Understanding the molecules of neural cell contacts: emerging patterns of structure and function

Development of BDNF/NGF/IKVAV Peptide Modified and Gold Nanoparticle Conductive PCL/PLGA Nerve Guidance Conduit for Regeneration of the Rat Spinal Cord Injury

Spinal cord injuries are very common worldwide, leading to permanent nerve function loss with devastating effects in the affected patients. The challenges and inadequate results in the current clinical treatments are leading scientists to innovative neural regenerative research. Advances in nanoscience and neural tissue engineering have opened new avenues for spinal cord injury (SCI) treatment. In order for designed nerve guidance conduit (NGC) to be functionally useful, it must have ideal scaffold properties and topographic features that promote the linear orientation of damaged axons. In this study, it is aimed to develop channeled polycaprolactone (PCL)/Poly-D,L-lactic-co-glycolic acid (PLGA) hybrid film scaffolds, modify their surfaces by IKVAV pentapeptide/gold nanoparticles (AuNPs) or polypyrrole (PPy) and investigate the behavior of motor neurons on the designed scaffold surfaces in vitro under static/bioreactor conditions. Their potential to promote neural regeneration after implantation into the rat SCI by shaping the film scaffolds modified with neural factors into a tubular form is also examined. It is shown that channeled groups decorated with AuNPs highly promote neurite orientation under bioreactor conditions and also the developed optimal NGC (PCL/PLGA G1-IKVAV/BDNF/NGF-AuNP50) highly regenerates SCI. The results indicate that the designed scaffold can be an ideal candidate for spinal cord regeneration.

Design of IKVAV peptide/gold nanoparticle decorated, micro/nano-channeled PCL/PLGA film scaffolds for neuronal differentiation and neurite outgrowth

In the field of neural tissue engineering, intensive efforts are being made to develop tissue scaffolds that can support an effective functional recovery and neural development by guiding damaged axons and neurites. Micro/nano-channeled conductive biomaterials are considered a promising approach for repairing the injured neural tissues. Many studies have demonstrated that the micro/nano-channels and aligned nanofibers could guide the neurites to extend along the direction of alignment. However, an ideal biocompatible scaffold containing conductive arrays that could promote effective neural stem cell differentiation and development, and also stimulate high neurite guidance has not been fully developed. In the current study, we aimed to fabricate micro/nano-channeled polycaprolactone (PCL)/Poly-d,l-lactic-co-glycolic acid (PLGA) hybrid film scaffolds, decorate their surfaces with IKVAV pentapeptide/gold nanoparticles (AuNPs), and investigate the behavior of PC12 cells and neural stem cells (NSCs) on the developed biomaterial under static/bioreactor conditions. Here we show that channeled groups decorated with AuNPs highly promote neurite outgrowth and neuronal differentiation along linear lines in the presence of electrical stimulation, compared with the polypyrrole (PPy) coating, which has been used traditionally for many years. Hopefully, this newly developed channeled scaffold structure (PCL/PLGA-AuNPs-IKVAV) could help to support long-distance axonal regeneration and neuronal development after different neural damages.

Invertebrate models of kallmann syndrome: molecular pathogenesis and new disease genes

Kallmann Syndrome is a heritable disorder characterized by congenital anosmia, hypogonadotropic hypogonadism and, less frequently, by other symptoms. The X-linked form of this syndrome is caused by mutations affecting the KAL1 gene that codes for the extracellular protein anosmin-1. Investigation of KAL1 function in mice has been hampered by the fact that the murine ortholog has not been identified. Thus studies performed in other animal models have contributed significantly to an understanding of the function of KAL1. In this review, the main results obtained using the two invertebrate models, the nematode worm Caenorhabditis elegans and the fruit fly Drosophila melanogaster, are illustrated and the contribution provided by them to the elucidation of the molecular pathogenesis of Kallmann Syndrome is discussed in detail. Structure-function dissection studies performed in these two animal models have shown how the different domains of anosmin-1 carry out specific functions, also suggesting a novel intramolecular regulation mechanism among the different domains of the protein. The model that emerges is one in which anosmin-1 plays different roles in different tissues, interacting with different components of the extracellular matrix. We also describe how the genetic approach in C. elegans has allowed the discovery of the genes involved in KAL1-heparan sulfate proteoglycans interactions and the identification of HS6ST1 as a new disease gene.

Expression of small leucine-rich proteoglycans in the developing retina and kainic acid-induced retinopathy in ICR mice

The aim of this study was to determine the developmental changes of small leucine-rich proteoglycans (PGs), decorin, biglycan and fibromodulin, in ICR mouse retinas and to elucidate their role in the adult retina using kainic acid (KA)-induced retinal degeneration model. Retinas of prenatal, postnatal and adult mice were collected for histological and immunohistochemical staining to investigate the changes in distribution of these PGs. Decorin-and fibromodulin-immunostainings were diffusely distributed at prenatal and early postnatal stages and were stronger in the adult retina. However, biglycan was moderately distributed in the prenatal and early postnatal stages and was faint in the adult retina. Retinas were collected at 1, 3 and 7 days after intravitreal injection of KA. Retinas of KA injected eyes underwent shrinkage accompanied by serious damage in the inner layers. Decorin and fibromodulin were upregulated in the inner retinal layers of KA-injected eyes compared to the normal ones. Our results suggest that decorin and fibromodulin play key roles in retinal differentiation, and contribute to the retinal damage and repair process. However, biglycan may have no or only a limited role in the mouse retinal development or repair process.

Treatment with triamcinolone acetonide prevents decreased retinal levels of decorin in a rat model of oxygen-induced retinopathy

PURPOSE

To investigate the effect of triamcinolone acetonide (TA) on retinal expression of decorin in a rat model of oxygen-induced retinopathy (OIR).

