One of the two X chromosomes in female mammalian cells is subject to 
inactivation (XCI) initiated by the Xist gene. In this study, we examined in 
rodents (voles and rat) the conservation of the microsatellite region DXPas34, 
the Tsix gene (antisense counterpart of Xist), and enhancer Xite that have been 
shown to flank Xist and regulate XCI in mouse. We have found that mouse regions 
of the Tsix gene major promoter and minisatellite repeat DXPas34 are conserved 
among rodents. We have also shown that in voles and rat the region homologous to 
the mouse Tsix major promoter, initiates antisense to Xist transcription and 
terminates around the Xist gene start site as is observed with mouse Tsix. A 
conservation of Tsix expression pattern in voles, rat and mice suggests a 
crucial role of the antisense transcription in regulation of Xist and XIC in 
rodents. Most surprisingly, we have found that voles lack the regions homologous 
to the regulatory element Xite, which is instead replaced with the Slc7a3 gene 
that is unassociated with the X-inactivation centre in any other eutherians 
studied. Furthermore, we have not identified any transcription that could have 
the same functions as murine Xite in voles. Overall, our data show that not all 
the functional elements surrounding Xist in mice are well conserved even within 
rodents, thereby suggesting that the regulation of XCI may be at least partially 
taxon-specific.