Doublecortin (DCX) is a microtubule-associated protein expressed almost exclusively in immature neurons. Neuronal precursors begin to express DCX shortly after exiting the cell cycle, and continue to express DCX for 2-3 weeks as the cells mature into neurons. Downregulation of DCX begins after 2 weeks, and occurs at the same time that these cells begin to express, a marker for mature neurons. Due to the nearly exclusive expression of DCX in developing neurons, this protein has been used increasingly as a marker for neurogenesis. Indeed, the levels of DCX expression increase in response to exercise, which occurs in parallel with increased BrdU labelling, currently a gold standard in measuring neurogenesis.