Eukaryotic Pathogenesis; Microbial Pathogenesis; Microbiology; Molecular and Cellular Biology
Human African trypanosomiasis (commonly called Sleeping Sickness) is one of the global great neglected diseases, causing ~10,000 cases annually according to most recent estimates (2009). The related veterinary disease of livestock (Nagana) also has significant impact on human economic well being throughout sub-Saharan Africa wherever the insect vector (tsetse flies) are found. Both diseases are caused parasitic protozoa called trypanosomes (Trypanosoma brucei ssp.) Because trypanosomes are eukaryotic cells, organized similarly to every cell in our bodies, treatment of infection is not unlike cancer treatment in that chemotherapy against the parasite has harsh consequences for the patient. However, infection is invariably fatal without intervention, consequently new more specific drugs are desperately needed. In addition, because trypanosomes are an anciently divergent evolutionary lineage, they provide a unique model system for studying basic eukaryotic biology. My laboratory focuses on the cell biology of these protozoa, specifically on intracellular trafficking of lysosomal and cell surface proteins as key aspects of the host:parasite relationship. The trypanosome lifecycle alternates between the mammalian bloodstream and the tsetse midgut, and each stage has a unique protein surface coat that forms the first line of contact with the host. These coat proteins are anchored in membranes by glycosylphosphatidylinositol (GPI) anchors and are essential for survival in each stage. Consequently, correct protein targeting to the cell surface is critical to the success of the parasite. Also, endocytic and lysosomal functions are greatly up-regulated in the pathogenic bloodstream stage for both nutritional and defensive purposes. Using classic and current cell biological and biochemical approaches we work on four distinct areas: 1) GPI-dependent targeting of surface coat proteins; 2) machinery of secretory trafficking; 3) stage-specific lysosomal biogenesis and proteomics; and 4) role of sphingolipids in secretory transport. Our ultimate goal is to define aspects of trypanosomal secretory processes that may provide novel avenues to chemotherapeutic intervention.
Eukaryotic Pathogenesis; Immunology; Infectious Disease; Microbial Pathogenesis; Microbiology; Molecular Basis of Disease; Signal Transduction; Vision science
Toxoplasma gondii is an obligate intracellular parasite that has the unique ability of infecting most nucleated cells in almost all warm-blooded animals. It is one of the most widespread infections in the world: approximately 50 percent of the world‘s population is infected. Luckily, most infected people are asymptomatic; however, in AIDS patients and other immune-compromised individuals, Toxoplasma causes serious and life-threatening disease. Besides its own medical importance, we study Toxoplasma because it represents an ideal model system to study how other related pathogens cause disease. These include Plasmodium, which is the causative agent of malaria that is responsible for millions of deaths worldwide, and Cryptosporidium, which causes another important secondary infection in AIDS patients. Toxoplasma is a great model system because it can easily be grown in vitro, its genome has been sequenced and it can be genetically manipulated. My research team and I are focused on two different but related questions. First, we want to know how the parasite grows inside of its host cell. One of the important things Toxoplasma must do to grow is hijack host cell pathway and factors. We are using functional genomic assays such as microarrays and genome-wide RNA interference (RNAi) screens to identify these host factors. Identifying them is important because if the parasite cannot use these pathways, the parasite will not grow or cause disease. Thus, these pathways represent novel drug targets. As an example, we discovered that oxygen-regulated transcription factors in the host cell are necessary to support parasite growth. We are currently identifying how these transcription factors function and how the parasite adapts to the various oxygen environments it encounters during its lifecycle. Second, we want to know how Toxoplasma affects the central nervous system and how anti-Toxoplasma immune responses function in the central nervous system. These questions are important because Toxoplasma primarily causes disease in the brain and retina. Our work has revealed that when Toxoplasma actively grows in the brain (a condition known as toxoplasmic encephalitis), it causes a massive reorganization of inhibitory synapses. These changes inhibit GABAergic synaptic transmission and this inhibition is a major factor in the onset of seizures in infected individuals. A second line of research using an ocular infection model has focused on defining how immune responses in the central nervous system are generated by Toxoplasma and then resolved once the infection is under control.
Eukaryotic Pathogenesis; Gene Expression; Infectious Disease; Microbial Pathogenesis; Microbiology; RNA; Signal Transduction
There are estimated to be over one million species of fungi on the earth, yet very few of these species are capable of causing deadly systemic infections in humans. One of the major limiting factors for most fungi is their inability to grow at mammalian core body temperature. We utilize the fungal pathogen Cryptococcus neoformans var. grubii as a representative fungal pathogen to understand how these few fungi have adapted to growth at mammalian body temperature. C. neoformans is a worthy pathogen, as it is estimated to cause over 500,000 deaths from meningoencephalitis per year, primarily in Africa and Southeast Asia as an HIV/AIDS comorbidity. We use the temperature-limited Cryptococcus amylolentus as a comparator; it is an environmental strain that produces similar virulence factors to C. neoformans and is fully virulent in surrogate invertebrate hosts at permissive temperatures. We have discovered that host temperature adaptation in C. neoformans is accompanied by a reprogramming of gene expression at the level of messenger RNA (mRNA) stability. In response to temperature stress, C. neoformans rapidly degrades mRNAs that encode energy consuming machinery such as ribosomes. At the same time, it prioritizes the translation of stress-responsive mRNAs on existing ribosomes. Because mRNA synthesis and decay are coupled processes, we seek to identify the protein components of mRNA complexes that mediate the specificity of this decay process and posttranslational modifications, such as arginine methylation and phosphorylation, that modify their function. In addition, we are investigating the signaling pathways that accelerate or slow mRNA decay in response to specific environmental stimuli such as host temperature and nutrient deprivation. Finally, mRNA decay not only alters gene expression at the posttranscriptional level, but the degradation of abundant mRNAs during stress releases nucleotide intermediates that can be utilized by the stressed cell to promote genome stability. We are investigating the process of mRNA degradation as well as nucleotide metabolic pathways as drug targets in C. neoformans and other fungal pathogens. Our goal is to define the unique attributes of C. neoformans that confer pathogenicity and to identify potential targets for novel therapeutics. Each of my students has a project that contributes to the overall goals of my research team. Students in my laboratory work independently, though with frequent interaction with me regarding the direction of investigation and interpretation of data. Regular meetings allow us to provide input on each other’s projects. I expect my students to present their work at least once per year at a national or international meeting, and I expect them to do the bulk of the work in writing papers describing their findings for publication.
