Posttraumatic activity of signal pathways of nuclear factor κB in mature sensory neurons

The aim of this study was to clear out whether injury to the peripheral nerve leads to activation of nuclear factor κB in mature spinal ganglia. Analysis of matrix RNA of nuclear factor κB-dependent genes (monocyte chemoattractant protein MCP-1 and inhibitor of nuclear factor κB IκBα) showed different levels of expression of these genes in the spinal ganglia in vivo after axotomy and in vitro after TNF-α stimulation. On the other hand, DNA-binding activity of nuclear factor κB increased in the spinal ganglia 6 h after axotomy and after 10-min incubation of sensory neuron culture with TNF-α. These data attest to possible involvement of nuclear factor κB in the posttraumatic regulation of gene transcription in spinal ganglion cells.

Comparative genomic analysis of the gut bacterium Bifidobacterium longum reveals loci susceptible to deletion during pure culture growth

Background

Bifidobacteria are frequently proposed to be associated with good intestinal health primarily because of their overriding dominance in the feces of breast fed infants. However, clinical feeding studies with exogenous bifidobacteria show they don't remain in the intestine, suggesting they may lose competitive fitness when grown outside the gut.

Results

To further the understanding of genetic attenuation that may be occurring in bifidobacteria cultures, we obtained the complete genome sequence of an intestinal isolate, Bifidobacterium longum DJO10A that was minimally cultured in the laboratory, and compared it to that of a culture collection strain, B. longum NCC2705. This comparison revealed colinear genomes that exhibited high sequence identity, except for the presence of 17 unique DNA regions in strain DJO10A and six in strain NCC2705. While the majority of these unique regions encoded proteins of diverse function, eight from the DJO10A genome and one from NCC2705, encoded gene clusters predicted to be involved in diverse traits pertinent to the human intestinal environment, specifically oligosaccharide and polyol utilization, arsenic resistance and lantibiotic production. Seven of these unique regions were suggested by a base deviation index analysis to have been precisely deleted from strain NCC2705 and this is substantiated by a DNA remnant from within one of the regions still remaining in the genome of NCC2705 at the same locus. This targeted loss of genomic regions was experimentally validated when growth of the intestinal B. longum in the laboratory for 1,000 generations resulted in two large deletions, one in a lantibiotic encoding region, analogous to a predicted deletion event for NCC2705. A simulated fecal growth study showed a significant reduced competitive ability of this deletion strain against Clostridium difficile and E. coli. The deleted region was between two IS30 elements which were experimentally demonstrated to be hyperactive within the genome. The other deleted region bordered a novel class of mobile elements, termed mobile integrase cassettes (MIC) substantiating the likely role of these elements in genome deletion events.

Conclusion

Deletion of genomic regions, often facilitated by mobile elements, allows bifidobacteria to adapt to fermentation environments in a very rapid manner (2 genome deletions per 1,000 generations) and the concomitant loss of possible competitive abilities in the gut.

The Calyptogena magnifica chemoautotrophic symbiont genome

Chemoautotrophic endosymbionts are the metabolic cornerstone of hydrothermal vent communities, providing invertebrate hosts with nearly all of their nutrition. The Calyptogena magnifica (Bivalvia: Vesicomyidae) symbiont, Candidatus Ruthia magnifica, is the first intracellular sulfur-oxidizing endosymbiont to have its genome sequenced, revealing a suite of metabolic capabilities. The genome encodes major chemoautotrophic pathways as well as pathways for biosynthesis of vitamins, cofactors, and all 20 amino acids required by the clam.

The genome of the obligately intracellular bacterium Ehrlichia canis reveals themes of complex membrane structure and immune evasion strategies

Ehrlichia canis, a small obligately intracellular, tick-transmitted, gram-negative, alpha-proteobacterium, is the primary etiologic agent of globally distributed canine monocytic ehrlichiosis. Complete genome sequencing revealed that the E. canis genome consists of a single circular chromosome of 1,315,030 bp predicted to encode 925 proteins, 40 stable RNA species, 17 putative pseudogenes, and a substantial proportion of noncoding sequence (27%). Interesting genome features include a large set of proteins with transmembrane helices and/or signal sequences and a unique serine-threonine bias associated with the potential for O glycosylation that was prominent in proteins associated with pathogen-host interactions. Furthermore, two paralogous protein families associated with immune evasion were identified, one of which contains poly(G-C) tracts, suggesting that they may play a role in phase variation and facilitation of persistent infections. Genes associated with pathogen-host interactions were identified, including a small group encoding proteins (n = 12) with tandem repeats and another group encoding proteins with eukaryote-like ankyrin domains (n = 7).

Nature of signals that initiate the immune response during Wallerian degeneration of peripheral nerves

Monocyte chemoattractant protein-1 is produced by Schwann cells during Wallerian degeneration of a peripheral nerve and contributes to a selective accumulation of macrophages in the degenerating segment. An in vitro preparation has been developed to analyze the molecules from axons and non-neuronal cells in nerves that stimulate an increased production of monocyte chemoattractant protein-1 mRNA by Schwann cells. For this purpose, Schwann cells obtained from neonatal rats were maintained in culture, exposed to putative molecular stimuli and analyzed for their content of monocyte chemoattractant protein-1 mRNA. Under basal conditions, the concentration of monocyte chemoattractant protein-1 in Schwann cells was low. Freeze-killed fragments or homogenates of nerve (or brain) but not viable nerve or freeze-killed muscle were effective in inducing monocyte chemoattractant protein-1 mRNA. The inductive activity was abolished by heating. Results of dialysis of supernatants of nerve homogenates indicate that a protein or proteins of 1-10 kDa were capable of stimulating synthesis of monocyte chemoattractant protein-1 by Schwann cells. Also, the activity in nerve homogenates was partially inhibited by antibodies to Toll-like receptor-4. The observations suggest that a non-secreted protein is released from disintegrating axons to initiate the innate immune response that characterizes Wallerian degeneration.

