Jumping Genes Add Diversity To Human Brain

Fred Gage's lab at the Salk Institute have just reported finding that human brain cells are hyper-variable because their DNA harbours variable numbers of small DNA elements called LINE-1 elements (formerly referred to as junk DNA) which copy and paste themselves in great numbers throughout the genome. In this way, brain cells resemble immune system cells which are also hyper-variable because they have to constantly counter the barrage of different antigens that bombard our bodies. They discovered that LINE-1 jumping occurred much more frequently in brain tissue than in tissue from heart and liver and that the LINE-1 promotor, the switch that turns LINE-1 elements on and off, is permanently switched to "on" in the human brain. In this sense, LINE-1 insertion follows a pattern of several other means of gene regulation where the brain differs markedly from other body organs, in keeping with its need to remain flexible in response to rapidly changing environmental conditions throughout life. What Gage's team have not yet looked at is whether LINE-1 insertion and self-copying is extremely different between chimps and humans. My guess, obviously, is that it will be.