Comparison of proteins synthesized by anterior and posterior regions of Dictyostelium discoideum pseudoplasmodia.

In migrating pseudoplasmodia of the cellular slime mold Dictyostelium discoideum, cells in approximately the anterior quarter of the structure give rise to stalk cells, while the remainder produce spore cells. Certain biochemical and structural components have been found to differ between cells occupying these two positions, indicating that some differentiation has already occurred by this stage. To evaluate the degree of this differentiation we have compared the proteins being synthesized in different regions of the pseudoplasmodia. Migrating pseudoplasmodia were labeled with [³⁵S]methionine and cut into five segments, and the labeled proteins were resolved by two-dimensional gel electrophoresis and visualized by autofluorography. Of 500 polypeptides detected, 57 showed regional variations in labeling. Nearly all of these differences in labeling occurred between the anterior fifth and posterior four-fifths of the pseudoplasmodia, indicating that by this stage a marked degree of differentiation has occurred between the two cell types.