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Spatio-temporal expression of transcriptional regulators in concert with the maternal to embryonic transition during bovine in vitro embryogenesis

C Vigneault, Animal Sciences, Laval University, Quebec, Quebec, Canada
S McGraw, Animal Sciences, Laval University, Quebec, Quebec, Canada
M Sirard, Animal Sciences, Laval University, Quebec, Quebec, Canada

Correspondence: Christian Vigneault, Email: christian.vigneault{at}gmail.com

Abstract

Cleavage stage bovine embryos are transcriptionally quiescent until they reach the 8- to 16-cell stage, and thus rely on the reserves provided by the stored maternal mRNAs and proteins found in the oocytes to achieve their first cell divisions. The objective of this study was to characterize the expression and localization of the transcriptional and translational regulators, MSY2, TBP and ATF2, during bovine early embryo development. GV stage and MII stage oocytes as well as two-, four-, eight-, 16-cell stage embryos, morula and blastocysts produced in vitro were analysed for temporal and spatial protein expression. Using Q-PCR, ATF2 mRNA expression was shown to remain constant from the GV stage oocyte to the 4-cell embryo, and then decreased through to the blastocyst stage. In contrast, the protein levels of ATF2 remained constant throughout embryo development and were found in both the cytoplasm and the nucleus. Both TBP and MSY2 showed opposite protein expression patterns, as MSY2 protein levels decreased throughout development while TBP levels increased through to the blastocyst stage. Immunolocalization studies revealed that TBP protein was localized in the nucleus of 8- to 16-cell stage embryos, whereas the translational regulator MSY2 was exclusively cytoplasmic and disappeared from the 16-cell stage onwards. This study shows that MSY2, TBP and ATF2 are differentially regulated through embryo development and provides insight on the molecular events occurring during the activation of the bovine genome during embryo development in vitro.