PGP9.5, a ubiquitin C-terminal hydrolase; pattern of mRNA and protein expression during neural development in the mouse

Cloning and expression analysis of a Parkinson’s disease gene, uch-L1, and its promoter in zebrafish

Three genes, alpha-synuclein, parkin, and ubiquitin C-terminal hydrolase L1 (UCH-L1), have been associated with inherited forms of Parkinson's disease (PD), although their in vivo functions have remained largely unknown. To develop an animal model for the molecular study of PD, we cloned zebrafish uch-L1 cDNA and its gene promoter. Sequence analysis revealed that the zebrafish Uch-L1 is highly homologous (79%) to the human UCH-L1, which is a member of the deubiquitinating enzymes. By whole-mount in situ hybridization, we examined the spatiotemporal expression of uch-L1 mRNA in developing zebrafish embryos. The uch-L1 mRNAs are detected in neuronal cells at the first day of embryo development. The expression domain of uch-L1 overlaps with that of tyrosine hydroxylase, a molecular marker for dopaminergic neurons, in the ventral diencephalon, an equivalent structure to the substantia nigra where PD progresses in human. To further analyze the tissue-specific regulation of uch-L1 gene expression, we also tested its gene promoter activity and showed a preferential neuronal expression in transient transgenic zebrafish embryos. These results suggest that uch-L1 may have an important role in the development of neuronal cells in early embryos as well as in the degeneration and disease of neuronal cells in late adult brain.

HOXB5 expression is spatially and temporarily regulated in human embryonic gut during neural crest cell colonization and differentiation of enteric neuroblasts

HOX genes from paralogous groups 4 and 5 are particularly relevant to the gut neuromusculature development because these genes are expressed at the splanchnic mesoderm surrounding the gut diverticulum, and at the level of the neural tube from where the vagal neural crest cells (NCCs) originate. In this study, we examined the migration and differentiation of NCCs, and investigated the expression patterns of HOXB5 in human embryonic guts. Human embryos of gestational week-4 to -8.5 were studied. Vagal NCCs enter the esophagus, migrate, and colonize the entire gut in a rostrocaudal manner between week-4 and week-7. The migrating NCCs in gut express HOXB5. Two separate and discontinuous mesenchymal expression domains of HOXB5 were detected in the gut: the distal domain preceding the migratory NCCs; and the proximal domain overlapping with the NCCs. The two expression domains shift caudally in parallel with the rostrocaudal migration of NCCs between week-4 and week-5. Neuron and glia differentiation of NCCs are concomitant with HOXB5 down-regulation in NCCs and the mesenchyme. By week-7, myenteric plexuses have formed; HOXB5 expression is switched on in the plexuses. We found that (1) the migratory route of NCCs in human embryonic gut was similar to that in mice and chicks; and (2) the expression pattern of HOXB5 correlated with the migration and differentiation of NCCs, suggesting a regulatory role of HOXB5 in the development of NCCs.

The monkey (Macaca fascicularis) heart neural structures and conducting system: an immunochemical study of selected neural biomarkers and glutamate receptors

The neural markers, protein gene product 9.5 (PGP 9.5), neurofilaments (NF) and glutamate receptors (GluRs) were visualized by immunohistochemistry in the monkey heart. PGP 9.5 showed the greatest affinity for intramural ganglia cells and nerve fibres. Structural components of the conducting system were also stained, particularly the bundle of His, AV node and Purkinje fibres. Anti-NF 200 and NF 160 showed strong, preferential affinity to nerve fibres and ganglia throughout the heart. Further studies concentrated on the presence and the distribution of glutamate receptors: NMDAR 1, GluR 1, GluR 2/3, GluR 5/6/7, mGluR 2/3, and mGluR 5. Positive immunoreactivity of GluRs was evident in nerve terminals within the atrium, myocardium, intramural ganglia and elements of the conducting system. The intensity of the stain varied for each antibody according to the anatomical distribution within neural structures and conducting system. The specificity of immunolabelling was confirmed by absorption studies with each corresponding peptide. There is preferential affinity to and differential distribution of staining with PGP 9.5, NFs and several subtypes of GluRs in the various components of the cardiac conducting system in adult monkeys. The expression of specific neural markers and glutamate receptors common to nerve fibers and ganglia cells is consistent to our previous report in rodents. These expressions suggests that such structures in the heart share common characteristics with a variety of neural tissues and hence are potential targets for neurotoxins. Furthermore, the strong affinity and specific distribution of several subtypes of GluRs in the monkey heart fosters our view that these receptors may be able to influence the physiology and pathophysiology of cardiac rhythm and excitation. Hence as in the brain, the GluRs may be involved in the mediation of excitatory effects in the heart.

