ADAR-mediated RNA editing suppresses sleep by acting as a brake on glutamatergic synaptic plasticity.

It has been postulated that synaptic potentiation during waking is offset by a homoeostatic reduction in net synaptic strength during sleep. However, molecular mechanisms to support such a process are lacking. Here we demonstrate that deficiencies in the RNA-editing gene Adar increase sleep due to synaptic dysfunction in glutamatergic neurons in Drosophila. Specifically, the vesicular glutamate transporter is upregulated, leading to over-activation of NMDA receptors, and the reserve pool of glutamatergic synaptic vesicles is selectively expanded in Adar mutants. Collectively these changes lead to sustained neurotransmitter release under conditions that would otherwise result in synaptic depression. We propose that a shift in the balance from synaptic depression towards synaptic potentiation in sleep-promoting neurons underlies the increased sleep pressure of Adar-deficient animals. Our findings provide a plausible molecular mechanism linking sleep and synaptic plasticity.

Class II cytoplasmic and transmembrane domains are not required for class II-mediated B cell spreading.

B cells cultured on immobilized anti-class II monoclonal antibody (mAb) change from round to flattened cells, with lamellipodia and filopodia. This change in cell morphology, termed 'spiders', occurs within 30 min upon culture and is mediated through either I-A or I-E molecules. Class II molecules that are defective in mediating protein kinase C (PKC) due to the deletions of both alpha and beta chain's cytoplasmic (Cy) domain sequences can induce spider formation. B-cell transfectants that express chimeric MHC class II/class I molecules, where the ectodomains are class II sequences and the transmembrane and Cy domains are class I sequences also form spiders when cultured on anti-class II mAb. The spider morphology is not induced by either anti-immunoglobulin (Ig) or anti-MHC class I mAb. Treatment of B cells to increase intracellular cAMP, a component of the class II signaling pathway also results in spider formation with the same kinetics and percent change in the responding population as that induced by anti-class II mAb. Cytochalasin A treatment which disrupts cytoskeletal actin filaments and the tyrosine kinase inhibitor, genistein, both inhibit spider formation. Actin redistributes from a concentric ring in round cells to the ends of the filopodia in the spiders. The mechanism of spider induction whether resultant from second messengers following class II signaling or from non-signaling-induced physical interactions of class II with intracellular cytoskeletal components only requires the extracellular domains of class II. The biologic relevance of B-cell spiders is currently not known but has been reported to be associated with class II signal transduction and efficient Ag presentation.