Unveiling the bovine embryo transcriptome during the maternal-to-embryonic transition

Abstract

Bovine early embryos are transcriptionally inactive and subsist through the initial developmental stages by the consumption of the maternal supplies provided by the oocyte until its own genome activation. In bovine, the activation of transcription occurs during the 8-to 16-cell stages and is associated with a phase called the maternal-to-embryonic transition (MET) where maternal mRNA are replaced by embryonic ones. Although the importance of the MET is well accepted, since its inhibition blocks embryonic development, very little is known about the transcripts expressed at this crucial step in embryogenesis. In this study, we generated and characterized a cDNA library enriched in embryonic transcripts expressed at the MET in bovine. Suppression subtractive hybridization followed by microarray hybridization was used to isolate more than 300 different transcripts overexpressed in untreated late eight-cell embryos compared with those treated with the transcriptional inhibitor, a-amanitin. Validation by quantitative RT-PCR of 15 genes from this library revealed that they had remarkable consistency with the microarray data. The transcripts isolated in this cDNA library have an interesting composition in terms of molecular functions; the majority is involved in gene transcription, RNA processing, or protein biosynthesis, and some are potentially involved in the maintenance of pluripotency observed in embryos. This collection of genes associated with the MET is a novel and potent tool that will be helpful in the understanding of particular events such as the reprogramming of somatic cells by nuclear transfer or for the improvement of embryonic culture conditions.

Candidate gene expression patterns in rabbit preimplantation embryos developed in vivo and in vitro

“…The role of HDAC1 regulation of KLF4 also could have an influence in these high levels of KLF4 expression. KLF4 expression was also reported to increase at the 8-cell embryo in bovine embryos [49]. This study showed that KLF4 localisation in both the in vitro and in vivo developed rabbit preimplantation embryos was diffused.…”

“…Housekeeping genes and apoptotic regulators were reported to peak at the ZGA in bovine and murine embryos [48,49]. The early BCLXL expression peak in in vitro embryos indicates either a compensative measure for enhanced protein degradation or a higher pro-apoptotic signal being balanced for the embryo survival.…”

Retrotransposon expression as a defining event of genome reprograming in fertilized and cloned bovine embryos

“…This expression had not been evidenced by previous analyses of the massive changes in the embryonic transcriptome accompanying EGA in the bovine. This may be explained by the use of nondedicated arrays (Misirlioglu et al 2006, Kues et al 2008, by the size of the custom array, or the precise methods used in custom array construction (Vigneault et al 2009). Moreover, our results show that the expression of LTR transposons is faithfully recapitulated in bovine SCNT embryos, where their transcriptional activation results in a quantity of expressed transcripts that does not differ from fertilized embryos.…”

Silencing CENPF in bovine preimplantation embryo induces arrest at 8-cell stage

“…A large number of genes expressed from the embryonic genome during embryonic genome activation (EGA) were identified using all sorts of molecular genetic methods including microarray analysis (Hamatani et al 2004, Wang et al 2004, Misirlioglu et al 2006, Kanka et al 2009, Vigneault et al 2009). However, the functions of many transcripts during mammalian embryogenesis are still not known.…”