Understanding genomic-context specific deposition and function of H3.V and H4.V histone variants in Trypanosoma brucei

• Applicant: Professor Dr. Tim Nicolai Siegel
• Subject Area: General Genetics and Functional Genome Biology
• Term: from 2013 to 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 244748328

Studies in numerous organisms have shown that the replacement of canonical histones with histone variants can affect DNA accessibility. Thus, histone variant deposition represents a means to regulate any DNA-templates process, such as transcription, replication or DNA repair. A large number of different histone variants and complex genome-wide chromatin patterns have slowed progress towards a comprehensive understanding of the mechanisms leading to the deposition of histone variants at specific genomic loci and the role of the genomic context in determining the function of histone variants. Thus, for most histone variants it is not understood how and why they are targeted to specific genomic locus and whether they can have different functions depending on their genomic context.To overcome these hurdles, we propose to study histone variant deposition and function in T. brucei, a unicellular eukaryote with many features that make it ideally-suited to investigate basic mechanisms of histone variant biology. T. brucei possess only one variant for each canonical histone and, due to the arrangement of genes into polycistronic transcription units (PTUs), a relatively small number of only ~200 transcription start sites (TSSs) and transcription termination sites (TTSs). In addition, we have shown that in T. brucei the four different histone variants, H2A.Z, H2.V, H3.V and H4.V, exhibit a very distinct genome-wide distribution, making it easy to detect small changes in variant distribution.Recently, we have found that loss of H3.V leads to a defect in transcription termination and changes in genome organization. In addition, we have observed that concurrent deletion of H3.V and H4.V strongly affects chromatin compaction at specific genomic loci and increases antigen switching by recombination.Based on these findings we hypothesize that, depending on its genomic context, H3.V has different biological functions. We suspect that it is deposited at sites of double stranded break to aid in DNA repair and at the end of PTUs to ensure proper transcription termination. To test these hypotheses, we will investigate how and why H3.V is targeted to specific genomic loci and determine whether the genomic context affects the role it plays in local chromatin structure and higher order genome organization.

• DFG Programme: Research Grants