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Antigenic variation in Giardia lamblia is regulated by RNA interference

Nature volume 456, pages 750–754 (2008)Cite this article

Abstract

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.

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Figure 1: Several VSP genes are simultaneously transcribed in Giardia.
Figure 2: Dicer activity and detection of VSP small RNAs in Giardia.
Figure 3: Expression of different VSPs in Giardia rdrp - and dicer -knockdown transgenic trophozoites.

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Accession codes

Primary accessions

GenBank/EMBL/DDBJ

Data deposits

The GenBank accession numbers for Giardia Dicer, RdRP and AGO are AY142144, AF293414 and AY142143, respectively.

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Acknowledgements

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.

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  1. César G. Prucca and Ileana Slavin: These authors contributed equally to this work.

Authors and Affiliations

  1. Laboratorio de Bioquímica y Biología Molecular, Facultad de Medicina, Universidad Católica de Córdoba, Córdoba X5004ASK, Argentina

    César G. Prucca, Ileana Slavin, Rodrigo Quiroga, Eliana V. Elías, Fernando D. Rivero, Alicia Saura, Pedro G. Carranza & Hugo D. Luján

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  1. César G. Prucca
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Correspondence to Hugo D. Luján.

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Prucca, C., Slavin, I., Quiroga, R. et al. Antigenic variation in Giardia lamblia is regulated by RNA interference. Nature 456, 750–754 (2008). https://doi.org/10.1038/nature07585

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