Transforming growth factor-β (TGF-β) has been shown to have a positive effect on in vitro fertilization (IVF) and has been reported to stimulate meiosis at follicular level in variety of species. The study was designed to determine the expression patterns of TGF-β1, TGF-β receptors type Ⅰ, Ⅱ and Smads gene in bovine oocytes and embryos. TGF-β1 and their receptors were observed in the unfertilized oocytes. TGF-β1 and type Ⅱ receptor were not expressed at the blastocyst stage, however, only type I receptor was exclusively observed at the same stage. The blastocyst stage, in particular, showed high levels of mRNA expression patterns containing a TGF-β type Ⅰ receptor. The mRNA expression pattern of Smad 2 at all stages of embryonic development was similar in all respect with TGF-β1 type I receptor. On the contrary, Smad 3 and 4 were expressed with high and low level mRNA at the blastocyst stage. In conclusion, it is suggested that TGF-β signaling may be regarded as an important entity during the preimplantation embryo development.

There are replete numbers of reports which have apparently shown that established patterns of methylation are critical for normal mammalian development. Here, we report expression of the DNA methyltransferases (Dnmts) family during mouse early development. Transcription of Dnmt1o occurs in one-cell and morula stage embryos, whereas Dnmt1s transcripts were detectable in all cells and tissues examined during the study. Dnmt3a1 transcript was detected in all cells and Dnmt3a2 transcript was particularly detected in the oocyte and 1-cell stages. Low level Dnmt3b1 transcripts were expressed ubiquitously in oocyte, 1-cell, and preimplantation embryos except 2～4 cell stages. Dnmt3b3 transcripts were only detected in E7.5 embryo and ovary. Furthermore, Dnmt3l transcripts were detectable in all cells and tissues examined. Unlike Dnmt1, both Dnmt3a and Dnmt3b proteins existed in the nucleus of preimplantation embryos till the morula stage. These Results suggest that differences Dnmts expression level exist and genomic DNA methylation patterns may be determined partly through differential expression of Dnmts during early development.