Gene editing can make fruit flies into ‘monarch flies’

Gene-edited fruit flies have gained some of monarch butterflies’ superpowers — specifically, the ability to digest milkweed toxins and become poisonous to predators.

Making just three genetic changes turned regular fruit flies into “monarch flies,” able to withstand plant toxins and store the chemicals as the flies transformed from maggots to adults, researchers report October 2 in Nature.

Researchers previously had suspected that three amino acid changes in a protein called the sodium pump alpha subunit, or ATPalpha, were involved in making butterflies insensitive to chemicals known as cardiac glycosides, which are found in milkweed and some other plants. The sodium pump is part of a cellular system that moves charged sodium and potassium atoms in and out of cells. But it still was possible that the changes were just coincidental.  

So evolutionary biologist Noah Whiteman of the University of California, Berkeley and colleagues used the gene editor CRISPR/Cas9 to alter the sodium pumps of fruit flies and retrace the evolutionary steps that resulted eventually in monarchs becoming resistant to the chemicals. Monarchs store some of the chemicals in their bodies, making them poisonous and unpalatable to predators.

Changing amino acids one at a time, the researchers discovered that all three are needed to produce fruit flies that, from the egg stage through adulthood, can survive exposure to the chemicals.

Milkweed tolerance has its price, though. Monarch flies became temporarily paralyzed when the vial they were contained in was banged on a table, an indication that the flies’ nervous systems were less able to handle stress. That cost may be worth it for monarch butterflies because the benefit of being noxious to predators is so much more valuable, Whiteman says.