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BIOLOGICAL SCIENCES / MICROBIOLOGY
Discovery of parasite virulence genes reveals a unique regulator of chromosome condensation 1 ortholog critical for efficient nuclear trafficking
Department of Medical Microbiology and Immunology, University of Wisconsin, 1300 University Avenue, Madison, WI 53706
Edited by Stanley Falkow, Stanford University, Stanford, CA, and approved April 27, 2007 (received for review March 1, 2007)
Eukaryotic parasites are a leading cause of morbidity and mortality worldwide, yet little is known about the genetic basis of their virulence. Here, we present a forward genetic screen to study pathogenesis in the protozoan parasite Toxoplasma gondii. By using modified signature-tagged mutagenesis, the growth of 6,300 T. gondii insertional mutants was compared in cell culture and murine infection to identify genes required specifically in vivo. One of the 39 avirulent mutants is disrupted in a divergent ortholog of the regulator of chromosome condensation 1 (RCC1), which is critical for nuclear trafficking in model systems. Although this RCC1 mutant grows similar to wild type in standard tissue culture conditions, it is growth-impaired under nutrient limitation. Genetic complementation of mutant parasites with the T. gondii RCC1 gene fully restores both virulence in mice and growth under low-nutrient conditions. Further analysis shows that there is a significant defect in nuclear trafficking in the RCC1 mutant. These findings suggest that the rate of nuclear transport is a critical factor affecting growth in low-nutrient conditions in vivo and in vitro. Additionally, we observed that although RCC1 proteins are highly conserved in organisms from humans to yeast, no protozoan parasite encodes a characteristic RCC1. This protein divergence may represent a unique mechanism of nucleocytoplasmic transport. This study illustrates the power of this forward genetics approach to identify atypical virulence mechanisms.
nuclear transport | Toxoplasma
*Present address: Department of Microbiology and Immunology, New York Medical College, Valhalla, NY 10595.
This article is a PNAS Direct Submission.
The authors declare no conflict of interest.
Data deposition: The sequence reported in this paper has been deposited in the National Center for Biotechnology Information database (accession no. EF591127).
This article contains supporting information online at www.pnas.org/cgi/content/full/0701893104/DC1.
To whom correspondence should be addressed. E-mail: ljknoll{at}wisc.edu
© 2007 by The National Academy of Sciences of the USA
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