We study the parasite Toxoplasma gondii as a model for intracellular pathogens that cause many of the world’s most debilitating infectious diseases. Toxoplasma is extremely widespread, infecting almost 25% of the human population. Although infections are normally benign, toxoplasmosis is an important pathogen in immunocompromised patients including newborns, elderly, and those with underlying immune deficiencies. We are exploring the molecular mechanisms whereby T. gondii disrupts host cell signaling and blocks immunity using a variety of cellular and molecular approach. We are also developing in vitro methods to cultivate and develop genetic tools in Cryptosporidium, a widespread cause of diarrheal disease in the developing world.
Genetics – comparative genomics
Comparative genomic approaches are being used to investigate genetic differences that mediate important biological diversity as well as to define unique adaptations for parasitism in T. gondii and related parasites. Toxoplasma is equipped with both forward and reverse genetics, including efficient system for gene editing with CRISPR/Cas9, making it a model for studying both basic biology and pathogenesis. Genetic approaches are being applied to identify the molecular basis of intracellular survival, enhanced transmission, and persistence of chronic infection.
Virulence factors: modulating host transcription and signaling
The laboratory mouse is an excellent model for Toxoplasma and forward genetic approaches have revealed that pathogenesis depends on the ability of the parasite to disrupt innate immunity, block apoptosis, and alter host transcription. Acute virulence is mediated by secretion of polymorphic serine threonine kinases that block innate immunity pathways. The parasite also co-opts host gene expression by modifying chromatin and activating transcription factors. We are using a variety of omics approaches to define the alterations in host gene expression and signaling networks that are driven by parasite infection and which underlie pathogenesis.
Developing systems to study Cryptosporidium
Cryptosporidium is a major cause of childhood diarrheal disease in the developing world. There are currently no vaccines or effective treatments for preventing illness in children. We are utilized stem-cell derived culture systems to differentiate intestinal epithelial cells from human and animal biopsies as a method to growth C. parvum in vitro. Developing in vitro cultivation and genetic tools will allow development of genetic systems to define pathogenesis as well as support screening for new therapeutics and attenuated vaccines.
Shen, B., Brown, K., Long, S., Sibley, L.D. (2017) Development of CRISPR/Cas9 for Efficient Genome Editing in Toxoplasma gondii. Methods Mol Biol. 1498:79-103. PubMed PMID: 27709570.
Olias. P., Etheridge, R.D., Zhang. Y., Holtzman, M.J., Sibley, L.D. (2016) Toxoplasma Effector Recruits the Mi-2/NuRD Complex to Repress STAT1 Transcription and Block IFN-γ-Dependent Gene Expression. Cell Host Microbe. 20:72-82. PubMed Central PMCID:
Lorenzi, H., Khan, A., Behnke, M.S., et al., Sibley LD.(2016) Local admixture of amplified and diversified secreted pathogenesis determinants shapes mosaic Toxoplasma gondii genomes. Nat Commun. 7:10147. PMCID: PMC4729833.
Etheridge, R.D., Alaganan, A., Tang, K., Lou, H.J., Turk, B.E., Sibley, L.D. (2014) The Toxoplasma pseudokinase ROP5 forms complexes with ROP18 and ROP17 kinases that synergize to control acute virulence in mice. Cell Host Microbe. 15:537-50.PMCID:PMC4086214.
Alaganan, A., Fentress, S.J., Tang, K., Wang, Q., Sibley, L.D. (2014) Toxoplasma GRA7 effector increases turnover of immunity-related GTPases and contributes to acute virulence in the mouse. Proc Natl Acad Sci U S A. 111:1126-31.PMCID: PMC3903209.
Skillman, K.M., Ma, C., Fremont, D.H., Cooper, J.A., Sept, D., & Sibley, L.D. (2013) The unusual dynamics of Toxoplasma actin result from isodesmic polymerization.
Nat. Commun. 4:2285.
Su CL, Khan A, Zhou P, Majumdar D, Ajzenberg D, Dard ML, Zhu XQ, Ajioka JW, Rosenthal B, Dubey JP, Sibley LD: Globally diverse Toxoplasma gondii isolates comprise six major clades originating from a small number of distinct ancestral lineages.
Proc. Natl. Acad. Sci. (USA), 2012, 109:5844-9.
Behnke MS, Khan A, Wootton JC, Dubey JP, Tang K, Sibley LD. Virulence differences in Toxoplasma mediated by amplification of a family of polymorphic pseudokinases.
Proc. Natl. Acad. Sci. (USA) 2011 108: 9631-9636.
Fentress SJ, Behnke MS, Dunay IR, Mashayekhi M, Rommereim LM, Fox BA, Bzik DJ, Taylor GA, Turk BE, Lichti CF, Townsend RR, Qiu W, Hui R, Beatty WL, Sibley LD. Phosphorylation of immunity-related GTPases by a parasite secretory kinase promotes macrophage survival and virulence.
Cell Host Microbe 2010 16;8(6):484-95.
Lourido S, Shuman J, Zhang C, Shokat KM, Hui R, and Sibley LD. Calcium dependent kinase 1 is an essential regulator of microneme secretion in Toxoplasma gondii.
Nature 2010 465: 359-362.