DNA’s absence makes us who we are

PENN STATE (US) — Missing segments of non-coding DNA, lost around 7 millions years ago, is what separates humans from chimpanzees and other animals.

“The technology now lets us look at the genomes of humans and other mammals and find sites where humans are unique,” says Philip Reno, assistant professor of anthropology, at Penn State.

“We can now correlate that information with specific human physical characteristics.”

DNA is composed of gene segments that code for proteins and non-coding segments that initiate and regulate the work of the coding segments. While the coding segments are important, the non-coding segments are the control mechanism of the organism.

Without changing the coding gene, increasing or decreasing the amount the gene is expressed can have significant influence on what the organism looks like and how it functions, Reno says.

Researchers first compared the human genome with that of chimpanzees and other mammals to locate areas of complete deletion in the human genome.

In the study, published in the journal Nature, the researchers write “We confirm 510 such deletions in humans, which fall almost exclusively in non-coding regions and are enriched near genes involved in steroid hormone signaling and neural function.”

The absence of one sequence next to the androgen receptor gene may have two consequences—the human loss of sensory whiskers and small keratinous spines on the penis.

“We often think of brain size and bipedalism as key characteristics of what makes us human,” Reno says, “but another difference is our sexual behavior.”

Chimpanzees have quick intercourse because the male chimpanzees are in a competition to see which male can fertilize the one receptive female. This situation occurs when many males copulate with one or a few females. Because they are tactile, the chimpanzee’s penile spines may enhance this rapid copulation.

Human ancestors, however, likely evolved to favor pair-bonding relationships and group living—the loss of penile spines may have prolonged intercourse to reinforce the pair bond where partners are beneficial for the successful raising of offspring.

“We now have the genetic sequence of three separate Neanderthal individuals,” Reno says. “Looking at these same non-coding areas, the Neanderthal genome lacks them as well.”

The absence of these non-coding locations in Neanderthal positions the DNA losses to around 7 million years ago, when human ancestors split from chimpanzees, and 800,000 years ago, when human ancestors split from Neanderthal.

Another area of missing non-coding DNA is near a tumor suppressor gene expressed in the brain.

“During development of mammals, a lot of neurons die in the formation of the brain,” Reno says. “The absence of this sequence down regulates expression of the gene that leads to cell death and leads to larger brains.”

Researchers from Stanford University contributed to the research, which was funded by the Howard Hughes Medical Institute, National Institutes of Health, and the Edward Mallinckrodt, Jr. Foundation.

More news from Penn State: http://live.psu.edu/