When one cell becomes two, it must divide its chromosomes equally. To accomplish this feat, each chromosome comes equipped with a centromere. As a chromosome duplicates, the centromeres connect the old and new copies in an X shape. This union provides the mitotic spindle a place to latch onto so that it can tug the two chromosomes apart during cell division. Without centromeres, cells would fail to evenly separate their chromosomes. This could lead to aneuploidy conditions, such as Down syndrome, in which people are born with an unbalanced set of chromosomes.
Six years ago, when Glennis Logsdon was a graduate student, everyone assumed that centromeres had conserved sequences and structures given their essential role in divvying up genetic material. “We had one consensus sequence that we used for all centromeres, and we thought, ‘this is all we need to know,’” said Logsdon, a geneticist at the University of Pennsylvania. Now, in a paper published in Nature, Logsdon and her colleagues reported that centromeres differ greatly between people. Their findings could allow researchers to explore which centromere characteristics predispose humans to aneuploidy.
One reason scientists remained unaware of the rich diversity of centromeres was because of how tough they are to sequence. “In fact, most people just throw it out because it’s the only part of the genome you couldn’t touch,” said Yamini Dalal, a molecular biologist at the National Institutes of Health (NIH) who was not involved with the study. Normally, researchers decode a chromosome by sequencing short segments and piecing them into a single string at points where their sequences overlap, just as someone completing a jigsaw puzzle might use objects in the image to guide them. Centromeres, however, are mostly made up of repeating sequences. Just as one might struggle to solve a jigsaw puzzle of a recurring pattern, scientists fail to string together short reads collected from the chromosome’s repetitive core.
By Kamal Nahas, PhD
Article can be accessed on: The Scientist