Regulation of cell differentiation and pattern formation in Dictyostelium development.

Free-living cells of Dictyostelium discoideum aggregate to form a slug-shaped cell mass and differentiate into prestalk and prespore cells. The differentiation of prespore cells is characterized by expression of Dp87 gene, the earliest event of prespore differentiation. It encodes a protein which first appears in ER of aggregating cells in a precursor form, is then translocated to prespore vacuoles and modified to a mature form and finally exocytosed to constitute the sorus matrix. The transcription of Dp87 is regulated by the cis-acting region consisting of positive, prespore-specific, negative, non-prespore-specific and positive, cell-type-non-specific elements. Cells expressing Dp87 appear at random in early aggregation streams and centers and then sort out to the posterior part of the slug. Intercellular signals required for prestalk and prespore differentiation were investigated by incubation at a low cell density of disaggregated cells. cAMP is inhibitory at the first and second stages of prespore differentiation, while it is required at the third stage. The stalk differentiation is divided into four stages: cAMP is required at the second stage and differentiation inducing factor (DIF) at the third stage, where a low molecular weight secretory substance is also required. At the third stage, cAMP inhibits both ecmA and ecmB expression, while 8-Br-cAMP specifically induces ecmB and maturation of prestalk to stalk cells. The relationship between the differentiation tendency of preaggregative cells and the cell-cycle phase at the initiation of development was studied by the use of cells synchronized for growth by a temperature-shift method.(ABSTRACT TRUNCATED AT 250 WORDS)