Morphology and Dynamics of the Endocytic Pathway inDictyostelium discoideum

Abstract

Dictyostelium discoideum is a genetically and biochemically tractable social amoeba belonging to the crown group of eukaryotes. It performs some of the tasks characteristic of a leukocyte such as chemotactic motility, macropinocytosis, and phagocytosis that are not performed by other model organisms or are difficult to study.D. discoideum is becoming a popular system to study molecular mechanisms of endocytosis, but the morphological characterization of the organelles along this pathway and the comparison with equivalent and/or different organelles in animal cells and yeasts were lagging. Herein, we used a combination of evanescent wave microscopy and electron microscopy of rapidly frozen samples to visualize primary endocytic vesicles, vesicular-tubular structures of the early and late endo-lysosomal system, such as multivesicular bodies, and the specialized secretory lysosomes. In addition, we present biochemical and morphological evidence for the existence of a micropinocytic pathway, which contributes to the uptake of membrane along side macropinocytosis, which is the major fluid phase uptake process. This complex endosomal compartment underwent continuous cycles of tubulation/vesiculation as well as homo- and heterotypic fusions, in a way reminiscent of mechanisms and structures documented in leukocytes. Finally, egestion of fluid phase from the secretory lysosomes was directly observed.

Possible roles of the endocytic cycle in cell motility

“…If the primary endocytic vesicles are spherical, their mean diameter can be estimated, from the rates of volume and surface uptake, as around 50 nm (see Materials and Methods). This is somewhat smaller than Dictyostelium coated vesicles (Swanson et al, 1981) and early endosomes (Neuhaus et al, 2002) but in the range of other small trafficking vesicles, such as synaptic vesicles (Takamori et al, 2006). It seems that aggregationcompetent cells rapidly endocytose their plasma membrane in small vesicles, and return it to the surface within a few minutes.…”

Mucolipin controls lysosome exocytosis in Dictyostelium

“…To circumvent this limitation, we also measured the pH of post-lysosomes directly in cells loaded with fluorescent-tagged Dextrans and chased for 30 minutes. Post-lysosomes can easily be identified because they are large compartments where endocytosed fluid-phase is markedly concentrated (Neuhaus et al, 2002) (supplementary material Fig. S4D).…”

Gluconeogenesis: A Metabolic Pathway in Eukaryotic Cells such as Cellular Slime Molds

“…D. discoideum considered as a model organism to study chemotaxis and developmental biology. D. discoideum obtained energy through lysosomal degradation and phagocytosis process [36]. Because of that intra-lysosomal nutrient levels are increasing so, the lysosome and the vacuole collect amino acids and other nutrients from cellular components through the autophagy process [37].…”