Major changes in gene expression occur during at least four stages of development of Dictyostelium discoideum

The spectrum of proteins synthesized at different stages of development of the cellular slime mold Dictyostelium discoideum was analyzed by two-dimensional (2D) gel electrophoresis. Of the approximately 400 proteins detected by this method 189 show changes in their relative rate of synthesis. Most of these changes occur during four distinct stages of development: commencement of development immediately following removal of nutrients (early interphase), early aggregation, late aggregation, and culmination. During commencement the synthesis of 19 proteins begins, the relative rate of synthesis of 21 other proteins increases, and 16 proteins show a rapid decrease in their synthetic rate. During early aggregation the largest change occurs in the spectrum of proteins being synthesized. Specifically, the synthesis of 29 new proteins begins and an increase occurs in the relative synthetic rate of 43 others. During late aggregation, when tight cell-cell contacts form, a reduction takes place in the synthetic rate of most of these induced proteins in addition to the synthesis of 12 new proteins. At least two of these induced proteins are synthesized exclusively in prespore and eventually spore cells. Finally, during culmination, 23 new proteins begin to be synthesized and the synthetic rate of 12 other proteins increases. Five of the 23 newly synthesized proteins appear to be stalk-cell specific. In general, synthesis of spore-cell specific proteins begins just following the formation of tight aggregates while stalk-cell specific proteins are induced during culmination. The relative amounts of mRNAs coding for most of the early developmentally regulated proteins have been estimated by their translation in rabbit reticulocyte lysates and subsequent analysis of protein products by 2D gel electrophoresis. For most of those proteins whose rate of synthesis increases in vivo following starvation there is a parallel increase in the cellular level of the functional mRNAs encoding them. This suggests that the genes coding for these mRNAs may be under transcriptional control. In contrast, the mRNAs coding for most of the proteins whose synthetic rate decreases early in development are under translational control and persist in the cell in an inactive state.