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Updated: Sep 12, 2025

Toxoplasma gondii Cyst Wall Formation in Activated Bone Marrow-derived Macrophages and Bradyzoite Conditions
Published on: August 12, 2010
Toxoplasma gondii RAD51 recombinase is required to overcome DNA replication stress and its inactivation leads to
Ana M Saldarriaga Cartagena1, Ayelén Aparicio Arias2, Constanza Cristaldi1
1Laboratorio de Parasitología Molecular, Instituto Tecnológico de Chascomús (INTECH), Consejo Nacional de Investigaciones Científicas y Tecnológicas (CONICET)/Universidad Nacional General San Martin (UNSAM), Chascomús, Prov Buenos Aires, Argentina; Escuela de Bio y Nanotecnologías, CONICET/UNSAM, Chascomús, Prov Buenos Aires, Argentina.
Abstract:
Toxoplasma gondii is an obligate intracellular parasite with a high replication rate that can lead to DNA replicative stress, in turn associated with the generation of DNA double-strand breaks (DSBs). Cells have two main pathways to repair DSBs: non-homologous end joining and homologous recombination repair (NHEJ and HRR respectively). RAD51 is the key recombinase in the HRR pathway. In this work, we achieved endogenous tagging of the RAD51 gene using the Auxin Inducible Degron (AID) system, to generate the clonal line RH RAD51HA-AID. Here we demonstrate that RAD51 is expressed in replicative tachyzoites and establishes damage foci. Auxin-induced knock-down (KD) affects the correct replication of tachyzoites which show loss of synchronization. The use of the RAD51 inhibitor B02 also affects parasite growth, with an IC50 of 4.8 µM. B02 produced alterations in tachyzoite replication and arrest in the S phase of the cell cycle. Additionally, B02 induced tachyzoite to bradyzoite differentiation showing small cyst-like structures. In conclusion, RAD51 is necessary for maintaining proper tachyzoite replication under normal growth conditions, supporting that genome instability occurs during the cell cycle. Our findings also suggest that DNA replication stress can induce bradyzoite differentiation.
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