Disgorgin localized in lvsA− cells to pierce structures next to the plasma membrane that have been co-located with dajumine RFP, suggesting that they are CV structures (Figure 6C; Data not displayed). Since Disgorgin was only located in the CV at the end of the loading phase, this suggests that the deviant CV structures in the lvsA− cells are remnants of CV that stopped growing after discharge. We propose that LvsA maintain the integrity of the CV during the discharge phase. Since previous reports have shown that LvsA transfers to the CV membrane after the vacuole has reached its maximum diameter (De Lozanne, 2003), we examined the detailed kinetics of the LvsA association with the CV membrane to better understand the function of LvsA. Accelerated video microscopy of cells that co-expressed GFP-LvsA and RFP-Dajumin revealed that GFP-LvsA was only transferred to the CV membrane in the very last phase of discharge immediately before the CV bubbles were flattened against the plasma membrane (additional film S5). The period during which LvsA was associated with CVs was short (18±5 s (n = 30 cells)) as opposed to 57±18 s (n = 30 cells) between the time of localization of disgorgine in CVs and complete discharge of vacuoles. The complete cycle, from the onset of cvian growth to discharge, is ∼100±22 s (n = 30 cells). The kinetics of the LvsA association with the CV membrane is consistent with the role of LvsA in maintaining membrane integrity during the melting process. This localization of the LvsA CV membrane is independent of disgorgine (Figure 6C). Surprisingly, LvsD did not localize on CV membranes and was still cytosolic in all cell lines tested, whether the cells were in isotonic or hypotonic media (data not shown). 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. In summary, the contractile vacuol system now appears as an unexpected dynamical system – far beyond its impressive systole/diastole cycle. PtSyb2 and PtSyx2 are SNAREs found exclusively in this complex organelle, in all its parts except the decorated spongioma (where only atPase H+ is found). There is no evidence of actin in this organelle. Luykx et al. (1997a) conducted an in-depth study of the structural and dynamic aspects of contractile vacuoles in C. reinhardtii. Using video microscopy, they established three steps in the vacuole cycle of about 15 seconds in the hypotonic medium. In the first 3 seconds (early diastoles), small vesicles with a diameter of 70 to 120 nm appear, which then merge together in the intermediate stage of 6 seconds to form the vacuole (Figure 2.14). Additional small vesicles form and fuse with the vacuole in the remaining 6 seconds of the cycle (late diastole), and the vacuole touches the plasma membrane.
The culmination of the process (systole) is a rapid discharge (0.2 seconds) of the vacuol content into the medium. In the hypertonic medium, small vesicles similar to those of the primitive diastole are observed, but they do not transform into fusion and systole (Denning and Fulton, 1989a; Hellebust et al., 1989). Try PMC Labs and let us know what you think. Find out more. The contractile vacuole, as the name suggests, expels water from the cell by contracting. The growth (water retention) and contraction (water excretion) of contractile vacuoles are periodic. A cycle lasts several seconds, depending on the type and osmolarity of the environment. The stage at which water flows into the CV is called diastole. The contraction of the contractile vacuole and the expulsion of water from the cell are called systole. Although several suspected regulatory components have been shown to be associated with the Dictyostelium CV system, including vacuolar-H+ ATPase (V-ATPase), LvsA, drainin, rab11A and Rab14, little is known about the regulation of the CV system and the pathways that control CV discharge (Heuser et al., 1993; Bush et al., 1996; Becker et al., 1999; Harris et al., 2001; Gerald et al., 2002; Wu et al., 2004). . .