The Importance of DTC in Biological Functions

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In worms, DTC functions as GSC niche (Kimble and White, 1981). In hermaphrodites, distal end of each gonad has one DTC while in males; both DTCs are located at the end of a single gonad. DTC sends cytoplasmic processes which envelop the neighboring cells and hence, provide them a niche. DTC signals nearby cells to remain mitotically proliferating and as cells move away from it; they are no longer under the influence of these signals and hence, enter meiosis. DTC is crucial for larval germ cell proliferation and for the maintenance of GSCs in adults. Laser ablation of DTC results in the loss of mitotically dividing due to precocious meiotic entry. Conversely, ectopic localization of DTC relocates stem cell population and its duplication forms a new pool of mitotically proliferating stem cells. Therefore, DTC is necessary as well as sufficient for the mitotic proliferation of GSCs (Byrd and Kimble, 2009; Kimble and White, 1981). Approximately 230 mitotically proliferating cells are present at the distal end of the gonad, which spreads to ~ 20 cell diameters from the DTC (Crittenden et al., 1994; Hansen et al., 2004a). Label retaining assays using BrdU and EdU; and other studies of cell cycle kinetics have revealed that there are two subpopulations within the 230 mitotically dividing cells. Distal most ~130-160 cells are actively proliferating while ~ 70-90 cells present more proximal to distal end within the mitotic zone are in premeiotic S-phase (Crittendenet al., 2006 ;

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