DIFFERENTIAL PREIMPLANTATION REGULATION HOMOLOGS OF THE YEAST SWI2 PROTEIN

Epigenetic regulation of gene expression through modification of chrom atin organization is an important mechanism in the development of euca ryotic organisms. We investigated the developmentally regulated expres sion of the mouse mBRG1 and mbrm genes, which are homologous to the ye ast SWI2 gene. Both proteins are involved in chromatin remodeling as c omponents of the mammalian SWI/SNF complex. The analysis was performed at a Lime in mouse development when the formation of a functional zyg otic nucleus is closely linked to extensive chromatin modifications. R everse transcription-polymerase chain reaction (RT-PCR) analysis in ma ture oocytes and through the first cleavage stages showed that both ge nes were highly expressed as maternal products but that they subsequen tly exhibited considerable differences in their level of expression wh en the transition to zygotic transcription occurred. Immunodetection o f the two proteins with specific antibodies paralleled the RT-PCR anal ysis. The mBRG1 protein was present throughout preimplantation develop ment, whereas zygotic mbrm was clearly detectable only when differenti ation first occurs at the blastocyst stage. At this stage, mbrm was re stricted to the inner cell mass. Cell type-specific expression of mbrm was also observed after in vitro differentiation of embryonic stem ce lls. These results indicate that the two murine homologues of SWI2 hav e substantially different roles in chromatin organization during the o nset of embryonic development. (C) 1998 Wiley-Liss, Inc.