Monarch butterflies (Danaus plexippus) and some other insects deter predators such as frogs or birds through eating milkweed, which contains the toxin ouabain. Resistance to ouabain has evolved many times, but it’s not found in all insects. A team of researchers led by Noah Whiteman at the University of California, Berkeley, edited the genome of fruit flies (Drosophila melanogaster) to allow them to safely eat the plant too. The findings were published in Nature yesterday (October 2).
The team made multiple CRISPR-Cas9 edits to the Atpα gene, which codes for a sodium pump subunit. Normally, ouabain works by blocking this pump, throwing off potassium and sodium gradients in the cell and overstimulating the heart in some animals. (If humans ingest too much ouabain, they can die from cardiac arrest.) Monarchs and other insects with particular variants in the gene are unaffected.
The researchers showed that making different edits conferred different levels of resistance in the flies. One genotype with three Atpα edits was 1,000 times less sensitive to milkweed than wildtype flies’ gene. This experiment is the first time evolutionary mutations leading to a new environmental adaptation have been recreated in a multicellular organism, according to a press release sent to The Scientist.
“All we did was change three sites, and we made these superflies,” says Whiteman in the press release. “But to me, the most amazing thing is that we were able to test evolutionary hypotheses in a way that has never been possible outside of cell lines.”
M. Karageorgi et al., “Genome editing retraces the evolution of toxin resistance in the monarch butterfly,” doi:10.1038/s41586-019-1610-8, Nature, 2019.
Emily Makowski is an intern at The Scientist. Email her at firstname.lastname@example.org.