Expression of trans-sialidase and 85-kDa glycoprotein genes in Trypanosomacruzi is differentially regulated at the post-transcriptional level by labile protein factors

To adapt to different environments, Trypanosoma cruzi, the protozoan parasi te that causes Chagas' disease, expresses a different set of proteins durin g development, To bean to understand the mechanism that controls this diffe rential gene expression, we have analyzed the levels of amastin and trans-s ialidase mRNAs and the mRNAs encoding members of the 85-kDa glycoprotein ge ne family, which are differentially expressed in the T, cruzi stages found in the mammalian host. Amastin mRNA is expressed predominantly in intracell ular and proliferative amastigotes. trans-Sialidase mRNAs are found mostly in forms undergoing transformation from amastigotes to trypomastigotes insi de infected cells, whereas mRNAs encoding the 85-kDa glycoproteins appear o nly in the infective trypomastigotes released from the cells. The genes cod ing for these mRNA species are constitutively transcribed in all stages of T, cruzi cells, suggesting that expression is controlled post-transcription ally during differentiation. Inhibition of transcription by actinomycin D r evealed that each mRNA species has a relatively long half-life in stages wh ere it accumulates. In the case of the trans-sialidase and 85-kDa glycoprot ein genes, mRNA accumulation was induced by treatment with the protein synt hesis inhibitor cycloheximide at the stages that preceded the normal accumu lation. Therefore, mRNA stabilization may account for mRNA accumulation. mR NA degradation could be promoted by proteins with high turnover, or stabili zation could be promoted by forming a complex with the translational machin ery at defined times in development. Identification of the factors that ind uce mRNA degradation or stabilization is essential to the understanding of control of gene expression in these organisms.