Preimplantation Embryos Affect Expressions Of DNA Methyltransferase-1 In Mouse Oviductal Epithelium

Background The oviduct or fallopian tube, as it is called, is the tubular organ connecting the periovarian space with the uterus. It provides the space and biological environment for fertilization, contributes to removal or addition of oocyte coatings, nourishes the embryo while it is being carried to the uterus, and transduces and amplifies signals from the embryo to the mother. Finally, it delivers the embryo to the endometrial environment at a time and stage of development in line with the synchrony they both require. Normal establishment and maintenance of pregnancy should be realized by intact embryo-maternal communication. A number of cytokines, growth factors, angiogenic factors, apoptotic factors, adhesion molecules and their receptors secreted from maternal reproductive tract and embryos themselves play important roles in blastocyst formation, protein synthesis, apoptosis decreasing, blastocoel expansion and gene regulation through autocrine, paracrine and endocrine models. Expressions of these factors would fluctuate along with embryos development. However, the true mechanism of embryo-maternal communication has not totally identified.In 2002, Lee et al firstly reported identification of genes in the oviduct that are upregulated in the presence of embryos during the preimplantation period, this suggesting embryo-maternal communication should be related with gene regulation.It is known to all, DNA methylation at CpG dinucleotides, which is mainly attributed to Dnmts, plays an important role in regulation of gene expression both in normal mammlian early embryo development and part somatic cells genes. In general, DNA methylation functions in the regulation of specific genes through a transcriptional repression mechanism. Dnmts family, which are now considered responsible for DNA methylation, consist of Dnmtl, Dnmt2, Dnmt3a and Dnmt3b. Dnmtl is known as maintenance Dnmts, while Dnmt2 has been characterized to have no activity in vivo, Dnmt3a and Dnmt3b are considered as de novo Dnmts. Dnmtl, the most frequently and best-characterized mammalian Dnmts, which is widely present in mammalian adult tissues and embryo tissues, is responsible for catalyzing the transfer of a methyl group from s-adenosyl-L-methionine to the 5-position of cytosine in DNA, perfoming preference for hemi-methylated subtstrate. Mammalian Dnmtl is the most important among the Dnmts family, whose level may indirectly reflect genomic DNA methylation patterns. Up to now, there is no obvious evidence manifesting there are relationships between preimplantation embryo development and DNA methylation level of maternal ovidutal epithelium.Objective To investigate the effects of mouse preimplantational embryos on the expressions of Dnmtl of maternal oviductal epithelium.Materials and Methods Eighty ICR female mice and forty males were randomly divided into two groups, named A and B, each of which consisted of forty females and twenty males. Males in group B were vasectomized, all females were superovulated by an injection of 7.5 IU PMSG followed 46-48 h later by 7.5 IU hCG and mated with males of the same group. Next moring, females with plugs of group A were defined as pregnant mice and those of group B were named as pseudopregnant mice. Both groups consisted of thirty females. Two groups of females were killed at 2-cell embryonic stage, 4-cell embryonic stage and 8-cell embryonic stage and oviducts were collected. A streptavidin peroxidase conjugated (SP) immunohistochemistry assay was used to determine the location of Dnmtl protein in the oviduct. Real-time reverse transcription polymerase chain reaction (RT-PCR) and western-blot of Dnmtl were applied to examining the expression of Dnmtl mRNA andprotein in the oviductal epithelium of both groups.Results 1. Immunohistochemical staining: Dnmtl protein was found to accumulate predominantly in the epithelium of mouse oviduct with weak serosa staining. 2. Rreal-time RT-PCR: (1) There were no significantly differences (p>0.05) of Dnmtl mRNA levels among all stages detected in pregnant mice. (2) There we...