1. A var gene promoter controls allelic exclusion of virulence genes in Plasmodium falciparum malaria.
- Author
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Voss TS, Healer J, Marty AJ, Duffy MF, Thompson JK, Beeson JG, Reeder JC, Crabb BS, and Cowman AF
- Subjects
- Animals, Animals, Genetically Modified, Antigenic Variation genetics, Antigenic Variation immunology, Cell Nucleus metabolism, Epigenesis, Genetic genetics, Genes, Protozoan genetics, Malaria, Falciparum immunology, Multigene Family genetics, Plasmodium falciparum immunology, Transcription, Genetic genetics, Transfection, Transgenes genetics, Virulence genetics, Alleles, Gene Silencing, Malaria, Falciparum parasitology, Plasmodium falciparum genetics, Plasmodium falciparum pathogenicity, Promoter Regions, Genetic genetics, Virulence Factors genetics
- Abstract
Mono-allelic expression of gene families is used by many organisms to mediate phenotypic variation of surface proteins. In the apicomplexan parasite Plasmodium falciparum, responsible for the severe form of malaria in humans, this is exemplified by antigenic variation of the highly polymorphic P. falciparum erythrocyte membrane protein 1 (PfEMP1). PfEMP1, encoded by the 60-member var gene family, represents a major virulence factor due to its central role in immune evasion and intravascular parasite sequestration. Mutually exclusive expression of PfEMP1 is controlled by epigenetic mechanisms involving chromatin modification and perinuclear var locus repositioning. Here we show that a var promoter mediates the nucleation and spreading of stably inherited silenced chromatin. Transcriptional activation of this promoter occurs at the nuclear periphery in association with chromosome-end clusters. Additionally, the var promoter sequence is sufficient to infiltrate a transgene into the allelic exclusion programme of var gene expression, as transcriptional activation of this transgene results in silencing of endogenous var gene transcription. These results show that a var promoter is sufficient for epigenetic silencing and mono-allelic transcription of this virulence gene family, and are fundamental for our understanding of antigenic variation in P. falciparum. Furthermore, the PfEMP1 knockdown parasites obtained in this study will be important tools to increase our understanding of P. falciparum-mediated virulence and immune evasion.
- Published
- 2006
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