Eukaryotic Pathogenesis; Gene Expression; Genomics and proteomics; Infectious Disease; Microbial Pathogenesis; Microbiology; Molecular and Cellular Biology; Molecular genetics; Protein Function and Structure; RNA
Trypanosoma brucei is a eukaryotic pathogen that causes human African trypanosomiasis, a disease that is invariably fatal if not treated. Essential and novel processes in this parasite may serve as starting platforms for new chemotherapeutics, which are urgently needed. Our laboratory combines biochemical, genetic, genomic and proteomic approaches toward understanding gene regulation and protein modification in this pathogenic eukaryote. One focus in my laboratory is RNA editing, a novel mechanism for regulating mitochondrial gene expression in which sequence information is added to mRNAs after transcription by specific insertion and deletion of uridine residues. RNA editing is essential for creating translatable open reading frames (ORFs). We are performing functional and biochemical characterization of the large, dynamic RNA-protein complex termed MRB1, which coordinates multiple aspects of the RNA editing process. A second focus is on regulating RNA stability and translational control in T. brucei, which constitute the major methods of gene regulation in this organism. We identified an RNA binding protein, DRBD18, that impacts the stabilities of hundreds of mRNAs. Our data support a model in which posttranslational modification of DRBD18 by arginine methylation acts as a switch to change DRBD18 from an mRNA destabilizer to an mRNA stabilizer by regulating specific protein-protein and protein-RNA interactions. We are testing this model in vitro and in vivo using reporter assays, in vivo protein-RNA cross-linking and protein-protein interaction assays. A third focus is on understanding the mechanisms by which protein arginine methylation modulates trypanosome biology. We performed a global proteomic analysis of the arginine methylome of T. brucei, identifying >1100 methylproteins spanning most cellular compartments and a wide array of functional classes. We are now analyzing novel mechanisms of protein arginine methyltransferase regulation and defining the physiological and molecular functions of arginine methylmarks on selected proteins. I foster a collaborative and flexible laboratory environment, and I encourage my students to explore the research topics that interest them.
Infectious Disease; Microbiology; Microbial Pathogenesis; Molecular and Cellular Biology; Gene Expression; Transcription and Translation; Protein Function and Structure; RNA; Eukaryotic Pathogenesis
In my laboratory, we use molecular biological and biochemical approaches to study Trypanosoma brucei, the causative agent of African sleeping sickness, and Trypanosoma cruzi, which causes Chagas disease in South and Central America. Treatment for these diseases is severely limited due to increasing drug resistance and lack of available drugs. The goal of our work is to discover and exploit critical events that occur in the parasite life cycle that may be used to prevent growth or transmission of the parasite. The major project in my laboratory examines the ribosome, the complex molecular machine that drives protein synthesis. While many features of the ribosome and its assembly pathway are conserved in the parasites we study, we have identified features that are very different from the human host. Our laboratory discovered a pair of trypanosome-specific RNA binding proteins, P34 and P37, that are part of a unique preribosomal complex that is essential for ribosomal biogenesis and survival of trypanosomes. This may suggest that the interaction of these proteins with other components of the ribosomal assembly pathway can be developed as targets for chemotherapy. We are developing a high-throughput screen for small molecules that disrupt the complex in trypanosomes and do not harm the human host. My team and I also collaborate with Dr. Joachim Frank at Columbia University on a project to examine the structure of the ribosome and intermediates in the pathway of assembly using cryo-electron microscopy (cryo-EM). These experiments will provide important information about the unique features of the structure and function of the trypanosome ribosome and further our discovery of potential drug targets. In addition, we continue in a long-standing collaboration with Dr. Beatriz Garat at the Universidad de la Républica in Uruguay, examining both DNA and RNA binding proteins which regulate gene expression in Trypanosoma cruzi. The balance of graduate, undergraduate and medical students and postdoctoral researchers I mentor changes from year to year, though the international quality I strive to maintain has distinguished my laboratory for years: I enjoy having students from around the world as part of my research team. I am the course director for, and lecture in Critical Analysis and Eukaryotic Pathogens. I am also the course director for Eukaryotic Gene Expression and the co-course director for Molecular Parasitology.