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Clue to Language Development

The human brain has different regions with different functions: vision in the occipital lobe, hearing in the temporal lobe. But how are these specialty regions formed? A study by HHMI Investigator Christopher Walsh at Boston Children’s Hospital shows that selective regulation of a particular gene may control brain development on a section-by-section basis. Their findings may be relevant to understanding human brain evolution.

In a study published February 14, 2014, in Science, Walsh and his colleagues looked at five people with abnormal folds near a deep furrow in the brain known as the Sylvian fissure, a region that includes the brain’s primary language center. As expected, the five subjects had impairments in cognition and language, yet none had mutations in the protein-coding regions of genes associated with brain function or formation.

All of them, however, were missing 15 nucleotide base pairs in a noncoding segment of their DNA. The mutations had inactivated a stretch of DNA that was promoting the expression of GPR56, a gene critical for normal brain fold development. “The mutation caused the gene to be deficient, but only in the parts of the brain that did not develop properly,” Walsh explains.

Interestingly, evolutionary studies have shown that, around 100 million years ago, placental mammals acquired some additional DNA in the very area where Walsh’s team discovered the inactivated element. Because those nucleotides determine whether or not GPR56 will create brain folds around the Sylvian fissure, and may even account for the language center’s existence, Walsh believes that it may have helped set the stage for humans to develop language.