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Butterfly wing patterns emerge from ancient 'junk' DNA

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Butterfly wing patterns have a basic blueprint, manipulated by noncoding regulatory DNA, to create the diversity of wings seen in different species, according to new research.

The study, titled “Deep cis regulatory homology of the butterfly wing pattern groundplan,” published as the cover letter in the October 21 issue of Science, explains how the DNA involved in genes—the so-called ‘junk’ DNA or non-coding regulatory DNA. DNA – while harboring a fundamental blueprint that has been preserved for tens of millions of years, also allows wing patterns to evolve extremely quickly.

Gulf fritillar butterfly – Agaulis vanilla.

Research supports the idea that it is an ancient color pattern floor plan. it is already encoded in the genome, and this non-coding regulatory DNA works like switches to open some patterns and close others.

Ph.D. “We want to know how the same gene can create these very different looking butterflies,” said Anyi Mazo-Vargas. ’20, first author of the study and a former graduate student in senior author Robert Reed’s lab, professor of ecology and evolutionary biology in the School of Agriculture and Life Sciences. Mazo-Vargas is currently a postdoctoral fellow at George Washington University.

“We see that there is a very conserved set of keys. [non-coding DNA] It works and is activated in different positions and drives the gene,” Mazo-Vargas said.

previous job In Reed’s lab, he uncovered key color pattern genes: one (WntA) controls the stripes, while the other (Optix) controls the color and iridescence in butterfly wings. When the researchers disabled the Optix gene, the wings appeared black, and the stripe patterns disappeared when the WntA gene was deleted.

This study focused on the effect of noncoding DNA on the WntA gene. Specifically, the researchers conducted experiments on 46 of these noncoding elements in five species of nymphal butterflies, the largest butterfly family.

In order for these non-coding regulatory elements to control genes, tightly coiled DNA coils become coil-less; this is a sign that a regulatory element is interacting with a gene to activate it or in some cases turn it off.

In the study, the researchers used a technology called ATAC-seq to identify regions in the genome where this unraveling occurred. Mazo-Vargas compared ATAC-seq profiles from the wings of five butterfly species to identify genetic regions involved in wing pattern development. They were surprised to find that so many regulatory regions are shared between so many different butterfly species.

Mazo-Vargas and colleagues then used CRISPR-Cas gene editing technology to deactivate 46 regulatory elements one at a time to see the effects on wing patterns when each of these noncoding DNA sequences is broken. When deleted, each non-coding item changed one aspect of the butterflies’ wing patterns.

Researchers in four species – Junonia coenia (buckeye), Vanessa cardui (painted female), Heliconius himera and Agaulis vanillae (bay fritillary) – each of these noncoding elements had similar functions with respect to the WntA gene, proving that they are ancient and conserved, possibly descending from a distant common ancestor.

They also discovered that D. plexippus (the monarch) used different regulatory elements from the other four species to control the WntA gene, perhaps losing some of its genetic information throughout its history and having to reinvent its own regulatory system to develop its own unique coloration. patterns.

“We’re starting to gradually understand that most of evolution happens because of mutations in these noncoding regions,” Reed said. “What I hope is that this article is a case study that demonstrates how people can use this combination of ATAC-seq and CRISPR to start interrogating these interesting sites in their own working systems, whether they study birds, flies or worms.”

The study was funded by the National Science Foundation (NSF).

“This research is a breakthrough for our understanding of the genetic control of complex traits, not just in butterflies,” said NSF program director Theodore Morgan. “The study not only showed how the instructions for butterfly color patterns were deeply conserved throughout evolutionary history, but also uncovered new evidence of how segments of regulatory DNA positively and negatively affect traits such as color and shape.”