Dynamic repositioning of genes in the nucleus of lymphocytes preparing forcell division

We show that several transcriptionally inactive genes localize to centromer ic heterochromatin in the nucleus of cycling but not quiescent (noncycling) primary B lymphocytes. In quiescent cells, centromeric repositioning of in active loci was induced after mitogenic stimulation. A dynamic repositionin g of selected genes was also observed in developing T cells. Rag and TdT lo ci were shown to relocate to centromeric domains following heritable gene s ilencing in primary CD4(+)8(+) thymocytes, but not in a phenotypically simi lar cell line in which silencing occurred but was not heritable. Collective ly, these data indicate that the spatial organization of genes in cycling a nd noncycling lymphocytes is different and that locus repositioning may be a feature of heritable gene silencing.