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.