Degradation of the epidermal-dermal junction by proteolytic enzymes from human skin and human polymorphonuclear leukocytes.

The degradation of normal human skin by the human polymorphonuclear leukocyte proteinases cathepsin G and elastase, and by a human skin chymotrypsin-like proteinase that appears to be a mast cell constituent, was examined. Enzymes were incubated with fresh, split-thickness skin for up to 8 h; the tissue was examined ultrastructurally and immunohistochemically using antibodies to known basement membrane constituents. In all cases, the primary damage observed was at the epidermal-dermal junction. Elastase degraded the lamina densa leaving scattered and disorganized anchoring fibrils, dermal microfibril bundles, and normal-appearing collagen fibers. Immunohistochemically, type IV collagen, laminin, KF1 antigen, and EBA antigen were absent. The bullous pemphigoid antigen was present and localized on the basal cells. Epidermal-dermal separation produced by the chymotrypsin-like proteinases, cathepsin G, and the human skin proteinase, was confined to the lamina lucida. The lamina densa and sub-lamina densa fibrillar network remained intact. The human skin chymotrypsin-like proteinase produced extensive epidermal-dermal separation, while cathepsin G, at comparable concentrations, produced only focal separations. Immunohistochemically, all antigens were present after incubation with enzyme. The bullous pemphigoid antigen, however, was found on the epidermal side of the split, while laminin was found on the dermal side. These results show that the epidermal-dermal junction is highly susceptible to neutral serine proteinases located in mast cells and polymorphonuclear leukocytes. Although all the proteinases produce epidermal-dermal separation, the patterns and extent of degradation are different. The distinctive patterns of degradation may provide a clue to the involvement of these proteinases in skin diseases.

Rapid and specific conversion of precursor interleukin 1 beta (IL-1 beta) to an active IL-1 species by human mast cell chymase.

Secretory granules of human dermal mast cells contain a chymotrypsin-like serine proteinase called chymase. In this study, we demonstrate that the inactive cytokine, 31 kD interleukin 1 beta (IL-1 beta), can be converted rapidly to an 18 kD biologically active species by human mast cell chymase. The product formed is three amino acids longer at the amino terminus than the mature IL-1 beta produced by peripheral blood mononuclear cells and has comparable biological activity. Because chymase is a secretory granule constituent, it is likely to be released into the surrounding tissue when mast cells degranulate. It is also known that non-bone marrow derived cells resident in skin (keratinocytes, fibroblasts) produce but do not process 31 kD IL-1 beta. In this context, chymase may be a potent activator of locally produced 31 kD IL-1 beta. Mast cells lie in close apposition to blood vessels in dermis; therefore, chymase mediated conversion of 31 kD IL-1 beta might be expected to have a critical role in the initiation of the inflammatory response in skin.

A type II keratin is expressed in glial cells of the goldfish visual pathway.

The predominant intermediate filament proteins of the goldfish visual pathway consist of neuronal and non-neuronal isoelectric variants (58 kd). We have isolated a cDNA clone for the glial intermediate filament protein (ON3) from an optic nerve expression library. The predicted amino acid sequence of this clone reveals that it codes for a type II keratin representing the goldfish equivalent of mammalian keratin K8. K8 has been shown to be associated with embryogenesis and development. Unlike the mammalian visual system, the goldfish visual pathway displays a remarkable capacity for functional regeneration. The expression of K8, a protein not usually expressed in glial cells but shown to be associated with development, in the goldfish optic nerve may be involved with the processes of growth and regeneration in the goldfish visual pathway.

Plasticin, a novel type III neurofilament protein from goldfish retina: increased expression during optic nerve regeneration.

The goldfish visual pathway displays a remarkable capacity for continued development and plasticity. The intermediate filament proteins in this pathway are unexpected and atypical, suggesting these proteins provide a structure that supports growth and plasticity. Using a goldfish retina lambda gt10 library, we have isolated a full-length cDNA clone that encodes a novel type III intermediate filament protein. The mRNA for this protein is located in retinal ganglion cells, and its level dramatically increases during optic nerve regeneration. The protein is transported into the optic nerve within the slow phase of axonal transport. We have named this protein plasticin because it was isolated from a neuronal pathway well known for its plasticity.

