Giardia lamblia (also called Giardia intestinalis) is one of the most common intestinal parasites of humans. To evade the host’s immune response, Giardia undergoes antigenic variation—a process that allows the parasite to develop chronic and recurrent infections. From a repertoire of ∼190 variant-specific surface protein (VSP)-coding genes, Giardia expresses only one VSP on the surface of each parasite at a particular time, but spontaneously switches to a different VSP by unknown mechanisms. Here we show that regulation of VSP expression involves a system comprising RNA-dependent RNA polymerase, Dicer and Argonaute, known components of the RNA interference machinery. Clones expressing a single surface antigen efficiently transcribe several VSP genes but only accumulate transcripts encoding the VSP to be expressed. Detection of antisense RNAs corresponding to the silenced VSP genes and small RNAs from the silenced but not for the expressed vsp implicate the RNA interference pathway in antigenic variation. Remarkably, silencing of Dicer and RNA-dependent RNA polymerase leads to a change from single to multiple VSP expression in individual parasites.
Access optionsAccess options
Subscribe to Journal
Get full journal access for 1 year
only $3.90 per issue
All prices are NET prices.
VAT will be added later in the checkout.
Rent or Buy article
Get time limited or full article access on ReadCube.
All prices are NET prices.
We thank N. Gottig and M. E. Alvarez for technical support. This work was supported by grants from the Agencia Nacional para la Promoción de la Ciencia y la Tecnología (ANPCYT), the Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), the Universidad Católica de Córdoba (UCC), the Howard Hughes Medical Institute (HHMI), and the European Union CONTENT project. H.D.L. is an HHMI International Research Scholar and a Member of the Scientific Investigator’s Career of the CONICET.
Author Contributions C.G.P. knocked down the expression of AGO and VSP9B10, expressed VSPH7 in WB strain trophozoites, performed confocal immunofluorescence assays, northern blots and quantitative RT–PCRs, and cloned and sequenced small RNAs; I.S. knocked down the expression of Dicer and RdRP, performed nuclear run-on and Dicer activity experiments, and cloned and sequenced RdRP, Dicer and VSP genes; R.Q. performed immunofluorescence assays, quantitative RT–PCRs and flow cytometry experiments; P.G.C. performed DNA methylation experiments; and F.D.R., E.V.E. and A.S. generated different monoclonal antibodies and performed immunofluorescence and immunoblotting assays. C.G.P., I.S. and H.D.L wrote this manuscript. H.D.L. conceived and coordinated the project. All authors discussed the results and commented on the manuscript.
This file contains Supplementary Figures 1-10 with Legends, Supplementary Table 1, Supplementary Methods and Supplementary References
About this article
Current Tropical Medicine Reports (2015)