Expression of PGP9.5 in ductal cells of the rat pancreas during development and regeneration: can it be a marker for pancreatic progenitor cells?

The expression of protein gene product 9.5 (PGP9.5), a known neuron marker, was immunohistochemically investigated in rat pancreas. In fetal pancreas, a cluster of cells expressed PGP9.5 among the initial epithelial buds at embryonic day 11.5 (E 11.5). At E 13.5, PGP9.5 appeared among elongated and branching epithelial cells as well as along nerve fibers in the mesenchyme. On E 17.5, tubular cells became ductal cells with lumen, which strongly expressed PGP9.5. In newborn rats, ductal cells of the common bile duct (CBD) to the centroacinar cells and islet cells expressed PGP9.5. Ten days after birth, the number of the ductal cells expressing PGP9.5 was reduced, and PGP9.5-negative cells appeared in half of the duct cells. On day 21, all centroacinar cells and intercalated ductal cells became PGP9.5-negative, but some CBD and interlobular ductal cells remained positive for PGP9.5. On day 28 and thereafter, PGP9.5 was no longer detected. In a pancreatic duct ligation model, acinar cells changed to cells with duct-like structure after duct ligation. These cells strongly expressed PGP9.5 on the fifth day after duct ligation. Three to four weeks after ligation, the cells with duct-like structure changed to acinar cells, islets of Langerhans and ductal cells, but the ductal cells were PGP9.5-negative at this point. These results suggested that PGP9.5 is expressed in ductal cells that possess a potential for differentiation to pancreatic endocrine cells, and therefore can serve as a marker for the progenitor of pancreatic endocrine cells.

Methylation status in the promoter region of the human PGP9.5 gene in cancer and normal tissues

PGP 9.5 is a neurospecific peptide that functions to remove ubiquitin from ubiquitinated cellular proteins, thereby preventing them from targeted degradation by the proteasome-dependent pathway or regulating their localization, activity or structure. Using the serial analysis of gene expression method (SAGE), we initially found that the PGP9.5 transcript and protein was highly expressed in more than 50% of primary lung cancers and nearly all lung cancer cell lines but was not detectable in the normal lung. This increased expression could be the result of transcriptional regulation accompanied by methylation changes at the CpG island of the promoter region. We studied the methylation status of the cytosines at the promoter region of human PGP9.5 using sodium bisulfite genomic sequencing in normal and neoplastic cells. Although no methylation of PGP9.5 promoter was observed in the normal lung, normal cervical tissue, and lung cancer cell lines, this region was densely methylated in the HeLa cell line. Exposure to HeLa cells to the demethylating agent, 5-aza-2'-deoxycytidine, led to re-expression of PGP9.5. This data suggested that while other mechanisms may be involved in the frequent overexpression of PGP9.5 gene in lung tumors and lung cancer cell lines, promoter methylation may play a role in the transcriptional suppression of PGP9.5 gene expression in the cervical tissue-derived HeLa cell line.

