For the first time, researchers have successfully edited the tick genome at the embryo stage, an achievement that may one day help scientists alter parts of the genome responsible for ticks acquiring and spreading harmful pathogens.
Ticks are common throughout North America and are a vector for several animal and human diseases. Lyme disease is the leading vector-borne disease in the United States and is commonly transmitted by the black-legged tick (Ixodes scapularis). Although approximately 35,000 cases of Lyme disease are reported each year to the Centers for Disease Control and Prevention, actual cases predicted by seroprevalence are estimated to exceed 300,000 annually due to unrecorded cases.
Tick research has lagged behind research on mosquitoes and other arthropod vectors largely because of challenges in applying available genetic and molecular tools to ticks.
“For many years, people thought it would be impossible to make a transgenic tick because tick eggs are coated in a hard wax that shattered the delicate glass needles used for injections,” explained Jason Rasgon, PhD, professor of entomology and disease epidemiology at Pennsylvania State University, in a statement.
Dr. Rasgon was among the researchers who finally solved the problem. The team also included researchers from the University of Nevada-Reno and the University of Maryland. The team’s study, published this February in the online journal iScience, details how the researchers used the CRISPR-Cas9 system to alter genes in black-legged tick embryos.
The team removed the maternal organs that make the wax prior to the ticks laying their eggs, resulting in eggs that could be injected. The researchers were then able to inject the CRISPR-Cas9 complex and successfully make deletions in two different genes.
The team then took the process a step further by injecting the CRISPR-Cas9 complex directly into the mothers and using Dr. Rasgon’s patent-pending CRISPR technology to target the complex to the mothers’ ovaries. Dr. Rasgon had demonstrated the process, called receptor-mediated ovary transduction of cargo, to be successful in several types of insects. He identified a small peptide that binds to receptors on the ovaries of most insect species.
In the new research, the team showed that this peptide is functional in ticks. The researchers fused the peptide to the Cas9 enzyme and injected the CRISPR-Cas9 complex into pregnant adult ticks. The peptide successfully delivered the enzyme into the ticks’ ovaries, where the complex could edit the genome of the offspring.
Co–senior study author Monika Gulia-Nuss, PhD, a molecular biologist at the University of Nevada-Reno, explained the significance of the breakthrough as follows: “Having genome-editing tools available will allow us to unlock some of the secrets of the tick genome and allow us to determine how these unique animals survive in the environment, how they interact with pathogens, and how we might prevent ticks from spreading diseases to humans and livestock.”