Presence of Ras guanyl nucleotide-releasing protein in striosomes of the mature and developing rat

Ras signal transduction pathways have been implicated as key regulators in neuroplasticity and synaptic transmission in the brain. These pathways can be modulated by Ras guanyl nucleotide exchange factors, (GEF) which activate Ras proteins by catalysing the exchange of GDP for GTP. Ras guanyl nucleotide-releasing protein (RasGRP), a recently discovered Ras GEF, that links diacylglycerol and probably calcium to Ras signaling pathways, is expressed in brain as well as in T-cells. Here, we have used a highly selective monoclonal antibody against RasGRP to localize this protein within the striatum and related forebrain structures of developing and adult rats. RasGRP immunolabeling was found to be widespread in the mature and developing rat forebrain. Most notably, it presented a prominent patchy distribution throughout the striatum at birth and at all postnatal ages examined. These patches were found to correspond with the striosomal compartment of the striatum, as identified by micro-opioid receptor labeling in the adult. RasGRP-immunoreactivity was also observed in the matrix-like compartment surrounding these patches/striosomes but appeared later in development and was always weaker than in the patches. In both striatal compartments, RasGRP was exclusively expressed by medium-sized spiny neurons and showed no preference for neurons that project either directly or indirectly to the substantia nigra. At the ultrastructural level, immunogold labeling of RasGRP was confined to the cell bodies and dendritic shafts of these output neurons. We conclude that the prominent expression of RasGRP in striosomes may be of significance for diacylglycerol signaling in the striatum, and could be of importance for the processing of limbic-related activity within the basal ganglia.

Cellular and subcellular localization of Ras guanyl nucleotide-releasing protein in the rat hippocampus

Ras guanyl nucleotide-releasing protein (RasGRP) is a recently discovered Ras guanyl nucleotide exchange factor that is expressed in selected regions of the rodent CNS, with high levels of expression in the hippocampus. Biochemical studies suggest that RasGRP can activate the Ras signal pathway in response to changes in diacylglycerol and possibly calcium. To investigate potential sites for RasGRP signaling, we have determined the cellular and subcellular localization of RasGRP protein in adult rat hippocampus, and have also examined the appearance of RasGRP mRNA and protein during hippocampal development. RasGRP immunoreactivity is predominately localized to those neurons participating in the direct cortico-hippocampo-cortical loop. In both hippocampal and entorhinal neurons, RasGRP protein appeared to be localized to both dendrites and somata, but not to axons. Electron microscopy of hippocampal pyramidal cells confirmed RasGRP immunoreactivity in neuronal cell bodies and dendrites, where it appeared to be associated with microtubules. The localization of RasGRP to dendrites suggests a role for this pathway in the regulation of dendritic function. Examination of developing hippocampal structures indicated that RasGRP mRNA and protein appear synchronously during the first 2 weeks of postnatal development as these neurons become fully mature. This result indicates that the RasGRP signal transduction pathway is not required during early hippocampal development, but is a feature of mature neurons during the later stages of development.

High-throughput plasmid purification for capillary sequencing

The need for expeditious and inexpensive methods for high-throughput DNA sequencing has been highlighted by the accelerated pace of genome DNA sequencing over the past year. At the Joint Genome Institute, the throughput in terms of high-quality bases per day has increased over 20-fold during the past 18 mo, reaching an average of 18.3 million bases per day. To support this unprecedented scaleup, we developed an inexpensive automated method for the isolation and purification of double-stranded plasmid DNA clones for sequencing that is tailored to meet the more stringent needs of the newer capillary electrophoresis DNA sequencing machines. The protocol is based on the magnetic bead method of solid phase reversible immobilization that has been automated by using a CRS-based robotic system. The method described here has enabled us to meet our increases in production while reducing labor and materials costs significantly.

Synthesis of leukemia inhibitory factor in injured peripheral nerves and their cells

The time and site of induction of leukemia inhibitory factor mRNA in injured rat sciatic nerves and its regulation in Schwann cells and fibroblasts from neonatal rat nerves were investigated. Leukemia inhibitory factor mRNA is induced at the lesion site within 6 h of sciatic nerve transection but only after 24 h in the more distal segments. In vitro, interleukin-1beta increases the concentration of leukemia inhibitory mRNA in nerve fibroblasts but not in Schwann cells. Changes in leukemia inhibitory factor mRNA concentration in injured nerves and peripheral nerve cells are similar to those for nerve growth factor mRNA.

Influence of injury and cytokines on synthesis of monocyte chemoattractant protein-1 mRNA in peripheral nervous tissue

The signals and the source of the signals for monocyte/macrophage entry into the injured peripheral nervous tissue are not yet defined. This study was undertaken to determine the distribution of the chemokine monocyte chemoattractant protein-1 mRNA in injured rat and mouse nerves and to investigate the mechanisms that regulate its synthesis in rat Schwann cells. Results from RNase protection assays showed that, following sciatic nerve transection in rats, mRNA for monocyte chemoattractant protein-1 was induced at the site of lesion within 3 h of surgery and in more distal segments from 24 h for at least 8 days. In cultured Schwann cells, tumour necrosis factor-alpha but not interleukin-1 beta, interleukin-6, transforming growth factor-beta 1, platelet-derived growth factor-BB or nerve growth factor induced monocyte chemoattractant protein-1 mRNA in a time- and dose-dependent fashion. The induction of monocyte chemoattractant protein-1 mRNA in Schwann cells treated with tumour necrosis factor-alpha was reduced by inhibitors of nuclear factor-kappa B and the p38 mitogen-activated protein kinase. In mice that lack the two receptors for tumour necrosis factor, the message for JE, a murine homologue of monocyte chemoattractant protein-1, was still induced within 6 h of injury at the lesion site. However, in more distal segments 4 days after transection the concentration of JE mRNA was lower than that of control mice. Tumor necrosis factor-alpha is the only cytokine that was shown to induce monocyte chemoattractant protein-1 mRNA in cultured Schwann cells and is one of the factors that regulate the synthesis of monocyte chemoattractant protein-1 in injured nerves.