MATERIALS AND METHODS

OIR was stimulated by exposing Sprague-Dawley (SD) rats to hyperoxia (80 +/- 1.3% O2) from postnatal day (P) 2 to P14 and then returning them to normoxia (room air, 21 +/- 1.5% O2). Control rats were maintained in normoxia. At P15, TA (40 mg/ml) was injected into the right vitreous of OIR rats and saline into the left vitreous of control rats. All rats were sacrificed at P18. RT-PCR, western blot and immunohistochemistry, TUNEL assay were performed to detect the effects of TA on molecular and morphological changes in retinal decorin levels in P18 OIR rats.

RESULTS

In P18 OIR rats, mRNA and protein of retinal levels and immunoreactivity of retinal decorin were significantly less (p-value = 0.0000000012, 0.0007, 0.000003; n = 5; respectively) than in control rats. In addition, neuronal cell death was increased in P18 OIR rats (p-value = 0.0028; n = 5) relative to controls. However, treatment with TA prevented the decrease of mRNA, protein levels, and immunoreactivity in retinal decorin in P18 OIR rats (p-value = 0.00023, 0.003, 0.000079; n = 5, respectively), and restored neuronal cell death in P18 OIR rats (p-value = 0.0022, n = 5).

CONCLUSION

Our results suggest that decorin is involved in hypoxic retinal damage and that TA protects retinal neurons damaged by relative hypoxia from decreased decorin levels.

The product of X-linked Kallmann's syndrome gene (KAL1) affects the migratory activity of gonadotropin-releasing hormone (GnRH)-producing neurons

X-linked Kallmann's syndrome (KS) is a genetic disease characterized by anosmia and hypogonadism due to impairment in the development of olfactory axons and in the migration of gonadotropin-releasing hormone (GnRH)-producing neurons. Deletions or point mutations of a gene located at Xp22.3 (KAL1) are responsible for the disease. This gene encodes for a secreted heparin-binding protein (KAL or anosmin-1) which exhibits similarities with cell-adhesion molecules. In the present study, we show for the first time a direct action of anosmin-1 on the migratory activity of GnRH neurons. Specifically, we exposed immortalized migrating GnRH neurons (GN11 cells) to conditioned media (CM) of COS or CHO cells transiently transfected with human KAL1 gene in microchemotaxis and collagen gel assays. We found that anosmin-1-enriched media produced a cell-specific chemotactic response of GN11 cells. None of the CM enriched on three forms of anosmin-1 carrying different missense mutations (N267K, E514K and F517L) found in patients affected by X-linked KS affected the chemomigration of GN11 cells. Anosmin binds to the GN11 cell surface by interacting with the heparan sulphate proteoglycans, and the chemotactic effect of anosmin-1-enriched CM can be specifically blocked by heparin or by heparitinase pretreatment. These results strongly suggest an involvement of anosmin-1 in the control of the migratory behaviour of GnRH neurons and provide novel information on the pathogenesis of KS.

Functional analysis of the domains of the C. elegans Ror receptor tyrosine kinase CAM-1

cam-1 encodes a Caenorhabditis elegans orphan receptor tyrosine kinase (RTK) of the Ror family that is required for cell migration and to orient cell polarity. Ror RTKs share a common domain structure. The predicted extracellular region contains immunoglobulin (Ig), cysteine-rich (CRD), and kringle (Kri) domains. Intracellularly are tyrosine kinase (Kin) and serine- and threonine (S/T)-rich domains. To investigate the functional requirement for CAM-1 domains in mediating cell migration, we engineered deletions that remove various domains and assessed the ability of these CAM-1 derivatives to rescue cam-1 mutant phenotypes. We find that the Ig, Kri, Kin, and S/T domains are dispensable for cell migration, but the CRD is required. Surprisingly, the entire intracellular region of CAM-1 is not required for proper cell migration. Most notably, a version of CAM-1 from which all domains besides the CRD and transmembrane domains have been deleted is able to rescue the migration of a single cell type, although not those of other cell types. Our results show that CAM-1 does not function exclusively as a canonical RTK and that it may function, at least in part, to regulate the distribution of a secreted ligand-possibly a Wnt protein.

RGD modified polymers: biomaterials for stimulated cell adhesion and beyond

Since RGD peptides (R: arginine; G: glycine; D: aspartic acid) have been found to promote cell adhesion in 1984 (Cell attachment activity of fibronectin can be duplicated by small synthetic fragments of the molecule, Nature 309 (1984) 30), numerous materials have been RGD functionalized for academic studies or medical applications. This review gives an overview of RGD modified polymers, that have been used for cell adhesion, and provides information about technical aspects of RGD immobilization on polymers. The impacts of RGD peptide surface density, spatial arrangement as well as integrin affinity and selectivity on cell responses like adhesion and migration are discussed.

Molecular modelling and experimental studies of mutation and cell-adhesion sites in the fibronectin type III and whey acidic protein domains of human anosmin-1