Cloning, expression, and mapping of a mouse gene, Uchl4, highly homologous to human and mouse Uchl3

Ubiquitin carboxyl-terminal hydrolases (UCHs) are implicated in the proteolytic processing of polymeric ubiquitin. We have isolated a novel mouse gene for ubiquitin carboxyl-terminal hydrolase isozyme L4. The gene named Uchl4 encodes a novel member of the family of ubiquitin carboxyl-terminal hydrolases (UCHs) whose predicted amino acid sequence shows 95% identity to mouse UCH-L3 and 94% identity to human UCH-L3. Genomic structure, chromosome localization, and expression pattern of Uchl3 and Uchl4 were characterized in the mouse. Both Uchl3 and Uchl4 were expressed in various tissues examined; however, expression level was quite lower in Uchl4. While Uchl3 consists of at least 9 exons spanning about 12 kb, Uchl4 was an intronless gene with a size of about 2 kb. By PCR-based analysis with T31 radiation hybrid mapping panel, Uchl3 and Uchl4 were mapped on mouse chromosome 9 and 14, respectively.

Ubiquitin C-terminal hydrolase-L1 (PGP9.5) expression in human neural cell lines following induction of neuronal differentiation and exposure to cytokines, neurotrophic factors or heat stress

Dysfunction of the ubiquitin-dependent proteolytic pathway contributes to progressive accumulation of ubiquitinated protein inclusions in neurodegenerative disorders, such as Parkinson's disease (PD). Ubiquitin C-terminal hydrolase-L1 (UCH-L1), alternatively designated protein gene product 9.5 (PGP9.5), is a neural deubiquitinating enzyme which is identified as a principal constituent of Lewy bodies. To clarify the regulatory mechanism of UCH-L1 expression in human neural cells, we studied the constitutive, cytokine/neurotrophic factor-regulated, and heat stress-induced expression of UCH-L1 in cultured human neural cell lines by Western blot analysis. The constitutive expression of UCH-L1 was identified in SK-N-SH neuroblastoma cells, IMR-32 neuroblastoma cells, U-373MG astrocytoma cells, and NTera2 teratocarcinoma-derived differentiated neurones (NTera2-N). The levels of UCH-L1 expression were unaltered in these cell lines following treatment with TNF-alpha, IL-1beta, BDNF, GDNF, dibutyryl cyclic AMP, or phorbol 12-myristate 13-acetate, and remained unchanged by exposure to heat stress. In contrast, its levels were elevated substantially in NTera2 teratocarcinoma cells following retinoic acid-induced neuronal differentiation, accompanied with an increased expression of alpha-synuclein and synaptophysin. These results indicate that UCH-L1 is expressed constitutively in human neual cell lines, where it is upregulated following induction of neuronal differentiation, but unaffected by exposure to heat stress, cytokines, or growth/differentiation factors which are supposed to be invloved in the nigral neuronal death and survival in PD.

Immunocytochemical characteristics of cells and fibers in the nasal mucosa of young and adult macaques

The mammalian nasal cavity is lined by an olfactory mucosa (OM) and a respiratory mucosa (RM). The principal OM cell type is the olfactory receptor neuron (ORN). However, little is known about ORNs in the life histories of primates. The RM, similar to the RM in the tracheobronchial tract (TBT), is dominated by ciliated columnar cells. Neuroendocrine cells (NECs) are essential in the TBT; little is known about nasal NECs. This study examined the immunolabeling characteristics of primate OM and RM for three important proteins-calretinin (CR), olfactory marker protein (OMP), and protein gene product 9.5 (PGP). Tissues from newborn to 15-year-old macaques were analyzed to determine the expression of these proteins during various stages of development. Standard immunocytochemistry on aldehyde-fixed tissues was applied, utilizing the avidin-biotin peroxidase (ABC) method. Immuno-electron microscopy confirmed the immunoreactive cell types. ORNs were immunoreactive for CR, OMP, and PGP at all ages studied. Immunoreactivity for PGP also was displayed in a subset of ciliated, columnar epithelial cells in the RM and in an extensive network of subepithelial fibers spread throughout both mucosae. The results suggest that macaque ORNs express three important proteins over a wide life history, and that the macaque may be a reliable model for studying primate/human olfaction during aging. The PGP-labeling results also suggest that the macaque nasal peptidergic fibers express PGP and that the respiratory epithelium contains NECs with labeling characteristics similar to those in the TBT.