The gene encoding TBC1D1 with homology to the tre-2/USP6 oncogene, BUB2, and cdc16 maps to mouse chromosome 5 and human chromosome 4

TBC1D1 is the founding member of a family of related proteins with homology to tre-2/UPS6, BUB2, and cdc16 and containing the tbc box motif of 180-220 amino acids. This protein family is thought to have a role in differentiation and in regulating cell growth. We set out to map the TBC1D1 gene in mouse and human. Segregation analysis of a TBC1D1 RFLP in two independent mouse RI (recombinant inbred) lines reveals that mouse Tbc1d1 is closely linked to Pgm1 on chromosome 5. The human TBC1D1 gene was assigned to human chromosome 4p15.1-->4q21 using Southern blot analyses of genomic DNAs from rodent-human somatic cell lines. A human-specific genomic fragment was observed in the somatic cell lines containing human chromosome 4 or the 4p15.1-->4q21 region of the chromosome. TBC1D1 maps to the region containing the ortholog of mouse Pgm1 adding another locus to this long region of conserved synteny between mouse and man.

Distribution of ras guanyl releasing protein (RasGRP) mRNA in the adult rat central nervous system

In the nervous system, Ras signal transduction pathways are involved in cellular differentiation, neuronal survival and synaptic plasticity. These pathways can be modulated by Ras guanyl nucleotide exchange factors (Ras GEFs), which activate Ras protein by catalyzing the exchange of GDP for GTP. RasGRP, a recently discovered Ras GEF is expressed in brain as well as in T cells. In addition to the catalytic domain which catalyzes dissociation of Ras-GDP, RasGRP has a pair of calcium-binding EF hands and a diacylglycerol binding domain. The structure of RasGRP suggests that it serves to link calcium and lipid messengers to Ras signaling pathways. We have used an RNase protection assay to detect RasGRP mRNA in various regions of the rat brain and we have determined the cellular distribution of RasGRP mRNA by in situ hybridization. RasGRP mRNA is widely distributed and is present in both interneurons and projection neurons but not confined to any neuronal type or neurotransmitter phenotype. The presence of RasGRP mRNA in archicortical neurons suggests that this pathway may be important in phylogenetically older regions of the CNS. The restriction of RasGRP mRNA to subsets of neurons suggests that activation of Ras by RasGRP has a specific function in certain neuronal types. We did not detect RasGRP in glial cells.

Reciprocal actions of interleukin-6 and brain-derived neurotrophic factor on rat and mouse primary sensory neurons

In low-density, serum-free cultures of neurons from embryonic rat dorsal root ganglia, interleukin-6 supports the survival of less than one third of the neurons yet virtually all of them bear interleukin-6 alpha-receptors. A finding that might explain this selectivity is that interleukin-6 acts on sensory neurons in culture through a mechanism requiring endogenous brain-derived neurotrophic factor. Antibodies or a trkB fusion protein that block the biological activity of brain-derived neurotrophic factor synthesized by dorsal root ganglion neurons also block the survival-promoting actions of interleukin-6 on these neurons. Two results indicate that interleukin-6 influences synthesis of brain-derived neurotrophic factor in adult dorsal root ganglion neurons. Intrathecal infusion of interleukin-6 in rats increases the concentration of brain-derived neurotrophic factor mRNA in rat lumbar dorsal root ganglia. The induction of brain-derived neurotrophic factor in dorsal root ganglion neurons that is seen after nerve injury in rats or wild-type mice is severely attenuated in mice with null mutation of the interleukin-6 gene. In brief, the ability of interleukin-6 to support the survival of embryonic sensory neurons in vitro depends upon the presence of endogenous brain-derived neurotrophic factor and the induction of brain-derived neurotrophic factor in injured adult sensory neurons depends upon the presence of endogenous interleukin-6.

Endogenous interleukin-6 contributes to hypersensitivity to cutaneous stimuli and changes in neuropeptides associated with chronic nerve constriction in mice

Partial nerve injury is a potential cause of distressing chronic pain for which conventional analgesic treatment with opiates or anti-inflammatory agents is not very effective. Constriction nerve injury, widely used to study neuropathic pain, was shown here to induce interleukin-6 (IL-6) mRNA in a subset of rat primary sensory neurons. When we inflicted chronic nerve constriction on mice with null mutation of the IL-6 gene, the hypersensitivity to cutaneous heat and pressure that is induced in wild-type mice was not evident, the loss of substance P in sensory neurons was excessive and the induction of galanin in central sensory projections was reduced. In additional experiments, intrathecal infusion of IL-6 in rats was shown to stimulate synthesis of galanin in approximately one-third of lumbar dorsal root ganglion neurons. The results of these experiments indicate that endogenous IL-6 mediates some of the hypersensitive responses that characterize peripheral neuropathic pain, and influences two neuropeptides that have been implicated in pain transmission.

Nature of the retrograde signal from injured nerves that induces interleukin-6 mRNA in neurons

In previous studies, interleukin-6 was shown to be synthesized in approximately one-third of lumbar dorsal root ganglion neurons during the first week after nerve transection. In present studies, interleukin-6 mRNA was found to be induced also in axotomized facial motor neurons and sympathetic neurons. The nature of the signal that induces interleukin-6 mRNA in neurons after nerve injury was analyzed. Blocking of retrograde axonal transport by injection of colchicine into an otherwise normal nerve did not induce interleukin-6 mRNA in primary sensory neurons, but injection of colchicine into the nerve stump prevented induction of interleukin-6 mRNA by nerve transection. Therefore, it was concluded that interleukin-6 is induced by an injury factor arising from the nerve stump rather than by interruption of normal retrograde trophic support from target tissues or distal nerve segments. Next, injection into the nerve of a mast cell degranulating agent was shown to stimulate interleukin-6 mRNA in sensory neurons and systemic administration of mast cell stabilizing agents to mitigate the induction of interleukin-6 mRNA in sensory neurons after nerve injury. These data implicate mast cells as one possible source of the factors that lead to induction of interleukin-6 mRNA after nerve injury. In search of a possible function of inducible interelukin-6, neuronal death after nerve transection was assessed in mice with null deletion of the interleukin-6 gene. Retrograde death of neurons in the fifth lumbar dorsal root ganglion was 45% greater in knockout than in wild-type mice. Thus, endogenous interleukin-6 contributes to the survival of axotomized neurons.

Galanin expression in neuropathic pain: friend or foe?

