Stage-specific expression of Trypanosoma cruzi trans-sialidase involves highly conserved 3' untranslated regions.

trans-Sialidases (TSs) are virulence factors that allow some trypanosomatids to incorporate sialic acid from host molecules. Trypanosoma cruzi bears a complex gene family coding for TS members, which can be broadly divided into two groups: one translated in stages present in the mammalian host (trypomastigote TS, tTS) and one translated in the insect vector stages (epimastigote TS, eTS). The molecular basis underlying the expression of different, nonoverlapping sets of TS proteins in either host is poorly understood, particularly because of the lack of transcription initiation control in this organism. Here we show that 3' untranslated regions (3'UTRs) of tTS and eTS are highly conserved within each gene group but completely different between both groups. Importantly, tTS-3'UTR but not eTS-3'UTR promoted high expression of the green fluorescent protein reporter gene in the mammalian-dwelling stages. In epimastigotes, both 3'UTRs lead to a comparatively low expression of the reporter gene, although eTS-3'UTR was more efficient than tTS-3'UTR. These results stress the importance of posttranscriptional events, mainly driven by specific 3'UTRs, in gene expression regulation in T. cruzi.