Changes in protein content of goldfish optic nerve during degeneration and regeneration following nerve crush

Proteomics and systems biology in optic nerve regeneration

We present an overview of current state of proteomic approaches as applied to optic nerve regeneration in the historical context of nerve regeneration particularly central nervous system neuronal regeneration. We present outlook pertaining to the optic nerve regeneration proteomics that the latter can extrapolate information from multi-systems level investigations. We present an account of the current need of systems level standardization for comparison of proteome from various models and across different pharmacological or biophysical treatments that promote adult neuron regeneration. We briefly overview the need for deriving knowledge from proteomics and integrating with other omics to obtain greater biological insight into process of adult neuron regeneration in the optic nerve and its potential applicability to other central nervous system neuron regeneration.

Neurofilament light chain as a potential biomarker of disease status in Friedreich ataxia

BACKGROUND

The present study evaluates serum neurofilament light chain (NfL) as a biomarker of disease features in Friedreich's ataxia (FRDA).

METHODS

NfL levels from serum of 117 subjects (85 FRDA patients, 13 carriers, and 19 controls) were assayed and correlated with disease features such as smaller GAA repeat length (GAA1), age, sex, and level of neurological dysfunction.

RESULTS

Mean serum NfL levels were higher in FRDA patients than in carriers or unaffected controls in two independent cohorts of subjects. In longitudinal samples from FRDA patients drawn monthly or 1 year apart, values changed minimally. No difference was noted between carriers and controls. NfL levels correlated positively with age in controls and carriers of similar age, (Rs = 0.72, p < 0.0005), whereas NfL levels inversely correlated with age in FRDA patients (Rs =  - 0.63, p < 0.001). NfL levels were not associated with sex or GAA1 length in patients, and linear regression revealed a significant relationship between NfL levels in the cohort with age (coefficient =  - 0.36, p < 0.001), but not sex (p = 0.64) or GAA1 (p = 0.13).

CONCLUSION

Because NfL is elevated in patients, but decreases with age and disease progression, our results suggest that age is the critical determinant of NfL in FRDA (rather than clinical or genetic severity).

The Role of Axon Transport in Neuroprotection and Regeneration

Retinal ganglion cells and other central nervous system neurons fail to regenerate after injury. Understanding the obstacles to survival and regeneration, and overcoming them, is key to preserving and restoring function. While comparisons in the cellular changes seen in these non-regenerative cells with those that do have intrinsic regenerative ability has yielded many candidate genes for regenerative therapies, complete visual recovery has not yet been achieved. Insights gained from neurodegenerative diseases, like glaucoma, underscore the importance of axonal transport of organelles, mRNA, and effector proteins in injury and disease. Targeting molecular motor networks, and their cargoes, may be necessary for realizing complete axonal regeneration and vision restoration.

Structural and functional evolution of 2',3'-cyclic nucleotide 3'-phosphodiesterase

2',3'-cyclic nucleotide 3'-phosphodiesterase (CNPase) is an abundant membrane-associated enzyme within the vertebrate myelin sheath. While the physiological function of CNPase still remains to be characterized in detail, it is known - in addition to its in vitro enzymatic activity - to interact with other proteins, small molecules, and membrane surfaces. From an evolutionary point of view, it can be deduced that CNPase is not restricted to myelin-forming cells or vertebrate tissues. Its evolution has involved gene fusion, addition of other small segments with distinct functions, such as membrane attachment, and possibly loss of function at the polynucleotide kinase-like domain. Currently, it is unclear whether the enzymatic function of the conserved phosphodiesterase domain in vertebrate myelin has a physiological role, or if CNPase could actually function - like many other classical myelin proteins - in a more structural role. This article is part of a Special Issue entitled SI: Myelin Evolution.

Time course Analysis of Gene expression patterns in ZebrafIsh Eye during Optic Nerve Regeneration

It is well-established that neurons in the adult mammalian central nervous system (CNS) are terminally differentiated and, if injured, will be unable to regenerate their connections. In contrast to mammals, zebrafish and other teleosts display a robust neuroregenerative response. Following optic nerve crush (ONX), retinal ganglion cells (RGC) regrow their axons to synapse with topographically correct targets in the optic tectum, such that vision is restored in ~21 days. What accounts for these differences between teleostean and mammalian responses to neural injury is not fully understood. A time course analysis of global gene expression patterns in the zebrafish eye after ONX can help to elucidate cellular and molecular mechanisms that contribute to a successful neuroregeneration. To define different phases of regeneration after ONX, alpha tubulin 1 ( tuba1) and growth-associated protein 43 ( gap43), markers previously shown to correspond to morphophological events, were measured by real time quantitative PCR (qPCR). Microarray analysis was then performed at defined intervals (6 hours, 1, 4, 12, and 21 days) post-ONX and compared to SHAM. Results show that optic nerve damage induces multiple, phase-related transcriptional programs, with the maximum number of genes changed and highest fold-change occurring at 4 days. Several functional groups affected by optic nerve regeneration, including cell adhesion, apoptosis, cell cycle, energy metabolism, ion channel activity, and calcium signaling, were identified. Utilizing the whole eye allowed us to identify signaling contributions from the vitreous, immune and glial cells as well as the neural cells of the retina. Comparisons between our dataset and transcriptional profiles from other models of regeneration in zebrafish retina, heart and fin revealed a subset of commonly regulated transcripts, indicating shared mechanisms in different regenerating tissues. Knowledge of gene expression patterns in all components of the eye in a model of successful regeneration provides an entry point for functional analyses, and will help in devising hypotheses for testing normal and toxic regulatory factors.

gRICH68 and gRICH70 are 2',3'-cyclic-nucleotide 3'-phosphodiesterases induced during goldfish optic nerve regeneration

