1. American Academy of Neurology Chicago – April 2008 Frontiers in Clinical Neuroscience Plenary Session Protein interactions and cell signalling pathways in SCA 1 pathogenesis – targets for therapeutics Harry T. Orr University of Minnesota

2. SCA 1 involves expansion of (CAG) n triplet repeat at starting end of ataxin 1 gene, leading to longer than normal string of glutamines (Q’s) conditional mouse model – enables gene with huge (Q 156 ) expansion to be switched on and off: –cerebellar damage is reversible early (to 6 weeks) –partly reversible in mid-course (6-12 weeks) –not reversible in late disease (32 weeks) Q 6-44 Normal ataxin-1 NLS Q 39-83 Expanded ataxin-1

3. Ataxin 1 ( full-length Q30); anti-ataxin 1 N-terminal

4. Ataxin 1 ( full-length Q85/FLAG); anti-ataxin 1 N-terminal

5. Ataxin 1 (truncated Q85/FLAG); anti-ataxin 1 N-terminal

6. SCA 1 expanded ataxin-1  aggregates, but toxicity is due to soluble expanded ataxin-1 not its aggregates absence of expanded ataxin-1 early in development (P 7-14 in mouse) makes cerebellum less susceptible to damage by expanded ataxin-1 in later (mouse) life – due to decreased disruption of another gene (ROR  ) important for normal development of cerebellum

7. What causes toxicity in SCA 1? – 1) serine at position 776 can be phosphorylated (joined to a phosphate group to change its size and electrical charge) this is made much more likely by an expanded Q n at the other end of the protein (as occurs in SCA 1) mutating the serine to another amino-acid (alanine) that cannot be phosphorylated prevents toxicity from expanded ataxin-1 QnQn Serine 776 1 * –

8. What causes toxicity in SCA 1? – 2) mutating the serine to yet another amino acid (glutamic acid) mimics the size and charge effect of phosphorylating the serine, and causes normal ataxin-1 to become toxic Therefore, if we could prevent or reverse serine 776 phosphorylation, we could prevent or reverse early disease (specific kinase inhibitor/phosphatase activator?)