β-III-spectrin spinocerebellar ataxia type 5 mutation reveals a dominant cytoskeletal mechanism that underlies dendritic arborization

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Abstract

A spinocerebellar ataxia type 5 (SCA5) L253P mutation in the actin-binding domain (ABD) of β-III-spectrin causes high-affinity actin binding and decreased thermal stability in vitro. Here we show in mammalian cells, at physiological temperature, that the mutant ABD retains high-affinity actin binding. Significantly, we provide evidence that the mutation alters the mobility and recruitment of β-III-spectrin in mammalian cells, pointing to a potential disease mechanism. To explore this mechanism, we developed a Drosophila SCA5 model in which an equivalent mutant Drosophila β-spectrin is expressed in neurons that extend complex dendritic arbors, such as Purkinje cells, targeted in SCA5 pathogenesis. The mutation causes a proximal shift in arborization coincident with decreased β-spectrin localization in distal dendrites. We show that SCA5 β-spectrin dominantly mislocalizes α-spectrin and ankyrin-2, components of the endogenous spectrin cytoskeleton. Our data suggest that high-affinity actin binding by SCA5 β-spectrin interferes with spectrin-actin cytoskeleton dynamics, leading to a loss of a cytoskeletal mechanism in distal dendrites required for dendrite stabilization and arbor outgrowth.

Original languageEnglish (US)
Pages (from-to)E9376-E9385
JournalProceedings of the National Academy of Sciences of the United States of America
Volume114
Issue number44
DOIs
StatePublished - Oct 31 2017

Bibliographical note

Funding Information:
ACKNOWLEDGMENTS. We thank Dr. Harry T. Orr at the University of Minnesota for critical review of the manuscript; Michael E. Fealey for assistance with protein purification and circular dichroism; Amanda L. Neisch for assistance with dissections and critical input on experiments; R. Grace Owens-Kurtz and Madison L. Irwin, undergraduates who helped with the dendritic arbor analyses; fellow laboratory members Min-Gang Li and Madeline Serr for intellectual input and critical reading; Dr. Sean D. Conner for advice on the mammalian cell culture work; and Dr. Hermann Aberle for the ankyrin-2 XL antibody. This work was supported by NIH Grant R01 GM44757 (to T.S.H.) and NIH Training Grant T32 AR007612 (to D.D.T.). A.W.A. received fellowship support from the National Ataxia Foundation and the Bob Allison Ataxia Research Center.

Publisher Copyright:
© 2017, National Academy of Sciences. All rights reserved.

Keywords

  • Ankyrin
  • Dendritic arborization
  • SCA5
  • Spectrin
  • Spinocerebellar ataxia type 5

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