Changes in polysome profiles accompany trypanosome development

Development of the protozoan pathogen Trypanosoma brucei involves regulated changes in parasite structure, biochemistry, and the cell cycle. The trans ition of slender blood forms into stumpy bloodforms includes cell cycle arr est and a decrease in protein synthesis. The next stage in the development cycle, the procyclic form, shows increased protein synthesis and proliferat es. To address the mechanism of the cyclical changes in protein synthesis, we examined two parameters: polyadenylation of mRNA and ribosome loading. W e developed a method for analytical polyribosome analysis in T. brucei whic h provided excellent results with regard to reproducibility, yield of mRNA densely loaded with ribosomes, and separation of mRNA associated with diffe rent numbers of polyribosomes. Use of this technique allowed us to determin e that the polysome profiles of the different developmental stages are dist inctly different, with higher ribosome loading in the proliferating stages. The lengths of the poly(A) tails on the total population of RNA from the d ifferent developmental stages showed no significant variation. These data i ndicate that changes in polysome loading of mRNAs accompany development, an d that they do not reflect bulk changes in polyadenylation. We speculate th at developmental changes in translation reflect reduced translational initi ation. (C) 1998 Published by Elsevier Science B.V. All rights reserved.