The effect of in vitro distamycin A exposure on metaphase chromosome structure.

Abstract

Distamycin A specifically binds to AT-clusters in DNA. In vitro exposure of cattle lymphoid cells to distamycin A induced a dose dependent modification of chromosome morphology: 24 h distamycin A exposure partially inhibited chromosome contraction. This effect was quantitated by length measurements of the X-chromosome from randomly selected metaphases. The average length of the X-chromo-some was significantly increased compared to control cultures. However, the centromeric region in chromosomes from distamycin A treated cultures always appeared totally contracted and darkly stained even in metaphases with slightly contracted chromosomes. Length measurements of chromosome no. 1 from human lymphoid cells also showed that in vitro exposure to distamycin A increased the average chromosome length significantly. But in these cells distamycin A induced a slight chromosome segmentation never observed in metaphases from exposed cattle lymphoid cells. In vitro exposure of other cell lines (Chinese hamster and Murine cells) to distamycin A induced both AT-bands at specific regions and a general elongation of chromosomes. This indicates either that the cattle karyotype does not possess AT-rich clusters as those found with the present technique in mouse, Chinese hamster, and to some degree in human chromosomes, or that the protein component of chromosomes responds differently to distamycin A exposure in different species. The finding of condensed centromeric regions after distamycin A treatment of cattle lymphoid cells is in agreement with the suggestion put forward by others that these areas are GC-rich.