Patterned Purkinje cell loss in the ataxic sticky mouse

The ataxic sticky (sti/sti) mouse is a spontaneous autosomal recessive mutant resulting from a disruption in the editing domain of the alanyl-tRNA synthetase (Aars) gene. The sticky phenotype is characterized by a small body size, a characteristic unkempt coat and neurological manifestations including marked tremor and ataxia starting at 6 weeks of age. The present study was undertaken to examine the spatiotemporal features of Purkinje cell degeneration in the sticky mouse. Purkinje cell loss was found to be both progressive and patterned, with vermal lobules VI, IX and X, crus 1 of the hemisphere, and the flocculus and paraflocculus being differentially resistant to degeneration. The pattern of Purkinje cell degeneration in sticky is not random - in general, the sphingosine kinase 1a-immunonegative Purkinje cell subset is preferentially susceptible to early cell death. In addition, zebrin II/aldolase C expression in the sticky cerebellum is profoundly downregulated, whereas the heat-shock protein 25 is both ectopically expressed in some scattered Purkinje cells and downregulated in other Purkinje cells in which it is normally expressed constitutively. Compared with many mouse mutants with patterned Purkinje cell death, in which successive stripes of cell loss are very clear, Purkinje cell loss in sticky shows a less clear-cut pattern between different Purkinje cell subtypes, with the result that preferential survival is less dramatic. This may represent a secondary consequence of the downregulation of zebrin II expression.