Molecular basis of cellular functions in Dictyostelium

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(1) Using the good method for cell synchrony, three genes (dia1, dia2, dia3) were isolated and identified as ones specifically expressed during the transition of Dictyostelium cells from growth to differentiation. Analyses of their functions have revealed that in response to starvation the expressions of a novel gene, dia2, and a mitochondrial gene cluster (dia3) including rps4 are required for the initiation of cell differentiation from the growth/differentiation checkpoint (PS point) in the cell cycle, but that the expression of a novel gene (dia 1) rather inhibits temporally the progression of differentiation from the PS point. In addition, a novel gene, amiB, was also found to be required for the transition of cells from growth to differentiation.(2) The signals for starvation response in Dictyostelium cells have been shown to be transduced through a temporally elevated cytoplasmic Ca2+-concentration ([Ca2+]i). In this connection, it was suggested that Dd-GRP94 (Dictyostelium gluco … More se-regulated protein 94) might be cruial in late differentiation as well as in starvation response. During the course of studies, some phosphoproteins resaonsible for starvation response were also found(3) The mitochondrion was Immunoelectron-microscopically found to be participated in the formation of a cell-type-specific organelle (PSV ; presnore-specific vacuole) as the structural basis, coupling with the Golgi complex.(4) Rappid patterning has been observed in confined 2-D cultures of D.discoideum Ax-2 cells as an outer dark zone and a inner light zone : the outer zone is basically formed by the O2 threshold for oxidative phosphorylation, while the inner cells mainly perform cyanide-resistant respiration. When cells around the early mound stage (just before prestalk and prespore differentiation) were cultured in 2-D cell masses, pstA cells, pstB cells and prespore cells arose in a position-dependent manner in the outer layer. In the inner zone, cell motility seemed to be markedly impared and neither prestalk nor prespore differentiation occurred. In sddition, once-differentiated prespore cells were found to dedifferentiate ranidly in the inr zone.(5) A new type of rappid paterning as observed in a 2-D confined cell mass of D.discoideum is formed due to a reaction-diffusion Turing instability. This may be the first biochemical structure in a developmental system with a controllable boundary condition. Less