Characterization of Caytaxin Protein in Animal Models of Cerebellar Dysfunction.

Abstract

Over 150,000 Americans have been diagnosed with ataxia, however most are untreatable due to yet-unknown etiologies. The work described within this dissertation aims to expand current knowledge regarding ataxia and the brain by elucidating the function of Caytaxin, a neuronal protein that is essential for nervous system processes. Caytaxin is encoded by the Atcay/ATCAY gene and is highly conserved. Two mutations in ATCAY, a splice and a non-synonymous exon variant, are associated with the rare hereditary disease Cayman ataxia in humans. Mutations in the murine ortholog Atcay have been identified as the cause of marked motor defects in four ataxic and dystonic mouse lines. While the function of Caytaxin has not been fully characterized, several lines of evidence and the data contained in this dissertation suggest that Caytaxin is required for maintaining nervous system processes. In Chapter II, we discuss the generation of novel anti-Caytaxin monoclonal antibodies and their use in characterizing endogenous Caytaxin expression in wild type and Atcay mutant mice, and in humanized ATCAY transgenic lines. Caytaxin protein is absent from brain tissues in the two severely ataxic jittery and sidewinder lines, and markedly decreased in the mildly ataxic/dystonic hesitant line, indicating a correlation between Caytaxin expression and disease severity. Biochemical analysis reveals that Caytaxin is expressed as three protein isoforms, two of which originate from different conserved methionine translation start sites. Phenotypic analysis of transgenic ATCAY mouse lines suggests a conserved physiological function between the human and mouse Caytaxin orthologs as expression of wild type human Caytaxin rescues the ataxic phenotype in mutant sidewinder and jittery mice. In Chapter III, we report preliminary data obtained from transgenic mouse lines generated to recapitulate the human Cayman ataxia mutations. We reveal that the splice mutation results in a protein truncation, but fails to completely abrogate Caytaxin function, indicating the possibility that both Cayman ataxia mutations may act synergistically to cause disease. Our characterization of Caytaxin protein and its expression in mouse models of cerebellar dysfunction presents novel methods for accurate assessment of how Caytaxin maintains normal nervous system function, thus providing insight into other forms of ataxia.