title: Trichocyst membrane fate in living Paramecium primaurelia visualized by multimodal confocal imaging.
abstract: Trichocysts are secretory organelles located at the surface of several ciliates, docked at the plasma membrane. Their secretion is similar to other exocytic processes: the trichocyst membrane fuses with the plasma membrane, its content is released outside the cell, and the membrane is retrieved back into the cell. The fate of the trichocyst membrane in living Paramecium primaurelia was investigated by inducing massive synchronous exocytosis in the presence of fluorescein isothiocyanate-conjugated lectins or of cationized ferritin. The marker is trapped within the retrieved trichocyst membrane sac, and many regularly spaced, fluorescent ghosts are formed. As time proceeds, the number of labeled ghosts decreases, and few fluorescent vacuoles appear within the cell. The relationship between trichocyst ghosts and the vesicles of the phagosome-lysosome system was examined by labeling cells with Texas Red-conjugated bovine serum albumin, a fluorescent marker for phagocytosis. Starting from two confocal images of the same cell labeled with the two fluorescent probes, a new single image was generated by associating each image with a different red or green value. This multimodal analysis showed that trichocyst ghosts fuse with secondary lysosomes or are incorporated into digestive vacuoles. The vacuolar content is degraded and fluorescence is then found in the vesicles of the phagosome-lysosome system, and, at last, in small weakly labeled vesicles located on the cell surface.
authors.affiliation: Institute of Zoology, University of Genoa, Italy.
authors.forename: P
authors.initials: P
authors.lastname: Ramoino
authors.forename: F
authors.initials: F
authors.lastname: Beltrame
authors.forename: A
authors.initials: A
authors.lastname: Diaspro
authors.forename: M
authors.initials: M
authors.lastname: Fato
mesh_terms: D000818:Animals; D005089:Exocytosis / Q000502:physiology; D005293:Ferritins; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D007425:Intracellular Membranes / Q000502:physiology*; D018613:Microscopy, Confocal / Q000379:methods*; D015388:Organelles; D010247:Paramecium / Q000166:cytology*; D010588:Phagosomes; D011107:Polylysine / Q000494:pharmacology
chemical_list: C010297:polycationic ferritin; D011107:Polylysine; D005293:Ferritins