Duplications of noncoding DNA could help explain human-primate split

Human-specific duplications are DNA strands of at least 1,000 base pairs that are repeated in humans but not primates or other animals. In order to identify genetic differences between humans and primates, scientists scan the human genome in search of HSDs.

In the latest study, scientists at the University of California, Davis, limited their search for HSDs to noncoding DNA -- segments that don't code for specific genes but play a role in the expression of specific genes.

"What's special about these regulatory elements is that they have the propensity to impact the expression of genes nearby on the same chromosome, as well as elsewhere in the genome," Megan Dennis, an assistant professor of biochemistry at UCD, said in a news release. "This means that one duplication could affect many genes, amplifying its impact."

Many of the first genome sequencing efforts ignored noncoding DNA. Some scientists controversially dubbed the code "junk DNA." However, newer research has shown noncoding DNA play an important role in gene expression.

Because 98 percent of noncoding DNA is identical, the segments are extremely difficult to parse. But by honing in on duplicating segments, researchers can increased the odds of identifying a relevant portion of noncoding DNA.

One of the newly identified duplicating segments is SRGAP2, which scientists believe enhances human-specific neurological traits like an enlarged prefrontal cortex and more efficient brain synapses.

When scientists genetically engineered lab mice to express SRGAP2C, the rodents developed a larger prefrontal cortex.

SRGAP2C is one of several duplicating segments researchers believe play a role in encouraging the neurological traits that separate humans from primates.

Dennis and her colleagues presented their latest research efforts to attendees of the annual meeting of the American Society of Human Genetics, held this week in Orlando, Fla.

Scientists believe further analysis of duplicating noncoding DNA segments could also reveal the genetic origins of certain diseases in humans -- specifically neurological disorders like autism, epilepsy and schizophrenia.

"Our results point to differences between humans and primates, and hint at what makes us unique as humans," Dennis said.