Abstract
Acanthamoebae are free-living protists and human pathogens, whose cellular functions and pathogenicity strongly depend on the transport of intracellular vesicles and granules through the cytosol. Using high-speed live cell imaging in combination with single-particle tracking analysis, we show here that the motion of endogenous intracellular particles in the size range from a few hundred nanometers to several micrometers in Acanthamoeba castellanii is strongly superdiffusive and influenced by cell locomotion, cytoskeletal elements, and myosin II. We demonstrate that cell locomotion significantly contributes to intracellular particle motion, but is clearly not the only origin of superdiffusivity. By analyzing the contribution of microtubules, actin, and myosin II motors we show that myosin II is a major driving force of intracellular motion in A. castellanii. The cytoplasm of A. castellanii is supercrowded with intracellular vesicles and granules, such that significant intracellular motion can only be achieved by actively driven motion, while purely thermally driven diffusion is negligible.
Highlights
On the diffusive behavior of macromolecules[18] and endogenous granules[19]
Analyzing the TA mean-square displacement (MSD) of the particle tracks revealed that the diffusion exponent α is close to 2 for almost all particle tracks (Fig. 3A, Table 1)
We have used time-lapse imaging and particle tracking algorithms to investigate the role of locomotion, cytoskeletal elements, and myosin II motors on intracellular particle movement in the protozoon and human pathogen A. castellani by analyzing mean-square displacements and velocity autocorrelations
Summary
On the diffusive behavior of macromolecules[18] and endogenous granules[19]. Due to its relatively simple, well-understood architecture and its non-motile behavior, fission yeast S. pombe is an excellent model system to study different theoretical aspects and concepts of subdiffusion[20] in living cells, e.g. weak ergodicity breaking[7] and the mean maximal excursion method[3]. There, intracellular particle motion is always superimposed by the locomotion of the cell body In spite of such large-scale movements, subdiffusion has been reported to still be present inside motile cells, e.g. for endothelial cells[21], for the social amoeba Dictyostelium discoideum[22], and for keratinocytes[23]. Understanding the basic mechanisms involved in intracellular motion and transport inside acanthamoebae is essential to get a complete picture of the pathogenicity of these protozoan parasites. This investigation is interesting, as the intracellular space in acanthamoebae appears densely packed with different types of endogenous particles, such as digestive and contractile vacuoles, smaller vesicles, and granules (Fig. 1). We use the notion of ‘supercrowdedvolume to point out that in the A. castellani cells considered here we find a large amount of vacuoles of several microns in size
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