We investigated a possible link between galanin expression and evoked pain accompanying painful partial sciatic nerve lesions. Increased galanin immunoreactivity (IR) in the dorsal horn, in gracile nucleus, and in sensory neurons following chronic constriction injury (CCI) compared to complete sciatic transection suggested a facilitatory role in thermal and mechanical hypersensitivity (allodynia). We therefore investigated the effects of endogenous interleukin-6 (IL-6) and nerve growth factor (NGF) on allodynia and neuropeptide expression. IL-6 knockout mice showed decreased allodynia and galanin-IR compared to wild-type mice, but also decreased substance P (SP)-IR in the dorsal horn. Anti-NGF-treated rats with CCI also showed decreased allodynia and SP-IR, but increased galanin-IR in the dorsal horn. These results suggest that evoked pain is more tightly linked to SP than to galanin expression. If galanin's effects are inhibitory as the bulk of the literature suggests, its effects are subordinate to those of SP and to other changes following CCI.

Collaborative and reciprocal effects of ciliary neurotrophic factor and nerve growth factor on the neuronal phenotype of human neuroblastoma cells

We have probed the molecular basis of functional effects of ciliary neurotrophic factor (CNTF) and nerve growth factor (NGF) on aspects of the neuronal differentiation of LA-N-2 neuroblastoma cells. The influence of CNTF on the cholinergic phenotype can be accounted for by transcriptional/translational effects without implicating posttranslational mechanisms. Although both NGF receptors are expressed constitutively by LA-N-2 cells, CNTF has a marked stimulatory effect on trkA mRNA and protein. The NGF receptors are functional in serum-free conditions where they mitigate CNTF effects on cell adhesion but do not support process extension. Following priming by CNTF, NGF and CNTF have synergistic influences on process formation but not on choline acetyltransferase-specific activity.

Entry of monocytes into the brain after injection of Corynebacterium parvum

The receptiveness of the brain to monocyte infiltration was studied in rats that had been injected intracerebrally with Corynebacterium parvum. At 0-17 days after intracerebral injection and 18 h after intravenous injection of diI-labeled isogenous mononuclear cells, host rats were sacrificed and cells from the vicinity of the injection site and from the contralateral cerebral hemisphere were dissociated and analyzed by flow cytometry. In rats sacrificed 4-11 days postinjection of C. parvum, diI-labeled mononuclear cells were detected in cell preparations from the hemisphere ipsilateral and, to a lesser extent, contralateral to the injection site. No extravasation of cells from the blood to the brain was detected in rats injected intracerebrally with saline. By immunohistochemistry, many macrophages were detected in the hemisphere ipsilateral to injection of C. parvum. In additional experiments, the dissociated CNS cell population was labeled with OX-42 antibodies to the type 3 complement receptor, which is present on monocytes but not lymphocytes. Some cells in the brain were labeled with both diI and OX-42 and therefore were identified as monocytes that had entered the brain from the blood. In conclusion, monocytes can home to both sides of the brain after unilateral injection of a strong inflammatory agent but monocyte infiltration into the brain is delayed in comparison to monocyte inflammatory responses that have been reported in nonneural tissues.

Delay of CNTF decrease following peripheral nerve injury in C57BL/Wld mice

In peripheral nerves, ciliary neurotrophic factor (CNTF) is localized to a subset of Schwann cells and is decreased in synthesis during Wallerian degeneration. This pattern of expression is similar to that of myelin protein genes. In the present study, C57BL/Wld mice, which exhibit delayed Wallerian degeneration, were used to determine the role of axonal contact on the regulation of CNTF synthesis. Western blot analysis showed that CNTF immunoreactivity in Wld nerves remained almost normal even 10 days after ligation when it was almost undetectable in control mice. Reverse transcriptase polymerase chain reaction (RT-PCR) analysis revealed that 4 days after ligation, concentrations of CNTF mRNA in Wld mice had decreased much less than in control mice, but that at 10 days CNTF mRNA concentrations in Wld and control mice were comparably low. These observations suggest that maintenance of axonal contact in the absence of axonal transport from the cell body delays the decrease of CNTF mRNA normally seen after injury. Also, during Wallerian degeneration in Wld mice, the decrease of CNTF protein is delayed for many days longer than the decrease in CNTF mRNA.

Recovery of biceps function after delayed repair for brachial plexus injury

BACKGROUND

In many cases of severe closed injury involving the upper trunk of the brachial plexus, the proximal stump is too damaged to permit direct repair. Under these circumstances, several alternative sources of neurotization have been described, three of which are analyzed here.

METHODS AND RESULTS

Thirteen patients with brachial plexus injury had paralysis of elbow flexion owing to damage of either the upper trunk or the lateral cord. In four patients, the musculocutaneous nerve was reinnervated through cross-union with the thoracodorsal nerve; all regained strong elbow flexion. One of three the patients with cross-union between the lateral or medial pectoral nerve regained useful elbow flexion. Of six patients with nerve grafting between spinal accessory and musculocutaneous nerves, four regained useful elbow flexion.

CONCLUSION

Cross-union between thoracodorsal and musculocutaneous nerves appears to be a reliable method of restoring elbow function even when delayed for 2 years after injury. Return of elbow flexion should be an obtainable goal in most brachial plexus injuries.

Neurotrophins and nerve injury in the adult

A role for neurotrophins in mature primary sensory neurons persists, extending beyond that of promoting survival during development, to one of maintaining phenotypic and functional properties. Many adaptive changes that occur after peripheral axotomy and in axonal repair are believed to be influenced by altered availability of neurotrophic molecules to the neuron in this state. Indeed, administration of exogenous nerve growth factor counteracts many degenerative changes observed in the subpopulation of axotomized neurons which are nerve growth factor-responsive. Current efforts focus on defining actions of other neurotrophins (brain-derived neurotrophic factor, neurotrophin-3 and neurotrophin-4/5) in nerve injury and repair, and the intracellular pathways involved. Knowledge gained from work focusing on nerve growth factor and neurotrophin-3 in supporting maintenance or modulation of aspects of the differentiated state of adult primary sensory neurons is discussed.

