Biological arms races are commonplace in nature. Cheetahs, for example, have evolved a sleek body form that lends itself to rapid running, enabling them to feast upon similarly speedy gazelles, the fastest of which may evade predation. On the molecular level, immune cells produce proteins to conquer pathogens, which may in turn evolve mutations to evade detection.
Though less well known, other games of one-upmanship unfold within the genome. In a new study, biologists at the University of Pennsylvania show, for the first time, evidence of a two-sided genomic arms race involving stretches of repetitive DNA called satellites. “Opposing” the rapidly evolving satellites in the arms race are similarly fast-evolving proteins that bind those satellites.
While satellite DNA does not encode genes, it can contribute to essential biological functions, such as formation of molecular machines that process and maintain chromosomes. When satellite repeats are improperly regulated, impairments to these crucial processes can result. Such disruptions are hallmarks of cancer and infertility.
Using two closely related species of fruit flies, researchers probed this arms race by purposefully introducing a species mismatch, pitting, for example, one species’ satellite DNA against the other species’ satellite-binding protein. Severe impairments to fertility were a result, underscoring evolution’s delicate balance, even at the level of a single genome.
“We typically think of our genome as a cohesive community of elements that make or regulate proteins to build a fertile and viable individual,” says Mia Levine, an assistant professor of biology in Penn’s School of Arts & Sciences and the senior author on the work, published in Current Biology. “This evokes the idea of a collaboration between our genomic elements, and that’s largely true.
“But some of these elements, we think, actually harm us,” she says. “This disquieting idea suggests that there needs to be a mechanism to keep them in check.”
The researchers’ findings, likely to also be relevant in humans, suggest that when satellite DNA occasionally escapes the management of satellite-binding proteins, significant costs to fitness can occur, including impacts on molecular pathways required for fertility and perhaps even those relevant in the development of cancer.
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