Gene editing now possible in ticks

Date:
February 15, 2022
Source:
Cell Press
Summary:
Researchers have successfully used CRISPR-Cas9 to edit the genomes
of the black-legged tick. To accomplish this feat, they developed
an embryo injection protocol that overcame a major barrier in
the field.



FULL STORY ========================================================================== Researchers have successfully used CRISPR-Cas9 to edit the genomes of
the black-legged tick. To accomplish this feat, they developed an embryo injection protocol that overcame a major barrier in the field.The work
appears February 15 in the journal iScience.


========================================================================== "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," says Monika Gulia-Nuss (@gulianusslab) a co-senior author of the study and a molecular biologist at the University
of Nevada, Reno.

"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," she says.

Despite the public health relevance of ticks -- which are vectors of
a wide variety of pathogens to humans, wildlife, and domestic animals
-- knowledge of the biology of ticks on a molecular level is still
limited. This is in contrast to insects such as mosquitoes, for which
numerous tools for transgenic development and genome editing are now
available. "Progress in this area is critical for the advancement of
research to solve the growing problem of tick- borne diseases," says
Andrew Nuss, the other co-senior author of the study and an entomologist
at the University of Nevada, Reno.

CRISPR-Cas9 has revolutionized functional genetics research in many
organisms.

This gene-editing technique has been applied to mosquitoes and other
arthropod disease vectors, but successful gene editing has not yet been reported in ticks. Technical challenges for injecting tick embryos to
attempt gene editing have further slowed research progress. Tick embryos
are extremely difficult to inject because of high pressure inside the
eggs, a hard chorion (the outer shell of the egg), and a wax layer
outside the embryo that must be removed before injection. Female ticks
use a specialized organ called Gene's organ to coat their eggs with a
tough wax layer.

In the iScience study, the researchers developed a successful tick-embryo injection protocol and targeted gene disruption with CRISPR-Cas9 using
two methods: embryo injection and Receptor-Mediated Ovary Transduction
of Cargo (ReMOT Control) -- a less-labor-intensive method of gene editing
in arthropods.

The researchers ablated Gene''s organ to prevent wax deposition and
then treated the eggs with chemicals called benzalkonium chloride and
sodium chloride to remove the chorion and to decrease 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. These wax-free eggs
permitted injection of tick embryos with materials necessary for genome modification," Gulia-Nuss says. "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 survival rate of injected embryos was approximately 10%, comparable
to well-established insect models. For ReMOT Control, all injected
ticks survived.

The data show the feasibility of tick embryo injection and genetic
manipulation in ticks by both methods, which had comparable editing
efficiency for the Proboscipedia (ProbP)gene, which is expressed in
appendages.

"Previously, no lab has demonstrated genome modification is possible
in ticks.

Some considered this too technically difficult to accomplish," Nuss
says. "This is the first study to demonstrate that genetic transformation
in ticks is possible by not only one, but two different methods." More research is needed to fully understand the molecular mechanisms underlying efficient gene editing in ticks. While these tools will accelerate tick
genetic research, improvements are needed in the embryo injection protocol
to enhance survival and larval hatching and gene-editing efficiencies.

"We expect that the tools we developed here will open new research
avenues that will dramatically accelerate our understanding of the
molecular biology of this and related tick species," Gulia-Nuss
says. "Targeted disruption of genes in tick vectors of human
pathogens is a powerful method to uncover the underlying biology
of tick-pathogen-host interactions that can inform the development
and application of new approaches to tick-borne disease control." ========================================================================== Story Source: Materials provided by Cell_Press. Note: Content may be
edited for style and length.


========================================================================== Journal Reference:
1. Arvind Sharma et al. Cas9-mediated gene editing in the black-legged
tick,
Ixodes scapularis, by embryo injection and ReMOT Control. iScience,
2022 DOI: 10.1016/j.isci.2022.103781 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/02/220215113405.htm

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