Feb. 23, 2022 — We hear a lot about the scourges of mosquitoes as they spread malaria, dengue fever, Zika, and other illnesses, but they’re certainly not the only tiny vector out there spreading disease.
Just ask anyone who’s dealt with Lyme disease. Ticks have long been a major source of infectious disease, but they haven’t received as much attention from researchers as mosquitoes. And we know a lot less about their biology and what makes them, well, tick. But that’s starting to change.
For the first time, scientists have used a form of CRISPR, a gene editing tool, to alter the genetic code of black-legged ticks.
The feat was remarkable because researchers have been struggling for years to find a way to successfully inject tick embryos. With the eggs’ high internal pressure, hard outer shell, and a wax layer around each embryo that needs to be removed before the shot, it’s been tough to get inside the embryo to edit its genes. But now, scientists have a way to get in there, and they’ve published their findings in the journal iScience.
The researchers were able to edit genes by injecting the embryo, as they would have with other creatures, but they also came up with a process that had greater success. It involved first removing the Gené’s organ — what female ticks use to coat their eggs with wax — from mother ticks, and then using two chemicals, benzalkonium chloride and sodium chloride, to remove the eggs’ hard outer shell and reduce their internal pressure.
That’s not to say it was suddenly easy to inject the eggs. The researchers still had to find the right time during gestation to use CRISPR to edit the genes. But their work paid off. Overall, only about 1 in 10 tick embryos survived the injection — about the same as gene editing survival rates for insects — and all the female ticks survived.
The new study describes for other researchers what they need to do to finally be able to modify the genome of ticks, opening the door to further research into understanding these arthropods and what kind of gene editing works best in them. Ultimately, the research could lead to better gene editing, more answers about how ticks survive and transmit disease, and possibly how to prevent such transmission.