A contractile vacuole (CV) is an organelle or subcellular structure involved in osmoregulation and waste disposal. Previously, a CV was known as a pulsed or pulsed vacuole. CVs should not be confused with vacuoles that store food or water. A CV is mainly found in protists and unicellular algae. In freshwater environments, the concentration of solutes inside the cell is higher than outside the cell. Under these conditions, water flows from the environment into the cell by osmosis. Thus, the CV acts as a protective mechanism against cell expansion (and possibly explosion) due to too much water; It expels excess water from the cell by contracting. However, not all species that have a CV are freshwater organisms; some marine and soil microorganisms also have a CV. VC is predominant in species that do not have a cell wall, but there are exceptions. During the evolutionary process, CV was mainly eliminated in multicellular organisms; However, there are still several multicellular fungi in the single-celled stage and in various types of cells in sponges, including amoebocytes, pinacocytes and choanocytes.
It has been implied that azidocalciums act alongside the contractile vacuole to respond to osmotic stress. They were detected near Trypanosoma cruzi vacuoles and were shown to merge with vacuole when cells were exposed to osmotic stress. Presumably, azidocalciums empty their ionic content into the contractile vacuole, which increases the osmolarity of the vacuoles. [6] The contractile vacuole remains stationary within the euglena and other flagellates. It is usually spherical and occurs in fresh water, where protozoa and other lower metazoans such as sponges and hydras are found. Then an accumulation of excess fluid is periodically emptied from the protoplasm into the surrounding environment. The number of contractile vacuoles per cell varies by species. Amoebae have one, Dictyostelium discoideum, Paramecium aurelia and Chlamydomonas reinhardtii have two, and giant amoebae, like Chaos carolinensis, have many. The number of contractile vacuoles in each species is generally constant and is therefore used for the characterization of species in systematics. The contractile vacuole has several structures in most cells, such as membrane folds, tubules, water channels, and small vesicles. These structures were called spongiomas; The contractile vacuole, along with the spongioma, is sometimes called the “contractile vacuole complex” (CVC).
The spongioma performs several functions by transporting water into the contractile vacuole and locating and docking the contractile vacuoles in the cell. To identify the properties of large vacuoles, we labeled disgorginous cells with markers for different types of organelles: TRITC-dextran (endosomes), lysotrackers (lysosomes) or RFP-dajumin (CV system) (Gabriel et al., 1999; Insall et al., 2001). Dajumine RFP, but not the other markers, clearly marked the large vacuol structures corresponding to those observed in phase contrast microscopy, suggesting that the large vacuoles in the disgorginous cells are enlarged CVs (Figure 2A and Additional Film S1). Interestingly, when we placed the disgorgin cells in low-salt buffers, the large vacuoles were no longer present; Instead, we observed many smaller bladder structures (Figure 2A and additional film S1), suggesting that CV activity in disgorginous cells changed dramatically under hypotonic stress. On the other hand, the tone of the medium did not affect the CV structures in the wild-type cells (Figure 2A and Additional Film S1). As visualized with RFP dajumin, the number of CV bladder structures in LvsAOE cells increased compared to wild-type cells (Figure 6B and Additional Figure S2B). Thus, the combination of LvsA overexpression and disruptive disgorgine (LvsAOE/Disgorgin− cells) leads to prolonged CVs enlargement (Figure 6B). In lvsD− cells, the size of the CV bladder is comparable to that of wild-type cells (Figure 6B). However, in lvsD/disgorgin cells, the CV bladder is significantly enlarged (Figure 6B). Overexpression of LvsD in wild-type cells does not result in any observed changes in cardiovascular structure (Figure 6B). The contractile vacuole is a part of the cell that helps regulate the amount of water in a cell. It acts as a protective mechanism to prevent the cell from absorbing too much water.
It also helps regulate the pressure in the cell. There is another rare way for amoebae to multiply, called encyclical or multiple fission. When amoebae feel that the environment is becoming unfavorable (for example. B, lack of nutrients, too acidic or too much bright light), they retract their pseudopod and release a protective layer (called a cyst) composed of a chitin-like substance to cover its cell membrane. This cyst is able to survive in much harsher conditions. At the same time, mitosis occurs several times in the cyst and produces more than two daughter cells. When the cyst wall ruptures (when the condition becomes favorable), these daughter cells are released to become several new amoebae. When the colonization environment becomes extremely unfavorable, amoebae multiply in spores. This sexual reproduction can create genetic diversity and increase their chances of survival in difficult conditions. Try PMC Labs and let us know what you think. Find out more.
