Deletion of multimerin-1 in α-synuclein-deficient mice

Inactivation of the mouse Atxn3 (ataxin-3) gene increases protein ubiquitination

Spinocerebellar ataxia type 3 is a neurodegenerative disease caused by expansion of a polyglutamine domain in the protein ataxin-3 (ATXN3). Physiological functions of ATXN3 presumably include ubiquitin protease and transcriptional corepressor activity. To gain insight into the function of ATXN3 and to test the hypothesis that loss of ATXN3 contributes to the pathology in SCA3 we generated Atxn3 knockout (ko) mice by targeted mutagenesis. Loss of Atxn3 did not affect viability or fertility and Atxn3 ko mice displayed no overt abnormalities. On the accelerating Rotarod Atxn3 ko mice performed as well as wildtype (wt) animals, but reduced exploratory behavior in the open field suggested a sense of heightened anxiety. While no gross deficits were apparent upon morphological examination, we found increased levels of ubiquitinated proteins in Atxn3 ko tissues. Thus Atxn3 ko mice provide the first in vivo reference to the deubiquitinating activity of ATXN3.

Subcellular localisation of recombinant alpha- and gamma-synuclein

alpha-Synuclein, a protein implicated in neurodegenerative diseases and of elusive physiological function owes its name to an observed presence in presynaptic and nuclear compartments. However, its nuclear localisation has remained controversial. We expressed synuclein-eGFP fusion proteins in organotypic rat hippocampal slice cultures and murine hippocampal primary neurons using a Sindbis virus expression system. Recombinant full-length alpha-synuclein accumulated in presynaptic locations, mimicking its native distribution. Expression of deletion mutant alpha-synuclein revealed that presynaptic targeting depended on the presence of its N-terminal and core region. This domain also causes nuclear exclusion of the alpha-synuclein fusion protein. In contrast, the C-terminal domain of alpha-synuclein directs fusion proteins into the nuclear compartment. The related protein gamma-synuclein contains a similar N-terminal and core domain as alpha-synuclein. However, gamma-synuclein lacks a C-terminal domain that causes nuclear localisation of the fusion protein, suggesting that the two synucleins might have different roles relating to the cell nucleus.