“…HDACs can be divided into several classes based on sequence homology and cofactor dependency: class I, II and IV HDACs are classical HDACs requiring Zn 2 þ as a cofactor, whereas class III HDACs, also known as Sirtuins, require NAD þ as a cofactor (Imai et al, 2000;Haigis and Guarente, 2006;Yang and Seto, 2007). Control of histone acetylation is associated with longevity regulation in lower organisms (Kaeberlein et al, 1999;Tissenbaum and Guarente, 2001;Rogina and Helfand, 2004;Wood et al, 2004;Dang et al, 2009), and changes in histone acetylation in tissues, such as the brain and liver, correlate with age-dependent declines in tissue function (Oh and Conard, 1972;Shen et al, 2008;Kawakami et al, 2009;Peleg et al, 2010). However, the importance of histone acetylation in aging stem cells is less well studied.…”