Signals Regulating Vesicle Trafficking in Paramecium Cells

Most data available from Paramecium, fewer from Tetrahymena, disclose essentially the same principles of signaling as in metazoans up to man. Microtubules serve for long-range signaling, whereas SNARE proteins, H-ATPase, GTPases and actin provide short-range molecular signals, with Ca as a most efficient, locally and spatially restricted signal particularly for membrane fusion. This is enabled by the strategic positioning of Ca-release channels, type InsP3 receptors and ryanodine-receptor-like proteins, also in ciliates. In Paramecium, the most evident trafficking routes encompass exo-/endocytosis, endo-/phagocytosis and the contractile vacuole complex. The high specificity, precision and efficiency of vesicle trafficking regulation in ciliates is facilitated by their highly regular, epigenetically controlled cell structure, with firmly installed microtubular rails. 6.1 Basic Aspects of Vesicle Trafficking and Signaling Pathways in Ciliates Ciliates are well designed cells, with a cell cortex composed of unit fields called kinetids, about 1 × 2 μm in size. Each kinetid possesses a cilium (or two) in its center and intermittently positioned dense core-secretory organelles. These are trichocysts in Paramecium and mucocysts in Tetrahymena—the most intensely studies genera. This epigenetically controled surface pattern (Beisson and Sonneborn 1965; Wloga and Frankel 2012) entails important consequences for signaling, e.g. by the universal second messenger, Ca, as it allows for alternative activation of cilia and of vesicle exocytosis, respectively, due to strict local and temporal signal confinement (Klauke and Plattner 1997; Husser et al. 2004). Exocytosis is an example of short-range signaling enabled by a pre-assembled signaling machinery and a local Ca impulse. H. Plattner (&) Department of Biology, University of Konstanz, P.O. Box M625, 78457 Konstanz, Germany e mail: helmut.plattner@uni konstanz.de