Embryo

Transcription Factor Expression Patterns in Bovine In Vitro-Derived Embryos Prior to Maternal-Zygotic Transition

Abstract
Maternal-zygotic transition (MZT) is a complex phenomenon characterized by the initiation of transcription in the embryo and the replacement of maternal mRNA with embryonic mRNA. In order for this to occur, transcriptional activation requires various factors and conditions. Our hypothesis is that the lack of transcription in the bovine pre-MZT embryo is due, in part, to an incomplete or dormant transcriptional apparatus. Therefore, in accordance with this hypothesis, functioning transcriptional mechanisms should appear in the 8-cell bovine embryo to facilitate embryonic transcription during the MZT. With this in mind, we examined the presence of selected transcription factors during preimplantation embryo development to establish how their transcript level change in bovine pre-MZT embryos. To achieve this goal, real-time RT-PCR was used to quantify the mRNA level of several different transcription factors (YY1, HMGA1, RY-1, P300, CREB, YAP65, HMGN1, HMGB1, NFAR, OCT-4, TEAD2, ATF-1, HMGN2, MSY2 and TBP) in germinal vesicle (GV) and metaphase II (MII) bovine oocytes and in 2-, 4-, 8-cell and blastocyst stage embryos produced in vitro. Our results demonstrate that all genes examined can be grouped into five different categories according to their mRNA expression patterns at the developmental stages observed. To summarize, all transcription factors studied were present in pre-MZT embryos and the expression pattern of a many of them suggest a potential role in MZT.

Key words: Embryo • Early development • Gene regulation • In vitro fertilization • Oocyte development

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