Molecular cloning of a cDNA with a novel domain present in the tre-2 oncogene and the yeast cell cycle regulators BUB2 and cdc16

In an effort to identify genes that are differentially regulated during mast cell development, subtracted cDNA prepared from wild-type murine P815 mastocytoma cells and a P815 subline that exhibits properties of mast cell differentiation was used to screen mast cell cDNA libraries. Several known mast cell-specific cDNAs were isolated including mast cell carboxypeptidase A (MC-CPA), murine mast cell protease-5 (MMCP-5), and gp49. A novel cDNA, designated Tbc1, was identified that showed differential expression in the two mast cell lines. The amino acid sequence predicted from the cDNA contains a 200 amino acid domain that is homologous to regions in the tre-2 oncogene and the yeast regulators of mitosis, BUB2 and cdc16. The N-terminal region contains a number of cysteine and histidine residues, potentially encoding a zinc finger domain. Tbc1 is a nuclear protein and is expressed in highest levels in hematopoietic cells, testis and kidney. Within these tissues, expression of Tbc1 is cell- and stage-specific. Based on sequence similarity, pattern of expression and subcellular localization, Tbc1 may play a role in the cell cycle and differentiation of various tissues.

Distribution of erb-B2, erb-B3, and erb-B4 in the developing avian nervous system

The neuregulin proteins (GGF/ARIA/NDF/Heregulin) are pleiotrophic growth and differentiation factors whose receptors, erb-B2, erb-B3, and erb-B4, are members of the epidermal growth factor receptor family of receptor tyrosine kinases. With western blots, we have examined the developmental and regional distribution of these receptors within the brain and sciatic nerve of chick embryos. The receptors erb-B2, erb-B3, and erb-B4 are developmentally and spatially regulated within the nervous system. In addition, cultures enriched for neurons or glia indicate that erb-B2 and erb-B4 are found in both neurons and glia, whereas erb-B3 is found in glia alone.

Induction of interleukin-6 in axotomized sensory neurons

RNA from rat dorsal root ganglia was analyzed in search of potentially beneficial cytokines that are induced in dorsal root ganglia by nerve injury. By reverse transcription, the PCR, and Southern blotting, interleukin-6 mRNA was detected during development but not in normal adult dorsal root ganglia, reappeared within 1 d of sciatic nerve transection, was maximally increased after 2 and 4 d, and decreased below the threshold of detection within 1 week. By RNase protection assay, interleukin-6 mRNA was consistently present in RNA from dorsal root ganglia removed from rats 4 d following transection but not in control dorsal root ganglia. Interleukin-6 bioactivity was also present in dorsal root ganglia following nerve injury. By in situ hybridization, interleukin-6 mRNA was localized within large and medium-sized axotomized neurons. In summary, some sensory neurons respond to axotomy with a brisk transient increase in synthesis of interleukin-6. Injury to the sciatic nerve also induced mRNAs for interleukin-1 beta and tumor necrosis factor-alpha in dorsal root ganglia. The inductions of interleukin-1 beta and tumor necrosis factor-alpha mRNAs were later and more sustained than that of interleukin-6 mRNA. The cellular sources of these two cytokines have not been defined.

Changes in neuronal mRNAs induced by a local inflammatory reaction

Injection of Corynebacterium parvum into the rat dorsal root ganglion has previously been shown to cause an inflammatory reaction dominated by macrophages and to enhance regeneration of the central axons of primary sensory neurons. Here, neuronal mRNAs that are modified by nerve transection were analyzed by in situ hybridization following injection of C. parvum into the dorsal root ganglion. Neuronal concentrations of mRNAs for the growth-associated protein (GAP-43) and the immediate early gene c-jun were increased by a local inflammatory response just as after axotomy. The concentration of mRNA for calcitonin gene-related peptide (CGRP) was also increased in a constant subpopulation of sensory neurons after injection of C. parvum in contrast to its decrease following axotomy. The results are consistent with the hypothesis that some of the responses to sensory neurons to axotomy are sustained by macrophages which accumulate within the dorsal root ganglion after nerve injury.

Differentiation effects of ciliary neurotrophic factor on human neuroblastoma cells

In the human neuroblastoma cell line LA-N-2, recombinant rat ciliary neurotrophic factor (CNTF) induced neurite growth and cholinergic differentiation that were both half-maximally saturated at < 100 pM of the neurokine, but was not required for cell survival in serum-free conditions over a 13-day period. CNTF markedly stimulated choline acetyltransferase activity and acetylcholine synthesis, whereas high-affinity choline transport was only slightly enhanced and acetylcholinesterase activity was unchanged. Leukemia inhibitory factor had effects identical to CNTF on neurite growth and choline acetyltransferase activity, but interleukin 6 had no effect. Radioiodinated CNTF binding and affinity cross-linking studies were consistent with tripartite receptor activation as a mediator of the observed biological effects.

Differential influence of nerve growth factor on neuropeptide expression in vivo: a novel role in peptide suppression in adult sensory neurons

In this study the actions of NGF in regulating peptide expression were examined in vivo in adult rat primary sensory neurons. The hypothesis that NGF might tonically inhibit expression of some peptides was tested specifically. In situ hybridization and immunohistochemistry were used to detect presence or absence of alpha-CGRP, beta-CGRP, SP, SOM, VIP, CCK, NPY, and GAL as well as their mRNAs. In neurons in normal lumbar DRG alpha-CGRP, beta-CGRP, SP, and SOM are abundantly and heterogeneously expressed whereas few neurons have detectable VIP, CCK, NPY, or GAL. Two weeks following sciatic nerve transection, concentrations of alpha-CGRP, beta-CGRP, SP, and SOM plus their mRNAs have decreased to background in all but a few neurons. In contrast, VIP, CCK, NPY, and GAL are now synthesized in many neurons. Delayed intrathecal infusion of NGF (125 ng/microliter/hr) for 7 d, starting 2 weeks after injury counteracted the decrease in expression of alpha-CGRP, beta-CGRP and SP expression, but not SOM. This lack of influence of NGF on SOM is consistent with the absence of high-affinity NGF receptors and trk mRNA in SOM-positive neurons. Delayed infusion of NGF also reduced the number of neurons expressing VIP, CCK, NPY, and GAL after injury by approximately one-half in each subpopulation. Therefore, we suggest that NGF suppresses expression of these four peptides but only if the neurons also have NGF receptors. The results show that NGF can regulate peptide expression differentially and may also be part of the signal that allows reversion to normal of responses to injury as axons regenerate.

