Spontaneous stage differentiation of mouse-virulent Toxoplasma gondii RH parasites in skeletal muscle cells: an ultrastructural evaluation

Abstract

Although the predilection for Toxoplasma gondii to form cysts in the nervous system and skeletal and heart muscles has been described for more than fifty years, skeletal muscle cells (SkMCs) have not been explored as a host cell type to study the Toxoplasma-host cell interaction and investigate the intracellular development of the parasite. Morphological aspects of the initial events in the Toxoplasma-SkMC interaction were analysed and suggest that there are different processes of protozoan adhesion and invasion and of the subsequent fate of the parasite inside the parasitophorous vacuole (PV). Using scanning electron microscopy,Toxoplasma tachyzoites from the mouse-virulent RH strain were found to be attached to SkMCs by the anterior or posterior region of the body, with or without expansion of the SkMC membrane. This suggests that different types of parasite internalization occurred. Asynchronous multiplication and differentiation of T. gondii were observed. Importantly, intracellular parasites were seen to display high amounts of amylopectin granules in their cytoplasm, indicating that tachyzoites of the RH strain were able to differentiate spontaneously into bradyzoites in SkMCs. This stage conversion occurred in approximately 3% of the PVs. This is particularly intriguing as tachyzoites of virulent Toxoplasma strains are not thought to be prone to cyst formation. We discuss whether biological differences in host cells are crucial to Toxoplasma stage conversion and suggest that important questions concerning the host cell type and its relevance in Toxoplasma differentiation are still unanswered.

Effect of 3-Bromopyruvate and Atovaquone on Infection during In Vitro Interaction of Toxoplasma gondii and LLC-MK2 Cells

“…In contrast, the same researchers demonstrated that tachyzoites of the RH strain (type I) showed a low conversion capacity (ϳ4% in 96 h). These data are similar to results previously obtained with skeletal muscle cells (conversion in 3% of vacuoles), in which the conversion was already established after 18 h of interaction (40). Thus, our results showing a 25% induction of cystogenesis by 3-BrPA reinforces the role of this compound in cellular events.…”

Toxoplasma gondii: determinants of tachyzoite to bradyzoite conversion

“…Recent studies have shown spontaneous and efficient tachyzoite to bradyzoite conversion in vitro for Type III strain VEG parasites in primary skeletal muscle cells differentiated to mature myotubes as well as in a rat myoblast cell line L6.C10 at higher rates than in fibroblasts (Ferreira-da-Silva et al 2009b). Recently, Type I RH strain which is less cystogenic was discovered to also undergo spontaneous tachyzoite to bradyzoite conversion in these cells but at a low rate of approximately 3% (Ferreira-da-Silva et al 2009a). These studies emphasize the potential importance of cell type specific microenvironments in bradyzoite development during an infection.…”

Development of dual fluorescent stage specific reporter strain of Toxoplasma gondii to follow tachyzoite and bradyzoite development in vitro and in vivo

“…Stress induction affects the host cell as well as the parasite by introducing another variable in studies of differentiation. The high rate of spontaneous conversion in EGS (30% bradyzoites in epithelial cells after 96 hours) suggests it will be a useful model to study induction in the absence of exogenous stress [29], [44],…”