Anosmin-1, the gene product of the KAL gene, is implicated in the pathogenesis of X-linked Kallmann's syndrome. Anosmin-1 protein expression is restricted to the basement membrane and interstitial matrix of tissues affected in this syndrome during development. The anosmin-1 sequence indicates an N-terminal cysteine-rich domain, a whey acidic protein (WAP) domain, four fibronectin type III (FnIII) domains and a C-terminal histidine-rich region, and shows similarity with cell-adhesion molecules, such as neural cell-adhesion molecule, TAG-1 and L1. We investigated the structural and functional significance of three loss-of-function missense mutations of anosmin-1 using comparative modelling of the four FnIII and the WAP domains based on known NMR and crystal structures. Three missense mutation-encoded amino acid substitutions, N267K, E514K and F517L, were mapped to structurally defined positions on the GFCC' beta-sheet face of the first and third FnIII domains. Electrostatic maps demonstrated large basic surfaces containing clusters of conserved predicted heparan sulphate-binding residues adjacent to these mutation sites. To examine these modelling results anosmin-1 was expressed in insect cells. The incorporation of the three mutations into recombinant anosmin-1 had no effect on its secretion. The removal of two dibasic motifs that may constitute potential physiological cleavage sites for anosmin-1 had no effect on cleavage. Peptides based on the anosmin-1 sequences R254--K285 and P504--K527 were then synthesized in order to assess the effect of the three mutations on cellular adhesion, using cell lines that represented potential functional targets of anosmin-1. Peptides (10 microg/ml) incorporating the N267K and E514K substitutions promoted enhanced adhesion to 13.S.1.24 rat olfactory epithelial cells and canine MDCK1 kidney epithelial cells (P<0.01) compared with the wild-type peptides. This result was attributed to the introduction of a lysine residue adjacent to the large basic surfaces. We predict that two of the three missense mutants increase the binding of anosmin-1 to an extracellular target, possibly by enhancing heparan sulphate binding, and that this critically affects the function of anosmin-1.

Developmentally regulated expression of Thy-1 in structures of the mouse sensory-motor system

Thy-1 is a cell-surface molecule of the immunoglobulin superfamily which is expressed at high levels in the mature nervous system. Thy-1 has been implicated in regulating axonal outgrowth and synaptic function, but little is known regarding its cellular localization and expression in the central nervous system (CNS) during development or in adulthood. In this study, Thy-1 gene expression and protein localization were examined in sensory-motor and related areas of the adult and postnatally developing mouse CNS. Thy-1 mRNA expression was restricted to neurons; immunoreactivity was densely distributed throughout the neuropil of all regions examined, often delineated the neuronal plasmalemma, and labeled axons in white matter tracts of the brain and spinal cord. In adulthood, immunolabeling was regionally widespread and was present relatively homogeneously throughout all cell-dense layers of sensory-motor cortex, throughout most thalamic nuclei, globus pallidus, and spinal cord. Developmentally, however, Thy-1 expression and localization exhibited a spatially and temporally staggered sequence leading to the adult pattern. In sensory-motor cortex, Thy-1 expression in layer V preceded expression in other layers; in the barrel field, labeling of barrel septa preceeded a gradually increasing intensity of immunolabeling of barrel centers; in the thalamus, Thy-1 exhibited a differential onset and temporal pattern of expression across different nuclei associated with motor, sensory, or limbic systems; in the caudate nucleus, Thy-1 expression was greatest during the first postnatal week of life before declining during subsequent development. Taken together, the adult distribution and developmental patterns leading to it form a unique profile in comparison with other structurally related glycosyl-phosphatidylinositol (GPI)-anchored neural cell adhesion molecules. The pattern and timing of Thy-1 expression across layers and nuclei during early postnatal development are more complex than previously recognized, thus perhaps reflecting varied roles for Thy-1 in aspects of structural or functional maturation which proceed independently of the timing of neurogenesis, migration, and dendritic and axonal growth.

Enzymatic incorporation of bioactive peptides into fibrin matrices enhances neurite extension

Fibrin plays an important role in wound healing and regeneration, and enjoys widespread use in surgery and tissue engineering. The enzymatic activity of Factor XIIIa was employed to covalently incorporate exogenous bioactive peptides within fibrin during coagulation. Fibrin gels were formed with incorporated peptides from laminin and N-cadherin alone and in combination at concentrations up to 8.2 mol peptide per mole of fibrinogen. Neurite extension in vitro was enhanced when gels were augmented with exogenous peptide, with the maximal improvement reaching 75%. When this particular fibrin derivative was evaluated in rats in the repair of the severed dorsal root within polymeric tubes, the number of regenerated axons was enhanced by 85% relative to animals treated with tubes filled with unmodified fibrin. These results demonstrate that it is possible to enhance the biological activity of fibrin by enzymatically incorporating exogenous oligopeptide domains of morphoregulatory proteins.

Monoclonal antibody against a neuronal antigen impairs formation of the axon scaffold in grasshopper central nervous system

The pathway a growing axon follows is determined by a number of cues, including differential adhesion to surface molecules on axons and the matrix of the fascicles along which they grow. We have characterized the differential expression of an extracellular antigen and the effects of a monoclonal antibody against this molecule on the development of the grasshopper central nervous system (CNS). The 5C1 monoclonal antibody was generated against ganglion chains of grasshopper embryos; it labels cell bodies of newly differentiated neurons and their axons as they extend. Electron microscopy of embryos at 42% of development reveals that 5C1 labels neuronal filopodia, axons and somata, and areas of glial membrane in apposition to neurite fascicles. After 70% of development, labeling is lost from axon bundles, but remains on cell bodies. 5C1 also cross-reacts with an epitope expressed in Drosophila CNS during embryonic development. Enzymatic digestion suggests that the antigen recognized by the antibody is likely to be a glycolipid. In embryos exposed to 5C1 during early stages of development of the CNS, at the time when the first axons begin to extend, the formation of axon pathways is blocked or greatly delayed. Our results suggest that the 5C1 antigen participates in the formation of the axon scaffold and may play a functional role in the initiation and maintenance of axon outgrowth during early development of the CNS.

