CHROMOSOMAL INSTABILITY AND TELOMERE LENGTH VARIATIONS DURING THE LIFE-SPAN OF HUMAN FIBROBLAST CLONES

Growth characteristics, karyotype changes, and telomere length variati ons were analyzed during the life span of 12 anchorage-independent clo nes isolated from a xeroderma pigmentosum fibroblast strain. After an initial period of comparable active growth, all the clones showed a de cline in the growth rate and finally entered a phase of replicative se nescence; however, the number of population doublings and the time req uired to enter senescence varied among the clones. Repeated cytogeneti c analyses during culture propagation showed the appearance of chromos ome anomalies, mainly telomeric association (tas) and unbalanced trans locations. In all the clones the percentage of abnormal mitoses increa sed with culture passage, but reached different levels (from less than 10% to about 100%). This finding indicates that the replicative block may be associated with differently altered cytogenetic patterns. Spec ific chromosome arms (5p, 16q, 19q, and 20q) were preferentially invol ved in tas, suggesting that alterations in chromosome ends may occur w hich predispose to fusion. In some clones it was possible to demonstra te the origin of marker chromosomes from the evolution of tas. Telomer e length analysis by Southern blotting on DNA samples prepared from 7 clones and from the parental cell lines showed that the terminal restr iction fragment (TRF) profiles were homogeneous in senescent parental cells and in the clones during the last part of their life in culture, regardless of the degree of karyotype abnormalities. The homogeneity of the TRF profiles supports the hypothesis of a critical telomere len gth at senescence. (C) 1997 Academic Press.