Electrophoretic similarity of the ciliary ganglion survival factors from different tissues and species

Reciprocal regulation of ciliary neurotrophic factor receptors and acetylcholine receptors during synaptogenesis in embryonic chick atria

Ciliary neurotrophic factor (CNTF) has been implicated in the development, survival, and maintenance of a broad range of neurons and glia in the peripheral nervous system and the CNS. Evidence also suggests that CNTF may affect development of cells outside the nervous system. We have found that functional CNTF and its receptor are expressed in developing embryonic chick heart and may be involved in parasympathetic synapse formation. CNTF and CNTF receptor mRNA levels were highest at embryonic day 11 (E11)-E13, the period of parasympathetic innervation in chick atria. Levels of atrial CNTF receptor mRNA were fourfold greater at E13 than at E6 and at E13 were 2.5-fold higher in atria than in ventricle, corresponding to the higher degree of parasympathetic innervation occurring in atria. Treatment of isolated atria or cultured atrial myocytes with recombinant human or avian CNTF resulted in the tyrosine phosphorylation and nuclear translocation of the signal transducer and activator of transcription STAT3. The developmental increase in atrial CNTF receptor mRNA was enhanced by stimulating muscarinic receptors with carbachol in ovo and was inhibited by blocking muscarinic cholinergic receptors with atropine. Treatment of cultured atrial myocytes with CNTF resulted in a twofold increase in the levels of muscarinic receptors. Thus, CNTF was able to regulate a key component of parasympathetic synapses on atrial myocytes. These results suggest a postsynaptic role for CNTF in the onset of parasympathetic function in the developing heart and provide new clues to molecular mechanisms directing synapse formation at targets of the autonomic nervous system.

Target-derived molecules that influence the development of neurons in the avian ciliary ganglion

The developing avian ciliary ganglion has been a particularly amenable system for the identification, isolation, and characterization of putative target-derived molecules that mediate retrograde interactions. To date a number of biochemically distinct activities that regulate neuronal survival, transmitter phenotype, and chemosensitivity of ciliary ganglion neurons have been identified. Of these, only two survival-promoting molecules have been purified to homogeneity: ciliary neurotrophic factor and a related molecule, growth-promoting activity. A somatostatin-inducing activity found in cultured choroid cells is very likely to be chick activin A. Other molecules that regulate acetylcholine and acetylcholine receptor expression comigrate on a gel filtration column at a molecular weight of 50-60 kD, but they have yet to be isolated. Once molecules that mimic retrograde influences are identified, a number of criteria must be met before their physiological significance can be established. These criteria are (1) availability of the molecule from the target at the appropriate time in development; (2) ability of the neurons to respond to the molecule at the appropriate time in development; (3) demonstration that blocking the activity or availability of the molecule is able to block the target-derived developmental change expressed in the neurons. Of the molecules that are thought to retrogradely influence ciliary neuron development, only growth-promoting activity is known to meet criteria 1 and 2, and experiments are currently underway to test whether inhibition of growth-promoting activity in vivo will exacerbate normal cell death.

Expression and characterization of recombinant human ciliary neurotrophic factor from Escherichia coli

The gene for ciliary neurotrophic factor (CNTF) was cloned from a human genomic DNA library by screening with a DNA fragment amplified from human genomic DNA using the polymerase chain reaction. A DNA sequence coding for human CNTF was placed under control of an regulatable promoter in the expression vector pJU1003 and transformed into Escherichia coli strain BL21(DE3). Induction of expression in cultures of this transformant led to the accumulation of approx. 25 mg/l per A600 unit of human CNTF. CNTF was purified to homogeneity from cell lysates via anion-exchange, cation-exchange and Zn(2+)-affinity chromatography. Purified CNTF contained less than 0.1% contaminating E. coli proteins, as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), Western blot analysis and reversed-phase high-pressure liquid chromatography (HPLC). The protein exhibited an ultraviolet absorption maximum at 279 nm with a calculated extinction coefficient of A1%(279) = 9.0. Peptide map and amino acid sequence analyses confirmed that the expressed protein has the amino acid sequence expected for human CNTF, except for the absence of the amino-terminal methionine. High-purified recombinant human CNTF supported the survival of chick embryo parasympathetic, sympathetic and sensory neurons in culture at low picomolar concentrations. These results indicate that the biological activities previously ascribed to impure CNTF preparations indeed reside in one molecule.

