Analysis ofLossofInactive XChromosomes inInterphase Cells

Summary Wehavedeveloped amethod that allows, forthefirst time, aspecific analysis oftheinactive X chromosome (Xi) ininterphase cells. Bycombining immunolabeling ofacetylated histone H4withspecific antisera andFISH withanX-chromosome centromere-specific DNA probe, micronucleated whole Xisinhumanfemale cells maybeidentified bytheir lack ofhistone H4acetylation. Asoneexample ofthepotential applications ofthis methodology ingenetic studies inhumans, anartifactfree X-chromosome aneuploidy detection inlymphocytes ofwomenofdifferent ages hasbeenperformed. Ourresults indicate that notonlytheXibutalso the active Xchromosome ispreferentially lost during aging, indicating that thehighfrequency ofsex-chromosome aneuploidy inhumanfemales cannot beexplained solely byalackofnegative selection ofXianeuploid cells. Further applications oftheproposed methodology in genetic studies arediscussed.