Ranvier nodes are flanked by paranodal regions, at the level of which oligodendrocytes or Schwann cells interact closely with axons. Paranodes play a critical role in the physiological properties of myelinated nerve fibers. Paranodin, a prominent 180 kDa transmembrane neuronal glycoprotein, was purified and cloned from adult rat brain, and found to be highly concentrated in axonal membranes at their junction with myelinating glial cells, in paranodes of central and peripheral nerve fibers. The large extracellular domain of paranodin is related to neurexins, and its short intracellular tail binds protein 4.1, a cytoskeleton-anchoring protein. Paranodin may be a critical component of the macromolecular complex involved in the tight interactions between axons and myelinating glial cells characteristic of the paranodal region.

Addition of dimethylsulfoxide at concentrations of 1% and 2% (vol/vol) to cells of mouse neuroblastoma clone NIE-115 in the confluent phase of growth resulted in the production of morphologicalfir differentiated cultures with extensive process formation. Cells maintained in 2% dimethylsulfoxide remained in a stable nondividing condition for periods of up to 4 weeks. A high degree of electrical excitability was found in these cells, but there was no clear correlation of this property with the level of induction of either acetylcholinesterase (acetylcholine hydrolase; EC 3.1.1.7) or tyrosine hydroxylase [L-tyrosine, tetrahydropteridine:oxygen oxidoreductase (3-hydroxylating); EC 1.14.16.2]. In addition, intracellular levels of cyclic 3':5'-AMP were not elevated in fully morphologically and electrically differentiated cells. While cell division was markedly inhibited by 2% or higher concentrations of dimethylsulfoxide, at 1% growth continued at a somewhat slowed rate and such cultures exhibited enhanced process formation and electrical activity for a relatively short period. High concentrations (3% or 4%) of dimethylsulfoxide totally suppressed process formation and did not result in increased excitability, but cells maintained high resting potentials. The results suggest that the development of the excitable membrane in neuroblastoma cells maybe expressed independently of neurospecific enzyme induction, and does not require a sustained elevation of cyclic 3'i5'-AMP levels.Nerve cells are characterized by their unique morphological appearance, the possession of an excitable membrane, and a specialized biochemical machinery. In order to study the expression of specific neuronal properties during the maturation process it is necessary to obtain sufficient quantities of a relatively homogeneous differentiating population. Cloned cell lines isolated from the C-1300 mouse neuroblastoma may serve as a useful system for exploring certain aspects of nerve cell differentiation. The transition of a culture of neuroblastoma cells from the actively dividing state to the confluent one is characterized by the synthesis of various enzymes involved in neurotransmitter metabolism (1), an enhancement of electrical excitability (2, 22), and some degree of process formation. To achieve a further expression of these properties, cells have been treated with various agents such as aminopterin (3, 4) or dibutyryl cAMP (5-7).In the present study, we show that in the presence of dimethylsulfoxide (Me2SO) neuroblastoma cells will extend neurites and develop a highly excitable membrane. It appears that this method offers certain advantages over those most commonly used, especially in that cells appear to reach a higher level of electrical differentiation and can be maintained in this state for extended periods. In experiments where logarithmically growing cells were used, cultures were trypsinized before attaining confluency and replated in 60 mm dishes at a density of 1 X 105 cells per dish. Two days later, the medium was replaced w...

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Background: Eukaryotic elongation factor-2 kinase (EF2K) inhibits the elongation phase of protein translation. Results: EF2K degradation by the ubiquitin-proteasome system (UPS) is regulated by cAMP-PKA signaling and SCF ␤TRCP .

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