When dividing to produce mammalian sex cells, cells coordinate how DNA breaks occur.

The cell-division process that forms these sex cells, which contain one set of chromosomes instead of the normal two, involves the swapping of bits of genetic material between matching pairs of chromosomes. This process can involve hundreds of breaks in the double-stranded DNA. A team led by Maria Jasin and Scott Keeney at the Memorial Sloan-Kettering Cancer Center in New York found that in male mice engineered to have reduced double-stranded breaks, chromosome pairs failed to exchange DNA properly. The resulting 'chromosome tangles' continued to accumulate breaks as cell division progressed, suggesting that a feedback mechanism stalls breaks as chromosomes successfully intermingle. The cells of the engineered mice eventually halted division, and the mice were left sterile.

Genes Dev. 27, 873–886 (2013)