Abstract
Most unexpectedly, there is now increasing evidence that mitochondria have novel and crucial functions in the regulatory machinery of the growth/differentiation transition, cell-type determination, cellular movement and pattern formation. Here we created rho delta cells with a reduced amount (about 1/4) of mitochondrial DNA (mtDNA) from Dictyostelium discoideum Ax-2 cells, by exposing Ax-2 cells to ca. 30 microg/ml of ethidium bromide (EtBr) in axenic growth medium. Importantly, the rho delta cells exhibited a series of fascinating behaviors: when they were starved, they showed a marked delay of differentiation and stopped their development at the slug stage, thus failing to construct fruiting bodies. Moreover, cell patterning and cell-type proportioning were found to be greatly modified in slugs (referred to as rho delta slugs) derived from rho delta cells. That is, prestalk differentiation was significantly enhanced in rho delta slugs, while prespore differentiation was markedly inhibited. In addition, the clear anterior prestalk/posterior prespore pattern was considerably disturbed in rho delta slugs, presumably because of incomplete sorting between the two types of differentiated cells. After the assay of phototaxis, rho delta slugs also exhibited highly disordered movement towards the light source. Taken together, these results suggest that mtDNA might have important multiple functions in a variety of cellular processes during Dictyostelium development.
Highlights
Mitochondrial diseases and mitochondria-dependent sterility, as well as a close relationship between mitochondria and programmed cell death, have been generally recognized in a variety of cell lines
Increasing evidence indicates that mitochondria have novel and crucial functions in the regulatory machinery of growth/differentiation transition, cell-type determination, cellular movement and pattern formation, in the development of Dictyostelium discoideum (Maeda, 1971; Matsuyama and Maeda, 1995; Wilczynska et al, 1997; Matsuyama and Maeda, 1998; Inazu et al, 1999; van Es et al, 2001)
Ax-2 cells were grown in axenic growth medium containing various concentrations of ethidium bromide (EtBr) to test its effect on growth
Summary
Mitochondrial diseases and mitochondria-dependent sterility, as well as a close relationship between mitochondria and programmed cell death (apoptosis), have been generally recognized in a variety of cell lines. A particular checkpoint (referred to as a PS-point) from growth to differentiation phase has been precisely specified in the midlate G2 phase of the cell cycle (Maeda et al, 1989). This is the point from which cells initiate differentiation when placed under conditions of nutritional deprivation. Dictyostelium development offers us a useful system for elucidating the cellular and molecular mechanisms of the growth/differentiation transition (GDT), pattern formation in cell masses and a variety of other problems of current interest in developmental biology
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