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General Information
Name
spinocerebellar ataxia 17
FlyBase ID
FBhh0000071
Overview

This report describes spinocerebellar ataxia 17 (SCA17), which is a subtype of spinocerebellar ataxia; SCA17 is inherited as an autosomal dominant. The human gene implicated in this disease is TBP, which encodes TATA box-binding protein, DNA-binding subunit of the RNA polymerase II transcription factor D. Expanded (CAG)n or (CAA)n trinucleotide repeats encoding polyglutamine in TBP are associated with SCA17; SCA17 is one of a number spinocerebellar ataxias caused by expansion of such repeats within the coding region of the causative gene. There is one high-scoring fly ortholog, Tbp, for which RNAi targeting constructs, alleles caused by insertional mutagenesis, and classical amorphic alleles have been generated. Dmel\Tbp is orthologous to a second human gene, TBPL2.

Multiple UAS constructs of the human gene Hsap\TBP have been introduced into flies, including wild-type TBP, and TBP genes with expanded polyglutamine repeats. Transgenic flies expressing a mutant Hsap\TBP protein with an expanded polyQ tract exhibit progressive neurodegeneration, late-onset locomotor impairment and shortened lifespan. Expression in the eye results in a neurodegenerative phenotype; this phenotype has been used to assess genetic interactions.

Variant(s) implicated in human disease tested (as transgenic human gene, TBP): Q58_Q95 (CAG)n EXPANSION; UAS-TBP constructs with differing numbers of the pathological trinucleotide repeat have been created.

Animals homozygous for loss-of-function alleles of Dmel\Tbp die during larval stages. Heterozygous animals can survive to adulthood without obvious morphological defects, but suffer severe locomotor defects and a shortened lifespan. Physical and genetic interactions for Dmel\Tbp have been reported; see below and in the gene report for Tbp.

Extensive studies have also been done with polyglutamine-only models in flies; see the disease report for polyglutamine diseases, polyQ models (FBhh0000001).

[updated Mar. 2017 by FlyBase; FBrf0222196]

Disease Summary Information
Parent Disease Summary: spinocerebellar ataxia, autosomal dominant
Symptoms and phenotype

The autosomal dominant cerebellar degenerative disorders are generally referred to as 'spinocerebellar ataxias,' (SCAs) even though 'spinocerebellar' is a hybrid term, referring to both clinical signs and neuroanatomical regions (Margolis, 2003, pubmed:14628900). Neuropathologists have defined SCAs as cerebellar ataxias with variable involvement of the brainstem and spinal cord, and the clinical features of the disorders are caused by degeneration of the cerebellum and its afferent and efferent connections, which involve the brainstem and spinal cord (Schols et al., 2004 pubmed:15099544; Taroni and DiDonato, 2004, pubmed:15263894). [From OMIM:164400, 2015.10.27]

The autosomal dominant cerebellar degenerative disorders are generally referred to as 'spinocerebellar ataxias' (SCAs). Neuropathologists have defined SCAs as cerebellar ataxias with variable involvement of the brainstem and spinal cord; the clinical features of the disorders are caused by degeneration of the cerebellum and its afferent and efferent connections, which involve the brainstem and spinal cord (Schols et al., 2004 pubmed:15099544; Taroni and DiDonato, 2004, pubmed:15263894). [From OMIM:164400, 2015.10.27]

Specific Disease Summary: spinocerebellar ataxia 17
OMIM report

[SPINOCEREBELLAR ATAXIA 17; SCA17](https://omim.org/entry/607136)

Human gene(s) implicated

[TATA BOX-BINDING PROTEIN; TBP](https://omim.org/entry/600075)

Symptoms and phenotype

Spinocerebellar ataxia type 17 (SCA17) is characterized by ataxia, dementia, and involuntary movements, including chorea and dystonia. Psychiatric symptoms, pyramidal signs, and rigidity are common. The age of onset ranges from three to 55 years. Individuals with full-penetrance alleles develop neurologic and/or psychiatric symptoms by age 50 years. Ataxia and psychiatric abnormalities are frequently the initial findings, followed by involuntary movement, parkinsonism, dementia, and pyramidal signs. Brain MRI shows variable atrophy of the cerebrum, brain stem, and cerebellum. The clinical features correlate with the length of the polyglutamine expansion but are not absolutely predictive of the clinical course. [From GeneReviews, Spinocerebellar Ataxia Type 17, pubmed:20301611, 2015.12.15]

SCA17 is an autosomal dominant neurologic disorder characterized by ataxia, pyramidal and extrapyramidal signs, cognitive impairments, psychosis, and seizures. Its clinical phenotype and inheritance pattern are similar to Huntington disease (HD; OMIM:143100). Individuals with normal TBP alleles have between 25 and 44 repeats, whereas SCA17 patients have between 47 and 63 repeats. Reduced penetrance is seen with 45 to 46 repeats (summary by Gao et al., 2008, pubmed:18043721). [From OMIM:607136, 2015.12.15]

Genetics

This form of autosomal dominant spinocerebellar ataxia, SCA17 can be caused by heterozygous expansion of a trinucleotide repeat encoding glutamine (CAG or CAA) in TBP, the gene encoding the TATA box-binding protein. Rarely, SCA17 has been found to be caused by homozygous or compound heterozygous TBP repeat expansions. [From OMIM:607136, 2015.10.30]

