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Eukaryotic Cell, March 2009, p. 398-409, Vol. 8, No. 3
1535-9778/09/$08.00+0     doi:10.1128/EC.00329-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

A Pseudouridine Synthase Homologue Is Critical to Cellular Differentiation in Toxoplasma gondii{triangledown}

Matthew Z. Anderson,1,2 Jeremy Brewer,2,{dagger} Upinder Singh,2,{ddagger} and John C. Boothroyd2*

Department of Genetics, Stanford University School of Medicine, Stanford, California 94305-5120,1 Department of Microbiology & Immunology, Stanford University School of Medicine, Stanford, California 94305-51242

Received 29 September 2008/ Accepted 24 December 2008

Toxoplasma gondii is a haploid protozoan parasite infecting about one in seven people in the United States. Key to the worldwide prevalence of T. gondii is its ability to establish a lifelong, chronic infection by evading the immune system, and central to this is the developmental switch between the two asexual forms, tachyzoites and bradyzoites. A library of mutants defective in tachyzoite-to-bradyzoite differentiation (Tbd–) was created through insertional mutagenesis. This library contains mutants that, compared to the wild type, are between 20% and 74% as efficient at stage conversion. Two mutants, TBD5 and TBD8, with disruptions in a gene encoding a putative pseudouridine synthase, PUS1, were identified. The disruption in TBD8 is in the 5' end of the PUS1 gene and appears to produce a null allele with a 50% defect in differentiation. This is about the same switch efficiency as obtained with an engineered pus1 deletion mutant ({Delta}pus1). The insertion in TBD5 is within the PUS1 coding region, and this appears to result in a more extreme phenotype of only ~10% switch efficiency. Complementation of TBD8 with the genomic PUS1 allele restored wild-type differentiation efficiency. Infection of mice with pus1 mutant strains results in increased mortality during the acute phase and higher cyst burdens during the chronic infection, demonstrating an aberrant differentiation phenotype in vivo due to PUS1 disruption. Our results suggest a surprising and important role for RNA modification in this biological process.

* Corresponding author. Mailing address: Department of Microbiology and Immunology, Stanford University School of Medicine, 299 Campus Drive, Stanford, CA 94305-5124. Phone: (650) 723-7984. Fax: (650) 725-6757. E-mail: jboothr{at}stanford.edu

{triangledown} Published ahead of print on 5 January 2009.

{dagger} Present address: Massachusetts College of Pharmacy, 179 Longwood Ave., Boston, MA 02115.

{ddagger} Present address: Department of Medicine, Stanford University School of Medicine, Stanford, CA 94305-5107.

Eukaryotic Cell, March 2009, p. 398-409, Vol. 8, No. 3
1535-9778/09/$08.00+0     doi:10.1128/EC.00329-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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