Loss of p53 in quaking viable mice leads to Purkinje cell defects and reduced survival

Gene Expression of Quaking in Sporadic Alzheimer's Disease Patients is Both Upregulated and Related to Expression Levels of Genes Involved in Amyloid Plaque and Neurofibrillary Tangle Formation

Quaking (QKI) is a gene exclusively expressed within glial cells. QKI has previously been implicated in various neurological disorders and diseases, including Alzheimer’s disease (AD), a condition for which increasing evidence suggests a central role of glia cells. The objective of the present study was to investigate the expression levels of QKI and three QKI isoforms (QKI5, QKI6, and QKI7) in AD. Genes that have previously been related to the ontogeny and progression of AD, specifically APP, PSEN1, PSEN2, and MAPT, were also investigated. A real-time PCR assay of 123 samples from human postmortem sporadic AD patients and control brains was performed. The expression values were analyzed with an analysis of covariance model and subsequent multiple regressions to explore the possibility of related expression values between QKI, QKI isoforms, and AD-related genes. Further, the sequences of AD-related genes were analyzed for the presence of QKI binding domains. QKI and all measured QKI isoforms were found to be significantly upregulated in AD samples, relative to control samples. However, APP, PSEN1, PSEN2, and MAPT were not found to be significantly different. QKI and QKI isoforms were found to be predictive for the variance of APP, PSEN1, PSEN2, and MAPT, and putative QKI binding sites suggests an interaction with QKI. Overall, these results implicate a possible role of QKI in AD, although the exact mechanism by which this occurs remains to be uncovered.

Oligodendroglial defects during quakingviable cerebellar development

The selective RNA-binding protein Quaking I (QKI) has previously been implicated in RNA localization and stabilization, alternative splicing, cell proliferation, and differentiation. The spontaneously-occurring quakingviable (qkv) mutant mouse exhibits a sharply attenuated level of QKI in myelin-producing cells, including oligodendrocytes (OL) because of the loss of an OL-specific promoter. The disruption of QKI in OLs results in severe hypomyelination of the central nervous system, but the underlying cellular mechanisms remain to be fully elucidated. In this study, we used the qkv mutant mouse as a model to study myelination defects in the cerebellum. We found that oligodendroglial development and myelination are adversely affected in the cerebellum of qkv mice. Specifically, we identified an increase in the total number of oligodendroglial precursor cells in qkv cerebella, a substantial portion of which migrated into the grey matter. Furthermore, these mislocalized oligodendroglial precursor cells retained their migratory morphology late into development. Interestingly, a number of these presumptive oligodendrocyte precursors were found at the Purkinje cell layer in qkv cerebella, resembling Bergman glia. These findings indicate that QKI is involved in multiple aspects of oligodendroglial development. QKI disruption can impact the cell fate of oligodendrocyte precursor cells, their migration and differentiation, and ultimately myelination in the cerebellum. © 2015 Wiley Periodicals, Inc. Develop Neurobiol 76: 972-982, 2016.

NF-κB induces miR-148a to sustain TGF-β/Smad signaling activation in glioblastoma

Background

Inflammatory cytokines and transforming growth factor-β (TGF-β) are mutually inhibitory. However, hyperactivation of nuclear factor-κB (NF-κB) and TGF-β signaling both emerge in glioblastoma. Here, we report microRNA-148a (miR-148a) overexpression in glioblastoma and that miR-148a directly suppressed Quaking (QKI), a negative regulator of TGF-β signaling.

Methods

We determined NF-κB and TGF-β/Smad signaling activity using pNF-κB-luc, pSMAD-luc, and control plasmids. The association between an RNA-induced silencing complex and QKI, mitogen-inducible gene 6 (MIG6), S-phase kinase–associated protein 1 (SKP1), and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) mRNA was tested with microribonucleoprotein immunoprecipitation and real-time PCR. Xenograft tumors were established in the brains of nude mice.

