Gluey Clue to Chromosome Sorting

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Meiosis, the process of creating eggs and sperm, is still poorly understood despite its importance in sexual reproduction. Though most cells in the human body hold two sets of DNA-containing chromosomes, egg and sperm cells have only one set. Knowing how chromosomes sort themselves to ensure that each daughter cell gets an equal amount of DNA may help explain what goes wrong in chromosome mis-segregation, the leading cause of miscarriages and a major cause of birth defects like Down syndrome.

Molecular biologist Angelika Amon, Ph.D., of the Massachusetts Institute of Technology in Cambridge used yeast cells to perform a detailed study of meiosis.

Before a cell divides, protein complexes called cohesins hold chromosomes together in pairs. Amon discovered that during the first step of meiosis, when chromosomes line up and exchange small pieces of DNA to create new genetic combinations, cohesins rip themselves from the tips of the chromosomes. She then found that later in meiosis, cohesins play an additional role at the spot where the chromosomes join their middle portions, called the centromere. There, Amon discovered, cohesins acquire a chemical tag that marks them for destruction.

Studying how the regulation of cohesins helps chromosomes separate, and tracking changes that occur in this process over time, may provide insights into whether cohesins play a role in the increased likelihood of chromosome number abnormalities in children born to older women.