Cellular phenotype and pathology
Molecular information

TBP is the DNA-binding subunit of the RNA polymerase II transcription factor D (TFIID; see OMIM:313650), a multisubunit complex essential for the expression of most, if not all, protein-encoding genes. [From OMIM:600075, 2015.10.30]

External links
Disease synonyms
SCA17
Huntington-disease-like 4
HDL4
spinocerebellar ataxia 17; SCA17
spinocerebellar ataxia type 17
Ortholog Information
Human gene(s) in FlyBase
Human gene (HGNC)
D. melanogaster ortholog (based on DIOPT)
Comments on ortholog(s)

Many to one (2 human to 1 Drosophila) (See DIOPT, link below)

Other mammalian ortholog(s) used
    D. melanogaster Gene Information (1)
    Gene Snapshot
    TATA binding protein (Tbp) encodes a basal transcription factor required at most RNA Pol I and Pol II-transcribed genes. Traditionally thought to be recruited only to TATA box containing promoters, recent work shows that promoters with very weak TATA box consensus sequences also recruit the product of Tbp as a part of the multisubunit TFIID basal transcription factor or via the SAGA histone acetyltransferase complex. [Date last reviewed: 2019-03-14]
    Gene Groups / Pathways
    Comments on ortholog(s)

    Ortholog of human ITPR1, and ITPR3 (1 Drosophila to 2 human).

    Dmel\Tbp shares 58% identity and 63% similarity with human TBP, and 54% identity and 62% similarity to human TBPL2.

    Orthologs and Alignments from DRSC
    DIOPT - DRSC Integrative Ortholog Prediction Tool - Click the link below to search for orthologs in Humans
    Synthetic Gene(s) Used (0)
    Summary of Physical Interactions (34 groups)
    protein-protein
    Interacting group
    Assay
    References
    anti bait coimmunoprecipitation, western blot
    anti bait coimmunoprecipitation, western blot
    anti bait coimmunoprecipitation, western blot
    ion exchange chromatography, molecular sieving, western blot
    two hybrid, anti tag coimmunoprecipitation, peptide massfingerprinting, experimental knowledge based
    anti bait coimmunoprecipitation, western blot
    anti bait coimmunoprecipitation, molecular weight estimation by staining, western blot, ion exchange chromatography, molecular sieving
    anti bait coimmunoprecipitation, western blot
    anti tag coimmunoprecipitation, western blot, ion exchange chromatography, molecular sieving, anti bait coimmunoprecipitation
    anti tag coimmunoprecipitation, peptide massfingerprinting, experimental knowledge based
    anti tag coimmunoprecipitation, peptide massfingerprinting, experimental knowledge based
    anti bait coimmunoprecipitation, western blot, pull down, anti tag coimmunoprecipitation
    anti tag coimmunoprecipitation, western blot, anti bait coimmunoprecipitation
    ion exchange chromatography, molecular sieving, western blot
    pull down, western blot
    anti bait coimmunoprecipitation, western blot
    anti bait coimmunoprecipitation, western blot
    ion exchange chromatography, molecular sieving, western blot
    anti bait coimmunoprecipitation, western blot
    anti bait coimmunoprecipitation, western blot
    anti bait coimmunoprecipitation, western blot, molecular weight estimation by staining, pull down, ion exchange chromatography, molecular sieving, anti tag coimmunoprecipitation, affinity chromatography technology, peptide massfingerprinting, experimental knowledge based
    anti tag coimmunoprecipitation, western blot, autoradiography, anti bait coimmunoprecipitation, molecular weight estimation by staining
    anti bait coimmunoprecipitation, western blot, molecular weight estimation by staining
    anti bait coimmunoprecipitation, molecular weight estimation by staining, western blot
    anti bait coimmunoprecipitation, western blot, molecular weight estimation by staining, anti tag coimmunoprecipitation, peptide massfingerprinting
    anti bait coimmunoprecipitation, western blot
    anti bait coimmunoprecipitation, western blot
    anti bait coimmunoprecipitation, western blot, molecular weight estimation by staining, peptide massfingerprinting
    anti bait coimmunoprecipitation, peptide massfingerprinting, molecular weight estimation by staining, anti tag coimmunoprecipitation, western blot
    anti bait coimmunoprecipitation, western blot
    pull down, autoradiography, anti tag coimmunoprecipitation, anti tag western blot
    pull down, autoradiography
    protein-protein
    Interacting group
    Assay
    References
    anti bait coimmunoprecipitation, western blot
    Alleles Reported to Model Human Disease (Disease Ontology) (4 alleles)
    Models Based on Experimental Evidence ( 1 )
    Allele
    Disease
    Evidence
    References
    Modifiers Based on Experimental Evidence ( 2 )
    Models Based on Experimental Evidence ( 2 )
    Modifiers Based on Experimental Evidence ( 2 )
    Genetic Tools, Stocks and Reagents
    Sources of Stocks
    Contact lab of origin for a reagent not available from a public stock center.
    Bloomington Stock Center Disease Page
    Selected mammalian transgenes
    Allele
    Transgene
    Publicly Available Stocks
    Selected Drosophila transgenes
    Allele
    Transgene
    Publicly Available Stocks
    RNAi constructs available
    Allele
    Transgene
    Publicly Available Stocks
    Selected Drosophila classical alleles
    Allele
    Allele class
    Mutagen
    Publicly Available Stocks
    ethyl methanesulfonate
    References (10)