A pseudouridine synthase homologue is critical to cellular differentiation in Toxoplasma

Eukaryot Cell. 2009 Jan 5. [Epub ahead of print]

A pseudouridine synthase homologue is critical to cellular differentiation in Toxoplasma gondii

Anderson MZ, Brewer J, Singh U, Boothroyd JC.

Deptartment of Genetics, Stanford University School of Medicine, Stanford, CA, 94305-5120; Department of Microbiology & Immunology, Stanford University School of Medicine, Stanford, CA 94305-5124.

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 wild-type, are between 20% and 74% as efficient at stage conversion. Two mutants, TBD5 and TBD8, were identified with disruptions in a gene encoding a putative pseudouridine synthase, PUS1. 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 (Deltapus1). The insertion in TBD5 is within the PUS1 coding region and this appears to result in a more extreme phenotype of only approximately 10% switch efficiency. Complementation of TBD8 or the Deltapus1 mutant 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.

PMID: 19124578 [PubMed - as supplied by publisher]