Alternative splicing is a central mechanism to diversify genetic information on the post-transcriptional level. Advances in sequencing technologies revealed shifts in alternative splicing patterns as key features in a variety of biologically relevant systems including embryo development, the adaptive immune response and cancer progression. A recent RNAseq study demonstrated that alternative splicing patterns for thousands of transcripts are altered in macrophages infected with Listeria. While proteins and mechanisms involved are not established, a protective cellular response to limit intracellular replication may be a consequence. The central goal of this proposal is to use this infection model system to gain insights into dynamics of non-coding RNAs and mechanisms of alternative splicing on a single cell level. Intriguingly, it was independently discovered that spliceosome components are transiently sequestered in cytosolic RNA-protein granules called U-bodies during Listeria infection, suggesting that spatiotemporal sequestration may contribute to alternative splicing regulation. Infection with Listeria and formation of U-bodies are highly heterogeneous both in space and time and ideally must be assessed on a single-cell basis. Fluorescence microscopy offers the possibility for long-term visualization of tagged proteins and fluorescently labeled pathogens, but robust tools to visualize cellular RNAs are limiting. To enable visualization of non-coding RNAs, a versatile tool to fluorescently label RNA in live cells will be developed (Aim 1). This tool will then be utilized to quantify spatiotemporal dynamics of U-bodies and simultaneously monitor Listeria replication (Aim 2). Contributions of spliceosome components will be dissected by monitoring RNA dynamics and Listeria replication as spliceosome components will be manipulated experimentally. Lastly, a time resolved quantitative mass spectrometry approach will be used to identify protein candidates that regulate re-shaping of the alternative splicing landscape (Aim 3). These candidate factors will be further investigated by knockdown and assessing consequences for U-body dynamics and intracellular bacterial replication in the microscopy assay. Together, this study will serve as a unique model system to unravel alternative splicing regulation on a single cell level in a physiologically relevant model system using fluorescence microscopy.
Alternative splicing greatly increases the diversity and complexity of genetic material and has been implicated in numerous disease states, yet insights in the proteins, pathways and mechanisms that govern this complex layer of gene regulation are only beginning to emerge. Bacterial infection represents a physiologically relevant cellular perturbation that triggers elaborate alternative splicing changes with consequences for intracellular bacterial replication. A novel RNA fluorescence tags and a multi-parameter single cell microscopy assay will be developed to investigate dynamics of RNA and protein components of the spliceosome and interrogate re-shaping of the alternative splicing.
