A sister of regulates genes expressed in pre-implantation human development.

The homeobox gene plays a pivotal role in self-renewal and maintenance of pluripotency in human， mouse and other vertebrate embryonic stem cells， and in pluripotent cells of the blastocyst inner cell mass. There is a poorly studied and atypical homeobox locus close to the gene in some mammals which could conceivably be a cryptic paralogue of even though the loci share only 20% homeodomain identity. Here we argue that this gene， ， is an extremely divergent duplicate of that underwent radical sequence change in the mammalian lineage. Like ， the gene is expressed in pre-implantation embryos of human and cow; unlike ， expression is restricted to 8-cell and morula stages， preceding blastocyst formation. When expressed ectopically in adult cells， human elicits gene expression changes， including downregulation of a set of genes that have an expression pulse at the 8-cell stage of pre-implantation development. We conclude that gene duplication and massive sequence divergence in mammals generated a novel homeobox gene that acquired new developmental roles complementary to those of