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New research by UC Santa Barbara’s Kenneth S. Kosik, Harriman Professor of Neuroscience, reveals some very unique evolutionary innovations in the primate brain.

In a study published online today in the journal Neuron, Kosik and colleagues describe the role of microRNAs – so named because they contain only 22 nucleotides – in a portion of the brain called the outer subventricular zone (OSVZ). These microRNAs belong to a special category of noncoding genes, which prevent the formation of proteins.

“It’s microRNAs that provide the wiring diagram, dictating which genes are turned on, when they’re turned on and where they’re turned on,” said Kosik, who is also the co-director of UCSB’s Neuroscience Research Institute and a professor in the Department of Molecular, Cellular and Developmental Biology. “There’s a core set with which all kinds of really complex things can be built, and these noncoding genes know how to put it together.”

The researchers were looking for these noncoding genes, Kosik continued, because as organisms become more complex through evolution, the number of these noncoding genes has greatly expanded. “But the coding genes – the ones that make proteins – have really not changed very much,” he said. “The action has been in this noncoding area and what that part of the genome is doing is controlling the genes.”

Many of the microRNAs that Kosik’s team found and subsequently sequenced are newly evolved in primates. The work showed that these tiny control elements were overrepresented in the OSVZ of the developing macaque brain tissues they analyzed. The tissue samples were provided by a lab at the Stem-cell and Brain Research Institute near Lyon, France, headed by research director and co-author Colette Dehay.

Study results indicate that the appearance of the OSVZ is very much associated with the invention of new microRNAs. “There might be some relationship – although we can’t prove it – between the invention of some of these new noncoding genes, microRNAs, and the appearance of a new structure, the OSVZ,” Kosik said. “Trying to connect an anatomical, morphological invention with genes is very difficult, but our work shows a possible molecular basis for the tools that were needed to build this novel structure.”