Coupling Polar Adhesion with Traction, Spring, and Torque Forces Allows High-Speed Helical Migration of the Protozoan Parasite Toxoplasma
Abstract
Among the eukaryotic cells that navigate through fully developed metazoan tissues, protozoans from the Apicomplexa phylum have evolved motile developmental stages that move much faster than the fastest crawling cells owing to a peculiar substrate-dependent type of motility, known as gliding. Best-studied models are the Plasmodium sporozoite and the Toxoplasma tachyzoite polarized cells for which motility is vital to achieve their developmental programs in the metazoan hosts. The gliding machinery is shared between the two parasites and is largely characterized. Localized beneath the cell surface, it includes actin filaments, unconventional myosin motors housed within a multimember glideosome unit, and apically secreted transmembrane adhesins. In contrast, less is known about the force mechanisms powering cell movement. Pioneered biophysical studies on the sporozoite and phenotypic analysis of tachyzoite actin-related mutants have added complexity to the general view that force production for parasite forward movement directly results from the myosin-driven rearward motion of the actin-coupled adhesion sites. Here, we have interrogated how forces and substrate adhesion–de-adhesion cycles operate and coordinate to allow the typical left-handed helical gliding mode of the tachyzoite. By combining quantitative traction force and reflection interference microscopy with micropatterning and expansion microscopy, we unveil at the millisecond and nanometer scales the integration of a critical apical anchoring adhesion with specific traction and spring-like forces. We propose that the acto-myoA motor directs the traction force which allows transient energy storage by the microtubule cytoskeleton and therefore sets the thrust force required for T. gondii tachyzoite vital helical gliding capacity.
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