ROLE OF THE GENE ON TRISOMIC AND PENTASOMIC CHROMOSOME-13 IN MURINE MAMMARY TUMORIGENESIS

To study a possible role(s) played by the trisomy and pentasomy of chr omosome 13 in murine mammary tumors, we examined, in eight cloned esta blished cell lines derived from a single BALB/c mammary tumor induced by MTV, a correlation between the presence of trisomy or pentasomy 13 and transformation parameters and in vivo tumorigenicity in syngeneic mice. We found that cell lines with a higher incidence of trisomy or p entasomy 13 in cells of diploid and tetraploid chromosome numbers, res pectively, grew to a much higher cell density in flasks than did those with low incidence, and they formed tumors in syngeneic BALB/c mice, whereas those with a low incidence of trisomy or pentasomy 13 were poo rly tumorigenic. The presence in the tumorigenic cells of trisomy or p entasomy 13 was not correlated with their growth in soft agar. Further more, other chromosomes manifested a wide range of copy numbers in the presence of trisomy or pentasomy 13, indicating that no chromosomes c ounteracted chromosome 13 to prevent the tumorigenicity. In light of t he tumorigenic growth of the cells that maintain gene dosage of chromo some 13 at different ploidy levels, the possibility of the yeast G1 cy clin-like roles played by the gene(s) residing on chromosome 13 in mur ine mammary tumorigenesis is discussed.