Related Experiment Video
Updated: Jun 14, 2026
3-D Imaging and Analysis of Neurons Infected In Vivo with Toxoplasma gondii
Published on: December 9, 2014
GRA12 is a common virulence factor across Toxoplasma gondii strains and mouse subspecies
Francesca Torelli1,2, Simon Butterworth1, Eloise Lockyer1
1Signalling in Apicomplexan Parasites Laboratory, The Francis Crick Institute, London, UK.
Abstract:
Toxoplasma gondii parasites exhibit extraordinary host promiscuity owing to over 250 putative secreted proteins that disrupt host cell functions, enabling parasite persistence. However, most of the known effector proteins are specific to Toxoplasma genotypes or hosts. To identify virulence factors that function across different parasite isolates and mouse strains that differ in susceptibility to infection, we performed systematic pooled in vivo CRISPR-Cas9 screens targeting the Toxoplasma secretome. We identified several proteins required for infection across parasite strains and mouse species, of which the dense granule protein 12 (GRA12) emerged as the most important effector protein during acute infection. GRA12 deletion in IFNγ-activated macrophages results in collapsed parasitophorous vacuoles and increased host cell necrosis, which is partially rescued by inhibiting early parasite egress. GRA12 orthologues from related coccidian parasites, including Neospora caninum and Hammondia hammondi, complement TgΔGRA12 in vitro, suggesting a common mechanism of protection from immune clearance by their hosts.
Insights
Toxoplasma gondii virulence factors were identified using CRISPR-Cas9 screens. Dense granule protein 12 (GRA12) is crucial for parasite persistence and host cell survival across different strains and species.
Area of Science:
- Parasitology
- Immunology
- Molecular Biology
Background:
- Toxoplasma gondii exhibits broad host promiscuity due to numerous secreted proteins.
- Most known effector proteins are host or genotype-specific, limiting understanding of conserved virulence mechanisms.
Purpose of the Study:
- To identify conserved virulence factors of Toxoplasma gondii effective across diverse parasite isolates and host genetic backgrounds.
- To characterize the role of identified effectors in parasite persistence and host-pathogen interactions.
Main Methods:
- Systematic pooled in vivo CRISPR-Cas9 screens were employed to target the Toxoplasma secretome.
- Functional analysis of candidate effectors, including gene deletion and complementation studies in macrophages.
Main Results:
- Several secreted proteins essential for infection across different parasite strains and mouse species were identified.
- Dense granule protein 12 (GRA12) was identified as a critical effector during acute infection.
- GRA12 deletion led to parasitophorous vacuole collapse and increased host cell necrosis, with partial rescue by inhibiting parasite egress.
- Orthologues of GRA12 from related coccidian parasites complemented the defect in Toxoplasma gondii, indicating conserved function.
Conclusions:
- GRA12 is a key virulence factor for Toxoplasma gondii, mediating host cell integrity and immune evasion.
- The conserved function of GRA12 orthologues suggests a common mechanism for host immune clearance resistance among coccidian parasites.
More Related Videos
11:21Forward Genetics Screens Using Macrophages to Identify Toxoplasma gondii Genes Important for Resistance to IFN-γ-Dependent Cell Autonomous Immunity
Published on: March 12, 2015
11:37QTL Mapping and CRISPR/Cas9 Editing to Identify a Drug Resistance Gene in Toxoplasma gondii
Published on: June 22, 2017
