Trypanosoma brucei is a protozoan parasite that causes African sleeping sickness in humans and a similar disease in livestock, mainly in sub-Saharan Africa. T. brucei cycles between the insect vector (tsetse fly) and mammalian hosts. In the mammalian host, the parasite expresses a single species of surface coat protein (VSG, variant surface glycoprotein) at any given time, while having over 2000 VSG genes in the genome – known as the ‘VSG silencing’ (all VSGs are transcriptionally repressed, except one). To clear the parasite, the host immune system recognizes the expressed VSG and kills the parasite. However small populations of parasites escape the host immune killing by expressing a different subset of VSG genes – a process known as ‘VSG switching’. Therefore, T. brucei’s immune evasion via antigenic variation requires precisely controlled VSG silencing and switching mechanisms. Genome integrity factors play important roles in T. brucei antigenic variation, and my lab is interested in how DNA replication, transcription and chromatin structure factors talk to each other to control antigen gene diversification and to maintain genome integrity.
DNA replication, transcription and chromatin structure: Transcription in T. brucei occurs polycistronically, and start and stop sites of transcription are marked by specific chromatin modifications. Transcription termination sites (TTSs) are marked specifically by histone variants, H3v and H4v, and a Kinetoplastid-specific DNA modification, base J. I have discovered that simultaneous deletion of these TTS marks caused severe transcription defects and replication problems. Interestingly, depletion of MCM-BP (Kim et al, 2013 PLOS ONE), a replication protein, shares similar phenotypes as the chromatin mark mutants (unpublished data). My lab is interested in investigating how specific chromatin marks and chromatin structure changes can affect DNA replication as well as transcription. We are using high-throughput sequencing approaches as well as genetic and proteomic techniques.
Developing large-scale screening tools: T. brucei antigenic variation shares mechanistic features with many classic monoallelic gene expression systems both in pathogenic and non-pathogenic organisms. To find novel factors, I also focused on developing various genetic tools for large-scale screens. Recently, I have generated the first T. brucei overexpression library in collaboration with Drs. Nina Papavasiliou (DKFZ/University of Heidelberg), Christine Clayton (ZMBH/University of Heidelberg), Galadriel Hovel-Miner (George Washington University), and Danae Shulz (Harvey Mudd College). This overexpression library is a new resource in the field that can be used to identify novel factors via gain-of-function phenotypes. I am currently working on several screening projects using this library as well as previously described RNAi libraries.
Collaborators: I am collaborating with Dr. Nina Papavsiliou at DKFZ and the University of Heidelberg for library generation/screening as well as VSG structure projects, and Dr. Bibo Li at CSU for the DNA replication and telomere maintenance project.