Homologous expressed genes in the human sex chromosome pairing region.

The human sex chromosomes share a pair of homologous genes which independently encode a cell-surface antigen defined by the monoclonal antibody 12E7 (refs 1, 2; see refs 3, 4 for review). The X-located homologue, MIC2X, escapes X-inactivation and the equivalent Y-located locus, MIC2Y, was one of the first genes shown to reside on a mammalian Y chromosome. By using a bacterial expression system we have previously cloned a complementary DNA sequence corresponding to a MIC2 gene and have used this probe to show that the MIC2X and MIC2Y loci are closely related, if not identical. Here we report the use of the cloned probe to confirm the localization of the MIC2X locus to the region Xpter-Xp22.32 (ref. 7) and demonstrate, for the first time, that the MIC2Y locus is located on the short arm of the Y chromosome in the distal region Ypter-Yp11.2. The MIC2 sequences and the sequences described in the accompanying papers by Cooke et al. and Simmler et al. are the first which have been shown to be shared by the sex chromosomes in the pairing region.