Patterns of butterfly wings emerge from ancient 'junk' DNA |  Cornell Chronicle

Patterns of butterfly wings emerge from ancient ‘junk’ DNA | Cornell Chronicle

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

The study, “Deep cis-regulatory homology of the butterfly wing pattern ground plan,” published on the cover of the October 21 issue of Science, explains how the DNA that lies between genes – called “junk” or non-regulatory DNA encoding DNA – accommodates a basic blueprint conserved over tens to hundreds of millions of years while at the same time allowing wing patterns to evolve extremely rapidly.

Gulf Fritillary Butterfly – Agraulis vanillae.

Research supports the idea that an ancient color pattern ground plane is already encoded in the genome and that non-coding regulatory DNA works like switches to turn certain patterns on and off others.

“We are interested in how the same gene can construct these very different-looking butterflies,” said Anyi Mazo-Vargas, Ph.D. lead author, Robert Reed, professor of ecology and evolutionary biology at the College of Agriculture and Life Sciences. Mazo-Vargas is currently a postdoctoral fellow at George Washington University.

“We see that there is a very conserved group of switches [non-coding DNA] that work in different positions and are turned on and drive the gene,” Mazo-Vargas said.

Previous work in Reed’s lab discovered key color pattern genes: one (WntA) that controls striping and another (Optix) that controls the color and iridescence of butterfly wings. When the researchers turned off the Optix gene, the wings appeared black, and when the WntA gene was deleted, the stripe patterns disappeared.

This study focused on the effect of non-coding DNA on the WntA gene. Specifically, the researchers conducted experiments on 46 of these non-coding elements in five species of nymphalid butterflies, which make up the largest family of butterflies.

For these non-coding regulatory elements to control genes, tightly coiled DNA coils unwind, a sign that a regulatory element is interacting with a gene to turn it on or, in some cases, turn it off.

In the study, the researchers used a technology called ATAC-seq to identify regions of the genome where this disentangling occurs. Mazo-Vargas compared the ATAC-seq profiles of the wings of five species of butterflies, in order to identify the genetic regions involved in the development of the wing pattern. They were surprised to find that a large number of regulatory regions were shared by very different butterfly species.

Mazo-Vargas and his colleagues then used CRISPR-Cas gene-editing technology to turn off 46 regulatory elements one by one, to see the effects on wing patterns when each of these non-coding DNA sequences was broken. When removed, each non-coding element changed some aspect of the butterfly wing patterns.

The researchers found that in four of the species – Junonia coenia (buckeye), Vanessa cardui (painted lady), Heliconius himera and Agraulis vanillae (Gulf fritillary) – each of these non-coding elements had similar functions vis-à-vis the WntA gene, proving that they were ancient and conserved, probably descended from a distant common ancestor.

They also found that D. plexippus (monarch) used different regulatory elements from the other four species to control its WntA gene, possibly because it had lost some of its genetic information during its history and had to reinvent its own. regulation system to develop its unique color. patterns.

“We gradually realized that most evolution happens because of mutations in these non-coding regions,” Reed said. “What I hope is that this article will be a case study that shows how people can use this combination of ATAC-seq and CRISPR to start interrogating these regions of interest in their own study systems, whether they are working on 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, and not just in butterflies,” said Theodore Morgan, program director at NSF. “Not only did the study show how the instructions for butterfly color patterns are deeply conserved through evolutionary history, but it also revealed new evidence for how regulatory DNA segments influence positively and negatively of traits such as color and shape.”

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