Three-dimensional migration of neurites is mediated by adhesion site density and affinity

Three-dimensional neurite outgrowth rates within fibrin matrices that contained variable amounts of RGD peptides were shown to depend on adhesion site density and affinity. Bi-domain peptides with a factor XIIIa substrate in one domain and a RGD sequence in the other domain were covalently incorporated into fibrin gels during coagulation through the action of the transglutaminase factor XIIIa, and the RGD-dependent effect on neurite outgrowth was quantified, employing chick dorsal root ganglia cultured two- and three-dimensionally within the modified fibrin. Two separate bi-domain peptides were synthesized, one with a lower binding affinity linear RGD domain and another with a higher binding affinity cyclic RGD domain. Both peptides were cross-linked into fibrin gels at concentrations up to 8.2 mol of peptide/mol of fibrinogen, and their effect on neurite outgrowth was measured. Both two- and three-dimensional neurite outgrowth demonstrated a bi-phasic dependence on RGD concentration for both the linear and cyclic peptide, with intermediate adhesion site densities yielding maximal neurite extension and higher densities inhibiting outgrowth. The adhesion site density that yielded maximal outgrowth depended strongly on adhesion site affinity in both two and three dimensions, with lower densities of the higher affinity ligand being required (0.8-1.7 mol/mol for the linear peptide versus 0.2 mol/mol for the cyclic peptide yielding maximum neurite outgrowth rates in three-dimensional cultures).

A laminin and nerve growth factor-laden three-dimensional scaffold for enhanced neurite extension

Agarose hydrogel scaffolds were engineered to stimulate and guide neuronal process extension in three dimensions in vitro. The extracellular matrix (ECM) protein laminin (LN) was covalently coupled to agarose hydrogel using the bifunctional cross-linking reagent 1,19- carbonyldiimidazole (CDI). Compared to unmodified agarose gels, LN-modified agarose gels significantly enhanced neurite extension from three-dimensionally (3D) cultured embryonic day 9 (E9) chick dorsal root ganglia (DRGs), and PC 12 cells. After incubation of DRGs or PC 12 cells with YIGSR peptide or integrin beta1 antibody respectively, the neurite outgrowth promoting effects in LN-modified agarose gels were significantly decreased or abolished. These results indicate that DRG/PC 12 cell neurite outgrowth promoting effect of LN-modified agarose gels involves receptors for YIGSR/integrin beta1 subunits respectively. 1,2-bis(10, 12-tricosadiynoyl)-sn-glycero-3-phosphocholine (DC(8,9)PC)-based lipid microcylinders were loaded with nerve growth factor (NGF), and embedded into agarose hydrogels. The resulting trophic factor gradients stimulated directional neurite extension from DRGs in agarose hydrogels. A PC 12 cell-based bioassay demonstrated that NGF-loaded lipid microcylinders can release physiologically relevant amounts of NGF for at least 7 days in vitro. Agarose hydrogel scaffolds may find application as biosynthetic 3D bridges that promote regeneration across severed nerve gaps.

Mosaic distribution of chondroitin and keratan sulphate in the developing rat striatum: possible involvement of proteoglycans in the organization of the nigrostriatal system

The striatum of the mammalian basal ganglia is composed of two neurochemically distinct compartments termed patches and matrix that contribute overall to a mosaic organization. Glycosaminoglycans (GAGs), the sugar moieties of proteoglycans, provide specific spatio-temporal guidance cues during the development of several functional neural systems. However, their distribution within the nigrostriatal system has not been investigated yet. Here, the immunohistochemical distributions of unsulphated (C0S), 4-sulphated (C4S) and 6-sulphated chondroitin (C6S) and keratan sulphate (KS) were examined in the developing neostriatum of rat and compared with the distribution of dopaminergic terminals. All the chondroitin sulphate (CS) isomers are homogeneously expressed in the embryonic striatum. After birth, C0S and C6S reveal the striatal mosaic in being preferentially expressed within the matrix compartment and in boundaries around patches whereas the C4S epitope is present in both compartments, with a slight patchy distribution. KS expression is detected first in the patches during the early postnatal period and subsequently only in the matrix compartment. All these GAG expressions disappear as the brain matures except for C4S which remains high throughout adult life. Furthermore, studies within the developing medial forebrain bundle reveal that CS isomers, but not KS, are expressed in and around the dopamine axonal tract but show similar developmental patterns of distribution which do not appear to be specifically associated with the nigrostriatal pathway. These results suggest a possible implication of proteoglycans during the development of the striatum and may be useful for understanding the complex cellular and molecular interactions in degeneration and plasticity of the nigrostriatal circuit in Parkinson's disease.

Congenital hydrocephalus: nosology and guidelines for clinical approach and genetic counselling

Congenital hydrocephalus is a serious condition that can arise from multiple causes. It comprises a diverse group of conditions which result in impaired circulation and absorption of cerebrospinal fluid. Congenital malformations of the central nervous system, infections, haemorrhage, trauma, teratogens and, occasionally, tumours can all give rise to hydrocephalus. In this paper we focus on the genetic aspects of hydrocephalus, excluding neural tube defects. The incidence is 0.4-0.8 per 1000 liveborns and stillbirths. X-linked hydrocephalus comprises approximately 5% of all cases. This condition is caused by mutations in the gene at Xq28 encoding for L1, a neural cell adhesion molecule. Carrier detection and prenatal diagnosis can be offered to affected families by means of chorionic villus biopsy and linkage analysis or L1 mutation analysis. In general, recurrence risk for congenital hydrocephalus excluding X-linked hydrocephalus, is low; empiric risk figures found in various studies range from <1% to 4%. Unfortunately, prenatal diagnosis based on an early ultrasound scan is not always reliable as ventriculomegaly usually starts after 20 weeks of gestation. We stress the importance of additional clinical investigations. Prognosis in the prenatally diagnosed patients depends on additional malformations but in general, is not very good.

CONCLUSION

Congenital hydrocephalus may be non-syndromic and syndromic. Prognosis depends primarily on the underlying cause and/or associated malformations, which have to be delineated on the basis of clinical, cytogenetic and molecular analysis.

