Tick-borne illnesses infect thousands of people per year, but genetic research on ticks has lagged behind because of technical challenges in using existing genome-altering tools. Now, researchers have successfully changed the genes of black-legged ticks for the first time, which they say brings them closer to managing illnesses like Lyme disease. The research was published in the journal iScience.
“The inspiration was to fill the gaps that we had in tick research,” study author Monika Gulia-Nuss, a vector biologist at the University of Nevada, Reno, tells Popular Science’s Shi En Kim. “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.”
The researchers used the genome editing tool CRISPR-Cas9 to alter genes that help ticks develop mouthparts and armor, per Popular Science. CRISPR modifies a genome by “precisely delivering a DNA-cutting enzyme, Cas9, to a targeted region of DNA. The resulting mutation can delete or replace specific DNA pieces, thereby promoting or disabling certain traits,” per Penn State.
Scientists can use CRISPR to edit genes while organisms are in the embryo stage. For ticks, this process requires injections into eggs using a needle. Though this method has worked in other arthropods like mosquitoes, the tick eggs’ high internal pressure, hard outer shell and waxy layer outside the embryo make it difficult to pierce, per the study.
The researchers discovered a new way to alter the eggs so they could be injected.
"We were able to carefully dissect [pregnant] female ticks to surgically remove the organ responsible for coating the eggs with wax, but still allowing the females to lay viable eggs. These wax-free eggs permitted injection of tick embryos with materials necessary for genome modification," Gulia-Nuss says in a statement.
About ten percent of the embryo-injected ticks survived, per the study.
The researchers also used another method, called Receptor-Mediated Ovary Transduction of Cargo (ReMOT Control), to alter the ticks’ genes. This method has also been used successfully in mosquitoes. ReMOT Control injects the Cas9 into the blood of female adults, which is then introduced into the developing eggs, per Penn State. All ticks that were genetically altered using the ReMOT Control method survived.
"Previously, no lab has demonstrated genome modification is possible in ticks. Some considered this too technically difficult to accomplish," Andrew Nuss, co-senior author of the study and an entomologist at the University of Nevada, Reno says in a statement. "This is the first study to demonstrate that genetic transformation in ticks is possible by not only one, but two different methods."
Wannes Dermauw, a entomologist at Belgium’s Flanders Research Institute for Agriculture, Fisheries and Food who wasn’t involved in the study, tells Popular Science that the research is “a breakthrough,” and will pave the way for “studying the function of genes that are involved in or are important for transmitting diseases like Lyme.”