Tau isoforms which contain the domain encoded by exon 6 and their role in neurite elongation

Harvard University, Cambridge, Massachusetts, United States
Journal of Cellular Biochemistry (Impact Factor: 3.26). 04/2004; 91(5):880-95. DOI: 10.1002/jcb.20029
Source: PubMed


The regulation of tau protein expression during different stages of cellular differentiation and development as well as its functional role in morphogenesis, neurofibrillary tangle formation, and neurodegeneration have been topics of extensive study but have not been completely clarified yet. Tau undergoes complex regulated splicing in the mammalian nervous system. Our previous study with tau exon 6 demonstrated that it shows a splicing regulation profile which is distinct from that of the other tau exons as well as a unique expression pattern which is spatially and temporally regulated. In this study, we investigated the expression, localization, and effects of tau isoforms which contain exon 6 in neuroblastoma cells which stably overexpress them. We found that expression of one particular combination of tau exons (the longest adult isoform plus the domain of exon 6) significantly inhibits neurite elongation.

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    • "The isoform 6c has a microtubule-binding domain that is missing in the 6p and 6d isoforms. It has been determined that the presence of exon 6c inhibits neurite extension in RA-differentiated SY5Y cells, whereas the presence of exon 6d does not (Luo et al., 2004). Interestingly, Leroy et al. (2006b) found that inclusion of exon 6c decreases in DM1 brains compared with control brains whereas inclusion of 6d increases, and that alternative splicing modulators CELF5 and CELF6 influence exon 6 splicing in COS cells. "
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    ABSTRACT: Myotonic dystrophy type 1 (DM1) is a dominant neuromuscular disorder caused by the expansion of trinucleotide CTG repeats in the 3'-untranslated region (3'-UTR) of the DMPK gene. Prominent features of classical DM1 are muscle wasting and myotonia, whereas mental retardation is distinctive for congenital DM1. The main nervous system symptoms of DM1 are cognitive impairment, neuroendocrine dysfunction, and personality and behavior abnormalities. It is thought that expansion of CTG repeats causes DM1 pathology through different molecular mechanisms; however, a growing body of evidence indicates that an RNA gain-of-function mechanism plays a major role in the disease development. At the skeletal muscle level, three main molecular events can be distinguished in this model: 1) formation of nuclear foci that are composed at least of mutant DMPK mRNA and recruited RNA-binding proteins, such as splicing regulators and transcription factors; 2) disturbance of alternative splicing of specific genes; and 3) impairment of cell differentiation. Contrasting with the substantial advances in understanding DM1 muscle pathology, the molecular basis of DM1 in the nervous system has just started to be revealed. This review focuses in the DM1 nervous system pathology and provides an overview of the genetic and molecular studies analyzing the effects of the DMPK gene CUG expanded repeats on cell function in neuronal systems. A comparison between the molecular mechanisms of DM1 in the skeletal muscle and those identified in DM1 nervous system models is provided. Finally, future directions in the study of DM1 in the nervous system are discussed.
    Full-text · Article · Jan 2008 · Journal of Neuroscience Research
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    • "In support of this hypothesis, the 2 + 3 + 6 + 10 + isoform drastically decreases process length if over-expressed in SY5Y neuroblastoma cells (Luo et al. 2004a). This postulated role of exon 6 is consistent with its relative levels of expression in fetal versus adult brain (Wei and Andreadis 1998; Luo et al. 2004a; Leroy et al. 2006). "
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    ABSTRACT: Tau is a microtubule-associated protein whose transcript undergoes complex regulated splicing in the mammalian nervous system. Exon 6 of the gene is an alternatively spliced cassette whose expression profile differs from that of the other tau regulated exons, implying the involvement of distinct regulatory factors. Previous work had established the existence and use of two additional 3' splice sites within exon 6 and the influence of splicing factors polypyrimidine binding protein (PTB) and U2AF on its splicing. The present work shows that exon 6 isoforms exist in distinct ratios in different compartments of the nervous system and that splicing of exon 6 is governed by multiple branch points, exonic cis elements and additional trans factors. Recent results show that tau exon 6 is specifically suppressed in the brains of people who suffer from myotonic dystrophy type 1. The understanding of how tau exon 6 splicing is regulated may give us insights into the disease.
    Full-text · Article · Feb 2007 · Journal of Neurochemistry
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    • "Recently, expression of Tau isoform including exons 2 and 3 plus exon 6 in neuroblastoma cells was shown to inhibit neurite outgrowth [12]. Exon 1 is part of the promoter, and is transcribed but not translated. "
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    ABSTRACT: Microtubule-associated Tau proteins are the basic component of intraneuronal and glial inclusions observed in many neurological disorders, the so-called tauopathies. Many etiological factors, phosphorylation, splicing, and mutations, relate Tau proteins to neurodegeneration. Molecular analysis has revealed that hyperphosphorylation and abnormal phosphorylation might be one of the important events in the process leading to tau intracellular aggregation. Specific set of pathological tau proteins exhibiting a typical biochemical pattern, and a different regional and laminar distribution, could characterize five main classes of tauopathies. A direct correlation has been established between the regional brain distribution of tau pathology and clinical symptoms; for instance progressive involvement of neocortical areas is well correlated to the severity of dementia in Alzheimer's disease, overall suggesting that pathological tau proteins are reliable marker of the neurodegenerative process. Recent discovery of tau gene mutations in frontotemporal dementia with parkinsonism linked to chromosome 17 has reinforced the predominant role attributed to tau proteins in the pathogenesis of neurodegenerative disorders, and underlined the fact that distinct sets of tau isoforms expressed in different neuronal populations could lead to different pathologies. Overall, a better knowledge of the etiological factors responsible for the aggregation of tau proteins in brain diseases is essential for development of future differential diagnosis and therapeutic strategies. They would hopefully find their application against Alzheimer's disease but also in all neurological disorders for which a dysfunction of Tau biology has been identified.
    Full-text · Article · Feb 2005 · Biochimica et Biophysica Acta
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