An in vitro model for the study of taste papillae morphogenesis using branchial arch explants

It is generally accepted that innervation is required for the maintenance of taste papillae and taste buds, but it is not entirely clear what role, if any, innervation plays in papillae and taste bud formation. Events in taste papillae formation and differentiation take place almost entirely in utero and, therefore, the study of the role of innervation in these events requires a suitable in vitro model. In the past, investigators have made use of various culture techniques to study mammalian taste papillae development in vitro and the role of innervation in this process with varying success. All of these models examined papillae development in isolated tongue or tongue fragments and have lacked the ability to manipulate the innervation of developing taste papillae in these explants. We have established a protocol for an in vitro model of taste papillae morphogenesis using branchial arch explants and roller tube culture methodology. Our results demonstrate that this model supports the morphogenesis of the circumvallate papilla with an integrated nerve. In addition, the use of branchial arch explants allows the inclusion or exclusion of geniculate and petrosal ganglia to examine directly the effects of the presence or absence of innervation on papillae formation and maintenance.

USP25, a novel gene encoding a deubiquitinating enzyme, is located in the gene-poor region 21q11.2

We have identified a new gene, USP25, spanning over 150 kb at 21q11. 2, one of the lowest gene-density regions of the human genome. USP25 is made up of 25 exons and encodes a 1087-aa protein. Database comparisons reveal high homology with members of the ubiquitin protease family (UBP). Basal expression was observed in all human tissues tested, and two main transcripts were identified. The homologous murine gene has also been characterized. In situ hybridization in mouse embryonic brains showed a clear correlation of expression with proliferative neuroepithelial cells and postmitotic neurons. Moreover, high expression was observed in adult mouse testis. UBPs belong to a complex family of deubiquitinating enzymes that specifically cleave ubiquitin conjugates on a great variety of substrates. These enzymes have an essential role in protein degradation via the 26S proteasome and thus regulate many cellular pathways. An increase in USP25 gene dosage in Down syndrome patients could seriously disturb the balance between ubiquitinated and deubiquitinated substrates.

Expression of protein gene product 9.5, a neuronal ubiquitin C-terminal hydrolase, and its developing change in sertoli cells of mouse testis

Protein gene product 9.5 (PGP9.5), originally isolated as a neuron-specific protein, belongs to a family of ubiquitin carboxyl-terminal hydrolases that play important roles in the nonlysosomal proteolytic pathway. Antibodies against PGP9.5 have been used for immunohistochemical detection of neural elements, although some non-neuronal cells are also immunoreactive for PGP9.5. In the present study, developing testes of the mouse were immunostained after autoclave pretreatment of sections. In the testes of days 8 and 16, PGP9.5 was only localized on the spermatogonia, whereas on day 30 and in adults it appeared not only on spermatogonia, but also on Sertoli cells. In the testis of the male sterile W/W(v) mutant, very little, but strong, immunoreactivity was detected at some Sertoli cells, which were phagocytizing Sertoli cell aggregations that had fallen from the basal membrane. Additionally, it was confirmed that the nucleotide sequence of PGP9.5 in mice was highly conserved, like that in other mammals. These results suggest that PGP9.5 is a useful marker for activated Sertoli cells, playing an important role in degradation of abnormal proteins.

A bi-functional activator/repressor element required for transcriptional activity of the human UCH-L1 gene assembles a neuron-specific protein: single-strand DNA complex

The ubiquitin C-terminal hydrolase (UCH)-L1 gene is expressed in a tissue- and cell-specific manner with expression restricted to neurons and neuroendocrine cells. Regulatory DNA sequences from the 5' untranscribed region of the human UCH-L1 gene will promote neuron specific transcription providing that a 59 bp sequence located between nucleotides -182 and -123 is present in reporter gene constructs. We show that this 59 bp sequence is a bi-functional regulator of transcription, acting as an activator in human neuroblastoma cells (SH-SY5Y) and a strong repressor in HeLa cells. The sense strand of the UCH-L1 activator/repressor element can interact with nuclear proteins that recognize single stranded DNA in a sequence specific manner. Nuclear extracts from neuroblastoma cells generate a protein:ssDNA interaction called complex 1B could be converted into a lower mobility complex (1A) by increasing the protein:DNA ratio. This conversion was not observed when using nuclear extracts from HeLa cells. Formation of neuron specific complex 1A could be prevented by incubation of protein:ssDNA complexes at 2 degrees C or in the presence of mM concentrations of MgCl2. In conclusion, we have identified a novel bi-functional regulatory DNA element in the promoter of the human UCH-L1 gene that contributes to neuron-restricted transcription and which can assemble a neuron specific protein:ssDNA complex on its sense strand.

