MAPPING THE MURINE XCE LOCUS WITH (CA)N REPEATS

The X Chromosome (Chr) controlling element locus (Xce) in the mouse ha s been shown to influence the X inactivation process. Xce maps to the central region of the X Chr, which also contains the Xist sequence, it self possibly implicated in the X inactivation process. Three microsat ellite markers spanning the Xist locus have been isolated from an Xist containing YAC. All three microsatellite markers showed complete link age with Xce in recombinants for the central span of the mouse X Chr b etween Ta and Mob(blo) and strong linkage disequilibrium with Xce in a ll but one of the inbred mouse strains tested. In the standard Xce(b) typing strain JU/Ct, the two microsatellites most closely flanking Xis t fail to carry the allelic forms expected if Xist and Xce are synonym ous. Alternative explanations for this finding are presented in the co ntext of our search for understanding the relation between Xist and Xc e.