Biochemical characterization of changes in gene expression that accompany optic nerve regeneration has led to the identification of proteins that may play key roles in the regeneration process. In this report, a cDNA encoding gRICH70, a novel isoform of the regeneration-induced gRICH68 protein, has been identified and characterized in goldfish. Both gRICH68 and gRICH70 show significant homology (34-36%) to mammalian 2',3'-cyclic-nucleotide 3'-phosphodiesterases (CNPases), hence the name goldfish regeneration-induced CNPase homolog (gRICH). The predicted 431-amino acid gRICH70 protein is 88% homologous to gRICH68, and the retinal mRNA for gRICH70 is coordinately induced with gRICH68 mRNA during optic nerve regeneration. Enzymatic analysis of recombinant proteins confirms that both gRICH proteins possess CNPase activity. Despite the relatively limited sequence homology, the kinetic constants obtained suggest that both gRICH proteins are at least as efficient as recombinant mouse CNP1 in catalyzing the hydrolysis of 2',3'-cAMP. Immunoprecipitation studies indicate that gRICH proteins are responsible for the majority of the CNPase activity detected in regenerating goldfish retinas. The evidence presented demonstrates that gRICH68 and gRICH70 correspond to a previously described doublet of acidic proteins that are selectively induced in the goldfish retina during optic nerve regeneration. Thus, CNPase enzyme activity is implicated for the first time in the process of nerve regeneration.

Reggie-1 and reggie-2, two cell surface proteins expressed by retinal ganglion cells during axon regeneration

Fish--in contrast to mammals--regenerate retinal ganglion cell axons when the optic nerve is severed. Optic nerve injury leads to reexpression of proteins, which typically are first expressed in newly differentiated retinal ganglion cells and axons. Here we identified two new proteins of fish retinal ganglion cells, reggie-1 and reggie-2, with monoclonal antibody M802 and molecular cloning techniques. In normal fish, M802 stained the few retinal axons derived from newborn ganglion cells which in fish are added lifelong to the retinal margin. After optic nerve injury, however, M802 labeled all retinal ganglion cells and retinal axons throughout their path into tectum. Consistent with M802 staining, reggie-1 and reggie-2 mRNAs were present in lesioned retinal ganglion cells, as demonstrated by in situ hybridization, but were not detectable in their normal mature counterparts. In western blots with membrane proteins of the adult goldfish brain, M802 recognizes a 48x10(3) Mr protein band. At the amino acid level, 48x10(3) Mr reggie-1 and reggie-2 are 44% identical, lack transmembrane and membrane anchor domains, but appear membrane associated by ionic interactions. Reggie-1 and reggie-2 are homologous to 35x10(3) Mr ESA (human epidermal surface antigen) but are here identified as neuronal surface proteins, present on newly differentiated ganglion cells at the retinal margin and which are reexpressed in mature ganglion cells upon injury and during axonal regeneration.

Alterations in geniculate ganglion proteins following fungiform receptor damage

Previous anatomical studies in rat have shown that damage produced to fungiform receptors of the anterior tongue at postnatal age 2 (P2) alters the growth and ramification of primary gustatory axons in the rostral nucleus of the solitary tract (NST). Studies employing artificial rearing (AR) procedures, which functionally deprive rat pups of orochemical stimulation during critical periods of postnatal life, produce similar alterations in the development of primary gustatory axons in the NST. Therefore, orochemical stimulation during rat's early postnatal life is necessary for normal development of primary gustatory axons in the rostral NST. One hypothesis concerning receptor-damage effects and AR effects is that receptor damage during critical periods of development may alter the regulation (i.e. transcription/translation) and/or distribution (i.e. transport) of proteins in geniculate ganglion neurons, thereby affecting growth of primary gustatory axons in the rostral NST. Specific aims of the present experiments were to comprehensively examine electrophoretic profiles of geniculate ganglion proteins following P2 receptor damage and late (> P40) receptor damage. Results show that concentrations of particular geniculate ganglion proteins are differentially altered following P2 receptor damage and late receptor damage, and that early receptor damage and late receptor damage produces distinct effects on the electrophoretic profiles of particular classes of proteins. Between the ages of P7-P38, P2 receptor damage lowers ganglion concentration of an acidic membrane glycoprotein designated as A1, with an apparent M(r) of 64-67 kDa and a pI of 4.8-5.2 P2 receptor damage also lowers ganglion concentrations of GAP-43. P2 receptor damage produces transient decreases in ganglion concentrations of NF-160, NF-200, and 8 additional acidic proteins. Three of these proteins may correspond to peripheral nerve sheath proteins analyzed in previous studies of the sciatic nerve, and one of these proteins may correspond to a 24 kDa growth-associated protein characterized in regenerating optic nerve. The time-course for changes observed in ganglion proteins following P2 damage was consistent with that observed for normal anatomical development of primary gustatory axons in both the lingual epithelium and NST. Receptor damage produced at P40 and later yielded different patterns of changes in geniculate ganglion proteins. Late receptor damage produced a transient increase in ganglion concentrations of NF-160, NF-200, GAP-43 and four additional acidic proteins within the 29-57 kDa M(r) range. Late receptor damage also produced a transient decrease in the concentrations of protein A1 and a 30 kDa protein that was not affected by P2 damage. Therefore, proteins that were preferentially affected by P2 damage may be involved in the regulation of initial axonal growth within the lingual epithelium and NST, as opposed to the structural repair or maintenance of extant axons. Relationships between normal anatomical development in peripheral and central components of primary gustatory axons are discussed in relation to availability of particular cytoskeletal and growth-associated proteins.

