Involvement of myosin VI immunoanalog in pinocytosis and phagocytosis in Amoeba proteus

Formation of multicellular colonies by choanoflagellates increases susceptibility to capture by amoeboid predators

Many heterotrophic microbial eukaryotes are size-selective feeders. Some microorganisms increase their size by forming multicellular colonies. We used choanoflagellates, Salpingoeca helianthica, which can be unicellular or form multicellular colonies, to study the effects of multicellularity on vulnerability to predation by the raptorial protozoan predator, Amoeba proteus, which captures prey with pseudopodia. Videomicrography used to measure the behavior of interacting S. helianthica and A. proteus revealed that large choanoflagellate colonies were more susceptible to capture than were small colonies or single cells. Swimming colonies produced larger flow fields than did swimming unicellular choanoflagellates, and the distance of S. helianthica from A. proteus when pseudopod formation started was greater for colonies than for single cells. Prey size did not affect the number of pseudopodia formed and the time between their formation, pulsatile kinematics and speed of extension by pseudopodia, or percent of prey lost by the predator. S. helianthica did not change swimming speed or execute escape maneuvers in response to being pursued by pseudopodia, so size-selective feeding by A. proteus was due to predator behavior rather than prey escape. Our results do not support the theory that the selective advantage of becoming multicellular by choanoflagellate-like ancestors of animals was reduced susceptibility to protozoan predation.

Phagocytosis: what's on the menu? 1

Phagocytosis is an evolutionarily conserved process. In Protozoa, phagocytosis fulfills a feeding mechanism, while in Metazoa, phagocytosis diversified to play multiple organismal roles, including immune defence, tissue homeostasis, and remodeling. Accordingly, phagocytes display a high level of plasticity in their capacity to recognize, engulf, and process targets that differ in composition and morphology. Here, we review how phagocytosis adapts to its multiple roles and discuss in particular the effect of target morphology in phagocytic uptake and phagosome maturation.

A novel mutation in the DNM2 gene impairs dynamin 2 localization in skeletal muscle of a patient with late onset centronuclear myopathy

Centronuclear myopathies constitute a group of heterogeneous congenital myopathies characterized by the presence of abnormal, centrally located nuclei within muscle fibers. Centronuclear myopathies can be caused by mutations of several different genes, including DNM2, encoding dynamin 2 (DNM2) a large GTPase involved in membrane trafficking and endocytosis. We report a 52-year-old female with slowly progressive muscle weakness, and a family history of the disease. Clinical, morphological, biochemical and genetic analyses of the proband and her family members were performed, including analyses of the proband's muscle biopsy. A novel D614N mutation, located in the C-terminal region pleckstrin-homology (PH) domain of DNM2 was identified in the proband and four family members, who exhibited similar symptoms. The mutation was associated with profound changes in the localization of DNM2 in muscle fibers without significant changes in protein expression. Mutated DNM2 and proteins involved in the membrane trafficking or membrane compartments maintenance were dislocalized within the myofiber, and concentrated at centrally located nuclei. This novel causative mutation (D614N) within the DNM2 gene in a large Polish centronuclear myopathy family with a late age of overt clinical manifestation caused profound changes in DNM2 localization and impaired proper organization of myofibers, and skeletal muscle functioning.

A pre-embedding immunogold approach reveals localization of myosin VI at the ultrastructural level in the actin cones that mediate Drosophila spermatid individualization

Stable actin structures play important roles in the development and specialization of differentiated cells. How these structures form, are organized, and are used to mediate physiological processes is not well understood in most cases. In Drosophila testis, stable actin structures, called actin cones, mediate spermatid individualization, a large-scale cellular remodeling process. These actin cones are composed of two structural domains, a front meshwork and a rear region of parallel bundles. Myosin VI is an important player in proper actin cone organization and function. Myosin VI localizes to the cones' fronts and its specific localization is required for proper actin cone formation and function during individualization. To understand how these structures are organized and assembled, ultrastructural studies are important to reveal both organization of actin and the precise localization of actin regulators relative to regions with different filament organizations. In the present work, we have developed a novel pre-embedding immunogold-silver labeling method for high-resolution analysis of protein distribution in actin structures which allowed both satisfactory antibody labeling and good ultrastructural preservation. Electron microscopic studies revealed that myosin VI accumulated at the extreme leading edge of the actin cone and preferentially localized throughout the front meshwork of the cone where branched actin filaments were most concentrated. No myosin VI labeling was found adjacent to the membranes along the length of the cone or connecting neighboring cones. This method has potential to reveal important information about precise relationships between actin-binding proteins, membranes, and different types of actin structures.