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First published online June 28, 2004
doi: 10.1242/10.1242/jcs.01178

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Overexpression of myosin IB in living Entamoeba histolytica enhances cytoplasm viscosity and reduces phagocytosis

Sabrina Marion¹, Claire Wilhelm², Heike Voigt^3,*, Jean-Claude Bacri² and Nancy Guillén^1,

¹ Unité de Biologie Cellulaire du Parasitisme, INSERM U389, Institut Pasteur, 28 rue du Dr Roux 75724, Paris CEDEX 15, France
² Laboratoire des Milieux Désordonnés et Hétérogènes, UMR7603, and FR2438 CNRS `Matière et Systèmes Complexes', Université Pierre et Marie Curie, 4 Place Jussieu, 75005 Paris, France
³ Unité de Pathogénie Microbienne Moléculaire, INSERM U389, Institut Pasteur, 28 rue du Dr Roux 75724, Paris CEDEX 15, France

Author for correspondence (e-mail: nguillen{at}pasteur.fr)

Accepted 24 February 2004

The human parasite Entamoeba histolytica is an ancient protozoan that expresses only one unconventional myosin, which has homology with myosin IB from other amoebae. Myosin IB is involved in phagocytosis of human cells by E. histolytica. In this work, we developed a microrheological technique, analysing magnetic phagosomes, which allowed us to probe the density of the F-actin network in living cells. Using this technique, we showed that overexpression of myosin IB led to an increase in cytoplasm viscosity, which correlated with a delay in initiating human cell phagocytosis. To investigate which myosin IB domains sustain cell viscosity changes, we overexpressed truncated forms of the protein. Our results demonstrate that both actin-binding sites that are present in the heavy chain but not the SH3 domain are required to modulate the density of the actin network. These data suggested that, as well as the motor activity, myosin IB in E. histolytica plays a structural role on the actin network owing to its ability to cross-link filaments. The gelation state of cell cytoplasm and the dynamics of cortical F-actin during phagocytosis seem to be modulated by the myosin IB structuring cytoskeleton activity.

Key words: Myosin IB, Viscosity, F-actin, Entamoeba histolytica

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