CNTF or (-)-deprenyl in immature rats: survival of axotomized facial motoneurons and weight loss

The application of ciliary neurotrophic factor (CNTF) to the cut ends of transected facial nerves in newborn rats has been reported to reduce the death of facial motoneurons (FMns) axotomized by the transection. Systemically delivered CNTF has been found to cause cachexia in adult mice. We compared the influence of dosage of CNTF and (-)-deprenyl on FMn death, weight loss, and animal survival in rat pups that underwent facial nerve transection at the 14th postnatal day (P14). CNTF was administered by osmotic mini-pumps connected to tubing ending either intrathecally or extrathecally near the craniocervical junction. CNTF caused weight loss and animal death that was similar to the cachexia reported in mice if administered in amounts of 1.1 microgram/day or greater. At the same doses, intrathecal CNTF was more effective than extrathecal CNTF in inducing the cachexia. (-)-Deprenyl did not alter animal survival or weight gain, even at high doses (10 mg/kg every 2 days). Intrathecal CNTF and intraperitoneal (-)-deprenyl, but not extrathecal CNTF, significantly increased the survival of the axotomized FMns. (-)-Deprenyl administered twice daily at 0.01 mg/kg was considerably more effective than CNTF in increasing FMn survival due to the limitation on CNTF dosage caused by the animal death.

Inflammation and axonal regeneration

Inflammatory cells and their products contribute to neuronal survival and axonal regeneration after injury. Following sciatic nerve transection in rats, macrophages accumulate in the corresponding dorsal root ganglion, potentially supplying neurotrophic support to nerve cell bodies, and enhancing axonal regeneration. Growth factors characterized for their functions in the haematopoietic and immune systems also act on neurons and vice versa, by sharing common subunits among receptors for cytokines and neurotrophic factors.

Ciliary neurotrophic factor: a review

Ciliary neurotrophic factor (CNTF) is a 22-kDa protein predicted to share with leukemia inhibitory factor (LIF) and interleukin-6 a common amphipathic helical domain. Consistent with this prediction, the CNTF receptor complex is composed of the CNTF alpha receptor, the LIF beta receptor and gp130 a signalling molecule for LIF and interleukin-6. The major sources of synthesis of CNTF are Schwann cells and astrocytes, but it remains unclear how much CNTF is released from these glial cells and by what mechanism. In vitro, CNTF supports the survival of all classes of peripheral nervous system neurons plus many CNS neurons, induces neurite outgrowth, promotes a cholinergic phenotype in sympathetic neurons and arrests division of neuronal precursor cells. Several cell lines also respond to CNTF. In vivo, CNTF rescues several types of neurons from axotomy-induced death. The functions of CNTF in the development and maintenance of the nervous system remain enigmatic.

Studies of axonal regeneration in C57BL/6J and A/J mice

The genetic and biological nature of a deficiency in axonal regeneration in C57BL/6J mice was investigated. From analysis of recombinant inbred strains, the genetic basis for the deficient regeneration behaviours of C57BL/6J and A/J mice is deduced to involve multiple loci. The defect in axonal regeneration in C57BL/6J mice appears to be a delay rather than permanent impairment and appears to involve sensory more than motor axons.

Systemic administration of ciliary neurotrophic factor induces cachexia in rodents

Ciliary neurotrophic factor (CNTF) has previously been shown to promote the survival of several classes of neurons and glial. We report here that in addition to its effects on the nervous system, CNTF can induce potent effects in extra-neural tissues. Implantation of C6 glioma cells engineered to secrete CNTF either subcutaneously or into the peritoneal cavity of adult mice, or systemic injections of purified rat or human recombinant CNTF, resulted in a rapid syndrome of weight loss resulting in death over a period of 7-10 d. This weight loss could not be explained by a reduction in food intake and involved losses of both fat and skeletal muscle. CNTF also induced the synthesis of acute phase proteins such as haptoglobin. Implantation of C6 lines expressing a nonsecreted form of CNTF, or the parental C6 line itself, did not result in wasting effects. Analysis of this CNTF-induced wasting indicates similarities with the previously described cachectins, tumor necrosis factor, interleukin 6, and leukemia inhibitory factor, but does not involve the induction of these cytokines.

Trophic actions of ciliary neurotrophic factor on murine embryonic carcinoma cells

Recombinant rat CNTF (ciliary neurotrophic factor) at picomolar concentration prevents the death of P19 murine embryonic carcinoma cells that usually follows upon withdrawal of serum from the culture medium. For prolonged survival of P19 cells in serum-free medium, insulin must also be present. In the presence or absence of serum, CNTF stimulates the differentiation of P19 cells, inducing the formation of neurites and synthesis of neurofilament. The results of radioautographic studies with radioiodinated CNTF indicate the presence of high-affinity binding sites on P19 cells. Equilibration of P19 cells with [125I]CNTF followed by incubation with cross-linking reagents reveals evidence for at least two putative receptors of approximately 78 and approximately 167 kDa.

Responses of macrophages in rat dorsal root ganglia following peripheral nerve injury

Immunohistochemical studies with monoclonal antibodies to macrophage antigens were performed on sections of rat lumbar dorsal root ganglia. In confirmation of previous observations, cells with macrophage antigenicity were detected in normal ganglia. Many of these presumptive macrophages were perineuronal in contact with the neuron/satellite cell complex, a few were perivascular, and others were in interstitial position not in apparent contact with either blood vessels or neurons. The number of macrophages in lumbar dorsal root ganglia started to increase 2-4 days after sciatic nerve transection and remained elevated for four weeks. Perineuronal macrophages resembled satellite glial cells in light microscope appearance but were distinguished from glial cells by their lack of S-100 immunoreactivity. Following this sciatic nerve injury, macrophage counts were modestly increased in contralateral lumbar dorsal root ganglia but not in cervical dorsal root ganglia. Thus peripheral nerve injury induces a recruitment and/or proliferation of macrophages in the corresponding dorsal root ganglion. Although the functions of these macrophages are unclear, those in perineuronal position could contribute to the survival or regeneration of axotomized neurons.

