Investigation of the Cerebellar Degeneration in Ataxia-Telangiectasia Using Mouse Models with Combined Atm and Setx Genotypes - Genome Dynamics in Neuroscience and Aging

Marina Alfo ¹ Jonathan Aran ¹ Lior Bikovski ² Julia Shaknof ¹ Martin Lavin ³ Yael Ziv ¹ Yosef Shiloh ¹

¹Department of Human Molecular Genetics and Biochemistry, Sackler School of Medicine, Tel Aviv University, Tel Aviv 69978, The David and Inez Myers Laboratory for Cancer Genetics, Israel
²Sackler School of Medicine, Tel Aviv University, Tel Aviv 69978, The Myers Neuro-behavioral Core Facility, Israel
³Center for Clinical Research, Brisbane QLD 4072, Australia

Ataxia-telangiectasia (A-T) is an autosomal recessive disorder caused by loss of the ATM protein kinase. A-T is characterized primarily by progressive cerebellar atrophy, which begins with loss of Purkinje and granule cells. ATM is a homeostatic kinase that mobilizes the vigorous cellular network responding to DNA double-strand breaks, and is also involved in responding to other DNA lesions and in various metabolic pathways. Many symptoms of A-T can be explained by ATM’s role in the DSB response, but the origin of the cerebellar degeneration is still debated. We are studying this aspect of A-T using mouse models. Atm-deficient mice recapitulate many of the symptoms of the human disease but their cerebellar phenotype is extremely mild and has been reported inconsistently. Using an array of behavioral tests, we were able to show that these mice do develop a distinct, progressive neuro-motor phenotype, at 7 months of age and by 11 months of age leads to abnormal gait pattern. Our strategy to exacerbate this phenotype is to combine Atm loss with deficiency of another enzyme involved in maintenance of genome stability. In view of the extensive transcription in Purkinje cells, we added to Atm deficiency lack of the senataxin (Setx) protein. SETX is a DNA helicase that is involved in the resolution of DNA:RNA hybrid loops (R-loops) – a frequent event in highly transcribing cells and a source of genome instability. Notably, SETX is recruited to sites of DNA damage in an ATM-dependent manner and SETX loss in humans causes ataxia with oculomotor apraxia 2 (AOA2) – a disorder characterized primarily by cerebellar degeneration. We obtained all possible genotypic combinations of the Atm and Setx null alleles. Importantly, the double-knockout mouse (Atm-/-//Setx-/-) is born alive (at sub-Mendelian ratio) and, surprisingly, its neuro-motor phenotype is not significantly different from that of the Atm-/- mouse.