Regulation of Mouse Retroelement MuERV-L/MERVL Expression by REX1 and Epigenetic Control of Stem Cell Potency

About half of mammalian genomes is occupied by DNA sequences that originatefrom transposable elements. Retrotransposons can modulate gene expression indifferent ways and, particularly retrotransposon-derived LTRs, profoundly shapeexpression of both surrounding and distant genomic loci. This is especially important inpreimplantation development, during which extensive reprogramming of the genometakes place and cells pass through totipotent and pluripotent states. At this stage, themain mechanisms responsible for retrotransposon silencing i.e. DNA methylation, isinoperative. A particular retrotransposon called muERV-L/MERVL is expressed duringpreimplantation stages and contributes to the plasticity of mouse embryonic stem cells.This review will focus on the role of MERVL-derived sequences as controllingelements of gene expression specific for preimplantation development, two-cell stagespecific gene expression and stem cell pluripotency, the epigenetic mechanisms thatcontrol their expression, and the contributions of the pluripotency marker REX1 and therelated YY1 family of transcription factors to this regulation process.