Regulation of four functionally related enzymes during shifts in the developmental program of Dictyostelium discoideum

Abstract

Partially developed cell aggregates of Dictyostelium discoideum engaged in fruiting body construction can be disaggregated to single cells and redeposited on solid substratum. The cells almost immediately reaggregate, recapitulate within two to three hours a previous course of morphogenesis that might have taken as much as 18 to 20 hours the first time, and then complete the construction of fruiting bodies with approximately normal timing. During particular stages of fruit construction, four functionally related enzymes accumulate, reach characteristic levels of specific activity, and then disappear partly or completely. They are: UDP-glucose pyrophosphorylase, trehalose-6-phosphate synthetase, UDP-galactose-4-epimerase and UDP galactose: polysaccharide galactosyl transferase. The disaggregated cells discontinued the initial rounds of enzyme synthesis, but when permitted to reaggregate and develop further, they accomplished complete second rounds of enzyme accumulation. If disaggregated and redeposited a second time, they accomplished complete third rounds of enzyme synthesis as well. All such additional rounds required new periods of RNA synthesis. A characteristic level of each enzyme activity accumulated during each round of synthesis regardless of the amount previously accumulated. In these additional rounds the temporal relations between transcription and enzyme synthesis were drastically altered.