The Nature paper looks in depth at the region that has undergone the most change in the human lineage, which the researchers called HAR1 (for human accelerated region 1). Only two of the region's 118 bases changed in the 310 million years separating the evolutionary lineages of the chicken and the chimp. Incredibly, since the human lineage separated from that of the chimp, 18 of the 118 nucleotides have changed. This region "stood out," said Pollard.
But what does it do? To find out, Pollard began working with the wet lab, led by Sofie Salama. Haussler established the wet lab following his appointment as an HHMI investigator. After months of work, Salama and her lab mates determined that HAR1 is part of a larger DNA that is transcribed into RNA in the brain.
Then Salama got lucky. Pierre Vanderhaegen, a neuroscientist at the University of Brussels, was visiting Santa Cruz because he knew Salama's husband, who is also a neuroscientist. "I learned that Pierre was setting up to do in-situ hybridizations [at his lab in Brussels] to look at gene expression patterns in human embryonic brain samples," said Salama. "So I gave him a DNA probe from the HAR1 region and said, 'Try this.'"
A few months later Vanderhaegen e-mailed Salama with exciting news. He had discovered that RNA including the HAR1 region is first produced between the 7th and 9th weeks of gestation in human embryos. Furthermore, the RNA was produced by a Cajal-Retzius neuron, a particular type of cell that plays a critical role in creating the six layers of neurons in the human cortex.
Salama then determined that HAR1 actually lies in the region of overlap of two RNA genes that are transcribed in opposite directions along the DNA. Both genes appear to make RNAs that are not translated into proteins. The UC Santa Cruz
Source:Howard Hughes Medical Institute