A ciliary neuronotrophic factor from peripheral nerve and smooth muscle which is not retrogradely transported

We have found that a CNTF-like molecule which supports ciliary and sympathetic neurons is not retrogradely transported in either sympathetic or parasympathetic nerves. The factor has an apparent Mr of 21 kDa, a pI of 4.9, and is present in peripheral nerves and smooth muscle of the chick. Our experiments indicate that CNTF-like activity does not accumulate on the distal side of ligated chick expansor nerves. In contrast, there is a clear accumulation of NGF. The activity further differs from NGF in that it is not removed from a smooth muscle of the chick wing by innervating sympathetic fibers. Transection of these fibers does not lead to an accumulation of ciliary activity in the expansor secundariorum muscle, suggesting that neurons do not actively deplete the muscle of factor by retrograde transport. Finally, recombinant CNTF or semi-purified preparations of CNTF-like activity labelled with 125I were not transported to the ciliary ganglion of chicks following injection of biologically active material into the eye. Our results suggest either that endogenous CNTF does not act as a survival factor in vivo, or that retrograde transport is not a property inherent to all neuronotrophic molecules.

Blot and culture analysis of neuronotrophic factors in nerve regeneration chamber fluids

The fluid accumulating in silicone nerve regeneration chambers implanted between the cut ends of rat sciatic nerve contains neuronotrophic activities towards embryonic chick ciliary and sympathetic neurons. The blot and culture technique of Carnow et al. was used to determine if part of the neuronotrophic activities is due to ciliary neuronotrophic factor, which supports the survival of both types of neurons in vitro. The technique involves separating the fluid proteins by SDS-polyacrylamide gel electrophoresis, Western transfer, and then culturing of purified neurons on the nitrocellulose blots. After 24 hr surviving neurons are restricted to regions of the blot where neuronotrophic factor is present. Analysis of 1 and 2 day fluids showed that a multitude of factors are present, particularly in the 19-30 kD molecular weight range, with discrete peaks of activity at molecular weights consistent with those reported for ciliary neuronotrophic factor. There were several other peaks of activity present in the fluids in addition to these.

Purification, cloning, and expression of ciliary neurotrophic factor (CNTF)

Ciliary neurotrophic factor (CNTF) is one of a small number of proteins with neurotrophic activities distinct from nerve growth factor (NGF). CNTF has now been purified and cloned and the primary structure of CNTF from rabbit sciatic nerve has been determined. Biologically active CNTF has been transiently expressed from a rabbit complementary DNA clone. CNTF is a neural effector without significant sequence homologies to any previously reported protein.

The role of dihydropyridine-sensitive voltage-gated calcium channels in potassium-mediated neuronal survival

The survival of isolated neurons from chick embryo ciliary, sympathetic, and dorsal root ganglia is greatly enhanced by concentrations of extracellular potassium that significantly depolarize the neurons (ED50 = 20-25 mM). The survival-promoting effect of elevated potassium on each of these 3 types of neurons appears to be the result of the opening of voltage-gated calcium channels. The dihydropyridine, Bay K 8644, which increases calcium influx through L-type voltage-gated calcium channels in neurons, strongly potentiated the survival-promoting action of elevated potassium (ED50 = 10.8 +/- 7.0 nM). In contrast, chemically closely related dihydropyridines, PN200-110 (ED50 = 0.33 +/- 0.15 nM) and nitrendipine (ED50 = 1.3 +/- 0.3 nM), which block calcium influx through the same voltage-gated channels, completely inhibited potassium-mediated neuronal survival. Chemically different agents that also block calcium influx through voltage-gated channels also inhibited potassium-mediated neuronal survival: the phenylalkylamine verapamil (ED50 = 0.78 +/- 0.38 microM), the benzothiazepine diltiazem (ED50 = 1.7 microM), and the inorganic ion cadmium (ED50 = 5.8 microM). These calcium-channel blockers are not simply toxic to neurons, since they did not inhibit neuronal survival mediated by the neurotrophic proteins, nerve growth factor, basic fibroblast growth factor, or ciliary neurotrophic factor, also suggesting that voltage-gated calcium channels are not involved in the action of these factors. These results suggest that neuronal survival in elevated potassium in ciliary, sympathetic, and dorsal root ganglion neurons is the result of calcium influx through dihydropyridine-sensitive, L-type voltage-gated calcium channels. These findings are discussed in relation to the neuronal toxicity of excitatory amino acids which is also thought to occur through increased calcium influx.

