A team of international researchers has discovered a surprising genetic mechanism that influences the vibrant and complex patterns on butterfly wings. From a study published in the Proceedings of the National Academy of Sciencesthe team, led by Luca Livraghi of George Washington University and the University of Cambridge, discovered that an RNA molecule, rather than a protein as previously thought, plays a crucial role in determining the distribution of black pigment on butterfly wings.
Exactly how butterflies are able to generate the vibrant patterns and colors on their wings has fascinated biologists for centuries. The genetic code in the cells of developing butterfly wings dictates the specific arrangement of color on the wing’s scales (the microscopic tiles that form wing patterns), similar to the arrangement of colored pixels to form a digital image. Cracking this code is fundamental to understanding how our own genes build our anatomy. In the lab, researchers can manipulate that code in butterflies with gene-editing tools and observe the effect on visible characteristics, such as the coloration of a wing.
Scientists have long known that protein-coding genes are crucial for these processes. These types of genes create proteins that can dictate when and where a specific shell should generate a particular pigment. When it comes to black pigments, researchers thought this process would be no different, initially implicating a protein-coding gene. However, the new research paints a different picture.
The team discovered a gene that produces an RNA molecule (not a protein) and controls where dark pigments are made during butterfly metamorphosis. Using the genome editing technique CRISPR, the researchers showed that when you delete the gene that produces the RNA molecule, butterflies completely lose their black-pigmented scales, demonstrating a clear link between RNA activity and the development of dark pigment.
“What we discovered was astonishing,” says Livraghi, a postdoctoral scientist at GW. “This RNA molecule directly influences where the black pigment appears on the wings, shaping the butterfly’s color patterns in a way we didn’t expect.”
The researchers further investigated how the RNA molecule functions during wing development. By examining its activity, they observed a perfect correlation between where the RNA is expressed and where black scales form.
“We were surprised that this gene is turned on where the black scales will eventually develop on the wing, with exquisite precision,” says Arnaud Martin, associate professor of biology at GW. “It’s really an evolutionary brush in this sense, and a creative brush, judging by its effects in different species.”
The researchers examined the newly discovered RNA in several other butterflies whose evolutionary histories diverged about 80 million years ago. They found that in each of these species, the RNA had evolved to control new placements in the patterns of dark pigments.
“The consistent result obtained from CRISPR mutants in different species actually shows that this RNA gene is not a recent invention, but an important ancestral mechanism to control wing pattern diversity,” said Riccardo Papa, professor of biology at the University of Puerto Rico. Rio Piedras.
“We and others have now looked at this genetic trait in many different butterfly species, and remarkably, we find that the same RNA is used again and again, from long-wing butterflies to monarchs and painted lady butterflies,” says Joe Hanly, a postdoctoral researcher. scientist and visiting researcher at GW. “It’s clearly a crucial gene for the evolution of wing patterns. I wonder what other, similar phenomena biologists might have missed because they didn’t pay attention to the dark matter of the genome.”
The findings not only challenge long-standing assumptions about genetic regulation, but also open new avenues to study how visible traits evolve in animals.
