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Functional studies of the Quaking gene: Focus on astroglia and neurodevelopment
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Organismal Biology, Evolution and Developmental Biology.
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

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.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2014. , 59 p.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1152
Keyword [en]
QKI, RNA-binding protein, astrocyte, interferon, GFAP, neurodevelopment, zebrafish, neural progenitor cell
National Category
URN: urn:nbn:se:uu:diva-223332ISBN: 978-91-554-8960-1OAI: diva2:713119
Public defence
2014-06-12, Lindahlsalen, Norbevagen 18, Uppsala, 13:15 (English)
Available from: 2014-05-20 Created: 2014-04-17 Last updated: 2014-06-30Bibliographically approved
List of papers
1. QKI-7 regulates expression of interferon-related genes in human astrocyte glioma cells
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2010 (English)In: PloS one, ISSN 1932-6203, Vol. 5, no 9, e13079- p.Article in journal (Refereed) Published
Abstract [en]

BACKGROUND: The human QKI gene, called quaking homolog, KH domain RNA binding (mouse), is a candidate gene for schizophrenia encoding an RNA-binding protein. This gene was shown to be essential for myelination in oligodendrocytes. QKI is also highly expressed in astrocytes, but its function in these cells is not known. METHODS/PRINCIPAL FINDINGS: We studied the effect of small interference RNA (siRNA)-mediated QKI depletion on global gene expression in human astrocyte glioma cells. Microarray measurements were confirmed with real-time quantitative polymerase chain reaction (qPCR). The presence of QKI binding sites (QRE) was assessed by a bioinformatic approach. Viability and cell morphology were also studied. The most significant alteration after QKI silencing was the decreased expression of genes involved in interferon (IFN) induction (P = 6.3E-10), including IFIT1, IFIT2, MX1, MX2, G1P2, G1P3, GBP1 and IFIH1. All eight genes were down-regulated after silencing of the splice variant QKI-7, but were not affected by QKI-5 silencing. Interestingly, four of them were up-regulated after treatment with the antipsychotic agent haloperidol that also resulted in increased QKI-7 mRNA levels. CONCLUSIONS/SIGNIFICANCE: The coordinated expression of QKI-7 splice variant and IFN-related genes supports the idea that this particular splice variant has specific functions in astrocytes. Furthermore, a role of QKI-7 as a regulator of an inflammatory gene pathway in astrocytes is suggested. This hypothesis is well in line with growing experimental evidence on the role of inflammatory components in schizophrenia.

National Category
Biological Sciences Medical and Health Sciences
urn:nbn:se:uu:diva-132707 (URN)10.1371/journal.pone.0013079 (DOI)000282269400026 ()20927331 (PubMedID)
Available from: 2010-10-25 Created: 2010-10-25 Last updated: 2014-05-20Bibliographically approved
2. RNA-binding protein QKI regulates Glial fibrillary acidic protein expression in human astrocytes
Open this publication in new window or tab >>RNA-binding protein QKI regulates Glial fibrillary acidic protein expression in human astrocytes
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2013 (English)In: Human Molecular Genetics, ISSN 0964-6906, E-ISSN 1460-2083, Vol. 22, no 7, 1373-1382 p.Article in journal (Refereed) Published
Abstract [en]

Linkage, association and expression studies previously pointed to the human QKI, KH domain containing, RNA-binding (QKI) as a candidate gene for schizophrenia. Functional studies of the mouse orthologue Qk focused mainly on its role in oligodendrocyte development and myelination, while its function in astroglia remained unexplored. Here, we show that QKI is highly expressed in human primary astrocytes and that its splice forms encode proteins targeting different subcellular localizations. Uncovering the role of QKI in astrocytes is of interest in light of growing evidence implicating astrocyte dysfunction in the pathogenesis of several disorders of the central nervous system. We selectively silenced QKI splice variants in human primary astrocytes and used RNA sequencing to identify differential expression and splice variant composition at the genome-wide level. We found that an mRNA expression of Glial fibrillary acidic protein (GFAP), encoding a major component of astrocyte intermediate filaments, was down-regulated after QKI7 splice variant silencing. Moreover, we identified a potential QKI-binding site within the 3 untranslated region of human GFAP. This sequence was not conserved between mice and humans, raising the possibility that GFAP is a target for QKI in humans but not rodents. Haloperidol treatment of primary astrocytes resulted in coordinated increases in QKI7 and GFAP expression. Taken together, our results provide the first link between QKI and GFAP, two genes with alterations previously observed independently in schizophrenic patients. Our findings for QKI, together with its well-known role in myelination, suggest that QKI is a hub regulator of glia function in humans.

National Category
Natural Sciences Medical and Health Sciences
urn:nbn:se:uu:diva-198376 (URN)10.1093/hmg/dds553 (DOI)000316297000009 ()
Available from: 2013-04-15 Created: 2013-04-15 Last updated: 2016-06-15Bibliographically approved
3. The zebrafish qkib is essential for nervous system development
Open this publication in new window or tab >>The zebrafish qkib is essential for nervous system development
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(English)Manuscript (preprint) (Other academic)
National Category
urn:nbn:se:uu:diva-223331 (URN)
Available from: 2014-04-17 Created: 2014-04-17 Last updated: 2014-05-20

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