Production and activity of spore differentiation factors (SDFs) in Dictyostelium

SDF-1 and SDF-2 are peptides that promote terminal spore differentiation un der submerged conditions. The present study shows that they accumulate diff erentially and are released during the development of wild-type cells and c an promote spore formation in cells disaggregated from wildtype culminants, SDF-1 accumulates during the slug stage and is released in a single burst at the onset of culmination while SDF-2 accumulates during early culminatio n and is released in a single burst from mid-culminants. The effects of SDF -1 and SDF-2 on stalk cell formation in cell monolayers were investigated. SDF-1 by itself induces stalk cell formation in some strains and also syner gizes with the stalk-cell-inducing factor, DIF-1, cAMP has an inhibitory ef fect on stalk cell formation when either DIF-I or SDF-1 are present on thei r own but is almost not inhibitory when both are present, SDF-2 alone does not induce stalk cell formation and appears to inhibit the response to DIF- 1. At the same time, it increases the extent of vacuolization of the stalk cells that are produced. We propose that the release of SDF-1 and then of S DF-2 may mark irreversible steps in the developmental programme associated, respectively, with culmination and spore maturation.