Identification of Caenorhabditis elegans genes required for neuronal differentiation and migration

To understand the mechanisms that guide migrating cells, we have been studying the embryonic migrations of the C. elegans canal-associated neurons (CANs). Here, we describe two screens used to identify genes involved in CAN migration. First, we screened for mutants that died as clear larvae (Clr) or had withered tails (Wit), phenotypes displayed by animals lacking normal CAN function. Second, we screened directly for mutants with missing or misplaced CANs. We isolated and characterized 30 mutants that defined 14 genes necessary for CAN migration. We found that one of the genes, ceh-10, specifies CAN fate. ceh-10 had been defined molecularly as encoding a homeodomain protein expressed in the CANs. Mutations that reduce ceh-10 function result in Wit animals with CANs that are partially defective in their migrations. Mutations that eliminate ceh-10 function result in Clr animals with CANs that fail to migrate or express CEH-23, a CAN differentiation marker. Null mutants also fail to express CEH-10, suggesting that CEH-10 regulates its own expression. Finally, we found that ceh-10 is necessary for the differentiation of AIY and RMED, two additional cells that express CEH-10.

Genes necessary for C. elegans cell and growth cone migrations

The migrations of cells and growth cones contribute to form and pattern during metazoan development. To study the mechanisms that regulate cell motility, we have screened for C. elegans mutants defective in the posteriorly directed migrations of the canal-associated neurons (CANs). Here we describe 14 genes necessary for CAN cell migration. Our characterization of the mutants has led to three conclusions. First, the mutations define three gene classes: genes necessary for cell fate specification, genes necessary for multiple cell migrations and a single gene necessary for final positioning of migrating cells. Second, cell interactions between the CAN and HSN, a neuron that migrates anteriorly to a position adjacent to the CAN, control the final destination of the HSN cell body. Third, C. elegans larval development requires the CANs. In the absence of CAN function, larvae arrest development, with excess fluid accumulating in their pseudocoeloms. This phenotype may reflect a role of the CANs in osmoregulation.

The hypogastric and thirteenth thoracic ganglia of the rat: effects of age on the neurons and their extracellular environment

Morphometric analyses of the neurons and microvessels of perfusion-fixed hypogastric (HG) and 13th thoracic (T13) ganglia have been performed in male Wistar rats aged 4, 24 and 30 mo. Estimations of HG volume employing the Cavalieri principle have also been performed and showed that the size of the aged HG is increased by 42%. Routine histological staining of the ganglia with Masson's trichrome indicated that this may be due to the increased amount of interstitial connective tissue which was apparent in the aged animals. The number of neurons per unit area progressively decreased by 38% between ages 4 and 24 mo and by 16% between ages 24 and 30 mo in the HG and by 25% (4 and 24 mo) and 2% (24 and 30 mo) in the T13 ganglion. The total number of neurons in the HG however, estimated by a physical disector analysis, was constant with age. The number of microvessels per unit area, microvessel diameter, neuronal and nuclear areas did not differ significantly between the 3 age groups studied. This observed increase in ganglionic volume and decrease in neuronal packing density may be associated with changes in the extracellular matrix, in particular in glycosaminoglycans whose presence was indicated by metachromasia of the ganglia with toluidine blue. The extracellular matrix was therefore characterised using a panel of monoclonal antibodies against glycosaminoglycans and laminin. Chondroitin-6 sulphate and chondroitin-4 sulphate were present in the interstitial connective tissue, and there was an increase in the expression of both these epitopes at 24 mo, noteably surrounding neuron cell bodies. The expression of chondroitin-4 sulphate/dermatan sulphate was unchanged, thus implying a decreased expression of dermatan sulphate with age. Keratan sulphate and the native chondroitin sulphate epitopes were absent from the ganglia at both ages. Laminin expression was increased in the aged ganglia. It is therefore clear that the constituents of the extracellular matrix are not constant throughout the adult lifespan and that the extracellular matrix may influence neuronal survival in old age. This is the first report characterising age-related changes in the extracellular matrix of autonomic ganglia.

Spatiotemporal expression of CD15 in the developing chick retina

The spatiotemporal distribution pattern of the carbohydrate epitope CD15 was examined in the developing chick retina. CD15 expression appeared for the first time at E13 in the INL and GCL. The developmental profile of the INL, from E13 to E16, showed increasing numbers of stratified amacrine cells, whereas diffuse amacrine subtypes appeared later, beginning at E15. Smaller populations of bipolar cells were seen at E17. Three types of CD15-positive ganglion cells could be differentiated by E15. A gradient in the appearance of identified immunoreactive amacrine cells extended from the dorsotemporal to the ventral and nasal retina. The adult-like pattern of CD15 expression did not become established until E19. Adult-like densities of immunoreactive cells were reached toward the end of the embryonic period between E18 in the dorsotemporal and ventral retina, and E19 in the dorsonasal retina. In the adult-like retina, labelled cells became particularly numerous at its greatest circumference, and were most densely packed in the dorsotemporal retinal quadrant. From E16 to P5, three membrane-bound, CD15-positive glycoproteins of 20, 32 and 34 kDa were identified by Western blots. The time course in the appearance of the membrane-associated CD15 recognition molecule on differentiating amacrine, bipolar and ganglion cells is correlated to the establishment of synaptic contacts.

