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Brain gain

Brain gain

作者:隆貌沸  时间:2019-03-08 07:16:06  人气:

By Philip Cohen TO MAKE a brain, you may need to break a few chromosomes. Cutting and pasting DNA is essential for the development of neurons, a new report suggests, and this might account for some of the brain’s unique abilities. Enzymes that snip chromosomes into pieces and then glue them back together play a part in the development of immune cells. This ability to reshuffle genetic information gives these cells the potential to make billions of different antibodies and immune cells to fight off an ever-changing array of pathogens. But nobody suspected that these cut-and-paste tools played a role in the development of any other tissue. Fred Alt of the Harvard University Medical School in Boston and his colleagues were studying two of these tools—the genes XRCC4 and Lig IV, which code for proteins that rejoin the severed ends of immune cell chromosomes. As expected, they found that mice lacking either gene had crippled immune systems. But the animals had another problem: they died before birth. “The big question was what was killing them,” says Alt. Closer examination revealed that most of their neurons died just after they formed (Cell, vol 95, p 891). This may mean that as neurons develop, their chromosomes have to be rejoined, presumably having first been snipped apart. “If that is true, this will open up a new field of brain biology,” says biologist David Schatz of Yale University in Connecticut. Alt suggests that cutting and pasting could change gene expression, committing a neuron to a specific fate. Schatz speculates that neurons could even shuffle specific genes to somehow store memories directly in the genetic code. But Alt admits there are more prosaic explanations. The DNA of embryonic neurons might be particularly prone to random breaks, and rely on XRCC4 and Lig IV to heal those breaks. To sort that out,