THE ETL-1 GENE ENCODES A NUCLEAR-PROTEIN DIFFERENTIALLY EXPRESSED DURING EARLY MOUSE DEVELOPMENT

Recently, we isolated a novel mouse gene, Etl-1 (Enhancer-trap-locus-1 ), whose deduced amino acid sequence shows in its C-terminal portion s triking homology to the brahma protein (BRM), a transcriptional regula tor of homeotic genes in Drosophila, and to SNF2/SWI2, a transcription al regulator of various genes in Saccharomyces cerevisiae. Here we rep ort the generation of antibodies against the Etl-1 gene product (ETL-1 ) and describe the subcellular localization as well as the expression and distribution of the ETL-1 protein during mouse pre- and early post -implantation development. ETL-1 is a nuclear protein and is expressed in a biphasic manner during early embryogenesis. Moderate levels of E TL-1 were detected in unfertilized and fertilized eggs but in the latt er the protein was not concentrated in the pronuclei and seemed evenly distributed throughout the cytoplasm. In two-cell embryos nuclear ETL -1 protein accumulated transiently and levels decreased during subsequ ent cleavage development. After the morula stage, ETL-1 levels increas ed again; in blastocysts high levels of ETL-1 were present in inner ce ll mass cells whereas trophectoderm cells contained little or no ETL-1 . During subsequent development essentially all cell types except pari etal endoderm and trophoblast cells contained high levels of ETL-1. Ou r results imply that nuclear ETL-1 is dispensable for the progression to the two cell stage, and suggest that during cleavage ETL-1 might be needed at the onset of embryonic transcription. In blastocysts ETL-1 function might be specifically required in cells of the inner cell mas s and later in most cells of the embryo proper and extraembryonic ecto derm lineage. (C) 1993 Wiley-Liss, Inc.