The X chromosome dosage compensation program during the development of cynomolgus monkeys

X chromosome activity in primates Mammalian X and Y sex chromosomes differ greatly in structure and gene content. Therefore, mechanisms are in place to ensure that there is balanced gene dosage between the X chromosome and autosomes and between the sexes. Quite a bit is known about dosage compensation in mice; however, the mechanism in primates, including humans, is less clear. Okamoto et al . reveal that in cynomolgus monkeys, the X chromosomes display repressive modifications and compacted structure before being chosen as active or inactive X chromosomes (see the Perspective by Heard and Rougeulle). This work elucidates the pathway, timing, and progression of X chromosome dosage compensation during monkey development, creating a foundation for elucidating this mechanism in other primates, including humans. —BAP