Almost all tumors are aneuploid, and scientists have long suspected that the condition aids the renegade cells. Chromosome gain could provide extra copies of growth-promoting genes, and chromosome loss might jettison tumor suppressors. However, several studies, including work on cells from Down syndrome patients, suggest that aneuploidy inhibits cell proliferation.
To investigate aneuploidy's effects systematically, Torres and colleagues turned to mutant yeast that occasionally end up with spare chromosomes after mating. The researchers corralled cells that carried at least one extra copy of 13 of the yeast's 16 chromosomes. The fungi resembled cancer cells in their ravenous appetite for glucose.
But the yeast differed from cancer cells in a crucial way: they divided sluggishly. The reason for the slowdown was a tarry in G1. Although aneuploidy might be helpful in some circumstances, Amon says, cancer cells must get around the division limitation to reap the benefits. “What we're saying,” she explains, “is that cells have to evolve pathways to deal with the baggage that comes with aneuploidy.”