Ticks are the leading cause for the majority of vector-borne diseases in North America. Yet, the molecular tools to study and genetically modify these arthropods lag behind other insect vectors, such as mosquitoes. New research published in the journal iScience is the first to tinker with the DNA of black-legged ticks, better known as deer ticks, and successfully hatch a mutated larval brood from their eggs. The researchers targeted genes that aid in the development of the the animal's mouthparts and armor.

"The inspiration was to fill the gaps that we had in tick research," says study author Monika Gulia-Nuss, a vector biologist at the University of Nevada, Reno. "We wanted to see if we could [develop] similar tools that we have for mosquitoes and understand tick biology on a deeper, more molecular level." 

CRISPR/Cas9 is an up-and-coming genetic editing tool that can be widely applied to organisms to permanently alter the inherited traits in their progeny. But a suite of technical challenges hampers its use in ticks. While "ticks are pretty tough," says study author Andrew Nuss, an arthropod biologist at the University of Nevada, Reno, their eggs are simultaneously fragile and hardy. Laid during the fall to hatch the next spring, the eggs' shells are coated with a thick layer of wax to prevent them from drying out during their long dormancy. Each egg is also barricaded with a hard shell. Inside, the osmotic pressure is abnormally high—higher than that in other insects' eggs—which makes the sacs prone to popping like a water balloon when prodded. On top of these challenges, the parasites' long lifecycle and relatively mysterious embryonic stage make them a wily subject for CRISPR.

"Many other researchers in the past [carried out] unsuccessful experiments," says Nuss. For the five years it took to complete the project, "we just tried everything that hadn't been tried," he adds.