Cytologic characterization of two distinct alpha satellite DNA domains on human chromosome 7, using double-labeling hybridizations in fluorescence and electron microscopy on a melanoma cell line

The most prominent class of centromeric DNA sequences belongs to the alpha satellite family of tandemly repeated DNA. The human chromosome 7 has been shown to contain two distinct alpha satellite arrays: D7Z1 and D7Z2, separated by 1 Mb. The order of these arrays was analyzed in normal blood cells and in the melanoma cell line IPC182 with two approaches using in situ hybridization: (1) Relative mapping on high-resolution chromosomes in fluorescence and electron microscopy (EM); and (2) simultaneous visualization of the two sequences using fluorochromes of different colors or gold particles of different sizes. The location within the centromeric area of chromosome 7, on the side of the short arm for D7Z2 and near the long arm for D7Z1 is confirmed. In addition, the hybridization signal of D7Z2 is confined to two small areas of the centromeric region in external positions, whereas the D7Z1 signal covers the entire width of the primary constriction. In situ hybridization with D7Z1 and D7Z2, performed on the melanoma cell line IPC 182, allowed characterization of two isochromosomes, i(7)(q10) and idic(7)(q11), as well as the der(7)t(7;12) observed in this cell line. The three-derived chromosomes appeared to result from different breakpoints, but only D7Z1 was conserved in all cases, suggesting the importance of this sequence for the centromeric function.