DNA-CONTAINING CYTOPLASMIC BRIDGES IN A HUMAN BREAST-CANCER CELL-LINE, MX-1 - MORPHOLOGICAL MARKERS OF A HIGHLY MOBILE CELL-TYPE

We have used a CREST anti-centromere serum and a DNA-specific fluoresc ent dye to study the composition of extended cytoplasmic bridges betwe en interphase cells of a human carcinoma cell line, MX-1, grown on cov erslips. Under natural conditions, approximately 8% of the cells posse ssed cytoplasmic bridges up to GO mu m long. Elongated extensions from the cell surface were also observed and were interpreted as severed c ytoplasmic bridges. The bridges were extremely slender throughout most of their lengths and could not be properly resolved by phase-contrast microscopy. Staining with a DNA-specific fluorescent dye revealed, ho wever, the presence of a thin DNA thread. This finding strongly sugges ts that the bridges arise during mitosis through faults in chromosome segregation. The bridges persist and most probably elongate, when the cells separate from one another after completion of mitosis. Some brid ges showed also highly fluorescent DNA masses, which were detected by a CREST anti-centromere serum. Thus, a subset of the cytoplasmic bridg es contained centromeres. The DNA-containing bridges between carcinoma cells in culture signal continuous rearrangements of the karyotype at a relatively high rate. The presence of extended cytoplasmic bridges between the cells could be a morphological marker for highly mobile tu mor cell types and has, therefore, diagnostic value.