Realization of phosphorylation hypothesis of sleep by mammalian CaMKIIβ
The reduced sleep duration observed in Camk2a and Camk2b knockout mice revealed the role of Ca2+/calmodulin-dependent protein kinase II (CaMKII)/CAMKII{beta} as sleep-promoting kinases and lead to the phosphorylation hypothesis of sleep. However, the underlying mechanism of sleep regulation by kinases and protein phosphorylation is largely unknown. Here, we demonstrate that the phosphorylation states of CaMKII{beta} regulates sleep duration and sleep needs. Importantly, the activation or inhibition of CaMKII{beta} can increase or decrease sleep duration by almost two-fold, supporting the role of CaMKII{beta} as a core sleep regulator in mammals. This sleep regulation depends on the kinase activity of CaMKII{beta} in excitatory neurons. Furthermore, CaMKII{beta} mutants mimicking different phosphorylation states can regulate various sleep steps including sleep induction, sleep maintenance, and sleep cancelation. Key CaMKII{beta} residues responsible for the mode switch undergo ordered (auto-)phosphorylation. We thus propose that ordered multi-site phosphorylation of CaMKII{beta} underlies multi-step sleep regulation in mammals.