Ataxin-7 (ATXN7) is a nuclear protein and integral component of the SAGA (Spt-Ada-Gcn5 acetyltransferase) chromatin remodeling complex, which regulates transcription through histone acetylation and deubiquitination. CAG repeat expansion in ATXN7 causes Spinocerebellar Ataxia Type 7 (SCA7), a distinctive ataxia characterized by progressive cerebellar degeneration and retinal cone-rod dystrophy.[@david1997]
Ataxin-7 (ATXN7) is a nuclear protein and integral component of the SAGA (Spt-Ada-Gcn5 acetyltransferase) chromatin remodeling complex, which regulates transcription through histone acetylation and deubiquitination. CAG repeat expansion in ATXN7 causes Spinocerebellar Ataxia Type 7 (SCA7), a distinctive ataxia characterized by progressive cerebellar degeneration and retinal cone-rod dystrophy.[@david1997]
Splice variants — multiple isoforms with different domain compositions
The protein's integration into the SAGA complex is essential for its normal function and contributes to disease pathogenesis when mutated.[@helmlinger2004]
Normal Function
SAGA Complex Component
Ataxin-7 is a core subunit of the SAGA transcriptional coactivator:
Histone acetylation — SAGA contains the GCN5 histone acetyltransferase
Histone deubiquitination — Contains USP22 that removes H2Bub1
Transcription initiation — Recruits RNA polymerase II to promoters
TATA-binding protein interaction — Links SAGA to TBP
Neuronal Gene Regulation
SAGA with ataxin-7 regulates:[@mcmahon2011]
Neuronal differentiation genes
Synaptic plasticity genes
Photoreceptor-specific transcription
Stress-responsive genes
Retinal Function
Ataxin-7 is particularly important in photoreceptors:
Rod and cone gene expression — SAGA regulates phototransduction genes
[David G, et al, Cloning of the SCA7 gene reveals a highly unstable CAG repeat expansion (1997)](https://doi.org/10.1038/ng0497-065)
[Helmlinger D, et al, Ataxin-7 is a subunit of GCN5 histone acetyltransferase-containing complexes (2004)](https://doi.org/10.1093/hmg/ddl475)
[McMahon SJ, et al, The novel basal transcription factor TFIIS-related protein is required for craniofacial development (2011)](https://doi.org/10.1242/dev.029630)
[Ström AL, et al, Transcriptional alterations in the cerebellum of SCA7 patients and the SCA7 mouse model (2012)](https://doi.org/10.1007/s00401-011-0919-8)
[Mookherjee P, et al, HDAC inhibitor restores normal histone acetylation in SCA7 and improves cerebellar pathology (2011)](https://doi.org/10.1007/s00415-011-6075-z)