Isolation of cDNA clones encoding RICH: a protein induced during goldfish optic nerve regeneration with homology to mammalian 2',3'-cyclic-nucleotide 3'-phosphodiesterases

Using data derived from peptide sequencing of p68/70, a protein doublet induced during optic nerve regeneration in goldfish, we have isolated cDNAs that encode RICH (regeneration-induced CNPase homolog) from a goldfish regenerating retina cDNA library. The predicted RICH protein comprises 411 amino acids, possesses a pI of 4.48, and shows significant homology to the mammalian myelin marker enzyme 2',3'-cyclic-nucleotide 3'-phosphodiesterase (CNPase; EC 3.1.4.37). The mRNA encoding RICH was demonstrated, by both Northern blot analysis and RNase protection assays, to be induced as much as 8-fold in regenerating goldfish retinas at 20 days after nerve crush. Analysis of total RNA samples from various tissues showed a broad distribution of RICH mRNA, with the highest levels observed in gravid ovary. The data obtained strongly suggest that RICH is identical or very similar to p68/70. The molecular cloning of RICH provides the means for a more detailed analysis of its function in nerve regeneration. Additionally, the homology of RICH and CNPase suggests that further investigation may provide additional insight into the role of these proteins in the nervous system.

Purification and characterization of p68/70, regeneration-associated proteins from goldfish brain

Two acidic proteins (p68/70) previously shown to be associated with regeneration of the goldfish optic nerve were purified 887-fold from brain homogenates of Carassius auratus. Purification to homogeneity was achieved by sequential chromatography of a 100,000 g brain supernatant fraction on DEAE-Sephacel, Cu(2+)-charged iminodiacetic acid agarose, and gel filtration. The Stokes radius of the doublet was determined to be 5.8 nm, and the sedimentation coefficient calculated to be 5.2. From these values a molecular mass of 128 kDa and a frictional coefficient ratio of 1.6 were calculated. Chromatofocusing on a high-resolution DEAE column resolved the protein doublet into three dimeric species of p68, p68/70, and p70. These results indicate that the proteins are highly elongated and associate as homodimers or as a heterodimer. Subcellular localization and membrane extraction experiments indicated p68/70 to be a component of the plasma membrane associated primarily through hydrophobic interactions. p68/70 demonstrated biphasic behavior in phase partition experiments using Triton X-114. Analysis of hydrolytic products indicated p68/70 to be a glycoprotein, containing 11% carbohydrate.

Immunochemical studies of extracellular glycoproteins (X-GPs) of goldfish brain

Exoglycoproteins (X-GPs) are a family of soluble glycoproteins which are the most prominent constituent of the extracellular compartment of goldfish brain. On conventional two-dimensional polyacrylamide gels they typically display two primary molecular weight forms, averaging about 33 and 38 kDa, each appearing as a row of five to seven individual spots. When X-GP antibodies were applied by Western blotting, gels of goldfish brain extract prepared without a reducing agent showed, in addition to the primary molecular weight groups, at least one row of spots of slightly lower molecular weight and a major array of spots in the range of 45-60 kDa. The latter presumably represent dimers of the primary X-GP forms since they gave rise to the primary forms upon treatment with a reducing agent. However, on gradient gels prepared without detergents or reducing agents, X-GPs identified by immunostaining appeared only at 200 kDa and above, indicating that these proteins naturally occur in the form of large particles. Deglycosylation of the brain extract by N-glycosidase F reduced the molecular weight of each primary X-GP form by about 5 kDa, but did not abolish the microheterogeneity, which is at least partly due to minor differences in primary structure among the proteins in individual spots. Both rows of spots in the deglycosylated sample showed a coordinated shift toward the basic side of the gel, and a prominent new spot appeared on the basic end of the lower molecular weight group, which probably represents the fully deglycosylated form of the most abundant X-GP isoform.(ABSTRACT TRUNCATED AT 250 WORDS)

Extracellular proteins of goldfish optic tectum labeled by intraocular injection of 3H-proline

A prominent group of soluble glycoproteins with a molecular weight of 30K-40K and pI 5.0-5.6 was detected in various parts of the goldfish brain as well as in the optic nerves. Since these proteins are readily liberated from the tissue, we have designated them exoglycoproteins (X-GPs). The X-GPs in the optic tectum were found to be labeled after intraocular injection of radioactive tracers, in a manner consistent with the labeling of proteins transported in the optic axons. However, the labeling of X-GPs was blocked by intracranial injection of a protein synthesis inhibitor, whereas the labeling of axonally transported proteins was unaffected. This shows that the X-GPs can be synthesized locally within the brain. Nevertheless, when protein synthesis in the retina was blocked, the labeling of the X-GPs in the tectum was prevented, like the labeling of axonally transported proteins. Thus precursors for the synthesis of X-GPs can be derived from materials transported in the optic axons. This synthesis can occur in nonneuronal cells, as indicated by the incorporation of labeled amino acid into X-GPs in optic nerves directly exposed to the label. The synthesis of X-GPs was increased in regenerating nerves, suggesting that these proteins may play a role in regeneration. Partial amino acid sequencing of the proteins showed that they are identical to the proteins previously identified as "ependymins," which have been implicated in neuronal plasticity. There are minor differences in amino acid sequence among some individual spots.

Trying to understand axonal regeneration in the CNS of fish

In contrast to the situation in mammals and birds, neurons in the central nervous system (CNS) of fish--such as the retinal ganglion cells--are capable of regenerating their axons and restoring vision. Special properties of the glial cells and the neurons of the fish visual pathway appear to contribute to the success of axonal regeneration. The fish oligodendrocytes lack the axon growth inhibiting molecules that interfere with axonal extension in mammals. Instead, fish optic nerve oligodendrocytes support--at least in vitro--axonal elongation of fish as well as that of rat retinal axons. Moreover, the fish retinal ganglion cells re-express upon injury a set of growth-associated cell surface molecules and equip the regenerating axons throughout their path and up into their target, the tectum opticum with these molecules. This may indicate that the injured fish ganglion cells reactivate the cellular machinery necessary for axonal regrowth and pathfinding. Furthermore, the target itself provides positional marker molecules even in adult fish. These marker molecules are required to guide the regenerating axons back to their retinotopic home territory within the tectum.