Cumulative effects of multiple pain sites in youth with chronic pain.

BACKGROUND: The experience of persistent pain in multiple locations is common in youth. Based on current literature, youth with multiple pain sites (MPS) are at risk of experiencing poorer emotional outcomes and a spread of symptoms into late adolescence and adulthood. Little is known regarding the association between MPS with physical and school functioning domains, particularly after initiation of multidisciplinary pain treatment. Therefore, the objective of this study was to examine the association of MPS with disability and school functioning among youth with chronic pain. METHODS: A total of 195 patients with chronic pain, aged 8-17, and their parents completed measures assessing patient distress and functioning at a multidisciplinary pain clinic evaluation and at 4-month follow-up. RESULTS: At evaluation, 63% of patients presented with MPS; 25% reporting MPS endorsed pain in five or more locations. When controlling for relevant demographic and emotional distress factors, MPS were associated with lower school functioning at evaluation with a persistent trend at follow-up. Although MPS were not a significant predictor of pain-related disability at evaluation, it emerged as significant at follow-up. CONCLUSIONS: Potentially due to the MPS load and the inverse effects that such a pain state has on function, such patients may be at risk for poorer health and school-related outcomes. The mechanisms influencing these relationships appear to extend beyond psychological/emotional factors and warrant further investigation in order to aid in our understanding of youth with MPS. SIGNIFICANCE: Youth with MPS may be at risk for experiencing poorer physical and school functioning in comparison with single-site peers, despite treatment initiation. Further research is warranted to inform assessment and treatment approaches for this subgroup of patients.

A human lung mast cell chymotrypsin-like enzyme. Identification and partial characterization.

We have used a high performance liquid chromatography assay, which detects chymotryptic cleavage of the phe8-his9 bond of angiotensin I to yield angiotensin II, in order to examine human lung mast cells for the presence of chymotryptic activity. Mast cells, purified from human lung by enzymatic dispersion, countercurrent elutriation, and Percoll gradient centrifugation, were lysed or challenged with goat anti-human IgE. In multiple experiments angiotensin II-converting activity was detected in lysates of 10-99% pure mast cell preparations. Regression analysis of net percent release values of histamine and the angiotensin I-converting activity from dose-response experiments demonstrated a correlation between the two parameters, indicating that the chymotrypsin-like enzyme is a constituent of the mast cell secretory granule. The chymotryptic activity was completely inhibited by 10(-3) M phenylmethylsulfonylfluoride but not by 10(-3) M Captopril, and the pH optimum of activity was 7.5-9.5. Gel filtration of released material separated the activity from tryptase and demonstrated an approximate molecular weight of 30-35,000. The mast cell enzyme, like a human skin chymotrypsin-like proteinase, can be distinguished from leukocyte cathepsin G by lack of susceptibility to inhibition by bovine pancreatic trypsin inhibitor. Thus, an enzyme with limited chymotryptic specificity is present in human lung mast cells. The Michaelis constant of the enzyme for angiotensin I of 6.0 X 10(-5) M is similar to that of endothelial cell angiotensin-converting enzyme and is consistent with a reaction of physiologic importance.

Human skin tryptase: purification, partial characterization and comparison with human lung tryptase.

Human skin tryptase was isolated using stepwise low- and high-salt extraction and further purified 448-fold with 33% yield using octyl-Sepharose CL-4B hydrophobic affinity chromatography, Sephacryl S-200 gel filtration and finally octyl-Sepharose CL-4B or cellulose phosphate ion exchange chromatography. The skin tryptase, which has an apparent Mr of 120,000 by gel filtration in high-salt buffer, consisted of polypeptide chains of Mr 34,000 and 38,000 when resolved on SDS gels. Both polypeptide chains, labelled with [3H]diisopropyl fluorophosphate, indicated that they were representative of subunits and that the native proteinase was an aggregate of subunits. However, in some preparations only one band with Mr 34,000 was seen. In low-salt buffer the enzyme was labile and at least 1.4 M KCl was needed to keep the enzyme stabile when incubated at 37 degrees C for 30 min. Heparin glycosaminoglycan partially stabilized the tryptase but addition of protein (e.g. albumin, 80 micrograms/ml) to the tryptase-heparin mixture was needed to keep the enzyme stabile. Tryptases purified by exactly the same method from human lung tissue and from human skin had identical molecular size in gel filtration and in SDS-polyacrylamide gel electrophoresis. They also revealed identical enzyme kinetic parameters with several synthetic peptide substrates. The inhibition profile was identical for both enzymes, and they also crossreacted completely in immunodiffusion plates. These studies strongly indicate that mast cells found in skin as well as lung contain closely related, possible identical trypsin-like proteinases.