Distribution of vitronectin mRNA during murine development

Vitronectin (Vn) is not only a major adhesive glycoprotein in plasma but also regulates cell-mediated proteolytic enzyme cascades, including the complement, coagulation, and fibrinolytic systems. This broad functional activity suggests that Vn may also play a critical role in development. To begin to investigate this possibility, we studied Vn gene expression during murine embryogenesis. In situ hybridization analysis of embryonic tissues revealed Vn mRNA primarily in the liver and the central nervous system (CNS). In the liver, Vn mRNA was detected by day 10, the level increasing at later developmental stages. In the CNS, Vn mRNA was also detected as early as day 10 and was confined to the floor plate. However, as development proceeded, high levels of Vn transcripts became prominent in the meninges of the cortex and spinal cord, and in close proximity to brain capillaries. The perikarya of most neurons lacked Vn mRNA. Unexpectedly, high levels of Vn mRNA were associated with capillaries of the CNS, but not with blood vessels of peripheral organs. These results indicate that Vn is expressed in a spatially and temporally distinct pattern during murine embryogenesis, and suggest that the Vn transcript may be a CNS-specific vascular marker.

Distribution of a brain-specific proteoglycan, neurocan, and the corresponding mRNA during the formation of barrels in the rat somatosensory cortex

Neurocan is a developmentally regulated chondroitin sulphate proteoglycan in the rat brain. In the present study, spatiotemporal patterns of expression of neurocan and the corresponding mRNA were examined in the developing cortical barrel field of the rat brain by using a monoclonal antibody that was highly specific to neurocan and a riboprobe for a portion of the mRNA. Immunohistochemical analysis revealed that neurocan was distributed throughout the cerebral cortex during early postnatal development but was excluded from the centres of cortical barrels at the time of entry and arborization of thalamocortical axons. At this developmental stage, expression of neurocan mRNA was shown by in situ hybridization to be down-regulated in the barrel centres. When a row of whisker follicles was laser-cauterized on postnatal day 1, the pattern of expression of neurocan was disturbed in the row of barrels that corresponded to the lesioned whisker follicles in the contralateral somatosensory cortex. From these observations, it appears that neuronal stimuli through early thalamocortical fibres from the sensory periphery cause reduced expression of neurocan mRNA in neurocan-producing cells in the presumptive barrel centres. Our findings also suggest that the pattern of distribution of neurocan in early postnatal barrel fields may be due mainly to the down-regulation of expression of neurocan mRNA.

Recognition molecules myelin-associated glycoprotein and tenascin-C inhibit integrin-mediated adhesion of neural cells to collagen

Because of the importance of collagens in mediating cell-substrate interactions and the association of collagens with neural recognition molecules in the peripheral nervous system, the ability of neural recognition molecules to modify the substrate properties of collagens, in particular collagen type I, for cell adhesion was determined. Two cell lines, the N2A neuroblastoma and PC12 pheochromocytoma, were investigated for their capacity to adhere to different collagen types in the absence or presence of several neural recognition molecules. Adhesion of N2A or PC12 cells and membrane vesicles from PC12 cells to collagen type I was reduced when the collagen had been preincubated prior to its application as substrate with the extracellular domain of myelin-associated glycoprotein (s-MAG) or, as control, fibroblast tenascin-C (F-tenascin). In mixture with other collagen types, s-MAG was only able to reduce the adhesiveness of collagen types III and V, but not of collagen types II and IV. F-tenascin reduced the adhesiveness of all collagen types tested. In contrast to F-tenascin, s-MAG had to be present during fibrillogenesis to exert its effect, indicating that it must be coassembled into the collagen fibril to block the binding site. Cell adhesion to collagen type I was dependent on Mg2+ or Mn2+ and inhibited by a monoclonal antibody to the alpha 1 integrin subunit. The combined observations indicate that s-MAG and F-tenascin interfere with cell binding, most probably by modifying the integrin binding site, and that the two molecules act by different mechanisms, both leading to reduction of adhesion.

Segmental independence and age dependence of neurite outgrowth from embryonic chick sensory neurons

Targets in limb regions of the chick embryo are further removed from the dorsal root ganglia that innervate them compared with thoracic ganglion-to-target distances. It has been inferred that axons grow into the limb regions two to three times faster than into nonlimb regions. We tested whether the differences were due to intrinsic properties of the neurons located at different segmental levels. Dorsal root ganglia (DRG) were isolated from the forelimb, trunk, and hind limb regions of stage 25-30 embryos. Neurite outgrowth was measured in dissociated cell culture and in cultures of DRG explants. Although there was considerable variability in the amount of neurite outgrowth, there were no substantive differences in the amount or the rate of outgrowth comparing brachial, thoracic, or lumbosacral neurons. The amount of neurite outgrowth in dissociated cell cultures increased with the stage of development. Overall, our data suggest that DRG neurons express a basal amount of outgrowth, which is initially independent of target-derived neurotrophic influences; the magnitude of this intrinsic growth potential increases with stage of development; and the neurons of the DRG are not intrinsically specified to grow neurites at rates that are matched to the distance they are required to grow to make contact with their peripheral targets in vivo. We present a speculative model based on Poisson statistics, which attempts to account for the variability in the amount of neurite outgrowth from dissociated neurons.

In vitro analyses of neurite outgrowth indicate a potential role for tenascin-like molecules in the development of insect olfactory glomeruli

Tenascin-like material is associated with glial cells that form borders around developing glomerular units in the olfactory (antennal) lobe of the moth Manduca sexta and is present at critical stages of glomerulus formation (Krull et al., 1994, J. Neurobiol. 25:515-534). Tenascin-like immunoreactivity declines in the mature lobe, coincident with a wave of synapse formation within the glomeruli and glomerulus stabilization. Tenascin-like molecules associated with neuropilar glia are in the correct position to influence the branching patterns of growing neurites by constraining them to glomeruli. In this study, we examine the growth of cultured moth antennal-lobe neurons in response to mouse CNS tenascin. Uniform tenascin provides a poor substrate for cell-body attachment and neurite outgrowth. Neuronal cell bodies provided with a striped substratum consisting of tenascin and concanavalin-A (con-A)/laminin attach preferentially to con-A/laminin lanes. Most neurons restrict their branching to con-A/laminin lanes both at early and later times in culture but others send processes across multiple tenascin and con-/laminin lanes in an apparently indiscriminate manner. Tenascin can inhibit the neuritic outgrowth of most antennal-lobe neurons, and this raises the possibility that the tenascin-like molecules associated with neuropilar glia in vivo act to constrain growing neurites to glomeruli. Thus, glial cells, acting in concert with olfactory axons, might act to promote glomerular patterns of branching by antennal-lobe neurons.

