The RNA-binding protein Quaking (QKI) plays a fundamental role in post-transcriptional gene regulation during mammalian nervous system development. QKI is well known for advancing oligodendroglia differentiation and myelination, however, its functions in astrocytes and embryonic central nervous system (CNS) development remain poorly understood. Uncovering the complete spectrum of QKI molecular and functional repertoire is of additional importance in light of growing evidence linking QKI dysfunction with human disease, including schizophrenia and glioma. This thesis summarizes my contribution to fill this gap of knowledge.
In a first attempt to identify the QKI-mediated molecular pathways in astroglia, we studied the effects of QKI depletion on global gene expression in the human astrocytoma cell line. This work revealed a previously unknown role of QKI in regulating immune-related pathways. In particular, we identified several putative mRNA targets of QKI involved in interferon signaling, with possible implications in innate cellular antiviral defense, as well as tumor suppression. We next extended these investigations to human primary astrocytes, in order to more accurately model normal brain astrocytes. One of the most interesting outcomes of this analysis was that QKI regulates expression of transcripts encoding the Glial Fibrillary Acidic Protein, an intermediate filament protein that mediates diverse biological functions of astrocytes and is implicated in numerous CNS pathologies. We also characterized QKI splice variant composition and subcellular expression of encoded protein isoforms in human astrocytes. Finally, we explored the potential use of zebrafish as a model system to study neurodevelopmental functions of QKI in vivo. Two zebrafish orthologs, qkib and qki2, were identified and found to be widely expressed in the CNS neural progenitor cell domains. Furthermore, we showed that a knockdown of qkib perturbs the development of both neuronal and glial populations, and propose neural progenitor dysfunction as the primary cause of the observed phenotypes.
To conclude, the work presented in this thesis provides the first insight into understanding the functional significance of the human QKI in astroglia, and introduces zebrafish as a novel tool with which to further investigate the importance of this gene in neural development.