Protein phosphorylation: localization in regenerating optic axons

A number of axonal proteins display changes in phosphorylation during goldfish optic nerve regeneration (Larrivee and Grafstein, 1989). (1) To determine whether the phosphorylation of these proteins was closely linked to their synthesis in the retinal ganglion cell body, cycloheximide was injected intraocularly into goldfish whose optic nerves had been regenerating for 3 weeks. Cycloheximide reduced the incorporation of [3H]proline and 32P orthophosphate into total nerve protein by 84% and 46%, respectively. Of the 20 individual proteins examined, 17 contained less than 15% of the [3H]proline label measured in corresponding controls, whereas 18 proteins contained 50% or more of the 32P label, suggesting that phosphorylation was largely independent of synthesis. (2) To determine whether the proteins were phosphorylated in the ganglion cell axons, axonal transport of proteins was blocked by intraocular injection of vincristine. Vincristine reduced [3H]proline labeling of total protein by 88% and 32P labeling by 49%. Among the individual proteins [3H]proline labeling was reduced by 90% or more in 18 cases but 32P labeling was reduced only by 50% or less. (3) When 32P was injected into the cranial cavity near the ends of the optic axons, all of the phosphoproteins were labeled more intensely in the optic tract than in the optic nerve. These results suggest that most of the major phosphoproteins that undergo changes in phosphorylation in the course of regeneration are phosphorylated in the optic axons.

A polyclonal antibody to goldfish neuronal 145 kDa intermediate filament protein

A polyclonal antibody raised to a protein from goldfish optic tectum recognises, immunohistochemically, axons throughout normal goldfish visual pathway. In goldfish with injured optic nerve, this antibody recognises degenerating neuronal debris as well as regenerating fibres. On immunoblot, the antibody recognises, primarily, a neuronal intermediate filament protein in the region of 145 kDa. Such an antibody should prove useful in studies pertaining to goldfish visual pathway.

Expression of glial fibrillary acidic protein (GFAP) in goldfish optic nerve following injury

By using an antibody to goldfish glial fibrillary acidic protein (GFAP), the reaction of goldfish optic nerve to injury has been studied by immunoblotting and immunohistochemical methods. Goldfish optic nerve, which normally lacks GFAP immunoreactivity (Nona et al.: Glia, 2:189-200, 1989), expresses GFAP following injury. This immunoreactivity, which is observed as early as 10 days after crush and which is still evident at 30 days after crush, all but disappears by 150 days after crush. Since it is well established that functional restoration of synaptic connections and the recovery of vision takes place in goldfish following optic nerve injury, our results indicate that reactive astrocytes do not represent an impediment to regeneration in goldfish visual system.

Transfection of PC12 cells with the human GAP-43 gene: effects on neurite outgrowth and regeneration

The neuronal growth associated protein GAP-43 is expressed at high levels during axonal growth and regeneration. In this report, we describe the transfection of the nerve growth factor (NGF)-responsive pheochromocytoma cell line PC12 with the human GAP-43 cDNA under the control of the Moloney murine leukemia virus long terminal repeat (MoMuLV LTR). Two PC12 subclones were isolated that constitutively expressed GAP-43 from the transfected cDNA and showed increased responsiveness to NGF. Of the two transfected PC12 subclones, the subclone expressing the most human GAP-43 RNA showed an accelerated initial neurite outgrowth response and a 10-fold increased sensitivity to NGF. Neurite regeneration was significantly enhanced in both transfected subclones and, in contrast to untreated PC12 cells, could occur transiently in the absence of added NGF. These results suggest that GAP-43 may potentiate the action of NGF on neurite initiation and regeneration.

Organization of astrocytes in the visual pathways of the goldfish: an immunohistochemical study

We have used antisera directed against glial cytoskeletal proteins to examine the distribution and organization of astrocytes in the visual pathways of the goldfish. We describe two different types of cells, which may be distinguished by their unique cytoskeletal proteins. Antibodies raised against a 48 Kd optic nerve protein react with stellate astrocytes in the optic nerve but virtually no glial cells in the brain (although blood vessels and the meninges in the brain were stained). The optic nerve astrocytes form a dense meshwork of processes through which the optic fibers pass. The intraorbital and intracranial segments of the nerve are divided into fascicles, each bounded by a glia limitans, which extend across the optic chiasm. Astroglial cells in the brain bind antibodies raised against a 50 Kd brain cytoskeletal protein. These antibodies show a very limited cross-reactivity with optic nerve cells. Brain astrocytes have filiform profiles and most appear to be deployed as radial glia. The glial fabric of the brain, as revealed by these antibodies, is far more loosely woven than that of the optic nerve. There is a sharp boundary between the two types of glial cells, immediately behind the optic chiasm. Glial processes in the optic tracts arise from cells in the preoptic area, whereas those in the optic tectum arise from cells that reside locally. In the optic tract, a glia limitans was often difficult to discern, whereas in the tectum one was always evident and composed of endfeet at the pial extremities of radial glial processes. These findings are discussed both in the context of previous observations by other workers as well as with regard to their possible functional implications.