PGP9.5 as a candidate tumor marker for non-small-cell lung cancer

PGP9.5 is a neurospecific peptide that functions to remove ubiquitin from ubiquitinated proteins and prevents them from targeted degradation by proteasomes. Using the serial analysis of gene expression method (SAGE), we observed that the PGP9.5 transcript was highly expressed in primary lung cancers and lung cancer cell lines but was not detectable in the normal lung. Here we examined the expression of PGP9.5 protein in normal lung epithelium, lung tumor cell lines, and 98 resected primary non-small-cell lung carcinomas (NSCLCs). We found PGP9.5 reactivity in normal lung in a pattern compatible with K-cells of the diffuse neuroendocrine system. However, the PGP9.5 was present in both small-cell lung cancer (SCLC) and NSCLC cell lines (22/24) independent of neuronal differentiation. In primary NSCLCs, 54% (53/98) of the cases had positive PGP9.5 staining, and the expression of protein was strongly associated with pathological stage of the cancer. It was present in 44% (29/66) of stage I NSCLCs and in 75% (24/32) of stage II and IIIA NSCLCs (p = 0.0032). These results suggest that the increased expression of PGP9.5 is specifically associated with lung cancer development and may serve as a potential marker for the detection of lung cancer.

An evolutionarily conserved gene on human chromosome 5q33-q34, UBH1, encodes a novel deubiquitinating enzyme

While cloning breakpoint sequences of a leukemia patient exhibiting a t(5; 14) translocation, we identified a pseudogenic variant of a novel multigene family in proximity to the breakpoint. Chromosomal in situ hybridization suggested that the gene family is clustered on human chromosome 5q33-q34. The gene family is evolutionarily conserved. Northern blot analysis of mouse tissues revealed low-level expression of a functional member of this gene family in almost all samples. Marked levels of transcripts were detected by in situ hybridization in the retina, the olfactory epithelium, the peripheral neuronal ganglia, and distinct areas of the gut. The predicted protein displays striking similarity to a hypothetical protein of Caenorhabditis elegans (R10E11.3.) and to two yeast deubiquitinating enzymes, Ubp9 and Ubp13, albeit to a lesser extent. We expressed the putative coding region of the human gene in Escherichia coli and demonstrated that it indeed bears deubiquitinating activity based on its ability to cleave ubiquitin from a ubiquitin-beta-galactosidase fusion protein. This new deubiquitinating enzyme has been named UBH1, for ubiquitin hydrolyzing enzyme 1.

The expressions of epidermal growth factor receptor mRNA and protein gene product 9.5 in developing rat brain

To clarify the role of epidermal growth factor receptor (EGFR) in brain development, especially with regard to neuron differentiation, EGFR mRNA expression was studied by in situ hybridization in embryonic day (E)12, E16, postnatal day (P)1, P4, P15, P29 and adult rat, using protein gene product (PGP) 9.5 as a neuron marker. The primary germinal zone (neuroepithelium) expressed neither PGP 9.5 immunoreactivity (IR) nor EGFR mRNA. In the developing brain, cells expressing EGFR mRNA but not PGP 9.5 IR were found in the secondary germinal zone such as the subventricular zone and cerebellar external germinal layer, the cortical plate and, in later stage animals, the fiber tracts. Cells expressing both EGFR mRNA and PGP 9.5 IR appeared in a differentiating field. In the adult brain, strong EGFR mRNA expression was observed in Purkinje cells, Golgi cells, some hippocampal cells and neurons of the diencephalon, pontine and medullary nuclei, and weak expression was seen in neurons of the cerebral cortex. These results suggest that EGFR is related to the process of differentiation and maturation of neurons and the maintenance of some types of adult neurons.

