Ellie Teng ‘21

Monarch butterflies can consume toxic milkweed plants due to mutations in their genome. Both the caterpillar and the butterfly store the consumed toxins to defend against predators. Eating a monarch would cause a predator to regurgitate. Researchers at the University of California, Berkeley have utilized the CRISPR-Cas9 tool to genetically modified harmless fruit flies (Drosophila melanogaster) to have the ability to eat and store milkweed toxins. 

Three amino acid sites on the alpha subunit of the sodium/potassium pump (Na+/K+-ATPase)  (ATPα) are associated with cardiac glycoside, the toxin produced by milkweed. CRISPR-Cas9 editing was performed on the native ATPα gene. These edits were homologous to the mutations that would allow toxin consumption and sequestration in monarch butterflies. CRISPR-Cas9 was coupled with homology-directed repair (HDR) to generate Drosophila specimens carrying the mutations at sites 111, 119 and 122. Additionally, the mutations had to occur in the right sequence to ensure that the flies would survive the three separate mutations. Insects with only one amino acid change in the ATPα gene were most successful at resisting the poisons, but they also had their health effects repaired due to the third site mutation.

However, fruit flies with knock-in mutations took longer to recover from upsets, such as being shaken during tests known as “bang” sensitivity tests. The results from this experiment may allow researchers to better understand the evolution and convergence of monarch butterflies and apply this knowledge to other species. 

References

1. M. Karageorgi, et al., Genome editing retraces the evolution of toxin resistance in the monarch butterfly. Nature 574, 409-412 (2019). doi: 10.1038/s41586-019-1610-8
2. Image retrieved from: https://pixnio.com/fauna-animals/insects-and-bugs/butterflies-and-moths-pictures/monarch-butterfly/macro-yellowish-big-monarch-butterfly-flower