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 chromosome 13 in murine mammary tumors, we examined, in eight cloned established 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 pentasomy 13 in cells of diploid and tetraploid chromosome numbers, respectively, 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 poorly tumorigenic. The presence in the tumorigenic cells of trisomy or pentasomy 13 was not correlated with their growth in soft agar. Furthermore, other chromosomes manifested a wide range of copy numbers in the presence of trisomy or pentasomy 13, indicating that no chromosomes counteracted chromosome 13 to prevent the tumorigenicity. In light of the tumorigenic growth of the cells that maintain gene dosage of chromosome 13 at different ploidy levels, the possibility of the yeast G1 cyclin-like roles played by the gene(s) residing on chromosome 13 in murine mammary tumorigenesis is discussed.