A Mutant of Dictyostelium Discoideum Capable of Differentiating Without Morphogenesis

Abstract

A mutant which is capable of differentiating into spores and stalk cells without forming a cell aggregate was isolated from the cellular slime mould, Dictyosteliurn discoideum. The mutant stopped developing at various stages, before formation of mature fruits, and the cells differentiated into s p o r a and stalk cells at whichever stage the develop-nent stopped. Unaggregated cells also differentiated into spores or stalk cells, depending on the culture conditions; differentiation into spores predominated in nutrient rich medium, while differentiation into stalk cells predominated in nutrient poor medium. The ratio of spores to stalk cells or of prespores to total cells in cell masses depended on the terminal structures formed; the ratio was unusually high or unusually low in a structure which stopped developing before papilla formation, while the ratio was normal in a structure forimed after that stage. When isolated from a cell mass, prespore cells of the mutant did not dedifferentiate or resumed vegetative growth, indicating that they had lost plasticity of differentiation. The conditioned medium in which the mutant cells had grown was effective in inducing diikzntistion of wild type slug cells into spore-like or 'stalk-like cells.The development of the cellular slime mould Dictyostelium discoideum is initiated by aggregation of individual amebas into a hemispherical cell mass. A papilla develops on the top of the aggregate and then elongates and transforms into a slug shaped cell mass. After a period of migration, the slug constructs a fruiting body consisting of a cellular stalk supporting a mass of spores. During formation of the fruiting body, the anterior prestalk cells of the slug differentiate into stalk cells, while the posterior prespore cells differentiate into spores (14). The prespore cells are identified by the presence of a prespore antigen which is specifically stained with fluorescein conjugated antispore serum (17, 19).Free-living cells which have not aggregated do not differentiate into either spores or stalk cells under normal conditions. When cells disaggregated from a slug are replated without being allowed to reaggregate, they are inhibited from accumulating some stage specific enzymes (13). Similarly, isolated prespore cells lose the prespore antigen and dedifferentiate to become capable of vegetative growth (21). Furthermore, when a slug of a "cell contact temperature-sensitive" mutant was exposed to non-permissive conditions, the cells dedifferentiated in spite of the fact that they were still packed in the cell mass (1 1).BONNER ( Cell contact is required for cell differentiation in this organism.The following observations, however, seem inconsistent with these facts.

Three steps in prespore differentiationin Dictyostelium discoideum with different requirements of cellular interaction

“…These results suggest that DCF is not CAMP and that the competence is acquired independently of a high concentration of CAMP. The inhibitory effect of CAMP added at an early stage of development is consistent with previous reports [13,261. Ammonia is another factor known to stimulate prespore/spore differentiation [ 1 1, 31, 36, 39, 40, 411.…”

“…With respect to the pathway of prestalk/stalk differentiation, Kay and his coworkers [ 171 have shown that with the strain V12M2 terminal differentiation occurs even at low cell density only if cAMP and a lowmolecular-weight substance, stalk cell differentiation inducing factor (DIF), are supplied. In vitro and in vivo analysis of cAMP and DIF dependency indicates that the period during which cAMP acts precedes that of DIF, which subsequently induces prestalk and stalk characteristics [l, 14, 34, 351. Prespore/spore differentiation also requires extracellular cAMP and other cellular interactions [4,7,13,16,27,29,321, and in this case cAMP has been shown to act in later stages [26,30,331. However with respect to other interactions the time of action remains unclarified.…”

Factors controlling prespore cell differentiation in Dictyostelium discoideum: Minute amounts of differentiation – inducing factor promote prespore cell differentiation

“…In preliminary experiments, at least two types of prespore-inducing substances have been found in CM. One is a heat-stable dialysable factor (M, < 5x103), which may be prespore-inducing factor (PIF) or previously reported factors [16,40,441. It appears not to be spore protein-inducing factor (SPIF), whose action can be substituted by methionine [ l 11, because 20 pA.4 methionine had no effect on differentiation in the present system.…”

Wheat germ agglutinin binding proteins in the cellular slime moulds Dictyostelium and Polysphondylium

“…Dictyostelium cells were grown with Escherichia coli B/r on SM agar plates (Sussman, 1951). Polysphondylium cells were grown with the same bacteria on 5-LP agar plates (0.5% lactose, 0.5% peptone; Ishida, 1980). All were allowed to develop at 21 "C in the light.…”