From diabetes to rare blood disease, CRISPR gene-editing technology is changing the way we tackle many threats to public health, and there are few bigger than those posed by vector-borne diseases carried by tiny critters. We've seen much exciting progress made in genetically modifying mosquitos to slow the spread of malaria, and now scientists have leveraged the technology to demonstrate gene-editing in ticks for the first time, a significant breakthrough in the battle against Lyme disease.
Gene editing in ticks had been thought to be impossible until now, and with good reason. Tick embryos are very tricky to inject because the egg that contains them has a tough layer on the outside, high pressure levels inside, and is also coated in a waxy layer the mothers create using what's called the Gené's organ.
"Despite their capacity to acquire and pass on an array of debilitating pathogens, research on ticks has lagged behind other arthropod vectors, such as mosquitoes, largely because of challenges in applying available genetic and molecular tools," said Monika Gulia-Nuss, a co-senior author of the study and a molecular biologist at the University of Nevada, Reno.
Gulia-Nuss and her research team, which included scientists from the University of Maryland and Penn State University, believe they have finally cracked the code. The first step in the breakthrough technique involves ablating the Gené's organ to prevent the formation of the waxy coating. The eggs were then treated with chemicals benzalkonium chloride and sodium chloride to both eliminate the tough protective layer and lower the pressure inside the eggs.
"We were able to carefully dissect gravid female ticks to surgically remove the organ responsible for coating the eggs with wax, but still allowing the females to lay viable eggs," said Gulia-Nuss says. "These wax-free eggs permitted injection of tick embryos with materials necessary for genome modification. Another major challenge was understanding the timing of tick embryo development. So little is known about tick embryology that we needed to determine the precise time when to introduce CRISPR-Cas9 to ensure the greatest chance of inducing genetic changes."
The team was able to inject the eggs with the CRISPR-Cas9 complex, which carries enzymes that cut DNA at specific locations on the genome, to successfully delete two different genes, with a 10 percent embryo survival rate. Separately, the scientists used another form of CRISPR-Cas9 to injected a peptide into pregnant female ticks, delivering the complex to the developing ovaries to edit the genome of the offspring. This previously developed technology, called ReMOT Control, saw all the injected ticks survive.
"Previously, no lab has demonstrated genome modification is possible in ticks," said Nuss. "Some considered this too technically difficult to accomplish. This is the first study to demonstrate that genetic transformation in ticks is possible by not only one, but two different methods."
Having demonstrated this protocol, scientists can now begin editing the tick genome in a bid to prevent the transmission of Lyme disease, which infects around 300,000 people in the US each year, along with the more than 20 other diseases carried by the tiny arachnids. Generally speaking, these experiments will involve altering genes in the hope of finding tweaks that affect pathogen development and ultimately makes ticks harmless to humans, similar to the efforts taking place with regard to mosquitos.
"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," said Gulia-Nuss.
The research was published in the journal iScience.
Sources: Penn State University, University of Maryland, University of Nevada, Reno, Cell Press via ScienceDaily