Colocalization of NGF binding sites, trk mRNA, and low-affinity NGF receptor mRNA in primary sensory neurons: responses to injury and infusion of NGF

The distributions of mRNAs for the protooncogene trk and the low-affinity NGF receptor (LNGFR) were studied by hybridization with oligonucleotide probes on sections of adult rat primary sensory and sympathetic ganglia. For comparison with high-affinity binding sites, adjacent sections were processed for NGF receptor radioautography. Among neurons in lumbar dorsal root ganglia and trigeminal ganglia, trk mRNA and NGF-binding sites were closely colocalized; this finding together with previous direct evidence in other cell types is taken to indicate that trk protein is an essential component of the high-affinity NGF receptor in adult sensory neurons. In lumbar dorsal root ganglia and trigeminal ganglia, abundant LNGFR mRNA was found in all neurons with strong 125I-NGF labeling and on additional neurons lacking high-affinity NGF-binding sites. The presence of abundant LNGFR in neurons with high-affinity receptors could be the cause and/or consequence of their ability to respond to NGF. Neurons with abundant LNGFR mRNA but few high-affinity NGF-binding sites may have receptors for other members of the neurotrophin family. In nodose ganglia, neurons with high concentrations of LNGFR mRNA greatly outnumbered the small percentage with abundant trk mRNA. Following intrathecal infusion of NGF to otherwise normal dorsal root ganglia, the concentrations of LNGFR mRNA but not those of trk mRNA and NGF-binding sites were increased in NGF-responsive neurons. The usual single normal pattern of frequency histograms of LNGFR labeling indices became bimodal in response to NGF. Concentrations of NGF-binding sites, LNGFR mRNA, and trk mRNA were all decreased by peripheral nerve transection and restored by exogenous NGF, the restoration being complete for LNGFR mRNA and partial for trk mRNA and NGF-binding sites. The data indicate that NGF can regulate both LNGFR and trk mRNAs but do not clarify the possible contribution of the LNGFR protein to high-affinity binding sites.

Preparation and biological properties of native and recombinant ciliary neurotrophic factor

CNTF (ciliary neurotrophic factor), purified from rabbit sciatic nerves by a relatively simple procedure, is bioactive in tissue culture at low picomolar concentration and appears as a doublet on polyacrylamide gel electrophoresis (PAGE). In these nerves, CNTF accounts for more than one-half of the survival-promoting activity on ciliary neurons. The concentration of CNTF in rabbit sciatic nerves is estimated to be 5 nmol/kg, more than 1000 times higher than would seem to be required to support neurons if the neurotrophic factor were homogeneously distributed. With recombinant DNA technology, rat CNTF has been synthesized in Escherichia coli, purified without denaturating agents, and found to be bioactive at a slightly lower concentration than CNTF extracted from rabbit sciatic nerves. After radioiodination, CNTF retains biological activity but is not specifically internalized and retrogradely transported in motor and sensory axons. In peripheral nerves, ciliary neurotrophic factor differs biologically from nerve growth factor (NGF) by its much higher tissue concentration and apparent lack of internalization by peripheral nerve axons.

Decreased synthesis of ciliary neurotrophic factor in degenerating peripheral nerves

The mRNA for ciliary neurotrophic factor in normal and injured sciatic nerves has been assayed by an RNase protection assay. The endoneurial concentration of ciliary neurotrophic factor mRNA is diminished in the distal nerve stump within three days of sciatic nerve transection, is less than one tenth of normal after one week, and remains low if regeneration does not occur. The synthesis of ciliary neurotrophic factor in injured peripheral nerves is decreased when and where the synthesis of nerve growth factor is increased.

Neurotrophic factors in regeneration

Nerve growth factor, fibroblast growth factor, and ciliary neurotrophic factor can protect selected populations of neurons from some of the degenerative changes that otherwise follow axonal injury or other insults. The function of diffusible neurotrophic factors in axonal regeneration is still unclear, however. Knowledge of the nerve growth factor congeners, brain-derived neurotrophic factor and neurotrophin-3, is advancing rapidly as is the identification of neurotrophin receptors, several of which are membrane-bound tyrosine kinases.

Molecular interactions modulating neuronal survival and growth

The extracellular environment of the neuron provides a heterogeneous milieu of survival and growth modulating molecular species subserving regulatory signals that operate in development, mediate activity-dependent enduring changes in synaptic connectivity, and promote or inhibit survival and axonal regeneration following insult. Parallel distributed processing networks in neurons, activated by these molecular species, can likely be recruited selectively to serve specific needs of the organism.

vRel is an inactive member of the Rel family of transcriptional activating proteins

The vRel oncoprotein is member of a family of related proteins that also includes cRel, NF-kappa B, and Dorsal. We investigated the transcriptional regulatory properties of several Rel proteins in cotransfection assays with chicken embryo fibroblasts (CEF). Retroviral vectors expressing hybrid proteins that contain the DNA-binding domain of LexA fused to portions of the viral oncoprotein vRel or chicken, mouse, human, or Drosophila melanogaster (Dorsal) cRel proteins were cotransfected with a reporter plasmid that contains the DNA sequence recognized by LexA, a promoter, and the assayable gene for chloramphenicol acetyltransferase. In transient assays, a LexA-vRel protein did not activate transcription in CEF. Full-length chicken cRel, mouse cRel, and Dorsal fusion proteins all activated transcription weakly; however, deletion of N-terminal Rel sequences from each of these proto-oncogene encoded proteins resulted in strong activation by LexA fusion proteins containing only C-terminal sequences. Inhibition of the C-terminal chicken cRel gene activation domain by N-terminal sequences was seen in CEF and mouse and monkey fibroblasts. These results show that cRel proteins from different species have the same general organization: an N-terminal inhibitory domain and a C-terminal activation domain. Sequence comparison suggests that the inhibitory domain is conserved but the activation domain is species specific. In contrast, vRel lacks a strong C-terminal gene activation function, since a LexA fusion protein containing C-terminal vRel sequences alone only weakly activated transcription. In addition, the wild-type vRel protein (lacking LexA sequences) repressed transcription from reporter plasmids containing NF-kappa B target sequences; nontransforming vRel mutants did not repress transcription from these plasmids. Our results suggest that vRel transforms cells by interfering with transcriptional activation by cellular Rel proteins.