Treatment of mucosa-associated lymphoid tissue lymphoma of the stomach with radiation alone.

PURPOSE: Mucosa-associated lymphoid tissue (MALT) lymphoma of the stomach (MLS) has recently been defined as a distinct clinicopathologic entity, often associated with Helicobacter pylori infection. Many regard antibiotic therapy as the primary treatment of MLS, but in the absence of H pylori infection, or when salvage of antibiotic failures is required, gastrectomy and/or chemotherapy have frequently been used. This study evaluates the efficacy of low-dose radiotherapy alone as an alternative to surgery. PATIENTS AND METHODS: Seventeen patients with stage I to II(2) low-grade MLS without evidence of H pylori infection or with persistent lymphoma after antibiotic therapy of associated H pylori infection were included in this series. Median age was 69 years (range, 39 to 84). Median total radiation dose was 30 Gy (range, 28.5 to 43.5 Gy) delivered in 1.5-Gy fractions within 4 weeks to the stomach and adjacent lymph nodes. Following treatment, all patients underwent endoscopic evaluation and biopsy at a median of 4 months, at 6-month intervals to 2 years, and annually thereafter. RESULTS: All obtained a biopsy-confirmed complete response. At a median follow-up time of 27 months (range, 11 to 68) from completion of radiotherapy, event-free survival was 100%. Treatment was well tolerated, with no significant acute side effects. All remained asymptomatic at last follow-up. CONCLUSION: These results suggest that effective treatment of MLS with low-dose radiation therapy alone is feasible and safe, and allows stomach preservation. Longer follow-up evaluation is required to determine the long-term efficacy of this treatment approach and its side effects. Further studies should clarify the indications for radiotherapy in H pylori-negative or antibiotic-resistant cases of MLS.

The 2.2 A crystal structure of human chymase in complex with succinyl-Ala-Ala-Pro-Phe-chloromethylketone: structural explanation for its dipeptidyl carboxypeptidase specificity.

Human chymase (HC) is a chymotrypsin-like serine proteinase expressed by mast cells. The 2.2 A crystal structure of HC complexed to the peptidyl inhibitor, succinyl-Ala-Ala-Pro-Phe-chloromethylketone (CMK), was solved and refined to a crystallographic R-factor of 18.4 %. The HC structure exhibits the typical folding pattern of a chymotrypsin-like serine proteinase, and shows particularly similarity to rat chymase 2 (rat mast cell proteinase II) and human cathepsin G. The peptidyl-CMK inhibitor is covalently bound to the active-site residues Ser195 and His57; the peptidyl moiety juxtaposes the S1 entrance frame segment 214-217 by forming a short antiparallel beta-sheet. HC is a highly efficient angiotensin-converting enzyme. Modeling of the chymase-angiotensin I interaction guided by the geometry of the bound chloromethylketone inhibitor indicates that the extended substrate binding site contains features that may generate the dipeptidyl carboxypeptidase-like activity needed for efficient cleavage and activation of the hormone. The C-terminal carboxylate group of angiotensin I docked into the active-site cleft, with the last two residues extending beyond the active site, is perfectly localized to make a favorable hydrogen bond and salt bridge with the amide nitrogen of the Lys40-Phe41 peptide bond and with the epsilon-ammonium group of the Lys40 side-chain. This amide positioning is unique to the chymase-related proteinases, and only chymases from primates possess a Lys residue at position 40. Thus, the structure conveniently explains the preferred conversion of angiotensin I to angiotensin II by human chymase.

Crystallization, activity assay and preliminary X-ray diffraction analysis of the uncleaved form of the serpin antichymotrypsin.

