The direct relevance of neurogenesis in the adult mammalian brain to neural function and plasticity, and potentially to some neurological diseases, including Alzheimer's desease, depression and neurodegenerative conditions, is becoming well-established. Therefore, the molecular mechanisms underlying the control of adult neurogenesis have major implications for neurobiology. We have identified an important and surprisingly simple mechanism that triggers adult neurogenesis. The mechanism links intriguingly between genomic coding and non-coding regions including LINE-1 retro-elements, a family of mobile DNA elements that might contribute to neuronal diversification in the adult brain.