Determination of chromosomal area of double minute chromosomes and a homogeneously staining region in HL-60 human leukemia cells by the use of a color image analyzer

The surface area of chromosomes was measured in two sublines of HL-60 human leukemia cells using a color image analyzer. One subline, HL-60 (dmin), had double minute chromosomes (dmin) and the other line, HL-60 (HSR), showed an abnormal chromosome #8 (8q+) which contained a homogeneously staining region (HSR) within the long arm at band q24. Dmin were not seen in the latter cells. The area of individual chromosomes analyzed from metaphase plates of Giemsa-stained photographic prints proved to be reasonably accurate and reproducible. Moreover, the relative area of each chromosome correlated well both with the relative length of corresponding chromosomes and the relative DNA content. The results indicate that the mean area of a single dmin represents 0.16% of the total genomic area of HL-60 (dmin) cells. The average number of dmin per cell was 8.14, and the total area of all dmin in a representative cell was 1.32% of the entire genome. The 8q+ chromosome had 1.46 times the area of the normal homologous chromosome #8, and the HSR itself had 1.30% of the total chromosomal area of HL-60 (HSR) cells. Thus, perhaps coincidentally, the relative amount of DNA in the HSR in an HL-60 (HSR) cell was similar to the total found in multiple dmin in HL-60 (dmin) cells.