Immunoreactivity of protein gene product 9.5 (PGP 9.5) in the developing hamster olfactory bulb

BACKGROUND

Protein gene product 9.5 (PGP 9.5) is a soluble protein isolated from human brain and recently demonstrated to correspond to ubiquitin carboxyl terminal hydrolase. We examined the PGP 9.5 immunoreactivity in the developing hamster olfactory bulb to determine whether the olfactory bulb expresses PGP 9.5 from the early developmental stage and whether it is a useful marker for investigating the differentiation of bulbar neurons and the development of laminar organization.

METHODS

The developing hamster olfactory bulb was fixed in Bouin's solution without acetic acid or acetic alcohol (95% absolute alcohol with 5% acetic acid) and immunostained with human PGP 9.5 antiserum by the avidin-biotin peroxidase complex (ABC) method.

RESULTS

PGP 9.5 immunoreactivity was detected in the axons of olfactory and vomeronasal receptor cells and immature bulbar neurons from embryonic day 13 in the tissue fixed in Bouin's solution without acetic acid and in the immature bulbar neurons from embryonic day 11 in the tissue fixed in acetic alcohol. In some bulbar neurons, PGP 9.5 immunoreactivity was detected not only in the cytoplasm, but also in the nuclei. The pattern of immunostainings for PGP 9.5 became almost the same as in the adult at postnatal day 15. From the immunostaining for PGP 9.5, we found that the short axon cells in addition to mitral, tufted, and mitral/tufted cells were identified in the prenatal period and that the extension of the dendrites, formation of the glomeruli, and completion of the laminar organization were earlier in the main olfactory bulb than in the accessory olfactory bulb.

CONCLUSIONS

PGP 9.5 can be a useful marker to investigate the differentiation of bulbar neurons and the formation of laminar organization in the developing olfactory bulb.

The structure and autonomic innervation of the vesico-ureteric junction in cases of primary ureteric reflux

OBJECTIVE

To determine the histological structure and autonomic innervation of the vesico-ureteric junction (VUJ) in cases of primary ureteric reflux, to compare the results with those reported previously for non-refluxing VUJs and thus determine possible structural anomalies which could be responsible for vesico-ureteric reflux (VUR).

MATERIALS AND METHODS

Nineteen specimens of VUJs with reflux were obtained from four males and 10 females undergoing ureteric reimplantation. Serial frozen sections were cut and stained either with Masson's trichrome or immunostained for protein gene product (PGP 9.5), a general nerve marker, dopamine beta hydroxylase (D beta H), a marker for noradrenergic nerves, or neuropeptide Y (NPY).

RESULTS

Longitudinally orientated muscle bundles of narrow diameter accompanied the ureter to its termination at the ureteric orifice. Where they merged with those of the superficial trigone. In some specimens, an additional muscle component was identified, situated on the outer aspect of the ureteric muscle coat, consisting of an incomplete layer of distinctive muscle whose constituent cells formed an interlacing mesh-work. Occasionally, specimens included detrusor muscle which consisted of relatively large diameter compact bundles separated from the ureter by a connective tissue sheath. D beta H- and NPY-immunoreactive (-IR) nerves were numerous among the ureteric muscle bundles. Many NPY-IR nerves occurred within the detrusor muscle while D beta H-IR nerves were mainly perivascular. When present, the outer muscle component was richly innervated by both D beta H- and NPY-IR nerves. PGP immunoreactivity varied among regions in the same section, PGP-IR nerves frequently being less numerous than those containing D beta H or NPY.

CONCLUSION

These results indicate that the morphology of the VUJ in cases of VUR is indistinguishable from the normal VUJ described previously. Furthermore, the density and distribution of D beta H- and NPY-IR nerves is identical to that in controls. However, the antigenicity of PGP in the reflux specimens appears to be masked in some regions by an unknown factor.

