Synchronised secretory organelle docking in <i>Paramecium</i> saltatory movement along microtubules transiently formed from ciliary basal bodies and selective exclusion of microinjected heterologous organelles

Biocommunication of Ciliates

2016

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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 2+ as a most efficient, locally and spatially restricted signal particularly for membrane fusion. This is enabled by the strategic positioning of Ca 2+ -release channels, type InsP 3 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.

Signals Regulating Vesicle Trafficking in Paramecium Cells

Biocommunication of Ciliates

2016

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``Frustrated Exocytosis'' — A Novel Phenomenon: Membrane Fusion without Contents Release, Followed by Detachment and Reattachment of Dense Core Vesicles in Paramecium Cells

Klauke

2000

J. Membrane Biol.

Abstract. The lipophilic fluorescent dye, FM1-43, as now frequently used to stain cell membranes and to monitor exo-endocytosis and membrane recycling, induces a cortical [Ca 2+ ] i transient and exocytosis of dense core vesicles ("trichocysts") , for reasons to be elucidated, they are tubular, though both types are endocytosed and lose their FM1-43 stain. In contrast, in presence of [Mg 2+ ] o ‫ס‬ 3 mM (which inhibits contents release), the exocytotic openings reseal and intact trichocysts with labeled membranes and with still condensed contents are detached from the cell surface ("frustrated exocytosis") within ∼15 min. They undergo cytoplasmic streaming and saltatory redocking, with a half-time of ∼35 min. During this time, the population of redocked trichocysts amenable to exocytosis upon a second stimulus increases with a half-time of ∼35 min. Therefore, acquirement of competence for exocytotic membrane fusion may occur with only a small delay after docking, and this maturation process may last only a short time. A similar number of trichocysts can be detached by merely increasing [Mg 2+ ] o to 3 mM, or by application of the anti-calmodulin drug, R21547 (calmidazolium). Essentially we show (i) requirement of calmodulin and appropriate [Me 2+ ] to maintain docking sites in a functional state, (ii) requirement of Ca o 2+ or of some other Me o 2+ to drive membrane resealing during exo-endocytosis, (iii) requirement of an "empty" signal to go to the regular endocytotic pathway (with fading fluorescence), and (iv) occurrence of a "filled" signal for trichocysts to undergo detachment and redocking (with fluorescence) after "frustrated exocytosis".

The remembrance of the things past: Conserved signalling pathways link protozoa to mammalian nervous system

Verkhratsky

2018

Cell Calcium

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The aim of the present article is to analyse the evolutionary links between protozoa and neuronal and neurosecretory cells. To this effect we employ functional and topological data available for ciliates, in particular for Paramecium. Of note, much less data are available for choanoflagellates, the progenitors of metazoans, which currently are in the focus of metazoan genomic data mining. Key molecular players are found from the base to the highest levels of eukaryote evolution, including neurones and neurosecretory cells. Several common fundamental mechanisms, such as SNARE proteins and assembly of exocytosis sites, GTPases, Ca-sensors, voltage-gated Ca-influx channels and their inhibition by the forming Ca/calmodulin complex are conserved, albeit with different subcellular channel localisation, from protozoans to man. Similarly, Ca-release channels represented by InsP receptors and putative precursors of ryanodine receptors, which all emerged in protozoa, serve for focal intracellular Ca signalling from ciliates to mammalian neuronal cells, eventually in conjunction with store-operated Ca-influx. Restriction of Ca signals by high capacity/low affinity Ca-binding proteins is maintained throughout the evolutionary tree although the proteins involved differ between the taxa. Phosphatase 2B/calcineurin appears to be involved in signalling and in membrane recycling throughout evolution. Most impressive example of evolutionary conservation is the sub-second dynamics of exocytosis-endocytosis coupling in Paramecium cells, with similar kinetics in neuronal and neurosecretory systems. Numerous cell surface receptors and channels that emerge in protozoa operate in the human nervous system, whereas a variety of cell adhesion molecules are newly "invented" during evolution, enabled by an increase in gene numbers, alternative splice forms and transcription factors. Thereby, important regulatory and signalling molecules are retained as a protozoan heritage.