Dictyostelium myosin I double mutants exhibit conditional defects in pinocytosis

• Published in: The Journal of cell biology Vol. 131; no. 5; pp. 1205 - 1221
• Main Authors: Novak, K.D. (Duke University Medical Center, Durham, NC.), Peterson, M.D, Reedy, M.C, Titus, M.A
• Format: Journal Article
• Language: English
• Published: United States Rockefeller University Press 01.12.1995; The Rockefeller University Press
• Subjects: ABSORCION DE SUSTANCIAS NUTRITIVAS; ABSORPTION DE SUBSTANCES NUTRITIVES; Actins; Actins - metabolism; Animals; BIOCHIMIE; BIOQUIMICA; Cell growth; Cell lines; Cell membranes; Cells; Cellular biology; Chemical suspensions; DICTYOSTELIUM; Endocytosis; ESTRUCTURA CELULAR; Fungal Proteins - genetics; Fungal Proteins - physiology; Genetics; GLOBULINAS; GLOBULINE; Microfilaments; Mutagenesis; MUTANT; MUTANTES; Mutation; Myosin Type I; Myosins - genetics; Myosins - physiology; ORGANITE CELLULAIRE; ORGANULOS CITOPLASMICOS; Pinocytosis - genetics; Pinocytosis - physiology; Protozoan Proteins - genetics; Protozoan Proteins - physiology; Pseudopodia; STRUCTURE CELLULAIRE; ULTRAESTRUCTURA; ULTRASTRUCTURE; VACUOLA; VACUOLE; Vacuoles; Vacuoles - metabolism
• ISSN: 0021-9525; 1540-8140
• DOI: 10.1083/jcb.131.5.1205

The functional relationship between three Dictyostelium myosin Is, myoA, myoB, and myoC, has been examined through the creation of double mutants. Two double mutants, myoA-/B- and myoB-/C-, exhibit similar conditional defects in fluid-phase pinocytosis. Double mutants grown in suspension culture are significantly impaired in their ability to take in nutrients from the medium, whereas they are almost indistinguishable from wild-type and single mutant strains when grown on a surface. The double mutants are also found to internalize gp126, a 116-kD membrane protein, at a slower rate than either the wild-type or single mutant cells. Ultrastructural analysis reveals that both double mutants possess numerous small vesicles, in contrast to the wild-type or myosin I single mutants that exhibit several large, clear vacuoles. The alterations in fluid and membrane internalization in the suspension-grown double mutants, coupled with the altered vesicular profile, suggest that these cells may he compromised during the early stages of pinocytosis, a process that has been proposed to occur via actin-based cytoskeletal rearrangements. Scanning electron microscopy and rhodamine-phalloidin staining indicates that the myosin I double mutants appear to extend a larger number of actin-filled structures, such as filopodia and crowns, than wild-type cells. Rhodamine-phalloidin staining of the F-actin cytoskeleton of these suspension-grown cells also reveals that the double mutant cells are delayed in the rearrangement of cortical actin-rich structures upon adhesion to a substrate. We propose that myoA, myoB, and myoC play roles in controlling F-actin filled membrane projections that are required for pinosome internalization in suspension