ALTERNATIVE MECHANISMS OF GENE EXPRESSION MODULATION IN T. CRUZI MUCINS

MARIA DE LOS MILAGROS CAMARA; SANTIAGO BERTOTTI; TAKADA RAUL; BUSCAGLIA CA

Caxambu

Congreso; ALTERNATIVE MECHANISMS OF GENE EXPRESSION MODULATION IN T. CRUZI MUCINS; 2015

SBZ

Due to its predominant clonal proliferation, Trypanosoma cruzi exhibit a highly-structured population, composed of multiple strains displaying considerable genetic drift. This genetic variability, in turn have a major impact at the phenotypic level, when parameters such as antigenic profile, virulence, growth rate, pathogenicity, tissue tropism, and sensitivity to anti-chagasic drugs are considered. The surface coat of T. cruzi is covered in different glycoconjugates which contribute to parasite protection and to the establishment of a persistent infection. Mucins, glycoproteins attached to the parasite membrane through a glycosylphosphatidylinositol anchor in which the oligosaccharide chains are O-glycosidically linked to threonine or serine residues via NAcGlc units are major components of this coat. TcSMUG L is a group of genes coding for small T. cruzi mucins anchored to and secreted from the surface of replicative, insect-dwelling developmental forms (i.e. epimastigotes). We have shown that the N-terminal peptide of TcSMUG L mucins promotes adhesion of epimastigotes to the posterior midgut epithelial cells of the triatomine vector Rhodnius prolixus. Recent results obtained from transgenic lines over-expressing TcSMUG L products further support this idea, and indicate that these molecules play also a key role during metacyclogenesis (i.e. conversion of epimastigotes to infective, metacyclic trypomastigotes) in vitro and in vivo. Together, these data indicate that TcSMUG L mucins are key determinants of the infectivity of T. cruzi towards the insect population and, hence, on T. cruzi epidemiology. Interestingly, and in spite of showing a high degree of conservation across paralogues and orthologues from different isolates, TcSMUG L expression at both mRNA and protein levels is quite variable among strains. Here, we show that differences in TcSMUG L expression correlate with bias in threonine codon utilization between strains. This codon bias, in turn correlates with changes in the levels of adenosine-to-inosine editing of threonine decoding tRNAs, suggesting tRNA editing as a forcible step in controlling TcSMUG L (and likely other T. cruzi genes) expression and driving codon adaptation. Moreover, in vivo manipulation of the tRNA editing deaminase complex (ADAT) expression leads to increases in the levels of tRNA adenosine-to-inosine editing, and significantly impacts the expression of TcSMUG L proteins but not TcSMUG L transcripts. These variations were also observed upon ectopic expression of synthetic TcSMUG L constructs displaying contrasting threonine codon bias. Overall, our data support the existence of a novel control mechanism likely operating at the level of TcSMUG L mRNA translation elongation. These findings open a novel perspective on T. cruzi (and trypanosomatids in general) gene expression regulation, generally accepted to rely extensively on post-transcriptional mechanisms, and particularly mRNA abundance.