Genetic Manipulation of Ticks: A Paradigm Shift in Tick and Tick-Borne Diseases Research

Abstract

Ticks are obligate hematophagous arthropods that are distributed worldwide and are one of the most important vectors of pathogens affecting humans and animals. Despite the growing burden of tick-borne diseases, research on ticks has lagged behind other arthropod vectors, such as mosquitoes. This is largely because of challenges in applying functional genomics and genetic tools to the idiosyncrasies unique to tick biology, particularly techniques for stable genetic transformations. CRISPR-Cas9 is transforming non-model organism research; however, successful germline editing has yet to be accomplished in ticks. Here, we review the ancillary methods needed for transgenic tick development and the use of CRISPR/Cas9, the most promising gene-editing approach, for tick genetic transformation.

Transgenic approaches in medical entomology: 2022 highlights

“…Until very recently, the most functional genomic studies in ticks relied on RNA interference (RNAi). However, RNAi has diverse limitations, such as resulting in incomplete gene silencing which allows for a transient knockdown only, not being suitable for overexpression studies, and being mostly applicable to adult stages (Nuss et al 2021). Hence, alternative methods for genetic manipulation of ticks are needed.…”

“…For gene knockouts, the cell's repair machinery can introduce mutations through nonhomologous end joining in either technique. However, only embryo injections can introduce plasmids with homology arms necessary for homology directed repair for gene knock-ins (Nuss et al 2021). In summary, this 2022 paper is a highlight in medical entomology as it shows for the first time that CRISPR/Cas9-mediated gene editing is feasible in ticks and that tick gene knockout is achievable with both embryo and adult injection.…”

The environment, the tick, and the pathogen – It is an ensemble

“…With the understanding that tick saliva contains several immunomodulators that facilitate tick feeding-a process essential for tick-borne pathogens to enter or exit the tick ( Francischetti et al., 2009 ), the concept of saliva assisted transmission or SAT ( Nuttall, 2019 ) has been at the centre stage of research on tick transmission of human pathogens. The availability of the genome sequence of I. scapularis ( Gulia-Nuss et al., 2016 ) has allowed comprehensive cataloging of the salivary and midgut transcriptomes and proteomes and revealed new insights into tick biology and tick-host-pathogen interactions ( Chmelar et al., 2016 ; de la Fuente et al., 2017 ; Wikel, 2018 ; Nuss et al., 2021 ). The last decade has brought into focus the role of the commensal and symbiotic microbiota associated with the tick in the context of tick-pathogen interactions ( Bonnet et al., 2017 ; Narasimhan et al., 2021 ; Sonenshine and Stewart, 2021 ).…”

Cas9-mediated gene editing in the black-legged tick, Ixodes scapularis, by embryo injection and ReMOT Control

“…RNAi (RNAi) is currently the only technique available for functional genomics studies in ticks. However, this technique has significant limitations and has provided only a brief insight into our understanding of these organisms ( Nuss et al., 2021 ; Karim and Adamson, 2012 ; de la Fuente et al., 2007 ). The clustered regularly interspaced short palindromic repeats (CRISPR), CRISPR-associated protein 9 (Cas9), has revolutionized functional genetics research in many organisms ( Zhang and Reed, 2017 ).…”