Localization of a mouse centromeric DNA repeat in interphase nuclei

The position of a mouse DNA repeat located near the centromere of mouse chromosomes X, 11, 13, and 17 was examined in interphase nuclei of bone marrow and fibroblast cells by in situ hybridization of 3 H‐ or biotin‐labeled DNA probe 70‐38. In most laboratory mouse strains this probe recognizes a single repeat cluster ( DXWas70 ) close to the centromere of the mouse X chromosome. In a few mouse strains, a second locus ( D11Was70, D13Was70, or D17Was70 , depending on the mouse strain) is located near the centromere of an autosome. In interphase nuclei from mouse strains with the X‐linked locus only, two distinct sites of hybridization were found in female mice and one in male mice. These two sites remained separated during thedifferent phases of the cell cycle (G1, early S, late S, and G2) as demonstrated by in situ hybridization of the probe to flow‐sorted nuclei. In interphase nuclei from mouse strains with both the X‐linked locus and an autosomal locus, four distinct sites of hybridization were found in female mice and three in male mice. Further analysis of loci DXWas70 and D17Was70 showed that these loci were often located in the outer region of nuclei from bone marrow and fibroblast cells.