Background: Phagocytosis, the process by which cells internalize particles, is essential for the defense of multicellular organisms against invading pathogens and is the major means by which many unicellular organisms obtain nutrients. The actin cytoskeleton plays a critical role in phagocytosis and the observation that a significant amount of force (10-20 nN) is generated during internalization, suggests that a myosin participates in the process. Although more than 15 distinct classes of myosin have been identified, their roles in phagocytosis are unknown. Results: The identification of a class vii unconventional myosin (DdMVII) in the Dictyostelium discoideum amoeba, which is a model for phagocytosis, is reported here. Mutant cells lacking DdMVII exhibited an 80% decrease in the uptake of particles whereas all other actin-based behaviors that were tested, including pinocytosis, exocytosis, cytokinesis and morphogenesis, proceeded normally. The defect in phagocytosis was neither because of altered particle binding nor inability to form actin-filled phagocytic cups. Conclusions: Molecular genetic analysis of Dictyostelium myosin VII reveals that this motor protein plays a specific and significant role in phagocytosis.
Bibliographical noteFunding Information:
The author thanks Markus Maniak (LMCB, London), Gaku Ashiba, Dan Kiehart, Sheila Counce, Joe Kelleher and Richard Tuxworth for many stimulating discussions and helpful comments on the manuscript. Thanks also to Bill Loomis (UCSD, San Diego, California) for providing a partial cDNA clone of the myol 3′ region, Jeff Baker for performing the phylogenetic analysis, Joel Herbein for assistance with the cloning of the myol gene and Dan Elliot for contributing to the initial phenotypic characterization of the mutant. The work was supported by a grant from the National Science Foundation.