Culture conditions affect the cholinergic development of an isolated subpopulation of chick mesencephalic neural crest cells

Although neural crest cells are known to be very responsive to environmental cues during their development, recent evidence indicates that at least some subpopulations may be committed to a specific differentiation program prior to migration. Because the neural crest is composed of a heterogeneous mixture of cells that contributes to many vertebrate cell lineages, assessing the properties of specific subpopulations and the effect of the environment on their development has been difficult. To address this problem, we have isolated a pure subpopulation of chick mesencephalic neural crest cells by fluorescence no-flow cytometry after labeling them with monoclonal antibodies (Mabs) to a 75-kDa cell surface antigen that is associated with high affinity choline uptake. When cultures of chick mesencephalic neural crest cells are labeled with these Mabs and a fluorescent second step antibody, approximately 5% of the cells are antigen-positive (A+). After sorting, 100% of the resulting cultured mesencephalic neural crest cells are A+. The Mabs we used also label all of the neurons of the embryonic chick and quail ciliary ganglion in vivo and in vitro. We have compared the effect of various cell culture media on the isolated neural crest subpopulation and the heterogeneous chick mesencephalic neural crest from which it was derived. A+ cells were passaged and grown in a variety of media, each of which differently affected its characteristics and development. A+ cells proliferated in the presence of 15% fetal bovine serum (FBS) and high concentrations (10-15%) of chick embryo extract, but did not differentiate, although they retained basal levels of choline acetyltransferase (ChAT) activity. However, in chick serum and high (25 mM as opposed to 7 mM) K+, and heart-, iris-, or lung-conditioned medium, all of which are known to promote survival and/or cholinergic development of ciliary ganglion neurons, the cells ceased to proliferate and all of the cells in the culture became "neuron-like" within 10 days. No neuron-like cells were found in liver-, notocord-, or neural tube-conditioned media if FBS was used. When A+ cells were eliminated either by complement-mediated cytotoxicity or by laser-ablating A+ cells during no-flow cytometry, all ChAT activity was also eliminated, and no neuron-like cells or ChAT activity was found in cultures during a subsequent 3-week culture period.(ABSTRACT TRUNCATED AT 400 WORDS)

Species specificity in the responsiveness of chick embryo neural tube explants to target-conditioned medium

Explants from the metencephalic region of 40-h chick embryo neural tubes containing the trigeminal (V) motor nucleus were cultured in appropriate target muscle-conditioned media (MCM) derived from chick, quail and rat embryos. Enhanced neuritic outgrowth was found only in the presence of chick MCM, indicating that this early, initial responsiveness to target-released materials within this system is species-specific.

Neuroblastoma cells contain a trophic factor sharing biological and molecular properties with ciliary neurotrophic factor

Ciliary neurotrophic factor (CNTF) is a protein supporting the in vitro survival of a characteristic spectrum of embryonic chicken and rat peripheral neurons. High-speed supernatants of extracts from two neuroblastoma (NB) cell lines--the mouse C 1300 N2a and the human IMR 32--mimic the effects of CNTF on identical target neurons. Promotion of survival is dose-dependent with an ED50 of 80 micrograms (IMR 32) and 140 micrograms (C 1300 N2a) of protein per ml and saturable at plateau values for surviving neurons identical to those achieved with purified CNTF. Small amounts of a CNTF-like material are also detectable in medium conditioned by NB cells. The activity is destroyed by heat and trypsin and not blocked by antibodies to (mouse) nerve growth factor. Unlike the neurite-promoting and neuronal-survival modulating agent laminin, it cannot be depleted on poly(L-alpha-ornithine)-coated plastic surfaces. NB IMR 32 cell extracts were electrophoresed using NaDodSO4/PAGE and transferred to nitrocellulose. Ciliary ganglion neurons seeded on the blotting paper in culture medium lacking CNTF ("cell blot") exclusively survive on two distinct bands with apparent molecular masses of 24 and 48 kDa. Twenty-four kilodaltons is the molecular mass of a CNTF purified from rat sciatic nerve. These results suggest that NB cells may contain a CNTF-like protein and provide further evidence that neurons may store neurotrophic factors. Purified (chicken) CNTF failed to affect proliferation and neurite growth of NB cells. The biological relevance of CNTF for NB cells, therefore, remains to be elucidated.

Multiple influences of a heparin-binding growth factor on neuronal development

Heparin-binding growth factor-2 (HBGF-2; also known as basic fibroblast growth factor) is mitogenic for most anchorage-dependent cells. It is shown here that HBGF-2 stimulates cell-substratum adhesion and neurite extension in the sympathetic nerve cell line PC12. When HBGF-2 is adsorbed to artificial extracellular matrices consisting of heparin or chondroitin sulfate, it causes the formation of cellular aggregates or circles of cells, respectively. HBGF-2 is also a nerve cell survival molecule, for it potentiates the survival of primary cultures of embryonic chick ciliary ganglion cells but not of embryonic neural retina cells. Finally, a series of synthetic peptides from the HBGF-2 sequence is described that selectively alter the biological effects of HBGF-2. The amphiphilic nature of one of these peptides is discussed with respect to its ability to stimulate cell adhesion.

