Our work has also helped clarify the role for ATM

Our work has also helped clarify the role for ATM in human cell telomere maintenance specifically in the context of reprogramming. The observations of accelerated telomere shortening (Metcalfe et al., 1996; Xia et al., 1996) and spontaneous telomere fusions in primary (Kojis et al., 1989, 1991) and transformed (Metcalfe et al., 1996; Pandita et al., 1995) somatic A-T nmda led to the proposal that A-T is, at least in part, a syndrome of telomere dysfunction. Moreover, recent data indicates that ATM is required for telomerase-dependent telomere re-elongation is some contexts (Lee et al., 2015; Tong et al., 2015). In contrast, we find here that erythroblast-derived A-T iPS cells re-elongate telomeres to a length similar to that observed in human ES cells (Amit et al., 2000; Niida et al., 2000; Rosler et al., 2004), similar to a previous report on fibroblast-derived A-T iPS cells (Fukawatase et al., 2014). This observation has direct clinical relevance to regenerative medicine, as gene defect correction in the iPS cells would then restore telomere balance in their derived products. Consistent with previous findings in other iPS cell lines (Feng et al., 2010; Suhr et al., 2009; Vaziri et al., 2010), one carrier iPS cell line failed to maintain telomeres over time. These observations underscore the need to evaluate telomere dynamics in all newly generated iPS cell lines to assert pluripotency. Finally, our work has also examined the effect of ATM gene dose by generating and analyzing an A-T carrier cell line from the patient\'s father. These experiments were motivated by the previous observation that, when using fibroblasts as a source, the efficiency of reprogramming in the mother of a patient was markedly decreased (Nayler et al., 2012). Furthermore, A-T carriers show decreased lifespan due to increased risk of cancer and cardiovascular disease (Su and Swift, 2000). Although our protocol does not allow for quantitative analysis of the reprogramming efficiency, we observed large numbers (over 700) of TRA-1-60+ colonies in carrier cultures, suggesting no major defect in our experimental conditions. Furthermore, A-T carrier cells were comparable to a control iPS cell line generated from a healthy individual in all parameters assessed here, including activation of the DNA Damage Response, telomere maintenance and ability to maintain pluripotency and differentiate to the neural lineage. Finally, although murine cells deficient for ATM show severe reprogramming defects (Marion et al., 2009), we observed comparable in vivo teratoma formation in Atm+/− and control wild-type mice. Altogether, these findings indicate that, at least in some experimental conditions, heterozygocity for ATM does not represent a barrier to reprogramming.
Conclusions
Author contributions
Funding sources
Disclosure of potential conflict of interest
Acknowledgements
Introduction Spinocerebellar ataxia type 3 (SCA3) is a rare autosomal dominantly inherited neurodegenerative disease caused by a CAG-repeat expansion mutation in the ATXN3 gene, coding for a polyglutamine (polyQ) stretch in the protein ataxin-3. In healthy individuals, the CAG-repeat length spans from 10 to 51, whereas the repeat length in SCA3 patients ranges from 45 to 87, thus 45 to 51 repeats can result in either healthy or disease phenotypes (Matos et al., 2011). Although expanded (exp)-ataxin-3 is expressed throughout the human body (Paulson et al., 1997), only certain brain areas are affected in SCA3. Magnetic resonance imaging and macroscopic investigations of SCA3 brains have revealed severe atrophy of the hindbrain (cerebellum and brain stem) (Rüb et al., 2006; Scherzed et al., 2012). Histological studies have confirmed neuronal loss in these areas and several other brain areas (reviewed by Rüb et al., 2008). This degeneration results in a variety of symptoms of which the most common is progressive ataxia (Matos et al., 2011). Ultimately, SCA3 patients encounter approximately 15years reduction in life expectancy (Kieling et al., 2007).