Patterns of Nogo mRNA and Protein Expression in the Developing and Adult Rat and After CNS Lesions

Abstract

Nogo-A is a neurite growth inhibitor involved in regenerative failure and restriction of structural plasticity in the adult CNS. Three major protein products (Nogo-A, -B, and -C) are derived from the nogo gene. Here we describe the embryonic and postnatal expression of the three Nogo isoforms in the rat by in situ hybridization and immunohistochemistry. Northern and Western blot analysis indicated that Nogo-A is predominantly expressed in the nervous system with lower levels also present in testis and heart. In CNS myelin, confocal and immunoelectron microscopy revealed that Nogo-A is expressed in oligodendrocyte cell bodies and processes and localized in the innermost adaxonal and outermost myelin membranes. Additionally, we find Nogo-A to be expressed by projection neurons, in particular during development, and by postmitotic cells in the developing cortex, spinal cord, and cerebellum. The expression levels of Nogo-A/B were not changed significantly after traumatic lesions to the cortex or spinal cord. Nogo-B showed widespread expression in the central and peripheral nervous systems and other peripheral tissues. Nogo-C was mainly found in skeletal muscle, but brain and heart were also found to express this isoform. The localization of Nogo-A in oligodendrocytes fits well with its role as a myelin-associated inhibitor of regenerative fiber growth and structural plasticity. However, expression of Nogo-A in other tissues and, in particular, in neurons and the widespread expression of the two shorter isoforms, Nogo-B and -C, suggest that the Nogo family of proteins might have function(s) additional to the neurite growth-inhibitory activity.

Myelin-associated inhibitors of axonal regeneration in the adult mammalian CNS

“…The anchor is made of one molecule of phosphatidylinositol to which a carbohydrate chain is linked through the C6 hydroxyl of the inositol, and is attached to the protein through an ethanolamine phosphate moiety. the oligodendrocyte surface and on the innermost loop of the myelin membrane, where it could make contact with the axon 14,15 .…”

“…The most common topology of Nogo-A in the membrane places Nogo-66 outside the cell, and the N-and C-terminals in the cytoplasmic compartment 12 . A second topology has also been proposed whereby amino-Nogo is extracellular, and it has been suggested that the two different topologies might coexist simultaneously [11][12][13][14] . This issue remains to be resolved, but Nogo-66 and amino-Nogo both induce growth cone collapse, regardless of the topology.…”

Cell type-specific Nogo-A gene ablation promotes axonal regeneration in the injured adult optic nerve

“…In the neocortex of CnpCre þ / À xRtn4 flox/flox mice, Nogo-A levels were decreased by B50%, reflecting the higher proportion of neuronal Nogo-A (Figure 1d). 12 In the Cnp-Cre þ / À xRtn4 flox/flox hippocampus, we observed B30% decrease in Nogo-A (Figure 1e). The level of the Nogo-A splice variant Nogo-B was elevated in the optic nerve, spinal cord, cortex and hippocampus, suggesting a compensatory upregulation of this protein in oligodendrocytes 7 (Figures 1b-e).…”

“…[6][7][8][9][10][11] In addition to oligodendrocytes and myelin, Nogo-A is expressed in growing and immature neurons, as well as in some adult neurons. 12,13 Neurons express Nogo-A receptors such as the Nogo-66 receptor 1 (NgR1) 14 and the Nogo-A-D20-specific sphingosine 1-phosphate receptor 2 (S1PR2). 15 They can co-express them along with Nogo-A, 13 an observation that raises the possibility of cis-interactions between the ligand and its receptors within or at the cell surface of the same cell.…”

“…16,17 In the adult CNS, the expression of neuronal Nogo-A remains elevated mainly in plastic regions such as in the hippocampus, olfactory bulb or neocortex, and in the dorsal root ganglia. 12 Nogo-A and NgR1 were shown to regulate synaptic plasticity, for example, long-term potentiation in the hippocampus and in the sensory-motor cortex, [18][19][20][21][22] whereas the effects of neuronal Nogo-A after injury are not yet well understood. During development, neuronal Nogo-A influences neuronal migration, 23,24 survival, 25,26 cell spreading and neurite growth.…”