
톡소포자충의 MYR1 단백질은 기생충 증식에 필수적인 것은 아니지만, 감염된 숙주 세포 주변의 환경을 조성하여 다른 기생충의 성장을 돕는 파라크린 효과를 나타낸다.


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Toxoplasma gondii is an intracellular parasite that subverts host cell functions via secreted virulence factors. Up to 70% of parasite-controlled changes in the host transcriptome rely on the MYR1 protein, which is required for the translocation of secreted proteins into the host cell. Mice infected with MYR1 knock-out (KO) strains survive infection, supporting a paramount function of MYR1-dependent secreted proteins in Toxoplasma virulence and proliferation. However, we have previously shown that MYR1 mutants have no growth defect in pooled in vivo CRISPR-Cas9 screens in mice, suggesting that the presence of parasites that are wild-type at the myr1 locus in pooled screens can rescue the phenotype. Here, we demonstrate that MYR1 is not required for the survival in IFN-γ-activated murine macrophages, and that parasites lacking MYR1 are able to expand during the onset of infection. While ΔMYR1 parasites have restricted growth in single-strain murine infections, we show that the phenotype is rescued by co-infection with wild-type (WT) parasites in vivo, independent of host functional adaptive immunity or key pro-inflammatory cytokines. These data show that the major function of MYR1-dependent secreted proteins is not to protect the parasite from clearance within infected cells. Instead, MYR-dependent proteins generate a permissive niche in a paracrine manner, which rescues ΔMYR1 parasites within a pool of CRISPR mutants in mice. Our results highlight an important limitation of otherwise powerful in vivo CRISPR screens and point towards key functions for MYR1-dependent Toxoplasma -host interactions beyond the infected cell.

SIGNIFICANCE STATEMENT Pooled CRISPR screens are powerful tools to interrogate gene function in a high-throughput manner. Genes conferring fitness advantages or disadvantages upon disruption can be identified by sequencing. However, in Toxoplasma gondii pooled CRISPR screens in mice, fitness defects for some selected mutants drastically diverge from those observed in single-strain infections. Here, we show that a growth defect of a single Toxoplasma gene deletion mutant is rescued if co-infected with wildtype parasites. These results shine light on Toxoplasma ’s ability to subvert the host response beyond the infected cell, and highlight an important limitation of pooled CRISPR screens in mice. This limitation is probably encountered in CRISPR screens in general where paracrine effects occur.

### Competing Interest Statement

The authors have declared no competing interest.

Paracrine rescue of MYR1-deficient Toxoplasma gondii mutants reveals limitations of pooled in vivo CRISPR screens

myr1-결핍-톡소포자충-변이체의-파라크린-구출은-in-vivo-crispr-풀링-스크리닝의-한계를-보여준다


MYR1 결핍 톡소포자충 변이체의 파라크린 구출은 in vivo CRISPR 풀링 스크리닝의 한계를 보여준다
