The contractile vacuole complex of protists – New cues to function and biogenesis

Abstract

The contractile vacuole complex (CVC) of freshwater protists sequesters the excess of water and ions (Ca²⁺) for exocytosis cycles at the pore. Sequestration is based on a chemiosmotic proton gradient produced by a V-type H⁺-ATPase. So far, many pieces of information available have not been combined to a comprehensive view on CVC biogenesis and function. One main function now appears as follows. Ca²⁺-release channels, type inositol 1,4,5-trisphosphate receptors (InsP₃R), may serve for fine-tuning of local cytosolic Ca²⁺ concentration and mediate numerous membrane-to-membrane interactions within the tubular spongiome meshwork. Such activity is suggested by the occurrence of organelle-specific soluble N-ethylmaleimide sensitive factor attachment protein receptor (SNARE) and Ras-related in brain (Rab) proteins, which may regulate functional requirements. For tubulation, F-Bin–amphiphysin–Rvs (F-BAR) proteins are available. In addition, there is indirect evidence for the occurrence of H⁺/Ca²⁺ exchangers (to sequester Ca²⁺) and mechanosensitive Ca²⁺-channels (for signaling the filling sate). The periodic activity of the CVC may be regulated by the mechanosensitive Ca²⁺-channels. Such channels are known to colocalize with and to be functionally supported by stomatins, which were recently detected in the CVC. A Kif18-related kinesin motor protein might control the length of radial arms. Two additional InsP₃-related channels and several SNAREs are associated with the pore. De novo organelle biogenesis occurs under epigenetic control during mitotic activity and may involve the assembly of γ-tubulin, centrin, calmodulin and a never in mitosis A-type (NIMA) kinase – components also engaged in mitotic processes.

• Biogenesis
• calcium
• ciliate
• contractile vacuole
• Dictyostelium
• osmoregulation
• Paramecium
• protozoa
• Tetrahymena

Acknowledgements

I thank the respective coworkers for their continuous efforts as well as some of my colleagues for critically reading the text.

Declaration of interest

The author reports no conflicts of interest. The author alone is responsible for the content and writing of this article.

The author’s work cited herein has been supported by grants from the German Research Council.