Phosphorylation of superior cervical ganglion proteins during regeneration

The incorporation of radioactive phosphate into proteins of both normal and regenerating ganglia of the sympathetic nervous system of the rat is reported. The incorporation reactions were carried out in vitro by incubating homogenates of excised ganglia with [gamma-32P]ATP under various conditions. It was found that incorporation of phosphate into proteins of regenerating ganglia in the molecular mass range 10,000-100,000 daltons increased up to 40% over incorporation into proteins from control ganglia during the first 3 days following injury and returned to control levels after 14 days. Analysis of the proteins by two-dimensional electrophoresis revealed that only few, i.e., less than 20, became radioactively labelled in homogenates of superior cervical ganglia in the presence of Ca2+, and even fewer in the presence of cyclic AMP. Furthermore, all these proteins fell within a narrow pI range of 4-6. The growth-associated protein, variously designated GAP-43, B-50, F-1, and pp46, has an enhanced level of expression and phosphorylation in regenerating ganglia compared with controls at day 3. Injury also caused consistently higher levels of incorporation into two other proteins with molecular masses at positions 55,000 and 85,000 and pI values of 5.1 and 4.5, respectively; the former protein most probably is beta-tubulin. The fact that both proteins are found in the 15,000 g pellet after the tissue has been solubilized in 0.5% nonionic detergent indicates that they may indeed by components of filament assemblies. Thus, the results suggest that protein phosphorylation is a mechanism involved in cytoskeletal function in regenerating nerve.

Characterization of a goldfish antigen during development and regeneration of the visual system

Normal, regenerating, and developing optic nerves of the goldfish were studied utilizing a monoclonal antibody (mAb) 1E1T which has specificity for Müller cells in the retina, radial glial cells in the tectum, and non-neuronal cells in the optic nerve. Sections of the normal optic nerve revealed longitudinally oriented chains of non-neuronal cells, that were 4-8 cells long. The number of chains in the normal nerve was very few. In addition, short acellular septa, probably the connective tissue septa, were also labeled with mAb 1E1T. Sections of crushed optic nerves showed an increase in the antigen recognized by mAb 1E1T within the septa and new septa were now visualized. Furthermore, the existing septa were longer and extended the length of the optic nerve. The formation and elongation of the septa occurred as early as 3 day postcrush. Between 3 and 11 d postcrush, there was heavy labeling of the septa and a large accumulation of non-neuronal cells at the crush site. At 3 months postcrush, the accumulation of non-neuronal cells labeled by mAb 1E1T were no longer visible but heavy labeling of the septa was still apparent.

Cycloheximide-sensitive [35S]methionine labeling of proteins in goldfish retinal ganglion cell axons in vitro

Polypeptides of retinal ganglion cell axons of the goldfish, regenerating in culture, were labeled by [35S]methionine after decentralization from the explant. Microscopic samples, composed of isolated axonal fields, were analyzed by SDS ultramicroelectrophoresis and autoradiography. Of the several proteins exhibiting cycloheximide-sensitive labeling, beta-tubulin and actin were consistently and prominently labeled, although the possibility of a labeled alpha-isoform with a lower mol. wt. could not be ruled out.

Human GAP-43: its deduced amino acid sequence and chromosomal localization in mouse and human

The growth-associated protein (GAP-43) is considered a crucial component of an effective regenerative response in the nervous system. Its phosphorylation by protein kinase C correlates with long-term potentiation. Sequence analysis of human cDNAs coding for this protein shows that the human GAP-43 gene is highly homologous to the rat gene; this homology extends into the 3'-untranslated region. However, the human protein contains a 10 amino acid insert. Somatic cell hybrids demonstrate localization of the GAP-43 gene to human chromosome 3 and to mouse chromosome 16.

Distribution of specific intermediate-filament proteins in the goldfish retina

The intermediate-filament proteins expressed in the goldfish retina were investigated by immunohistochemistry and by immunoblotting. Polyclonal antibodies that previously had been raised against the goldfish optic nerve neurofilament (ON1 and ON2) and glial filament (ON3 and ON4) proteins were used in this study. Anti-ON1/ON2 antiserum reacted on a retinal immunoblot with two proteins having molecular weights and isoelectric points corresponding to those of ON1 and ON2. Histologically, the most pronounced anti-ON1/ON2 reactivity was observed in the ganglion cell layer of the goldfish retina. The anti-ON3/ON4 antiserum reacted with a single protein on a retinal immunoblot. This protein had a molecular weight and isoelectric point which corresponded to the goldfish optic nerve glial filament proteins. This anti-serum labeled horizontal cells in retina sections. Three previously unidentified goldfish visual-pathway intermediate-filament proteins sharing a molecular weight of 60K were observed on two-dimensional gels of retinal cytoskeletal proteins and on retinal immunoblots which were probed with a monoclonal antibody which recognizes an epitope common to all intermediate filament proteins. The possible existence of homologs of mammalian GFAP and vimentin in the goldfish retina was also explored. Antibodies directed against mammalian GFAP and vimentin labeled the Müller fibers and the cone horizontal cells, respectively. However, immunoblot analysis and a comparison of the two-dimensional gel electrophoresis patterns of goldfish retinal and rat spinal cord cytoskeletal proteins demonstrated a lack of goldfish proteins identical to the mammalian intermediate-filament proteins.

