Characterization of the Xp21-23 region in the wood lemming, a region involved in XY sex reversal.

The wood lemming (Myopus schisticolor) harbors two types of X chromosome, a normal X and a variant X, designated X*. The X* chromosome contains a mutation that causes XY sex reversal. We have previously demonstrated that the Xp21-23 region is deleted from X* and is associated with XY sex reversal. To further analyze the deleted region, we have constructed and characterized seven X chromosome- and region-specific recombinant DNA libraries. Further, we have screened mouse fetal gonad cDNA libraries with the microdissected Xp21-23 DNA as a probe in an attempt to identify homologous and expressed sequences from the deletion. Fourteen positive clones were isolated, and sequence analyses showed that ten of these contained identical sequences homologous to mouse gamma-satellite sequences. One of the remaining four was perfectly homologous to the mouse gene Ccth (chaperonin containing t-complex polypeptide 1, eta subunit). Southern blot indicated that the Ccth cDNA was located on the X chromosome, not deleted from the X* but closely linked to the deletion region. Although the role of the Ccth containing region in sex determination of the wood lemming requires additional studies, the isolation of the mouse Ccth gene by the deletion Xp21-23 probe could be important since this gene is mainly expressed in testis.