CRISPR For Fruitflies
Every year monarch butterflies migrate from the northern reaches of Canada to the Gulf Coast. Scientists are fascinated by several facets of this mysterious journey- from how it shapes monarch development to where, exactly, these astonishing flies end up. New research helps explain one aspect of the enigmatic trek—how the insects evolved the ability to turn themselves toxic, which keeps them from getting eaten en route.
During the caterpillar stage, monarchs feed on milkweed. That diet is sufficient even to kill most animals. The plants produce cardiac glycosides, which disable the sodium pumps that cells use to regulate salt levels. For species with heart, this can result in cardiac arrest.
But monarch butterflies never digest the toxins. Instead, they carry the cardiac glycosides inside their bodies, in a process called sequestration. Milkweed plants have evolved toxicity precisely so most insects won’t eat them. This gives them the benefit of survival—access to a food source without much competition. It also renders them toxic to potential predators.
Monarch butterflies handle milkweed better than the rest and giving fruit flies the same genetic resistance could help reveal why the butterflies can do so.
CRISPR For Fruitflies- The experiment
Researchers used the CRISPR
techniques to edit three mutations into a single fruit fly gene known to control the sodium pump. Two of the modifications, which prevent cardiac glycosides from binding to the pump. But those two mutations made the fruit flies far more prone to seizures. Adding a third, previously-unidentified mutation to the mix helped to compensate for the harmful impacts of the other two.The thrice-mutated “monarch flies” were as resistant to milkweed toxins as monarch butterflies, and 1000-times less sensitive to it than their wild counterparts.
They also carry the toxin with them from their larval stage to adulthood. It’s the first time scientists have used CRISPR to study evolution by actually recreating the development of a specific trait—in this case, toxin resistance.
The research demonstrates the way the three mutations work together to allow the monarch flies to eat otherwise-poisonous milkweed
CRISPR For Fruitflies- Planning for future
University of California biologist and study scientist Noah Whiteman says that this is also a cautionary tale about CRISPRing animals.
The fruit flies, even with three mutations, are susceptible to external motion: If you bang the test tube they’re flying in, they fall and take almost 2 minutes to get airborne again. Whiteman and his team of researchers are working on figuring out why that’s not true for monarch butterflies. According to scientists, the monarch butterflies may have off-target mutations. This means that CRISPR edited some as-yet-unidentified random genes along with the ones his team sought to tweak.
This study is a stark reminder that we’re a long way off from solving all our own species’ problems with genetic engineering.