Phosphorylation of proteins in normal and regenerating goldfish optic nerve

Within 6 h after radiolabeled phosphate was injected into the eye of goldfish, labeled acid-soluble and acid-precipitable material began to appear in the optic nerve and subsequently also in the lobe of the optic tectum, to which the optic axons project. From the rate of appearance of the acid-precipitable material, a maximal velocity of axonal transport of 13-21 mm/day could be calculated, consistent with fast axonal transport group II. Examination of individual proteins by two-dimensional gel electrophoresis revealed that approximately 20 proteins were phosphorylated in normal and regenerating nerves. These ranged in molecular weight from approximately 18,000 to 180,000 and in pI from 4.4 to 6.9. Among them were several fast transported proteins, including protein 4, which is the equivalent of the growth-associated protein GAP-43. In addition, there was phosphorylation of some recognizable constituents of slow axonal transport, including alpha-tubulin, a neurofilament constituent (NF), and another intermediate filament protein characteristic of goldfish optic axons (ON2). At least some axonal proteins, therefore, may become phosphorylated as a result of the axonal transport of a phosphate carrier. Some of the proteins labeled by intraocular injection of 32P showed changes in phosphorylation during regeneration of the optic axons. By 3-4 weeks after an optic tract lesion, five proteins, including protein 4, showed a significant increase in labeling in the intact segment of nerve between the eye and the lesion, whereas at least four others (including ON2) showed a significant decrease. When local incorporation of radiolabeled phosphate into the nerve was examined by incubating nerve segments in 32P-containing medium, there was little or no labeling of the proteins that showed changes in phosphorylation during regeneration. Segments of either normal or regenerating nerves showed strong labeling of several other proteins, particularly a group ranging in molecular weight from 46,000 to 58,000 and in pI from 4.9 to 6.4. These proteins were presumably primarily of nonneuronal origin. Nevertheless, if degeneration of the axons had been caused by removal of the eye 1 week earlier, most of the labeling of these proteins was abolished. This suggests that phosphorylation of these proteins depends on the integrity of the optic axons.

Effects of a conditioning lesion on bullfrog sciatic nerve regeneration: analysis of fast axonally transported proteins

We have shown that bullfrog sciatic nerves respond to a conditioning lesion similarly to goldfish optic nerve and rat or mouse sciatic nerve; that is, following a crush the rate of regeneration is faster in nerves that have received a conditioning lesion compared to nerves that have not. Also, damaged nerve fibres show initial growth or sprouting earlier in a previously conditioned nerve compared to nerves that have not received a prior conditioning lesion. We have not detected changes in the transport of fast axonally transported proteins with the conditioning lesion paradigm, other than those changes seen in regenerating nerves after receiving a single lesion. However, more label was present in a few fast axonally transported proteins at the lesion site in conditioned nerves compared to non-conditioned nerves, and this difference is not apparently due to increased transport. It seems that changes in fast axonally transported proteins probably do not contribute directly to the mechanism underlying the conditioning lesion effect of higher out growth rates, although some of the fast transported proteins may be involved in functions, possibly at the growing tip of damaged fibres, which promote or result from the conditioning effect.

Examination of a nerve injury-induced, 37 kDa protein: purification and characterization

Following traumatic injury to the adult rat sciatic nerve the synthesis and accumulation of soluble, extra-cellular, 37 kDa protein is increased. This protein, which accumulates in the extracellular space of the injured nerve, accounts for nearly 5% of the total soluble pool of protein in an injured nerve 3 weeks after injury. 8 weeks after injury, when regeneration is nearly complete, this accumulated pool returns to control levels, yet if regeneration is blocked synthesis of the 37 kDa protein remains high. Recently this 37 kDa protein has been shown to be nearly identical to apolipoprotein E, the protein component of various lipoprotein particles. This finding suggests a role for the 37 kDa protein in cholesterol and lipid transport and metabolism during nerve repair within the nervous system, functions that have been ascribed to apo E in serum. Results are presented here describing the purification of the nerve injury induced 37 kDa protein and the subsequent production of specific rabbit antisera directed against it. By centrifugation analysis in a sucrose gradient, a native mass of 37 kDa was determined, revealing the 37 kDa protein's monomeric, native structure. Additionally injections of [35S]methionine directly into the injured nerve allowed 1) a comparison of 37 kDa synthesis in vivo versus in vitro and 2) an examination of the presence or absence of retrogradely transported 37 kDa protein. The in vitro and in vivo collected material were found to share identical 2-dimensional electrophoretic mobilities, and no appreciable amount of transported 37 kDa protein was found in proximal regions of the injured nerve.

Activity-dependent sharpening of the regenerating retinotectal projection in goldfish: relationship to the expression of growth-associated proteins

During regeneration of the optic nerve in goldfish, manipulations that disrupt the transmission of patterned visual information, if applied within the so-called 'sensitive period', lead to the formation of a diffuse retinotopic map (Schmidt, Cell. Mol. Neurobiol., 5 (1985) 65). The present study examined: (a) whether the sensitive period (14-50 days postcrush) coincides with the period in which specific 'growth-associated proteins' are present in the regenerating optic nerve terminals; and (b) whether manipulations that alter physiological activity during the sensitive period influence the expression of these proteins. Following bilateral optic nerve crush, goldfish regenerated their optic nerves either under normal illumination conditions (control), in total darkness, or with physiological activity suppressed in the nerve by intraocular injections of tetrodotoxin (TTX). At various times postcrush, proteins conveyed from the retina to the developing nerve endings were visualized by labeling the eye with [35S]methionine and then analyzing, by 2-dimensional gel electrophoresis and fluorography, radiolabeled proteins present in the optic tectum 15 h later. Rapidly-transported proteins that underwent large, specific increases during regeneration included the previously described 48 kDa growth-associated protein (GAP-48); labeling of GAP-48 was maximal during axonal outgrowth and then declined, but still remained well above background levels throughout the 'sensitive period'. Another group of rapidly-transported proteins, mol. wt. = 110-140 kDa (HMW), followed a similar time course, while levels of a 28 kDa protein peaked at 2 weeks and then declined rapidly. Thus, activity-dependent 'sharpening' processes occur during a period in which the levels of GAP-48 and HMW remain elevated in the nerve terminals.(ABSTRACT TRUNCATED AT 250 WORDS)

Incorporation of [32P]phosphate into nucleotides of the dorsal root ganglia of regenerating rat sciatic nerve

[32P]Phosphate incorporation into nucleotides of the dorsal root ganglia (DRG) was studied after a crush lesion of the rat sciatic nerve. DRG were labelled during a 2-h, in vitro incubation in a balanced salt solution containing [32P]orthophosphate, 1, 2, 4 and 8 days after the crush lesion. Nucleotides were analyzed by HPLC on an ion-exchange column. An increased incorporation of 32P was found in DRG of the injured nerve for all the studied time periods. This increase was unevenly distributed among the nucleotides. UTP, CTP and ADP showed the largest and most persistent increases in labelling. The specific activity of 4 analyzed nucleotides (ATP, ADP, UTP and CDP) remained constant in DRG from crushed nerves. Thus, the observed increase in 32P-labelling could not solely be due to an increased uptake of label but must also reflect an enhanced metabolism of nucleotides in regenerating DRG. The finding that alterations of nucleotide metabolism could be observed within one day after the crush lesion suggests that this response can be used as a valuable tool for studies of the initial events of regeneration.

