Prespore-inducing factors in Dictyostelium discoideum

Abstract. In an attempt to investigate the pathway of prespore differentiation in the cellular slime mold, Dictyostelium discoideum , we examined the requirements for prespore differentiation under conditions involving no cellular interactions. Aggregation-competent cells of the wild-type NC4 strain incubated in an isolated state were found to differentiate into prespore cells depending on the presence of cAMP, bovine serum albumin, and the prespore inducing factors (PIF) obtained from the conditioned media. Vegetative cells did not differentiate into prespore cells under these conditions. The prespore-inducing activity found in extracts of cells was developmentally regulated and induced by cAMP. PIF was of a low molecular mass (150–400 kilodaltons), was heat, alkali, and acid stable, and was extractable from an acidified water phase using ethylacetate. Purification of the PIF in ethylacetate extracts by gel-permeation chromatography followed by reverse-phase chromatography revealed two major peaks with prespore-inducing activity. On mixing these two fractions, the original activity was restored, indicating that PIF is composed of at least two components.