Transcription Patterns Of Dnmt1 Gene During Murine Embryogenesis

The accurate genomic imprinting is extremely important for the proper development of mammals, while Dnmt1 protein is the predominant form of DNA (cytosine-5) methyltransferases in mammals and is mainly responsible for the maintenance of genomic imprinting that established during gametogenesis. Dnmtl gene has two different transcriptional forms: Dnmtls is somatic-specific and Dnmt1o is oocyte-specific. In the present studies, the transcription of Dnmtl gene during murine embryogenesis was evaluated. Single-copy template of oocytes or embryos was used in our trials. Besides oocytes (100%, 10/10, 15h-post hCG), Dnmtls transcripts were also found in embryos at various stages. There were 30% (3/10), 20% (2/10), 70% (7/10) of embryos at early pronuclei (20h-post hCG), late 1-c (30h-post hCG), and early 2-c stages (35h-post hCG) holded the Dnmt1s transcripts. Furthermore, the mRNA of Dnmt1s were found in all the embryos at late 2-c (10/10, 50h-post hCG), 4-c (65h-post hCG), 8-c (75h-post hCG), morula (93h-post hCG) and blastosyst (118h-post hCG) stages. On the contrary, oocyte-specific mRNA of Dnmt1o was only found in all oocytes (10/10) and 90% (9/10) of early 1-c, as well as 40% (4/10) of late 1-c embryos. These results of the ten-copy templates of oocytes or embryos showed that the mRNA of Dnmtls decreased after fertilization, and increased soon when the embryos cleavaged, while the mRNA of Dnmt1o decreased at all and would not be transcripted during the following development. These results implied that the oocyte-derived mRNA of Dnmtls disappeared rapidly in the zygote and began to be produced from the genome of embryos from the stage of 2-cell. However, after the oocyte-derived mRNA of Dnmt1o disappeared slowly in the zygote, the embryo-derived genome would not express the mRNA of Dnmt1o anymore.