Protrusion of cell surface coupled with single exocytotic events of secretion of the slime in Physarum plasmodia.
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 approximately 3.5 microm in diameter, shrank at the cell periphery at the average rate of approximately 1 microm/second, and became invisible. Immediately after exocytotic events, the neighboring cell surface extended to form a protrusion. The rate of extension was approximately 1 microm/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.
Sesaki
H
H
Department of Biology, Graduate School of Science, Osaka University, Toyonaka, Japan.
Ogihara
S
S
D000199:Actins / Q000032:analysis; D000818:Animals; D002462:Cell Membrane / Q000502:physiology / Q000648:ultrastructure; D005089:Exocytosis / Q000502:physiology*; D007091:Image Processing, Computer-Assisted; D008854:Microscopy, Electron; D018715:Microscopy, Video; D010804:Physarum / Q000737:chemistry / Q000502:physiology* / Q000648:ultrastructure; D011554:Pseudopodia / Q000737:chemistry / Q000502:physiology* / Q000648:ultrastructure; D013995:Time
D000199:Actins