Nogo-66 inhibits the dye-coupling of astrocytic gap junctions in vitro

Distinct roles of Nogo-a and Nogo receptor 1 in the homeostatic regulation of adult neural stem cell function and neuroblast migration

In the adult mammalian subventricular zone (SVZ), GFAP-positive neural stem cells (NSCs) generate neuroblasts that migrate tangentially along the rostral migratory stream (RMS) toward the olfactory bulb (OB). In the mouse brain, we found that the plasticity inhibitors Nogo-A and Nogo receptor 1 (NgR1) are differentially expressed in the SVZ-OB system, in which Nogo-A identifies immature neuroblasts and NgR1 germinal astrocytes. We therefore examined the role of Nogo-A and NgR1 in the regulation of neurogenesis. Pharmacological experiments show that Nogo-66/NgR1 interaction reduces the proliferation of NSCs. This is consistent with a negative-feedback loop, in which newly generated neurons modulate cell division of SVZ stem cells. Moreover, the Nogo-A-Δ20 domain promotes neuroblast migration toward the OB through activation of the Rho/ROCK (Rho-associated, coiled-coil containing protein kinase) pathway, without the participation of NgR1. Our findings reveal a new unprecedented function for Nogo-A and NgR1 in the homeostatic regulation of the pace of neurogenesis in the adult mouse SVZ and in the migration of neuroblasts along the RMS.

Gap junction communication in myelinating glia

Gap junction communication is crucial for myelination and axonal survival in both the peripheral nervous system (PNS) and central nervous system (CNS). This review examines the different types of gap junctions in myelinating glia of the PNS and CNS (Schwann cells and oligodendrocytes respectively), including their functions and involvement in neurological disorders. Gap junctions mediate intercellular communication among Schwann cells in the PNS, and among oligodendrocytes and between oligodendrocytes and astrocytes in the CNS. Reflexive gap junctions mediating transfer between different regions of the same cell promote communication between cellular compartments of myelinating glia that are separated by layers of compact myelin. Gap junctions in myelinating glia regulate physiological processes such as cell growth, proliferation, calcium signaling, and participate in extracellular signaling via release of neurotransmitters from hemijunctions. In the CNS, gap junctions form a glial network between oligodendrocytes and astrocytes. This transcellular communication is hypothesized to maintain homeostasis by facilitating restoration of membrane potential after axonal activity via electrical coupling and the re-distribution of potassium ions released from axons. The generation of transgenic mice for different subsets of connexins has revealed the contribution of different connexins in gap junction formation and illuminated new subcellular mechanisms underlying demyelination and cognitive defects. Alterations in metabolic coupling have been reported in animal models of X-linked Charcot-Marie-Tooth disease (CMTX) and Pelizaeus-Merzbarcher-like disease (PMLD), which are caused by mutations in the genes encoding for connexin 32 and connexin 47 respectively. Future research identifying the expression and regulation of gap junctions in myelinating glia is likely to provide a better understanding of myelinating glia in nervous system function, plasticity, and disease. This article is part of a Special Issue entitled: The Communicating junctions, roles and dysfunctions.