An examination of ciliary neuronotrophic factors from avian and rodent tissue extracts using a blot and culture technique

We have previously reported a technique for determining the apparent molecular weight (Mr) of ciliary neuronotrophic factors (CNTFs) in crude extracts. This method involves SDS-polyacrylamide gel electrophoresis of the extract. Western blotting and culture of purified ciliary ganglion neurons on the paper containing the blotted lane. Neurons will survive only if in direct contact with the trophic factor band and the surviving neurons, when stained with a vital dye, will outline the CNTF band thereby indicating the Mr of the active polypeptide. Here we have modified this 'blot and culture' technique by including Mr standard proteins in the same electrophoretic lane with the samples, identifying the proteins by staining the nitrocellulose blot with Amido black, marking the standard bands with pinholes and destaining the blot prior to seeding neurons onto it. The active CNTF polypeptides can then be identified by their ability to support the 24-h survival of cultured ciliary neurons. This modified technique was used to determine the Mr of CNTF activities in several chick and rat tissue extracts of selected developmental ages and to ascertain if the two forms of CNTF are exclusive to chick and rat, embryonic and adult, or eye and nerve tissues. We report that the above modifications permitted a more accurate method for Mr determination than the previous method, only two apparent forms of CNTF were recognized, the Mr found for each form is 25 kDa and 28 kDa, both forms can be present in chick and rat tissues and from embryonic and adult sources and the 28 kDa form is predominant in rat while the 25-kDa form is predominant in chicken tissues.

Comparative screening for ciliary neurotrophic activity in organs of the rat and chicken

A neuron-survival assay with dissociated ciliary ganglion neurons was used to examine the level of neurotrophic activity in organs of the rat and chicken. All tissue homogenates enhanced neuron survival at increasing protein concentrations, although 50% survival activity (1 trophic unit, TU, per ml) occurred at distinctly different levels in the different organs. Liver, spleen, T-cells, and submandibular gland from the rat were very low in survival-promoting activity (0.1-1.1 TU per mg of protein). Serum and lung were slightly richer (2.4-2.8 mg). Heart, brain, and skeletal muscle stimulated survival well (6.2-13 TU/mg). Unexpectedly, the highest activities were found in the rat kidney (44 TU/mg). The activity in adult chicken organs was less varied (1.6-9.1 TU/mg). Higher trophic activities were found in the chicken embryo, particularly at day 18 of development (20-30 TU/mg). The up to 100-fold difference in trophic level between organs should make it feasible to use subtractive hybridization, differential screening, and transient expression in eukaryotic cells for molecular cloning of the ciliary neurotrophic factor(s).

The induction of a regenerative propensity in sensory neurons following peripheral axonal injury

Injury of the peripheral axons of primary sensory neurons has been previously shown to increase the probability that the corresponding central axons would grow from the injured spinal cord into a peripheral nerve graft. This phenomenon has been used to investigate the nature of extrinsic cues from injured nerves that enhanced regenerative propensity within sensory neurons. In 13 groups of rats, a segment of the right sciatic nerve was grafted to the dorsal columns of the spinal cord and the left sciatic nerve was subjected to mechanical injury, injection of colchicine or infusion of nerve growth factor. Subsequently, neurons in lumbar dorsal root ganglia with axons growing from the spinal cord into a graft were identified by retrograde perikaryal labelling and compared for the two sides. The aim was to mimic or modify the inductive effect of nerve transaction by alternative or additional manipulation of the nerve. Growth of central axons was less enhanced by peripheral axonal interruption if the length of the proximal stump was increased or if a distal stump was present to permit rapid regeneration. However, the regenerative response following nerve transection was altered little by crushing the proximal stump or injecting it with colchicine or nerve growth factor. It is suggested that sensory neurons are stimulated to regenerate by peripheral axonal injuries that reduce some normal retrograde regulatory influence of Schwann cells.

A chick neural retina adhesion and survival molecule is a retinol-binding protein

A 20,000-D protein called purpurin has recently been isolated from the growth-conditioned medium of cultured embryonic chick neural retina cells (Schubert, D., and M. LaCorbiere, 1985, J. Cell Biol., 101:1071-1077). Purpurin is a constituent of adherons and promotes cell-adheron adhesion by interacting with a cell surface heparan sulfate proteoglycan. It also prolongs the survival of cultured neural retina cells. This paper shows that purpurin is a secretory protein that has sequence homology with a human protein synthesized in the liver that transports retinol in the blood, the serum retinol-binding protein (RBP). Purpurin binds [3H]retinol, and both purpurin and chick serum RBP stimulate the adhesion of neural retina cells, although the serum protein is less active than purpurin. Purpurin and the serum RBP are, however, different molecules, for the serum protein is approximately 3,000 D larger than purpurin and has different silver-staining characteristics. Finally, purpurin supports the survival of dissociated ciliary ganglion cells, indicating that RBPs can act as ciliary neurotrophic factors.