CRISPR-Cas13b mediated gene knockdowns in Leishmania infantum.

Chemotherapy is an effective means to control infections caused by the protozoan parasite Leishmania. However, available treatments are limited, expensive, and associated with considerable toxicity. Genomic strategies have contributed to a better understanding of Leishmania's response to drugs and in the characterization of drug targets. Nonetheless, there is no knockdown system operational for Leishmania. In this study, we show that the CRISPR-Cas13 system can be an effective strategy to knockdown expression levels of both exogenous and endogenous transcripts. We succeeded in effectively knocking down the expression of the firefly luciferase gene integrated in the genome of L. infantum. This Cas13-mediated decrease in mRNA was paralleled with a significant reduction in both the luciferase protein level and its activity. Furthermore, we tested the effectiveness of the Cas13 system to target the endogenous miltefosine transporter (MT) and the aquaglyceroporin 1 (AQP1) genes. Knockdown was effective and parasites with less MT or AQP1 mRNA levels exhibited reduced susceptibility to miltefosine or antimonials, respectively. While further optimization is warranted, this knockdown system has the potential to facilitate numerous studies related to various aspects of Leishmania biology.