Inflammation near the nerve cell body enhances axonal regeneration

Although crushed axons in a dorsal spinal root normally regenerate more slowly than peripheral axons, their regeneration can be accelerated by a conditioning lesion to the corresponding peripheral nerve. These and other observations indicate that injury to peripheral sensory axons triggers changes in their nerve cell bodies that contribute to axonal regeneration. To investigate mechanisms of activating nerve cell bodies, an inflammatory reaction was provoked in rat dorsal root ganglia (DRG) through injection of Corynebacterium parvum. This inflammation enhanced regeneration in the associated dorsal root, increasing 4-fold the number of regenerating fibers 17 d after crushing; peripheral nerve regeneration was not accelerated. A milder stimulation of dorsal root regeneration was detected after direct injection of isogenous macrophages into the ganglion. It is concluded that changes favorable to axonal regeneration can be induced by products of inflammatory cells acting in the vicinity of the nerve cell body. Satellite glial cells and other unidentified cells in lumbar DRG were shown by thymidine radioautography to proliferate after sciatic nerve transection or injection of C. parvum into the ganglia. Intrathecal infusion of mitomycin C suppressed axotomy-induced mitosis of satellite glial cells but did not impede axonal regeneration in the dorsal root or the peripheral nerve. Nevertheless, the similarity in reactions of satellite glial cells during 2 processes that activate neurons adds indirect support to the idea that non-neuronal cells in the DRG might influence regenerative responses of primary sensory neurons.

Influence of nerve growth factor on neurofilament gene expression in mature primary sensory neurons

To analyze the possible influence of nerve growth factor (NGF) on neurofilament synthesis in primary sensory neurons, adjacent cryostat sections of lumbar dorsal root ganglia (DRG) from adult rats were processed for either NGF-receptor radioautography or in situ hybridization with a neurofilament cDNA probe. Labeling by both procedures was quantified with computer assistance for approximately 300 neurons in each of selected ganglia. For uninjured neurons, no correction was detected between NGF binding and neurofilament mRNA, even after infusion of NGF into the lumbar subarachnoid space for 1 week. One or 3 weeks after sciatic nerve transection, neurofilament labeling densities in large DRG neurons were sharply reduced and the normal bimodal pattern in frequency histograms had become unimodal. Intrathecal infusion of NGF counteracted this injury-induced reduction of neurofilament mRNA but only in neurons with high-affinity NGF receptors. To explain the effects of NGF on axotomized neurons and the normal diversity of neurofilament gene expression among neurons with NGF receptors, we postulate that NGF permits NGF-sensitive DRG neurons to respond differentially to a second factor stimulating neurofilament synthesis.

Correlation between GAP43 and nerve growth factor receptors in rat sensory neurons

In mature rat sensory neurons, expression of the gene for the growth-associated protein, GAP43, was studied by in situ hybridization with a cDNA probe. Among neurons in normal lumbar dorsal root ganglia, labeling for GAP43 mRNA was heterogeneous, approximately one-half of the neurons being densely labeled. To characterize the latter population, individual neurons were examined in adjacent sections processed either for GAP43 hybridization or NGF-receptor radioautography. Virtually all neurons with high-affinity NGF binding sites had high basal levels of GAP43 mRNA and most GAP43-positive neurons bore NGF receptors. Another NGF-responsive population, sympathetic neurons in the superior cervical ganglion, also had high basal concentrations of GAP43 mRNA. Further co-localization studies in dorsal root ganglia were performed with immunohistochemistry for somatostatin and enzyme histochemistry for acid phosphatase. The latter 2 groups of sensory neurons have been previously shown to lack high-affinity receptors and were here shown to have low basal concentrations of GAP43 mRNA. From this and earlier studies, it can be assumed that substance P-immunoreactive neurons and strongly positive CGRP neurons synthesize GAP43 at high basal rate. One week following peripheral nerve transection, almost all neurons had high concentrations of GAP43 mRNA without correlation with NGF binding. Intrathecal infusion of NGF after the sciatic nerve was cut did not strongly influence this post-traumatic elevation in GAP mRNA. In normal dorsal root ganglia, neurons that have high-affinity NGF binding sites and are therefore potentially responsive to NGF also have high basal rates of synthesis of GAP43.(ABSTRACT TRUNCATED AT 250 WORDS)

A deficiency of axonal regeneration in C57BL/6J mice

Axonal regeneration within peripheral nerves and dorsal spinal roots was investigated in inbred strains of mice with known differences in macrophage recruitment and inflammatory functions. During the second week after sciatic nerve crush, counts of regenerating newly myelinated fibres were significantly lower in C57BL/6J mice than in 4 other strains. After dorsal root crush with or without concomitant sciatic nerve transection to enhance regeneration, fibre counts in roots of C57BL/6J were one-fifth of those in A/J mice. Axonal regeneration is subnormal in C57BL/6J mice but this defect appears not to be linked to known deficiencies in macrophage function.

Nerve growth factor induces functional nicotinic acetylcholine receptors on rat sensory neurons in culture

Neonatal sensory neurons from rat nodose ganglia express nicotinic acetylcholine receptors when grown in tissue culture without other cell types. The present study investigates the role of nerve growth factor in inducing these receptors. Nerve growth factor has little effect on the growth and survival of nodose neurons in culture, although most neurons were found by quantitative radioautography to have high-affinity nerve growth factor receptors. Nerve growth factor strongly influenced the expression of nicotinic receptors on these neurons: the proportion of acetylcholine-sensitive neurons was approximately 60% in cultures with nerve growth factor compared with 15% in cultures grown without nerve growth factor. The proportion of acetylcholine-sensitive neurons increased over the first week, plateaued by day 12 and remained high for at least three weeks. In contrast, without NGF, the proportion of acetylcholine-sensitive neurons was low throughout the three-week period. The results indicate that nerve growth factor is an important factor in promoting nicotinic receptors on these neurons in culture.