Debate ends: everyone was right

Centromeres, specialized chromosomal structures, which sit at the cross point of the “X” used to represent duplicated chromosomes, link those duplicated strands when cells are poised to divide. As division starts, a complex cellular machine drags each chromosome to opposite poles of the cell by grabbing onto centromeres and pulling each arm of the “X” into what will become a daughter cell. Researchers had known that a nucleosome—a short coil of DNA twisted around a core of proteins—forms at each centromere but the details had been murky.

An interdisciplinary Stowers team led by Associate Investigator Jennifer Gerton, PhD, developed an innovative method to count the number of fluorescent molecules in a cluster and then applied the novel approach to settle a debate rampant among cell biologists—namely, how DNA twists into the centromere. “Understanding centromeres is critical because of the role they play in maintaining genomic integrity,” says Gerton. “Losing a chromosome is catastrophic for any cell. And if it happens in sperm or egg cells, it is associated with conditions like Down syndrome.”

Gerton, whose lab uses both the yeast Saccharomyces cerevisiae and mammalian cells to study the mechanics of cell division, explains that, previously, people had proposed at least six different centromere structures. “What we found is that centromeric nucleosomes change their structure during cell division,” she says. ”That explained why people had observed different structures. They had likely been looking at different phases of the cell cycle.”

The study was published in the July 20, 2012, issue of Cell.