Post-transcriptional regulation of gene expression in trypanosomes

D'ORSO, I; DE GAUDENZI, JG; JÄGER, AV; CASSOLA, A; NOÉ, G; FRASCH, AC

Ashburn

Congreso; Meeting of International Research Scholars; 2006

Howard Hughes Medical Institute

Trypanosomatids are widespread protozoan microorganisms that cause serious health problems such as leishmaniasis, Chagas disease, and sleeping sickness. The parasites are unusual in that they are unable to control gene expression at the transcriptional level because transcription of protein-coding genes is polycistronic. Mature mRNAs result from processing of the polycistrons by trans-splicing and polyadenylation. Thus, regulation of gene expression in trypanosomatids is achieved essentially at the post-transcriptional level. Among several alternatives, modulation of mRNA stability is a widely used mechanism to modulate gene expression in the parasites. In Trypanosoma cruzi, we have shown that modulation of transcript half-life involves AU-rich elements (ARE), as well as other cis sequences, all located in the 3untranslated region (3UTR). We also identified RNA-binding proteins (RBPs), essentially those with RNA-recognition motives (RRMs), that recognize the cis sequences. In vivo, TcUBP1 and TcUBP2, two RRM-containing proteins, were found to be in the same ribonucleoprotein complex together with the polyA-binding protein. Overexpression of TcUBP1 allowed us to demonstrate that this RBP modulates the mRNA stability of a major surface glycoprotein of T. cruzi. TcUBP1 and TcUBP2 are located in the cytoplasm, but can accumulate in the nucleus under stress conditions. The coding sequences for both RBPs are present in a stable dicistronic transcript with a splice-leader sequence on the 5 end (the sequence was added through trans-splicing) and a polyA+ tail on the 3 end. Given that dicistronic and monocistronic units containing TcUBP1- and TcUBP2-coding sequences are detectable in the cytoplasm of the parasite, trypanosomes may use an alternative transsplicing process. Analysis of the complete genomes of Leishmania major, T. brucei, and T. cruzi revealed that all three parasites have similar sets of about 75 RRM-containing protein orthologues, thus suggesting common post-transcriptional processing and regulatory pathways.