Exocytosis has been proposed to participate in the formation of pseudopods. Using video-enhanced microscopy, we directly visualized exocytosis of single vesicles in living Physarum plasmodia migrating on a substrate. Vesicles containing slime, the plasmodial extracellular matrix, of ~ 3.5 μm in diameter, shrank at the cell periphery at the average rate of ~ 1 μm/second, and became invisible. Immediately after exocytotic events, the neighboring cell surface extended to form a protrusion. The rate of extension was ~ 1 μm/second. The protrusion showed lamella-like morphology, and contained actin microfilaments. Electron microscopy suggested that the organization of microfilaments in such protrusions may be a random meshwork rather than straight bundles. These morphologies suggest that protruded regions are pseudopods. Importantly, only the slime-containing vesicle preferentially invaded the hyaline layer that consists of dense actin microfilaments while the other vesicular organelles remained in the granuloplasm. Quantitative analysis demonstrated a linear relationship in terms of their surface area, between individual protrusions and single slime-containing vesicles. It is, therefore, likely that most of the plasma membrane of the protrusion was supplied by fusion of the slime-containing vesicle during exocytosis.
|Original language||English (US)|
|Number of pages||10|
|Journal||Journal of cell science|
|State||Published - Apr 1 1997|
- Extracellular matrix
ASJC Scopus subject areas
- Cell Biology