Several receptor tyrosine kinase genes of the Eph family are segmentally expressed in the developing hindbrain

Pattern formation in the hindbrain involves a segmentation process leading to the formation of metameric units, manifested as successive swellings known as rhombomeres (r). In search for genes involved in cell-cell interactions during hindbrain segmentation, we have screened for protein kinase genes with restricted expression patterns in this region of the CNS. We present the cloning of three novel mouse genes, Sek-2, Sek-3 and Sek-4 (members of the Eph subfamily of putative transmembrane receptor protein tyrosine kinases (RTKs)), the identification of their chromosomal locations, and the analysis of their expression between 7.5 and 10.5 days of development. Before morphological segmentation, Sek-2 is transcribed in a transverse stripe corresponding to prospective r4 and the adjacent mesoderm, suggesting possible roles both in hindbrain segmentation and signalling between neuroepithelium and mesoderm. Sek-3 and Sek-4 have common domains of expression, including r3, r5 and part of the midbrain, as well as specific domains in the diencephalon, telencephalon, spinal cord and in mesodermal and neural crest derivatives. Together with our previous finding that Sek (Sek-1) is expressed in r3 and r5 (Gilardi-Hebenstreit et al., 1992; Nieto et al., 1992), these data indicate that members of the Eph family of RTKs may co-operate in the segmental patterning of the hindbrain.

Domain-specific activation of neuronal migration and neurite outgrowth-promoting activities of laminin

The ECM glycoprotein laminin has profound and varied actions on neurons in vitro. Little is known about how laminin's multiple domains and receptor-binding sites interact in determining its overall effects. Here, it is shown that laminin's ability to promote migration of olfactory epithelium neuronal cells maps to distal long arm domain E8 and is mediated by alpha 6 beta 1 integrin. Surprisingly, treatment of laminin with antibodies against its short arms (domains E1' or P1') uncovered a new neuronal migration-promoting activity, mediated by a beta 1 integrin other than alpha 6 beta 1. Laminin treated with anti-short arm antibodies also promoted beta 1 integrin-dependent neurite outgrowth from late embryonic retinal neurons, which are normally unresponsive to laminin. These "antibody-induced" migration and neurite outgrowth activities mapped to laminin's distal long arm, far from the site(s) of antibody binding. Evidence is presented that the induced activities are not actually cryptic in laminin, but are suppressed by an activity that is located in laminin's P1' domain and that may be lacking in the laminin homolog merosin.

Expression of HB-GAM (heparin-binding growth-associated molecules) in the pathways of developing axonal processes in vivo and neurite outgrowth in vitro induced by HB-GAM

HB-GAM (heparin-binding growth-associated molecule; p18) was previously isolated as a neurite outgrowth-promoting protein that is expressed at high levels in perinatal rat brain. cDNA cloning and expression revealed that HB-GAM is a novel secretory protein that is homologous with the retinoic acid-inducible MK protein. In the present paper we have used affinity-purified anti-peptide and anti-protein antibodies to study the expression of HB-GAM in the developing nervous system of the rat. In general, HB-GAM accumulates to extracellular structures that line growing axonal processes but is absent or only occurs at low levels in the axonal pathways after neurite extension has essentially ceased. During early stages of the nervous system development, HB-GAM is strongly expressed in the developing fiber tracts of the peripheral nervous system on embryonic days 12-14 (E12-E14). In the early central nervous system, HB-GAM is first expressed in a radial pattern along the neuroepithelial cells on E11-E12 and in early ascending neuron fibers in superficial layers of the brain vesicles on E12-E14. On E16-E18, HB-GAM is strongly expressed in the subplate and the marginal zone of the primordial neocortex. After this local expression in the primordial brain, HB-GAM is more widely expressed in the pathways of the developing axons during the late embryonic and early postnatal period. We have also extended in vitro studies on the interactions of HB-GAM with perinatal rat brain neurons by creating patterned substrates of HB-GAM upon culture wells and upon mixtures of extracellular matrix structures. These studies confirm the neurite-promoting effect of HB-GAM and suggest, together with the patterns of tissue localization, that HB-GAM may also guide axonal processes of brain neurons. The interactions of HB-GAM with brain neurons are specifically inhibited by heparin and its fragments and by incubation of the neurons with heparitinase. We suggest that in developing nervous tissues HB-GAM is deposited to an extracellular location in developing axon pathways and it interacts with heparin-like molecules of the neuron surface to promote formation of neural connections.

