Polyglutamine expansion accelerates the dynamics of ataxin-1 and does not result in aggregate formation.
BACKGROUND
Polyglutamine expansion disorders are caused by an expansion of the polyglutamine (polyQ) tract in the disease related protein, leading to severe neurodegeneration. All polyQ disorders are hallmarked by the presence of intracellular aggregates containing the expanded protein in affected neurons. The polyQ disorder SpinoCerebellar Ataxia 1 (SCA1) is caused by a polyQ-expansion in the ataxin-1 protein, which is thought to lead to nuclear aggregates.


RESULTS
Using advanced live cell fluorescence microscopy and a filter retardation assay we show that nuclear accumulations formed by polyQ-expanded ataxin-1 do not resemble aggregates of other polyQ-expanded proteins. Instead of being static, insoluble aggregates, nuclear accumulations formed by the polyQ-expanded ataxin-1 showed enhanced intracellular kinetics as compared to wild-type ataxin-1. During mitosis, ataxin-1 accumulations redistributed equally among daughter cells, in contrast to polyQ aggregates. Interestingly, polyQ expansion did not affect the nuclear-cytoplasmic shuttling of ataxin-1 as proposed before.


CONCLUSIONS
These results indicate that polyQ expansion does not necessarily lead to aggregate formation, and that the enhanced kinetics may affect the nuclear function of ataxin-1. The unexpected findings for a polyQ-expanded protein and their consequences for ongoing SCA1 research are discussed.
Krol
Hilde A
HA
Department of Cell Biology and Histology, Academic Medical Centre, University of Amsterdam, Amsterdam, The Netherlands.
Krawczyk
Przemek M
PM
Bosch
Klazien S
KS
Aten
Jacob A
JA
Hol
Elly M
EM
Reits
Eric A
EA
D000067696:Ataxin-1; D000067528:Ataxins; D001483:Base Sequence; D002455:Cell Division; D002467:Cell Nucleus / Q000378:metabolism; D017931:DNA Primers; D006801:Humans; D007700:Kinetics; D018613:Microscopy, Confocal; D008856:Microscopy, Fluorescence; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D009687:Nuclear Proteins / Q000378:metabolism*; D010455:Peptides / Q000378:metabolism*; D020754:Spinocerebellar Ataxias / Q000378:metabolism*
C000593749:ATXN1 protein, human; D000067696:Ataxin-1; D000067528:Ataxins; D017931:DNA Primers; D009419:Nerve Tissue Proteins; D009687:Nuclear Proteins; D010455:Peptides; C097188:polyglutamine