Crystals of recombinant wild-type antichymotrypsin have been prepared by the method of vapor diffusion with polyethylene glycol 4000 as a precipitant at pH 5.7. Two crystal forms are observed. One form belongs to tetragonal space group P4(3)2(1)2 (or P4(1)2(1)2) and has unit cell dimensions a = b = 126 A, c = 243 A, with two molecules in the asymmetric unit. The other crystal form belongs to orthorhombic space group P2(1)2(1)2(1) and has unit cell parameters of a = 73 A, b = 78 A and c = 80 A, with one molecular in the asymmetric unit. Diffraction intensity measurements have been made on the tetragonal crystal form to a limiting resolution of 4.1 A, and reflections have been observed on X-ray still photographs to a limiting resolution of 2.5 A for the orthorhombic form. An activity assay of redissolved tetragonal form crystals indicates that the uncleaved, functional serpin has been crystallized.

Angiotensin I conversion by human and rat chymotryptic proteinases.

Human skin chymotrypsin-like proteinase, human neutrophil cathepsin G, rat mast cell chymase, and rat salivary gland tonin are cell-derived serine proteinases of similar size with specificity for amino acids of aromatic residues. Each enzyme was examined for its ability to convert angiotension I to angiotensin II and to cleave a panel of synthetic substrates. Skin chymotryptic proteinase, cathepsin G, and tonin cleaved the phe8-his9 bond of angiotensin I and converted angiotensin I to angiotensin II without further degradation. In contrast, chymase formed relatively small amounts of angiotensin II because it preferentially cleaved the tyr4-ile5 bond of angiotensin I. The rank order of angiotensin I converting activity was skin chymotryptic proteinase greater than tonin greater than cathepsin G greater than chymase. The Km and Kcat for angiotensin I conversion by the human skin enzyme were 6.6 X 10(-5) M and 50 s-1, respectively. The angiotensin I converting activity of human skin chymotryptic proteinase is equal to or greater than the peptidyl dicarboxypeptidase angiotensin-converting enzyme. Substrate specificities of each enzyme were further distinguished by use of benzoyl-L-tyrosine ethyl ester. A limited immunologic characterization of each enzyme was performed with monospecific goat antiserum to cathepsin G and chymase by Ochterlony gel diffusion. Each antiserum gave a precipitin line against its respective immunogen without evidence of cross-reactivity against the other enzymes. Human skin chymotryptic proteinase, cathepsin G, and tonin provide unique pathways for the generation of angiotensin II in tissue and may be of significance in regulation of biologic processes of the tissue microenvironment. The kinetic constants of the human skin chymotryptic proteinase for angiotensin I conversion, are consistent with the potential to carry out a reaction of physiologic importance.

Limited proteolysis of C1-inhibitor by chymotrypsin-like proteinases.

Limited proteolysis of C1-inhibitor was observed with human skin chymase, human cathepsin G, and bovine chymotrypsin. In each case, the inhibitor was degraded to one major product migrating slightly faster than the native inhibitor in an SDS-polyacrylamide gel. The inhibitory activity of C1-inhibitor against human plasma kallikrein was not altered by the modification with chymase. Edman degradation of the proteolyzed inhibitor revealed two sequences in a 1:1 ratio: NPNATSSSQ, the N-terminus of native C1-inhibitor, and VEPILEVSSL. This second sequence showed that the Phe33-Val34 bond was hydrolyzed. Our results provide another example of the susceptibility of the N-terminal region of C1-inhibitor to proteolytic cleavage.

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.

Plasticin, a newly identified neurofilament protein, is preferentially expressed in young retinal ganglion cells of adult goldfish.

The adult goldfish retina and optic nerve display continuous growth, plasticity, and the capacity to regenerate throughout the animal's life. The intermediate filament proteins in this pathway are different from those in adult mammalian nerves, which do not continuously grow or normally regenerate. One novel intermediate filament protein of the goldfish visual pathway is plasticin, which is synthesized in ganglion cells and transported into the optic nerve. Using specific polyclonal antibodies raised against a plasticin fusion protein, we investigated the distribution of this protein in the normal retina and nerve and in the retina and nerve following optic nerve crush. In the normal pathway, plasticin was localized predominantly to the axons of very young ganglion cells; however, there was considerable immunoreactivity in older axons as they approach the chiasm. In addition, following optic nerve crush, all ganglion cell somata and their axons proximal to the crush site became equally immunoreactive. The results suggest that plasticin may contribute to axonal growth, plasticity, and regeneration.

