Changes in some myelin protein markers and in cytoskeletal components during Wallerian degeneration of mouse sciatic nerve

Ndel1 promotes axon regeneration via intermediate filaments

Failure of axons to regenerate following acute or chronic neuronal injury is attributed to both the inhibitory glial environment and deficient intrinsic ability to re-grow. However, the underlying mechanisms of the latter remain unclear. In this study, we have investigated the role of the mammalian homologue of aspergillus nidulans NudE, Ndel1, emergently viewed as an integrator of the cytoskeleton, in axon regeneration. Ndel1 was synthesized de novo and upregulated in crushed and transected sciatic nerve axons, and, upon injury, was strongly associated with neuronal form of the intermediate filament (IF) Vimentin while dissociating from the mature neuronal IF (Neurofilament) light chain NF-L. Consistent with a role for Ndel1 in the conditioning lesion-induced neurite outgrowth of Dorsal Root Ganglion (DRG) neurons, the long lasting in vivo formation of the neuronal Ndel1/Vimentin complex was associated with robust axon regeneration. Furthermore, local silencing of Ndel1 in transected axons by siRNA severely reduced the extent of regeneration in vivo. Thus, Ndel1 promotes axonal regeneration; activating this endogenous repair mechanism may enhance neuroregeneration during acute and chronic axonal degeneration.

Myelin composition and activities of CNPase and Na+,K+-ATPase in hypomyelinated "pt" mutant rabbit

A disorder of CNS myelination was found in paralytic tremor ("pt") rabbits. The condition is inherited in a sex-linked recessive mode. Ultrastructurally, an obvious myelin deficiency with aberration of myelin sheath formation is observed. The yield of myelin isolation was reduced to 20-30% of control. Myelin isolated from 4-week-old "pt" rabbits contained reduced amounts of galactosphingolipids and of several myelin protein markers. Moreover, myelin basic protein, analyzed by two-dimensional gel electrophoresis, showed a deficit in its more basic components. All these facts suggest a delay in myelin maturation. Ganglioside content was increased as well as Na+,K+-ATPase specific activity. 2',3'-Cyclic nucleotide phosphodiesterase (CNPase) specific activity was the same in "pt" as in control myelin but differed by having greater sensitivity to detergent activation.

Control of isotubulin expression during neuronal differentiation of mouse neuroblastoma and teratocarcinoma cell lines

Mouse neuroblastoma and teratocarcinoma constitute adequate cellular systems to study the expression of tubulin isoforms during early as well as later steps of neuronal differentiation. Tubulin heterogeneity is extensively analyzed using both isoelectric focusing and two-dimensional electrophoresis. Multipotential embryonal carcinoma cells express mainly one alpha-tubulin isoform (alpha 1) and three beta-tubulin isoforms: a major one (beta 3) and two minor ones (beta 4 and beta 5). Early events of neuronal differentiation are shown to induce the expression of an additional beta-tubulin isoform, beta'1, which is encoded by a specific mRNA. Neurite extension further increases tubulin heterogeneity and leads to the appearance of post-translationally modified isoforms: beta'2 in neuroblastoma and alpha 2 in teratocarcinoma cells. beta' 2 is shown to derive from the above mentioned beta'1 by phosphorylation, while alpha 2 is probably an acetylated form of the common alpha 1-tubulin. These results show that specific changes in tubulin heterogeneity are induced at different steps of neuronal differentiation and are controlled both at the transcriptional (or post-transcriptional) and post-translational levels.

Gene expression in the presence or absence of myelin assembly

Regulation of myelin protein gene expression in the presence and absence of myelin assembly can be assessed using crushed or permanently transected adult sciatic nerves of rats. The P0 glycoprotein and the myelin basic protein (MBP) are the major myelin-specific proteins of the peripheral nervous system. The steady-state level of P0 and MBP messenger RNA was determined by dot-blot analysis of poly(A)+ RNA from crushed and transected nerves of rats at 35 days post operation. The rat P0-specific cDNA clone, pSN63c, and mouse MBP-specific cDNA clone, pHF43, were used as probes. The level and quality of the poly(A)+ RNA was assessed by in vitro translation and immunoprecipitation of the translation products with anti-chick P0 antibody. Comparison of the steady-state level of P0 and MBP transcripts and the level of anti-P0 immunoprecipitated translation products from RNA extracts of permanently transected, crushed, adult control and 21-day-old control rat nerves indicated that the level of P0 and MBP messages was significantly reduced in the permanently transected model, whereas it was restored to normal in the crushed sciatic nerve 35 days post injury. These results suggest that regulation of P0 and MBP gene expression most likely occurs at the transcriptional or post-transcriptional level in the two models of peripheral neuropathies. Northern blot analysis indicated the absence of differential splicing of the message in crushed or transected nerves. The experiments also indicate that these two important gene products required for myelin synthesis and assembly seem to be co-regulated. However, the data do not rule out the possibility that regulation of gene expression may also occur at the level of translation or post-translational processing.