and mPGES-1 mRNAs were significantly higher in blastocysts and expanded blastocysts than in morulae and early blastocysts. Furthermore, excellent-quality embryos (grade 1) displayed higher levels of both COX-2 and mPGES-1 than did embryos of good and medium qualities (grades 2-3). Our results suggest that bovine IVP embryos at the morula and blastocyst stages use exclusively the COX-2/mPGES-1 pathway for PGE(2) biosynthesis, and that PGE(2) is potentially involved in blastocyst expansion and developmental competence.