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A rhoptry-protein-associated mechanism of clonal phenotypic variation in rodent malaria

Abstract

The recognition and invasion of host cells are mediated by components of the apical complex of the ookinete, sporozoite and merozoite stages of Plasmodium parasites1. The paired rhoptries (organelles involved in host-cell recognition) in the apical complex contain many proteins of as-yet unknown function. In the rodent malaria agent P. yoelii yoelii, a multigene family codes for merozoite rhoptry proteins of relative molecular mass 235,000 (p235 proteins)2,3; these proteins are thought to determine the subset of erythrocytes that the parasites invade4,5. Further support for this idea came from the identification of a region in p235 with weak but significant homology to reticulocyte-binding protein-2 of P. vivax6,8 and the demonstration that at least one p235 member binds to the erythrocyte surface membrane9. Here, using single, micromanipulated P.y.yoelii parasites, we describe a new mechanism of gene expression by which the merozoites originating from a single schizont each express a distinct member of this multigene family. We propose that this new type of clonal phenotypic variation provides the parasite with a survival strategy in the mammalian host; this strategy contributes to the observed chronicity of malarial infections. This phenomenon is genetically and functionally distinct from classical antigenic variation, which is mediated by the var multigene family of P. falciparum10,11,12,13.

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Figure 1: Structure of the Py235 genes, highlighting areas of potential functional importance and the region analysed here.
Figure 2: Analysis of PCR and RT-PCR products obtained from Py. yoelii parasites at different morphological stages.
Figure 3: Representative results from RT-PCR analysis of RNA purified from single merozoites.
Figure 4: Proposed model for Py235 transcription in Py. yoelii, based on analysis of the four differently sized alleles used here (these have each been assigned a different colour).

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Acknowledgements

We thank C. Magnus and G. H. Mitchell for help with micromanipulation, and K.N.Brown, A. A. Holder, S. Khan, M. Knight, R. J. Wilkinson and R. J. M. Wilson for helpful advice and critical reading of the manuscript.

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Correspondence to P. R. Preiser.

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Preiser, P., Jarra, W., Capiod, T. et al. A rhoptry-protein-associated mechanism of clonal phenotypic variation in rodent malaria. Nature 398, 618–622 (1999). https://doi.org/10.1038/19309

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