Scientists edit butterfly wing spots and stripes

Scientists have knocked-out a single gene in butterflies that influences the exuberant diversity of their wing patterns in nature.
Researchers at Smithsonian Tropical Research Institute (STRI) in Panama rewired the WntA gene in the DNA of seven different butterfly species.
"Butterfly wing patterns are amazing, a true evolutionary novelty, highly diverse and strongly shaped by natural and sexual selection," said Owen McMillan, staff scientist at STRI.
"By genetically engineering individuals from different species, we are quickly coming to grips with how this diversity is generated," said McMillan, co-author of the study published in the journal Proceedings of the National Academy of Sciences.

The WntA protein is a very conserved signalling molecule. The WntA gene is part of a small family of genes influencing body plans and other patterns during insect development.
It codes for a secreted protein molecule that seems to act as a diffusible signal, a so-called morphogen, that establishes the positions of specialised cell types within a tissue.

"The instructions for colouring the wing are written in the genetic code. By deleting some of the instructions, we can infer which part says 'paint the number two's red' or 'paint the number one's black," said McMillan.
"Of course, it is a lot more complicated than this because what is actually changing are networks of genes that have a cascading effect on pattern and colour," he said.

The researchers injected butterfly eggs with an RNA probe that attached to part of the genetic code, a gene called WntA, which they suspected played a role in the expression of colour.
"After knocking out the gene, we let the butterflies grow up and compared the wing patterns of the knockout mutants with the original wing patterns," said Richard Wallbank a STRI and Cambridge postdoctoral fellow.
Repeating the same procedure in seven different butterfly species and comparing the results, the team discovered unexpected ways in which WntA gene influences wing pattern.
"In Monarchs, for example, the gene is expressed with fine precision along the wing veins. In contrast, in Heliconius, a group known for vivid wing patterns, the gene is expressed in bold brush strokes from essentially the tip to the base of the wing," said McMillan.

"In butterflies, colour is a function of both pigment and the structural properties of the scales cells that cover the wing," he said.