Restricted expression of a new paired-class homeobox gene in normal and regenerating adult goldfish retina.

We describe the cloning and expression pattern of a new paired-class homeobox gene, Vsx-1, in the continuously growing retina of the goldfish. Vsx-1 belongs to a subset of paired-class homeobox genes that lack a second DNA binding domain, the paired-domain, and is closely related to the C. elegans ceh-10 gene. In the adult goldfish, Vsx-1 expression is restricted to the neural retina. In the central, mature retina, Vsx-1 mRNA is synthesized in a subset of differentiated cells in the inner nuclear layer in a pattern suggestive of bipolar cells. In immature retina, adjacent to the retinal margin, Vsx-1 is expressed in a relatively broader subset of newly postmitotic cells but is downregulated in some of these cells to form the mature expression pattern. Following retinal injury, during the early phase of regeneration, Vsx-1 mRNA synthesis appears to be upregulated in cells in the inner nuclear layer and is expressed de novo in cells outside this layer. By virtue of its identity as a transcriptional regulatory gene and its patterns of expression, we speculate that Vsx-1 may stabilize the differentiated state of a subset of cells in the inner nuclear layer and may be involved in cellular differentiation during retinal development and regeneration.

Differential expression of keratins in goldfish optic nerve during regeneration.

The goldfish visual pathway, unlike the visual pathway of higher vertebrates, retains continuous growth and development throughout life and is capable of functional regeneration. The structure and expression of proteins that support the physiological attributes of this system are of interest. Glial cells in this pathway express keratins as the predominant intermediate filament proteins rather than the expected glial fibrillary acidic protein. Previously we identified and characterized cDNA clones representing two type I keratins from the goldfish optic nerve, GK48 and GK49. The GK48 protein is the type I keratin partner to the type II keratin ON3, while the GK49 protein is expressed in a different cell type. Here, we extend our studies on the expression of mRNA for the GK48, GK49, and ON3 proteins at the early stages of optic nerve regeneration. RNase protection assays show that at 10 days post-crush, there is no overall change in levels of mRNA for these proteins as compared to uncrushed control nerves and nerves from unoperated fish. In addition, we show by in situ hybridization that the GK49 protein shows no changes in its distribution of mRNA in the optic nerve after crush. In contrast, the levels of GK48 and ON3 mRNA are greatly reduced within the crush zone. However, these two mRNAs are differentially expressed at different time points during regeneration, with GK48 mRNA appearing in the crush zone before ON3. These results indicate that the mRNA for the GK48 and ON3 proteins are differentially regulated during regeneration and that these two proteins are expressed in a different cell type from the GK49 protein.

Vsx-1 and Vsx-2: differential expression of two paired-like homeobox genes during zebrafish and goldfish retinogenesis.

Vsx-1 and Vsx-2 are two homeobox genes that were cloned originally from an adult goldfish retinal library. They are members of the paired-like:CVC gene family, which is characterized by the presence of a paired homeodomain and an additional conserved region, termed the CVC domain. To analyze the possible roles for Vsx-1 and Vsx-2 in eye development, we used in situ hybridization to examine their expression patterns in zebrafish and goldfish embryos. Vsx-2 is initially expressed by proliferating neuroepithelial cells of the presumptive neural retina, then it is down-regulated as differentiation begins, and it is finally reexpressed at later stages of differentiation in a subset of cells, presumed to be bipolar cells, in the inner nuclear layer. In contrast, Vsx-1 is expressed only weakly in undifferentiated, presumptive neural retina and is then up-regulated selectively in presumptive bipolar cells at early stages of differentiation (when Vsx-2 is turned off), before decreasing to an intermediate level, which is maintained in the differentiated (adult) retina. The restricted expression patterns of Vsx-2 correspond to the observed phenotypes in mice with the ocular retardation mutation (orJ), further supporting the notion that Vsx-2 and Chx10 are homologues. The sequential complimentary and then corresponding expression patterns of Vsx-1 and Vsx-2 suggest that these similar transcription factors may be recruited for partially overlapping, but distinct, functions during the development of the retina.