Hair cycle-dependent plasticity of skin and hair follicle innervation in normal murine skin

The innervation of normal, mature mammalian skin is widely thought to be constant. However, the extensive skin remodeling accompanying the transformation of hair follicles from resting stage through growth and regression back to resting (telogen-anagen-catagen-telogen) may also be associated with alteration of skin innervation. We, therefore, have investigated the innervation of the back skin of adolescent C57BL/6 mice at various stages of the depilation-induced hair cycle. By using antisera against neuronal (protein gene product 9.5 [PGP 9.5], neurofilament 150) and Schwann cell (S-100, myelin basic protein) markers, as well as against neural cell adhesion molecule (NCAM) and growth-associated protein-43 (GAP-43), we found a dramatic increase of single fibers within the dermis and subcutis during early anagen. This was paralleled by an increase in the number of anastomoses between the cutaneous nerve plexuses and by distinct changes in the nerve fiber supply of anagen vs. telogen hair follicles. The follicular isthmus, including the bulge, the seat of epithelial follicle stem cells, was found to be the most densely innervated skin area. Here, a defined subpopulation of nerve fibers increased in number during anagen and declined during catagen, accompanied by dynamic alterations in the expression of NCAM and GAP-43. Thus, our study provides evidence for a surprising degree of plasticity of murine skin innervation. Because hair cycle-associated tissue remodeling evidently is associated with tightly regulated sprouting and regression of nerve fibers, hair cycle-dependent alterations in murine skin and hair follicle innervation offer an intriguing model for studying the controlled rearrangement of neuronal networks in peripheral tissues under physiological conditions.

Evidence that spinal interneurons undergo programmed cell death postnatally in the rat

Programmed cell death has been demonstrated in several specific neuronal populations as a mechanism for modulating the population size following differentiation, but its applicability to all neuronal types is unclear. Evidence for programmed cell death in some populations such as the numerous spinal interneurons has been lacking. We have studied the incidence of apoptosis in the rat spinal cord with three different methods and found a previously undocumented wave of apoptosis occurring in spinal grey matter shortly after birth. The apoptotic morphology was confirmed ultrastructurally. Dying cells were identified as neurons by immunocytochemical labelling for neuronal markers and had an anatomical distribution which indicated that most of the apoptotic cells were interneurons not motoneurons. This wave of apoptosis has the characteristics of a discrete developmental process and occurs later than that of either ventral horn motoneurons or dorsal root ganglion cells, to which most spinal interneurons are connected. These findings indicate that interneurons do undergo programmed cell death, and we suggest that this occurs in response to the earlier reduction in size of their main synaptic targets.

Detection of neuron-specific protein gene product (PGP) 9.5 in the rat and zebrafish using anti-human PGP9.5 antibodies

Protein gene product (PGP) 9.5 is a developmentally regulated neuron- and neuroendocrine cell-specific ubiquitin carboxy-terminal hydrolase (UCHL1) expressed throughout the mammalian central and peripheral nervous systems. We have compared the use of monoclonal and polyclonal antibodies raised against human PGP9.5 for immunodetection of the protein in tissues of the zebrafish and rat. We show that a monoclonal antibody 13C4, which recognises an N-terminal epitope, detects PGP9.5 on Western blots as a single 27 kDa band present at high levels in zebrafish and rat brain. By contrast, the polyclonal antisera recognises multiple tissue-specific proteins in the rat and fails to detect PGP9.5 in the zebrafish. Finally, we have developed a specific ELISA assay for detection of cellular PGP9.5 using MAb13C4 and have employed the assay to show that PGP9.5 is not upregulated during nerve growth factor (NGF)-induced differentiation of rat PC12 cells.

An age-dependent novel hyperinnervation of circumvallate papillae by tyrosine hydroxylase-containing nerve fibers in NGF-overexpressing transgenic mice

The density of protein gene product 9.5- and tyrosine hydroxylase-immunoreactive nerve fibers innervating circumvallate papillae of the tongue was substantially increased in transgenic mice that overexpressed nerve growth factor (NGF) when compared with age-matched controls. The fiber density was age-dependent. Only transgenic mice contained NGF-immunoreactive basal cells in the vicinity of taste buds, indicating that target-derived NGF induced novel hyperinnervation of the circumvallate papillae.