The elusive Dnmt1 and its role during early development.

摘要

In mammals, DNA methylation serves a number of essential roles primarily in regulation of transcriptional silencing establishing a heritable and stable mark in each replication cycle. In the preimplantation mouse embryo, DNA methylation is modulated extensively resulting in an overall loss of methylation progressively up to the morula stage. Curiously some imprinted loci and their controlling regions, as well as specific repetitive sequences, are excluded from this genome-wide loss of DNA methylation suggesting that mechanisms to distinguish between CpG motifs must exist from the earliest stage of development. Mechanistically an oocyte-specific form of Dnmtl, Dnmtlo, is known to enter the nucleus at the 8-cell stage to maintain imprinted methylation marks although the identification of activities responsible both before and immediately after the 8-cell stage has remained elusive.