CLONING AND CHARACTERIZATION OF A MURINE BRAIN-SPECIFIC GENE BPX AND ITS HUMAN HOMOLOG LYING WITHIN THE XIC CANDIDATE REGION

The X inactivation centre (Xic) is a cis-acting locus thought to play a key role in the initiation of X-inactivation. We have cloned and cha racterized a new gene, Bpx, lying distal to the murine Xist. Bpx,which is specifically expressed in the brain, shows strong homology to gene s encoding nucleosome assembly proteins and is normally X-inactivated in mice. Isolation and localization of BPX, its human homologue, has s hown the gene to be located centromeric to XIST in man. The Xq13 regio n, whose orientation is apparently globally conserved between man and mouse, must therefore contain an inversion of at least 600 kb spanning the XIST sequence and including the CDX4 and BPX genes.