Two newly published complimentary studies have utilized CRISPR genome editing technology to explore how specific genes affect wing pattern variation in butterflies. By selectively knocking out single genes and observing the effects, scientists have uncovered a key insight into how broad biodiversity can evolve.

The studies focused on two genes previously identified as being key in butterfly wing pattern development. Called WntA and optix the researchers have described these as "painting genes" and across several experiments they observed what happens in different butterfly species when each gene is selectively switched off.

A team at George Washington University examined the WntA gene and discovered that the gene had significantly different patterning effects across various butterfly species. In some species silencing the gene affected the development of stripe-like patterns, while in other species the gene controlled the boundaries between different color fields.

More generally, the gene could be seen to direct the borders of the patterns in each individual butterfly species. Speaking to Nature, one of the lead authors of the study Arnaud Martin explains, "It's laying the background to be filled in later. Like color by numbers or paint by numbers. It's making the outlines."

The second study, from Cornell University, focused on the optix gene, and after knocking it out in four species using CRISPR technology researchers found it to be fundamentally connected to wing coloration. Silencing the gene resulted in patterns remaining the same but all pigmented coloration disappeared, leaving the butterfly wings black and grey.

One of the stranger results noticed when researchers altered the optix gene was the appearance of a blue iridescence in some species. This stark blue that resulted seemed to be related not to an actual pigment, but to a deeper structural coloration resulting from the gene silencing.

One of the fundamental insights these dual studies reveal is how closely-related species can evolve a hugely diverse variety of effects that are controlled by the activity of single genes.

"Every single experiment has yielded unexpected results, and it's quite a eureka moment to have a new butterfly coming out of its cocoon and revealing the surprising effects of CRISPR," says Martin. "The mutations have had very specific effects."

This recent research seems simple enough, but its simplicity is deceptive. These kinds of studies could not have been achieved just a few short years ago. The breakthrough in CRISPR gene editing now allows scientists to explicitly target genes and identify their effects. This butterfly research demonstrates how single genes can evolve to direct similar functions, but with increasing levels of novelty.

The next big question for this research is to understand how these genes exert their patterning and coloring activity – and can that activity be rewired or customized?

The WntA gene study was published in PNAS, while the Optix gene study was published in PNAS.

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