Molecular properties of the growth-associated protein GAP-43 (B-50)

The protein that has been identified in different contexts as growth-associated protein (GAP)-43, GAP-48, protein 4, B-50, F-1 gamma 5, and pp46, has been implicated in neural development, axonal regeneration, and the modulation of synaptic function. The present study investigated various properties of this protein (designated here as GAP/B-50), including its correct molecular weight and possible polymeric structure. GAP/B-50 was purified to greater than 90% homogeneity using an alkaline extraction procedure followed by a two-stage separation on a size-exclusion HPLC column. The equivalence of the purified protein to the B-50 phosphoprotein was confirmed by peptide digests, comigration, immunostaining, and amino acid composition. On a series of sodium dodecyl sulfate-polyacrylamide gels the apparent molecular weight of the protein was seen to vary inversely with the concentration of acrylamide in the gels. Using these data in the method of Ferguson, the molecular weight of GAP/B-50 was calculated to be 32.8 kilodaltons (kD), considerably lower than the previously reported values of 43-67 kD. The low molecular weight of the protein in the presence of detergent was confirmed by density centrifugation. In the absence of detergent, however, the protein was found to be part of a polymeric structure whose retention time by size-exclusion chromatography indicated a size of 124 kD; this property was also confirmed by density centrifugation under nondetergent conditions. These data suggest the possibility that the native form of GAP/B-50 in the presynaptic membrane may be a tetramer of four identical subunits.

Expression of a 48-kilodalton growth-associated protein in the goldfish retina

One of the most striking molecular correlates of optic nerve regeneration in the goldfish is the increased labeling of a 48 kilodalton (kD) acidic protein that is conveyed to the developing nerve endings from the retina by rapid axonal transport. The present study examined the biosynthesis and molecular characteristics of this protein. Retinas derived either from intact controls or from goldfish undergoing optic nerve regeneration (10-14 days postcrush) were pulse-labeled with [3H]proline or [35S]methionine, followed by subcellular fractionation and analysis of protein synthesis patterns by two-dimensional gel electrophoresis and fluorography. Synthesis of the 48-kD acidic protein (termed here GAP-48) was detected only in retinas that were undergoing axonal regeneration. Pulse-chase labeling experiments demonstrated that the protein undergoes a post-translational modification that requires 15-20 min. This processing could be selectively blocked by tunicamycin, an inhibitor of protein N-glycosylation. The protein was also found to incorporate low levels of phosphate in vitro. Thus, the differential appearance of GAP-48 in regenerating axons might be regulated either at the level of gene expression or by selective posttranslational processing in retinal ganglion cells. By the criteria of molecular weight, isoelectric point, anomalous migration properties on sodium dodecyl sulfate-polyacrylamide gels, phosphorylation, subcellular distribution, and the pattern of digestion products generated by Staphylococcus aureus V8 protease, GAP-48 appears to be equivalent to the B-50 (F-1) phosphoprotein of the mammalian brain.

Fast axonally transported proteins in regenerating goldfish optic nerve: effect of abolishing electrophysiological activity with TTX

Blocking neural activity with intraocular tetrodotoxin (TTX) hinders regeneration of goldfish optic axons, and prevents the refinement of the retinotopic map that is formed in the optic tectum. The latter effect is not observed with TTX treatment confined to the first two weeks of regeneration, but is produced when the TTX treatment is delayed until after this time. In the present study, 2-dimensional gel electrophoresis was used to analyse the effects of two different schedules of TTX treatment (0-9 days or 14-32 days) on incorporation of [3H]proline into individual proteins conveyed by fast axonal transport in the optic nerve. The labelling of many of these proteins was somewhat reduced by either schedule of TTX treatment, but a number of proteins showed a larger reduction as a result of the delayed treatment. These included some glycoproteins, as well as a protein of about 45 kDa and pI 4.5, which shows greatly increased synthesis during regeneration, and which is probably identical to the 'growth-associated protein' GAP-43. By contrast, cytoskeletal proteins (alpha- and beta-tubulin and actin) were unaffected by the delayed TTX treatment. It is possible that the differential effects of the early and delayed TTX treatments on various transported proteins may account for differences in the effect of these treatments on the retinotectal projection.

In vivo phosphorylation of axonal proteins in goldfish optic nerve during regeneration

In vivo phosphorylation of axonal proteins was investigated in normal and regenerating optic nerves of goldfish by two-dimensional gel electrophoresis. By 6-24 h after intraocular injection of H3(32)PO4, approximately 20 optic nerve proteins ranging in size from 19 to 180 kilodaltons and in pI from 4.4 to 6.8 were seen to have incorporated radiolabel. Five of these proteins showed a robust increase in incorporation of phosphate during regeneration. Among the latter was an acidic (pI 4.5) 45-kilodalton protein, which has previously been shown to be conveyed by fast axonal transport and to increase dramatically in its rate of synthesis during regeneration of goldfish optic axons.

