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Updated: Aug 13, 2026
Genetic Manipulation in Δku80 Strains for Functional Genomic Analysis of Toxoplasma gondii
Published on: July 12, 2013
Requirement of Toxoplasma gondii metacaspases for IMC1 maturation, endodyogeny and virulence in mice
Muzi Li1,2, Jing Liu1,3, Yayun Wu1
1National Animal Protozoa Laboratory, College of Veterinary Medicine, China Agricultural University, Beijing, China.
Background:
Metacaspases are multifunctional proteins found in plants, fungi and protozoa, and are involved in processes such as insoluble protein aggregate clearance and cell proliferation. Our previous study demonstrated that metacaspase-1 (MCA1) contributes to parasite apoptosis in Toxoplasma gondii. Deletion of MCA1 from T. gondii has no effect on the growth and virulence of the parasites. Three metacaspases were identified in the ToxoDB Toxoplasma Informatics Resource, and the function of metacaspase-2 (MCA2) and metacaspase-3 (MCA3) has not been demonstrated.
Methods:
In this study, we constructed MCA1, MCA2 and MCA1/MCA2 transgenic strains from RHΔku80 (Δku80), including overexpressing strains and knockout strains, to clarify the function of MCA1 and MCA2 of T. gondii.
Results:
MCA1 and MCA2 were distributed in the cytoplasm with punctuated aggregation, and part of the punctuated aggregation of MCA1 and MCA2 was localized on the inner membrane complex of T. gondii. The proliferation of the MCA1/MCA2 double-knockout strain was significantly reduced; however, the two single knockout strains (MCA1 knockout strain and MCA2 knockout strain) exhibited normal growth rates as compared to the parental strain, Δku80. In addition, endodyogeny was impaired in the tachyzoites whose MCA1 and MCA2 were both deleted due to multiple nuclei and abnormal expression of IMC1. We further found that IMC1 of the double-knockout strain was detergent-soluble, indicating that MCA1 and MCA2 are associated with IMC1 maturation. Compared to the parental Δku80 strain, the double-knockout strain was more readily induced from tachyzoites to bradyzoites in vitro. Furthermore, the double-knockout strain was less pathogenic in mice and was able to develop bradyzoites in the brain, which formed cysts and established chronic infection.
Conclusion:
MCA1 and MCA2 are important factors which participate in IMC1 maturation and endodyogeny of T. gondii. The double-knockout strain has slower proliferation and was able to develop bradyzoites both in vitro and in vivo.
Insights
Metacaspase-1 (MCA1) and metacaspase-2 (MCA2) in Toxoplasma gondii are crucial for cell proliferation and inner membrane complex protein (IMC1) maturation. Deleting both MCA1 and MCA2 impairs parasite growth and promotes bradyzoite development.
Area of Science:
- Parasitology
- Cell Biology
- Molecular Biology
Background:
- Metacaspases are multifunctional proteins in plants, fungi, and protozoa involved in protein aggregate clearance and cell proliferation.
- Metacaspase-1 (MCA1) in Toxoplasma gondii contributes to parasite apoptosis, but its deletion does not affect growth or virulence.
- The functions of T. gondii metacaspase-2 (MCA2) and metacaspase-3 (MCA3) remain largely uncharacterized.
Purpose of the Study:
- To elucidate the functions of metacaspase-1 (MCA1) and metacaspase-2 (MCA2) in Toxoplasma gondii.
- To investigate the roles of MCA1 and MCA2 in parasite proliferation, cell structure, and differentiation.
Main Methods:
- Construction of MCA1, MCA2, and combined MCA1/MCA2 knockout and overexpressing transgenic strains in T. gondii RHΔku80.
- Analysis of parasite proliferation rates, endodyogeny, inner membrane complex protein 1 (IMC1) localization and solubility.
- Assessment of tachyzoite-to-bradyzoite differentiation in vitro and in vivo, and evaluation of mouse infectivity.
Main Results:
- MCA1 and MCA2 are localized in the cytoplasm and partially on the inner membrane complex.
- MCA1/MCA2 double-knockout strains exhibit significantly reduced proliferation and impaired endodyogeny, with abnormal IMC1 expression and detergent solubility.
- Single knockouts of MCA1 or MCA2 show normal growth, while the double knockout readily differentiates into bradyzoites in vitro and establishes chronic infection in mice with reduced pathogenicity.
Conclusions:
- Metacaspase-1 (MCA1) and metacaspase-2 (MCA2) are essential for IMC1 maturation and endodyogeny in T. gondii.
- The absence of both MCA1 and MCA2 leads to slower proliferation and enhanced bradyzoite development in vitro and in vivo.
- MCA1 and MCA2 play critical roles in regulating T. gondii tachyzoite-to-bradyzoite differentiation and chronic infection dynamics.
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