SV40 T antigen induced chromosomal changes reflect a process that is both clastogenic and aneuploidogenic and is ongoing throughout neoplastic progression of human fibroblasts.

In human fibroblasts, the expression of SV40 large T antigen is known to cause a variety of chromosomal aberrations and especially dicentric chromosomes. In some cases, the later aberrations have been reported to be reversible telomeric associations. We report here aberration and chromosome number studies of twenty-nine T antigen positive lineages, studied from their initiation by transfection of T antigen sequences into human diploid fibroblasts, until crisis or immortalization occurred or, in some cases until the lines became tumorigenic in nude mice. The data show that T antigen consistently produced chromosomal instability of both number and structure by an active process that began before transformation indicators were positive and continued throughout neoplastic progression. The most frequently observed aberrations were dicentric chromosomes, which were shown to be true dicentrics by examination by in situ hybridization with telomeric sequences. These data are consistent with the hypothesis that T antigen causes human fibroblasts to become neoplastically transformed by successive rounds of chromosomal mutation and lineage evolution.