Structural protein transport in elongating motor axons after sciatic nerve crush. Effect of a conditioning lesion

In elongating motor axons of the rat sciatic nerve, the maximum outgrowth rate increased from 4.6 to 5.3 mm/d (5.3-6.1 X 10(-8) m/s) when a testing lesion of spinal nerves L4 and L5 was preceded 2 wk earlier by a conditioning lesion of the sciatic nerve. Axonal outgrowth was examined by measuring the transport of 35[S]methionine-labeled structural proteins (tubulin, actin, and neurofilament triplet) from "parent" axon stumps into "daughter" axon sprouts. Since these proteins are conveyed by the slow component of axonal transport at 1-5 mm/d (1.2-6.0 X 10(-8) m/s), the isotope was injected into the spinal cord 1 wk before the testing lesion. Nerves were removed 8 d after the testing lesion, sectioned into 3-mm segments, and homogenized; soluble proteins were separated by polyacrylamide gel electrophoresis. Fluorographs were used as templates to identify gel segments for removal, solubilization, and liquid scintillation counting. Distributions of mean radioactivity for tubulin, actin, and neurofilament triplet were plotted for animals receiving a conditioning vs sham-conditioning lesion. Greater amounts of tubulin and actin were transported into daughter axons in the conditioned group. Tubulin was mainly increased in axon shafts, whereas actin was mainly increased in axon tips. These findings suggest that the axonal transport of tubulin and actin governs the rate of elongation.

Elevated levels of retinal neurofilament mRNA accompany optic nerve regeneration

RNA isolated from goldfish retinas before and during optic nerve regeneration, when translated in vitro, directed the synthesis of neurofilament proteins that are normally found in high levels in the optic nerve. The major neurofilament proteins of the goldfish optic nerve comprise a group of four isoelectric variants of molecular weight 58,000 (58K) which we have identified previously as ON1-ON4. The levels of ON1 and ON2 within the optic nerve had been shown to decrease shortly after optic nerve crush and then increase to precrush levels during the regeneration process. Employing two-dimensional electrophoretic analysis of in vitro translation products and immunoprecipitations with antibodies specific for the ON proteins and an anti-intermediate filament monoclonal antibody, we show that ON1 and ON2 are encoded by mRNA synthesized in the retinas. The synthesis of ON3 and ON4 by retina RNA was undetected. This confirms data from previous ex vivo experiments that indicated that ON1 and ON2 are of neuronal origin whereas ON3 and ON4 are nonneuronal. ON1 and ON2 synthesis increases dramatically during optic nerve regeneration to levels 10- and 30-fold over precrush levels, respectively. In addition to ON1 and ON2, the synthesis of a previously unidentified 52K protein is observed at relatively high levels 20 and 32 days after optic nerve crush, but is unobserved before regeneration. Thus, optic nerve regeneration can be correlated with specific changes in intermediate filament gene expression within the retina.

Immunohistochemical localization of intermediate filament proteins of neuronal and nonneuronal origin in the goldfish optic nerve: specific molecular markers for optic nerve structures

The predominant proteins (58K) of the intermediate filament complex in the goldfish visual pathway consist of a series of isoelectric variants. Previous biochemical studies have shown that proteins ON1 and ON2 are of neuronal origin, whereas ON3 and ON4 are of nonneuronal origin. Polyclonal antibodies, purified by affinity chromatography, that are specific for ON1 and ON2 or ON3 and ON4 have been used to localize histologically the ON proteins within the normal and crushed optic nerve. Anti-ON1/ON2 antiserum presented a pattern consistent with intraaxonal staining. A nonneuronal staining pattern was observed with anti-ON3/ON4 antiserum. The two patterns were distinct from and complementary to each other. The data suggest that ON3 and ON4 represent a novel glial fibrillary acidic protein. The results are discussed in terms of the function of these proteins in development, plasticity, and regeneration.

The optic tectum regulates the transport of specific proteins in regenerating optic fibers of goldfish

The pattern of rapidly-transported proteins in regenerating optic fibers of the adult goldfish is regulated by interactions between these fibers and their main target, the optic tectum. When the optic fibers are allowed to interact with the tectum, the transport of proteins with molecular weights in the range of 110-145 kilodaltons (kDa) increases, whereas the transport of proteins in the 24-27 kDa range declines from the previously high level which has been induced by axotomy. If the optic fibers are prevented from interacting with the tectum, the transport of the 24-27 kDa proteins remains elevated for months. Amounts of other rapidly-transported retinal proteins (e.g. the acidic 43-49 kDa proteins that increase in regenerating optic fibers after axotomy) are relatively unaffected by tectal ablation.

Homology and diversity between intermediate filament proteins of neuronal and nonneuronal origin in goldfish optic nerve

The predominant intermediate filament proteins of the goldfish optic nerve have molecular weights of 58K. They can be separated into a series of four major isoelectric variants of neuronal (ON1 and ON2) and nonneuronal (ON3 and ON4) origin. The extent of homology between the goldfish 58K intermediate filament proteins themselves and to rat optic nerve vimentin and glial fibrillary acidic protein (GFAP) was investigated. Unlabeled and [32P]orthophosphate-labeled proteins were subjected to partial hydrolysis by V8 protease, chymotrypsin, and CNBr. The results show that the goldfish intermediate filament proteins share with vimentin and GFAP a 40K chymotrypsin-resistant core fragment. Phosphorylated moieties appear to be located outside the core region since they are preferentially cleaved off by chymotrypsin and not found associated with the 40K core. In addition, the goldfish ON proteins contain the antigenic site within the core that is common to most intermediate filaments. V8 or CNBr digestion indicates that many fragments that are common to ON1 and ON2 are clearly distinct from fragments that are common to ON3 and ON4. In addition, structural variability is observed between the goldfish intermediate filament proteins and vimentin and GFAP. The results are discussed in terms of intermediate filament structure and their possible role in nerve growth.