Neural Cell Type-Specific Expression of QKI Proteins Is Altered in quakingviable Mutant Mice

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Proteomic diversity is frequently achieved by alternative RNAsplicing events that can be fine-tuned in tissue-specific and developmentally regulated ways. Understanding this type of genetic regulation is compelling because of the extensive complexity of alternative splicing found in the nervous system. quaking (qk), one of the classical mouse dysmyelination mutants, is defective for the expression of myelin-associated glycoprotein (MAG), and the misregulation of MAG pre-mRNA alternative splicing is implicated as a causal factor. The qk locus encodes several RNA-binding proteins with heterogeneous nuclear ribonucleoprotein K-type homology, a characteristic of several known alternative splicing regulators. Here we test the nuclear-localized qk isoform (QKI-5) for its ability to regulate alternative splicing of MAG pre-mRNA in transient coexpression assays. QKI-5 exhibits properties of a negative regulator of MAG exon 12 alternative splicing. An intronic sequence element required for the repressive function and binding of QKI-5 is also identified. Direct evidence for irregularities in alternative splicing of MAG and other myelin protein transcripts in the qk mouse is demonstrated.A lternative splicing is a powerful way to regulate gene expression at the posttranscriptional level and to generate protein diversity (1, 2). Understanding the molecular basis of such mechanisms is an urgent challenge, because the number of protein-coding genes in humans has been estimated at barely double the number in Drosophila and Caenorhabditis elegans. Between 35% and 59% of human genes are predicted to generate alternatively spliced mRNA isoforms (3).Mouse quaking (qk), also known as quaking viable (qk v ), is a classical recessive dysmyelination mutation (4). The qk locus produces a diverse set of proteins by alternative splicing (5, 6). They all contain a single heterogeneous nuclear ribonucleoprotein K homology (KH) RNA-binding domain and belong to the evolutionarily conserved signal transduction and activator of RNA (STAR) family (7,8). The first three studied in detail are constructed with the same 311-aa body, but have different carboxyl tails. QKI-5 is the only nuclear isoform and shuttles between the nucleus and cytoplasm (9, 10). The expression of QKI isoforms is developmentally regulated, with QKI-5 being highly expressed throughout the embryogenesis and neonatal stages and decreasing gradually thereafter (7, 9). In postnatal day 14 (P14) mutant mice QKI proteins are decreased exclusively in myelin-forming cells. In addition, the QKI-5 expression level in qk v brain correlates with the severity of dysmyelinating phenotype, suggesting a function of QKI-5 in myelination (9).The relationship between the decreased QKI protein in affected mice and their myelination defects is not understood. It has been shown that several myelin-specific genes are alternatively spliced, including myelin basic protein (MBP), proteolipid protein (PLP), and MAG (11-13). Some splicing events seem to be abnormal in qk v mice. The best-documented c...

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confidence: 97%

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confidence: 99%

Function of quaking in myelination: Regulation of alternative splicing

Reed

Grabowski

et al. 2002

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“…The function of the Qki gene has been well studied in mouse by using an autosomal recessive mutant (qk v ), characterized by body tremor and severe dysmyelination of the CNS (6). The mutation consists of a 1-Mb deletion including the 5Ј regulatory region of Qki (1) that causes oligodendrocyte dysfunction and reduced expression of myelin components in CNS (7). The Qki gene contains an RNA-binding domain (KH domain) that binds directly to cellular RNA (8).…”

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confidence: 99%

Human QKI, a potential regulator of mRNA expression of human oligodendrocyte-related genes involved in schizophrenia

Åberg

Saetre

Jareborg

et al. 2006

184

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The quaking viable mouse mutation (qk v ) is a deletion including the 5 regulatory region of the quaking gene (Qki), which causes body tremor and severe dysmyelination in mouse. The function of the human quaking gene, called quaking homolog KH domain RNAbinding (mouse) (QKI), is not well known. We have previously shown that QKI is a new candidate gene for schizophrenia. Here we show that human QKI mRNA levels can account for a high proportion (47%) of normal interindividual mRNA expression variation (and covariation) of six oligodendrocyte-related genes (PLP1, MAG, MBP, TF, SOX10, and CDKN1B) in 55 human brain autopsy samples from individuals without psychiatric diagnoses. In addition, the tightly coexpressed myelin-related genes (PLP1, MAG, and TF) have decreased mRNA levels in 55 schizophrenic patients, as compared with 55 control individuals, and most of this difference (68 -96%) can be explained by variation in the relative mRNA levels of QKI-7kb, the same QKI splice variant previously shown to be down-regulated in patients with schizophrenia. Taken together, our results suggest that QKI levels may regulate oligodendrocyte differentiation and maturation in human brain, in a similar way as in mouse. Moreover, we hypothesize that previously observed decreased activity of myelin-related genes in schizophrenia might be caused by disturbed QKI splicing.myelin ͉ quaking ͉ splice variant

“…The qk gene, which encodes for RNA binding proteins involved in posttranscriptional mRNA regulation (6,7), is in close proximity to the proximal deletion breakpoint of qk v (8). The qk v deficiency affects the region upstream of the qk gene to reduce the expression of qk mRNAs in oligodendrocytes, resulting in the CNS myelination defect (9,10). In addition to the spontaneous qk v deletion, several N-ethyl-N-nitrosourea (ENU)-induced alleles of quaking have been isolated (11)(12)(13).…”

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confidence: 99%

Deletion of the Parkin coregulated gene causes male sterility in the quaking ^viable mouse mutant

Lorenzetti

Bishop

Justice

2004

Quaking viable (qk v ) is a recessive neurological mouse mutation with severe dysmyelination of the CNS and spermiogenesis failure. The molecular lesion in the qk v mutant is a deletion of Ϸ1 Mb on mouse chromosome 17 that alters the expression of the qk gene in oligodendrocytes. Complementation analysis between the qk v mutation and qk mutant alleles generated through chemical mutagenesis showed that the male sterility is a distinctive feature of the qk v allele. This observation suggested that the sperm differentiation defect in qk v is due to the deletion of a gene(s) distinct from qk. Here, we demonstrate that the deletion of Pacrg is the cause of male sterility in the qk v mutant. Pacrg is the mouse homologue of the human PARKIN-coregulated gene (PACRG), which encodes for a protein whose biochemical function remains unclear. We show that Pacrg is highly expressed in the testes in both mice and humans. In addition, the expression pattern of Pacrg during spermiogenesis suggests that it plays a role in sperm differentiation. In support of this hypothesis, we show that transgenic expression of Pacrg in testes restores spermiogenesis and fertility in qk v males. This finding provides the first in vivo evidence, to our knowledge, for the function of Pacrg in a model organism. Immunolocalization experiments on isolated spermatozoa show that the Pacrg protein is present in mature sperm. Remarkably, the mammalian Pacrg protein shares significant sequence similarities with gene products from flagellated protozoans, suggesting that Pacrg may be necessary for proper flagellar formation in many organisms.