Dopamine neurons in the adult brain typically do not undergo mitosis, the process of cell division. But in patients with Parkinson's disease, neurons are inappropriately prompted to initiate a cell-division process, say neurologist Günter U. Höglinger of Philipps University, Marburg, Germany, and colleagues (Proc. Natl. Acad. Sci. USA, DOI: 10.1073/pnas.0611671104). Paradoxically, cells that start down the pathway to cell division also become more vulnerable to apoptosis, or controlled cell death. Activating the division pathway therefore contributes to the neuronal death seen in Parkinson's patients, the researchers conclude. In postmortem human brain tissue, they found that neurons had duplicated their DNA. The cells had also expressed regulatory proteins that participate in mitosis, including E2F-1 transcription factor. The researchers obtained similar results in a study of Parkinson's disease in mice. In addition, mice that were deficient in E2F-1 were significantly more resistant to neuronal cell death. The researchers suggest that drugs that reduce the activity of such cell-division regulators might be effective in slowing or halting the neurodegeneration of Parkinson's disease.