Using RFP-Dajumin to visualize the CV, we compared CV structures in different mutant strains. We confirmed that no bladder or tube structures were observed in lvsA− cells; Only small dot-shaped structures were observed, suggesting that a functional CV system was missing (Gerald et al., 2002). lvsA/disgorgin cells have a similar phenotype that explains how lvsA interference suppresses the large vacuole phenotype in disgorgin− cells (Figure 6B). V-ATPase, which is mainly localized in CVs, is always located in these dot-shaped structures, suggesting that in the absence of LvsA, immature CV structures form but cannot mature or enlarge (Gerald et al., 2002). Thus, the cells lvsA−/lvsD− and lvsA−/lvsD−/disgorgin− do not have enlarged bubbles and have point-shaped CV structures (data not shown). In addition, these two strains have all lvsA− cell phenotypes, including sensitivity to hypotonic stress, as well as phagocytosis and cytokine infections (data not shown) (Kwak et al., 1999; Gerald et al., 2002). Another feature that you can easily observe is the abundance of crystalline inclusions inside the protean amoeba. Most crystals of Amoeba proteus have a bipyramidal shape. These crystals are contained in vacuoles and consist of triuret, a nitrogenous waste. Other types of amoebae have their crystals of different shapes, such as balls, leaves, and even crescent-shaped crystals. Here are some examples of crystals in different types of amoebae. Disgorgin or Disgorgin in full length without F-Box (DisgorginΔF-Box; Figure 1A) in the cells Disgorgin− completes the phenotype of the large vacuole and does not cause an overexpression phenotype when expressed in wild-type cells (Figure 1D, data not shown).
Disgorgin, amino acid substitutions in any of the conserved residues necessary for GAP activity (DisgorginR515A; DisgorginQ551A) does not complete zero phenotypes and produces even larger vacuoles when placed in disgorgin or wild type cells (up to 11 μm; Figure 1D and Additional Figure S2A), suggesting that mutated proteins exert an effect as dominant-negative mutants, possibly by further blocking the intrinsic activity of GTPase Rab and/or competing with common substrates or essential components of the signaling pathway. These results suggest that disgorgin rabGAP activity in the signaling pathway is necessary to regulate vacuoles and that the F-box domain is not essential to this process. Plant cells do not have contractile vacuoles. On the contrary, most mature plant cells have a single large vacuole that occupies 30% of the space in the volume of a cell, which can then take up to 80% for certain cell types/conditions. Sometimes the strands of the cytoplasm circulate through the vacuole. Source To put it simply, a contractile vacuole in some protozoa expels the liquid during contraction. As a contractile vacuole, the subcellular structure works in parallel with osmoregulation, which occurs in protists and single-celled algae. It has also been called pulsating or pulsed vacuole. This is because the contractile vacuole is a type of vacuole that performs the function of draining excessive amounts of water into the cell. Without their presence, parasitic and marine protozoa can occur under isotonic conditions inside and outside cellular organisms. To understand the role of disgorgine, we compared the CV cycle in wild-type cells and disgorgine cells by marking the cells with RFP dajumine and placing the cells in water to activate the CV system.
As previously described (Gabriel et al., 1999; Heuser, 2006), when cells are placed under hypotonic conditions, CV network activity increases significantly and the dynamic load and discharge of vesicles can be easily monitored (Figure 2B). After vacuole discharge, dajumine RFP is visible as a spot on the plasma membrane, suggesting that the CV membrane is flattened against the plasma membranes. In addition, new CV bubbles preferably form at these sites, suggesting that the collapsed CV bubble is different from most of the plasma membrane, after which it regenerates into a new CV (Figure 2B) (Heuser, 2006). To study this in more detail, we used the dye styryl FM4-64, which marks both the plasma membrane and the CVs (Heuser et al., 1993). .
