Normally harmless fruit flies have been gene edited using CRISPR, with genes from the monarch butterfly, to make them poisonous to both their predators and humans.

The monarch caterpillars feed on the toxic plant milkweed. When the caterpillars metamorphosise into butterfly’s they retain the milkweed toxins in their tissues, which make them poisonous to potential predators.

The milkweed toxin binds to the sodium-potassium pumps in cells, to disrupt the transmissions of the nervous system. Monarch butterflies have three specific genetic mutations that change the shape of their sodium-potassium pumps to prevent the milkweed toxin from binding.

The researchers were interested in investigating the evolutionary origin of the monarch butterfly’s ability to eat milkweed safely and deter predators. They speculated that if the same mutations could be edited into fruit flies using CRISPR, the fruit flies would also gain the adaption.

The researchers inserted single, double and triple mutations into the sodium-potassium pump gene of the fruit flies. It was identified that one mutation was enough to increase the fruit fly’s ability to withstand the toxic milkweed but caused some highly detrimental side effects in the nervous system. The full three mutations made the fruit flies resistant to milkweed with no serious side effects.

However, the mutations came at a cost. The fruit flies were not as quick to recover from being shaken, suggesting that the mutations may still have some unknown impact on immune system function.

This is the first time that a CRISPR mutation has significantly changed the ecological niche of an organism, by altering the fly’s diet and deterring its predators.

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