Protein variation in blood-dwelling schistosome worms generated by differential splicing of micro-exon gene transcripts
- Ricardo DeMarco1,2,3,8,
- William Mathieson1,5,
- Sophia J. Manuel1,
- Gary P. Dillon1,6,
- Rachel S. Curwen1,
- Peter D. Ashton1,
- Alasdair C. Ivens4,7,
- Matthew Berriman4,
- Sergio Verjovski-Almeida2 and
- R. Alan Wilson1
- 1 Department of Biology, University of York, York YO10 5YW, United Kingdom;
- 2 Departamento de Bioquímica, Instituto de Química, Universidade de São Paulo, 05508-900 São Paulo, São Paulo, Brazil;
- 3 Departamento de Física e Informática, Instituto de Física de São Carlos, Universidade de São Paulo, 13566-590 São Carlos, São Paulo, Brazil;
- 4 Wellcome Trust Sanger Institute, Hinxton, Cambridge CB10 1SA, United Kingdom
Abstract
Schistosoma mansoni is a well-adapted blood-dwelling parasitic helminth, persisting for decades in its human host despite being continually exposed to potential immune attack. Here, we describe in detail micro-exon genes (MEG) in S. mansoni, some present in multiple copies, which represent a novel molecular system for creating protein variation through the alternate splicing of short (≤36 bp) symmetric exons organized in tandem. Analysis of three closely related copies of one MEG family allowed us to trace several evolutionary events and propose a mechanism for micro-exon generation and diversification. Microarray experiments show that the majority of MEGs are up-regulated in life cycle stages associated with establishment in the mammalian host after skin penetration. Sequencing of RT-PCR products allowed the description of several alternate splice forms of micro-exon genes, highlighting the potential use of these transcripts to generate a complex pool of protein variants. We obtained direct evidence for the existence of such pools by proteomic analysis of secretions from migrating schistosomula and mature eggs. Whole-mount in situ hybridization and immunolocalization showed that MEG transcripts and proteins were restricted to glands or epithelia exposed to the external environment. The ability of schistosomes to produce a complex pool of variant proteins aligns them with the other major groups of blood parasites, but using a completely different mechanism. We believe that our data open a new chapter in the study of immune evasion by schistosomes, and their ability to generate variant proteins could represent a significant obstacle to vaccine development.
Footnotes
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↵8 Corresponding author.
E-mail rdemarco{at}ifsc.usp.br.
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[Supplemental material is available online at http://www.genome.org. The sequence data from this study have been submitted to GenBank (http://www.ncbi.nlm.nih.gov/genbank) under accession nos. GU258169–GU258219. The microarray data from this study have been submitted to the Gene Expression Omnibus (http://www.ncbi.nlm.nih.gov/geo) under accession nos. GSE22037 and GPL10466. The proteomic data from this study have been submitted to the Proteomics Identification Database (http://www.ebi.ac.uk/pride/) under accession nos. 12831–12859 and 12873–12878.]
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Article published online before print. Article and publication date are at http://www.genome.org/cgi/doi/10.1101/gr.100099.109.
- Copyright © 2010 by Cold Spring Harbor Laboratory Press