Vsx-1 and Vsx-2: two Chx10-like homeobox genes expressed in overlapping domains in the adult goldfish retina.

The genetic linkages of the murine ocular retardation mutation with the Chx10 gene and the murine small eye mutation with the Pax-6 gene has demonstrated the importance of Paired class homeobox genes in the development of the mammalian retina. Previously, we identified a Paired-class homeobox gene, Vsx-1, whose expression in the adult goldfish retina is restricted to the inner nuclear layer (INL) and to postmitotic, differentiating progenitor cells in the growth zone at the retinal peripheral margin, where neurogenesis continues throughout life. Here, we report the molecular cloning and expression pattern of a new Paired class homeobox gene, Vsx-2, in the adult goldfish retina. Like Vsx-1, Vsx-2 expression is highly restricted to the retina in the adult goldfish and overlaps with Vsx-1 expression in the mature INL. At the peripheral margin, Vsx-2 is expressed in mitotically active neuronal progenitors and is downregulated as these cells become postmitotic and begin to differentiate. Comparison of the amino acid sequences of Vsx-2, Vsx-1, Chx10, and C. elegans ceh-10 reveal a conserved homeodomain and a unique domain termed the CVC domain. The similarities of the Vsx-2, Vsx-1, and Chx10 expression patterns suggest that genes containing the CVC domain have conserved functions during retinal development in vertebrates.

Complex expression of keratins in goldfish optic nerve.

Keratins are the predominant intermediate filament proteins in the nonneuronal cells of the goldfish optic nerve. At least three different keratin pairs are expressed in this tissue, indicating an unexpected complexity. Expression of the type II keratin ON3 in goldfish optic nerve astrocytes predicts the expression of a type I keratin partner. Here we report the cDNA sequence and predicted amino acid sequence of two type I keratins from the goldfish optic nerve, designated GK48 and GK49. The GK48 protein is the goldfish equivalent of mammalian keratin 18 (K18) and is the most likely type I keratin partner to the ON3 protein. The GK49 protein is similar to the GK50 protein, a type I keratin characterized previously from the goldfish optic nerve. The GK48 and ON3 mRNAs are expressed in a variety of goldfish tissues, whereas the expression of GK49 mRNA has a more limited expression. In addition, in situ hybridization experiments show that the expression of the GK48 and ON3 mRNAs are evenly distributed throughout the optic nerve, while the GK49 mRNA is expressed along longitudinal lines. These results show that there is a diversity of keratin expression within different cell types in the goldfish optic nerve.

Restricted expression of the neuronal intermediate filament protein plasticin during zebrafish development.

In the adult goldfish visual pathway, expression of the neuronal intermediate filament (nIF) protein plasticin is restricted to differentiating retinal ganglion cells (RGCs) at the margin of the retina. Following optic nerve injury, plasticin expression is elevated transiently in all RGCs coincident with the early stages of axon regeneration. These results suggest that plasticin may be expressed throughout the nervous system during the early stages of axonogenesis. To test this hypothesis, we analyzed plasticin expression during zebrafish (Danio rerio) neuronal development. By using immunocytochemistry and in situ hybridization, we found that plasticin is expressed in restricted subsets of early zebrafish neurons. Expression coincides with axon outgrowth in projection neurons that pioneer distinct axon tracts in the embryo. Plasticin is expressed first in trigeminal, Rohon-Beard, and posterior lateral line ganglia neurons, which are among the earliest neurons to initiate axonogenesis in zebrafish. Plasticin is expressed also in reticulospinal neurons and in caudal primary motoneurons. Together, these neurons establish the first behavioral responses in the embryo. Plasticin expression also coincides with initial RGC axonogenesis and progressively decreases after RGC axons reach the tectum. At later developmental stages, plasticin is expressed in a subset of the cranial nerves. The majority of plasticin-positive neurons are within or project axons to the peripheral nervous system. Our results suggest that plasticin subserves the changing requirements for plasticity and stability during axonal outgrowth in neurons that project long axons.