Results

QKI suppression induced an aggressive phenotype of glioblastoma cells both in vitro and in vivo. Interestingly, we found that NF-κB induced miR-148a expression, leading to enhanced-strength and prolonged-duration TGF-β/Smad signaling. Notably, these findings were consistent with the significant correlation between miR-148a levels with NF-κB hyperactivation and activated TGF-β/Smad signaling in a cohort of human glioblastoma specimens.

Conclusions

These findings uncover a plausible mechanism for NF-κB–sustained TGF-β/Smad activation via miR-148a in glioblastoma, and may suggest a new target for clinical intervention in human cancer.

Electronic supplementary material

The online version of this article (doi:10.1186/1476-4598-14-2) contains supplementary material, which is available to authorized users.

The QKI-5 and QKI-6 RNA binding proteins regulate the expression of microRNA 7 in glial cells

The quaking (qkI) gene encodes 3 major alternatively spliced isoforms that contain unique sequences at their C termini dictating their cellular localization. QKI-5 is predominantly nuclear, whereas QKI-6 is distributed throughout the cell and QKI-7 is cytoplasmic. The QKI isoforms are sequence-specific RNA binding proteins expressed mainly in glial cells modulating RNA splicing, export, and stability. Herein, we identify a new role for the QKI proteins in the regulation of microRNA (miRNA) processing. We observed that small interfering RNA (siRNA)-mediated QKI depletion of U343 glioblastoma cells leads to a robust increase in miR-7 expression. The processing from primary to mature miR-7 was inhibited in the presence QKI-5 and QKI-6 but not QKI-7, suggesting that the nuclear localization plays an important role in the regulation of miR-7 expression. The primary miR-7-1 was bound by the QKI isoforms in a QKI response element (QRE)-specific manner. We observed that the pri-miR-7-1 RNA was tightly bound to Drosha in the presence of the QKI isoforms, and this association was not observed in siRNA-mediated QKI or Drosha-depleted U343 glioblastoma cells. Moreover, the presence of the QKI isoforms led to an increase presence of pri-miR-7 in nuclear foci, suggesting that pri-miR-7-1 is retained in the nucleus by the QKI isoforms. miR-7 is known to target the epidermal growth factor (EGF) receptor (EGFR) 3' untranslated region (3'-UTR), and indeed, QKI-deficient U343 cells had reduced EGFR expression and decreased ERK activation in response to EGF. Elevated levels of miR-7 are associated with cell cycle arrest, and it was observed that QKI-deficient U343 that harbor elevated levels of miR-7 exhibited defects in cell proliferation that were partially rescued by the addition of a miR-7 inhibitor. These findings suggest that the QKI isoforms regulate glial cell function and proliferation by regulating the processing of certain miRNAs.

Developmental Coordination of Gene Expression between Synaptic Partners During GABAergic Circuit Assembly in Cerebellar Cortex

The assembly of neural circuits involves multiple sequential steps such as the specification of cell-types, their migration to proper brain locations, morphological and physiological differentiation, and the formation and maturation of synaptic connections. This intricate and often prolonged process is guided by elaborate genetic mechanisms that regulate each step. Evidence from numerous systems suggests that each cell-type, once specified, is endowed with a genetic program that unfolds in response to, and is regulated by, extrinsic signals, including cell–cell and synaptic interactions. To a large extent, the execution of this intrinsic program is achieved by the expression of specific sets of genes that support distinct developmental processes. Therefore, a comprehensive analysis of the developmental progression of gene expression in synaptic partners of neurons may provide a basis for exploring the genetic mechanisms regulating circuit assembly. Here we examined the developmental gene expression profiles of well-defined cell-types in a stereotyped microcircuit of the cerebellar cortex. We found that the transcriptomes of Purkinje cell and stellate/basket cells are highly dynamic throughout postnatal development. We revealed “phasic expression” of transcription factors, ion channels, receptors, cell adhesion molecules, gap junction proteins, and identified distinct molecular pathways that might contribute to sequential steps of cerebellar inhibitory circuit formation. We further revealed a correlation between genomic clustering and developmental co-expression of hundreds of transcripts, suggesting the involvement of chromatin level gene regulation during circuit formation.