In a study recently published in the Proceedings of the National Academy of Sciences, led by Luca Livraghi from the George Washington University and the University of Cambridge, it was revealed that an RNA molecule, not a protein as previously assumed, plays a crucial role in determining the distribution of black pigment on butterfly wings. This discovery challenges established beliefs and opens up new possibilities for understanding genetic mechanisms that drive the striking patterns on butterfly wings.
The intricate process by which butterflies produce their vivid patterns and colors has captivated biologists for centuries. The genetic code within the cells of developing butterfly wings dictates the precise arrangement of color on the wing’s scales – the microscopic tiles that form wing patterns – similar to the arrangement of colored pixels to create a digital image.
Deciphering this code is essential to understanding how our own genes construct our anatomy. In the lab, researchers can manipulate that code in butterflies using gene-editing tools to observe the effects on visible traits, such as wing coloration.
Scientists have long recognized the vital role of protein-coding genes in these processes. These genes generate proteins that can determine when and where a specific scale should produce a particular pigment. When it comes to black pigments, researchers initially pointed to a protein-coding gene. However, new research paints a different picture.
The research team discovered a specific gene that produces an RNA molecule, rather than a protein, influences the location of dark pigments in butterfly wings during metamorphosis. Using the powerful genome-editing tool CRISPR, the scientists showed that removing this RNA-producing gene caused butterflies to completely lose their black-pigmented scales, highlighting a direct connection between RNA activity and the development of dark pigmentation.
“What we found was astonishing,” said 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 hadn’t anticipated.”
Seeking to delve deeper into the workings of this RNA molecule during wing development, the researchers closely studied its activity and found a remarkable correlation between its expression and the formation of black scales.
“We were amazed that this gene is turned on where the black scales will eventually develop on the wing, with exquisite precision,” said Arnaud Martin, associate professor of biology at GW. “It is truly an evolutionary paintbrush in this sense, and a creative one, judging by its effects in several species.”
The research revealed that the recently unearthed RNA is responsible for orchestrating the distribution of dark pigments in multiple butterfly species that diverged roughly 80 million years ago.
“The consistent result obtained from CRISPR mutants in several species really demonstrate that this RNA gene is not a recent invention, but a key ancestral mechanism to control wing pattern diversity,” said Riccardo Papa, professor of biology at the University of Puerto Rico – Río Piedras.
“We and others have now looked at this genetic trait in many different butterfly species, and remarkably, we are finding that this same RNA is used again and again, from longwing butterflies to monarchs and painted lady butterflies,” said Joe Hanly, a postdoctoral scientist and visiting fellow at GW. “It’s clearly a crucial gene for the evolution of wing patterns. I wonder what other, similar phenomena biologists might have been missing because they weren’t paying attention to the dark matter of the genome.”
This discovery not only defies long-established beliefs about genetic control but also paves the way for a profound exploration of how observable traits emerge and evolve in the animal kingdom.
Journal reference:
- Luca Livraghi, Joseph J. Hanly, Elizabeth Evans, Charlotte J. Wright, Ling S. Loh, Anyi Mazo-Vargas, Kiana Kamrava, Alexander Carter, Eva S. M. van der Heijden, Robert D. Reed, Riccardo Papa, Chris D. Jiggins, and Arnaud Martin. A long noncoding RNA at the cortex locus controls adaptive coloration in butterflies. PNAS, 2024; DOI: 10.1073/pnas.2403326121