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 (Ca(2+)) 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. Ca(2+)-release channels, type inositol 1,4,5-trisphosphate receptors (InsP3R), may serve for fine-tuning of local cytosolic Ca(2+) 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(+)/Ca(2+) exchangers (to sequester Ca(2+)) and mechanosensitive Ca(2+)-channels (for signaling the filling sate). The periodic activity of the CVC may be regulated by the mechanosensitive Ca(2+)-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.

Principles of Intracellular Signaling in Ciliated Protozoa—A Brief Outline

“…(v) Vesicle recycling from the cytoproct to the nascent phagosome. (vi) In addition, the contractile vacuole complex impresses not only by its dynamic activity (Allen and Naitoh 2002) in the context of ongoing osmoregulation (Allen et al 2009), but it also represents a site endowed with the machinery typical of vesicle trafficking (Plattner 2015b) although vesicle trafficking within the organelle is less obvious. Steps (iii) to (v) have been documented in detail for Paramecium (Allen and Fok 2000) as well as for Tetrahymena (Frankel 2000).…”

“…It not only can expel fluid with an excess of Ca 2 + and other ions (Stock et al 2002), but it also shows some reflux of Ca 2 + into the cytosol via constitutively active lnsP~s (Ladenburger et al 2006). This may serve not only for fine tuning of cytosolic Ca 2 + but also to drive the extensive membrane flL<;ion and fission processes within the organelle during systole/diastole cycles (Plattner 2015b). Pore for periodic contents release by exocytosis: with specific SNAREs and CRCs at the pore periodic signal for vacuole contents release: mechanosensitive channels (suggested by occurrence ofstomatin [Reuter et al 2013] and in agreement with other systems [Plattner 2015b]), in conjunction with pore-specific SNAREs and CRCs…”

“…Below Parallel situations seen on ultrathin sections. a Data pertinent to trichocyst processing are based on previous reviews (Plattner et al 1993;Plattner 2014), those for endo /phagocytotic trafficking are mainly derived from Allen and Fok (2000) and c trafficking in context of the contractile vacuole complex is based on recent reviews (Plattner 2015b(Plattner , 2016a b is modified from Plattner (2014), c is modified from Plattner et al (1993Plattner et al ( , 1997 and SU-B (regulatory SU, with Ca 2 +· binding domain) also in ciliates respective protein kinases, protein kinase A (PKA) and protein kinase G (PKG) (Bonini and Nelson 1990); for review see Plattner (2016a). Also some metabolic Ca 2 + channel activators, such as cyclic adenosinediphosphoribose (cADPR) and nicotinic acid adenine cfmucleotidephosphate (NAADP) are derived from nucleotides, i.e.…”

Signals Regulating Vesicle Trafficking in Paramecium Cells

“…in mammalian epithelia and T-lymphocytes (Griffiths et al 2010). Some possible mechanisms relevant for the distinct positioning of the contractile vacuole complexes, also microtubule-based, have been discussed recently (Plattner 2013(Plattner , 2015c.…”

“…This counteracts the rapid permeation of water and Ca 2+ and-beyond pulsation activity-also involves less overt membrane dynamics and signaling (Plattner 2015c).…”