Biochemical and cytological characterization of DROP-1: a widely distributed proteoglycan in Drosophila

Using Drosophila testis as a source of antigen, 12 monoclonal antibodies were isolated that all recognize a set of three high molecular weight molecules present on Drosophila sperm and also in the fertilized egg. Among these antibodies, one is highly specific for sperm, while the remaining 11 detect epitopes present not only on sperm, but also in yolk spheres or in a punctate distribution in the egg. Here we cytologically and biochemically characterize the (common) antigens to five of these antibodies. Several biochemical properties suggest that these antibodies recognize a family of glycosaminoglycan-containing proteoglycans: (1) three diffuse, poorly focused high molecular weight bands, all in excess of 200,000 Da were observed on Western blots of denaturing SDS gels; (2) all three bands have a pI in the range of 3.0-3.5; (3) the molecules are strongly resistant to proteolysis; (4) mild periodate oxidation renders the molecules reactive towards the derivatizing agent digoxygenin-hydrazide, indicating the likely presence of saccharide moieties; (5) trifluoromethyl sulfonic acid treatment, which removes saccharide moieties, shifts the pI to 7.0; (6) beta-elimination increases electrophoretic mobility of the antigens on SDS gels; (7) nitrous acid treatment, which cleaves N-sulfated glycosaminoglycans, also increases the electrophoretic mobility of the antigens on SDS gels. We conclude that the antigens recognized by these antibodies are likely to be heparan sulfate proteoglycans. These results indicate that DROP-1 may represent a family of proteoglycans present during embryogenesis and later stages of development in Drosophila. DROP-1 represents the third proteoglycan to be characterized in Drosophila.

Spatiotemporal pattern of expression of tenascin-like molecules in a developing insect olfactory system

During the development of the olfactory (antennal) lobe of the moth Manduca sexta, olfactory sensory axons induce glomerular branching patterns in their target neurons. Glial cells, by surrounding the developing glomerular template, are thought to mediate the developmental influence of olfactory axons on these branching patterns. Previous studies have demonstrated that, in the absence of glia, neurons in the antennal lobe branch in an aglomerular fashion, even in the presence of competent antennal axons (Oland and Tolbert, 1988, J. Comp. Neurol. 278:377-387; Oland et al., 1988, J. Neurosci. 8:353-367). We have begun to explore the molecular basis by which glial cells could influence patterns of neurite branching. For this work, we have utilized immunocytochemical techniques and a partial biochemical analysis to demonstrate that molecules antigenically similar and comparable in size to mammalian tenascin are localized on the neuropil-associated glial cells that form borders around glomeruli in the developing antennal lobe. These tenascin-like molecules associated with neuropilar glia are present at critical stages of glomerulus development; tenascin-like immunoreactivity declines after glomeruli form and become stabilized. Neither the arrival nor the absence of antennal axons in the lobe induces changes in either the molecular forms or the amounts of tenascin-like molecules. The spatiotemporal pattern of expression of tenascin-like molecules suggests that they are in a position to participate in the formation of a glomerular neuropil and could form a molecular barrier that constrains neurite outgrowth strictly to glomeruli.

Isolation and partial characterization of a cell-surface heparan sulfate proteoglycan from embryonic rat spinal cord

Cell-surface heparan sulfate proteoglycans (HSPGs) are potential mediators of neuronal cell adhesion, spreading, and neurite outgrowth on various extra-cellular matrix molecules. One possible site of HSPG attachment is a heparin binding domain of fibronectin, which is present in the synthetic peptide FN-C/H II. In this study, HSPGs extracted from embryonic rat spinal cord by detergent were purified by ion-exchange chromatography, gel filtration, and affinity chromatography on an agarose column coupled with FN-C/H II conjugated to ovalbumin (OA). Heparitinase treatment of the iodinated HSPG fraction led to the appearance of a major protein core with a molecular size of 72 kDa, as determined by reducing SDS-PAGE. The intact proteoglycan has a molecular size of approximately 150-165 kDa, containing heparan sulfate glycosaminoglycan chains of about 10-15 kDa. Anti-HSPG antibodies recognized the 72 kDa core protein by immunoblotting, and stained the surface of spinal cord neurons, oligodendrocytes, and a subset of astrocytes. These results identify a cell-surface HSPG that may mediate neuron-substratum or neuron-glia interactions in embryonic central nervous system.

Expression and functional roles of neural cell surface molecules and extracellular matrix components during development and regeneration of peripheral nerves

By combining both immunocytochemical and functional investigations, a hypothetical framework will be developed for the molecular mechanisms underlying neuron-glia interactions during development and regeneration of peripheral nerves. In particular, the immunoglobulin-like molecules L1, N-CAM, MAG and P0, the extracellular matrix molecules laminin and tenascin, and the carbohydrates PSA and L2/HNK-1 will be considered. During early stages of limb bud innervation in embryos, L1 and N-CAM are expressed on axons and Schwann cells and are involved in axonal fasciculation, whereas tenascin is thought to be involved in forming a scaffold around the nerve possibly preventing axons and/or Schwann cells from leaving the nerve. PSA has been shown to be involved in pathway selection at initial stages of limb bud innervation. Later on, when motor axons enter muscles, the carbohydrates determine the branching pattern of the nerves. During myelination, L1 appears to play a pivotal role during the formation of the first Schwann cell loops around the prospective myelin-containing axons. MAG and P0 appear also to be functionally involved at initial stages of myelin formation. Additionally, MAG may contribute to the formation and maintenance of non-compacted myelin and axon-Schwann cell apposition whereas P0 is involved in myelin compaction. Under regenerative conditions, L1, N-CAM, laminin, and tenascin are strongly up-regulated by denervated Schwann cells. In vitro observations strongly suggest that these molecules might foster axonal regeneration. The carbohydrate PSA is confined to regrowing axons and is also a candidate to support axonal regrowth. L2/HNK-1, which is found on motor axon-associated Schwann cells, may provide regenerating motor axons with a selective advantage over others resulting in appropriate reinnervation of motor pathways. Since many of the functional studies this review refers to have been performed in vitro, some of the conclusions drawn need reexamination in vivo. Gene manipulations, such as the generation of null mutants followed by a thorough morphological and immunocytochemical investigation may be a powerful tool to resolve this problem.

Cerebroglycan: an integral membrane heparan sulfate proteoglycan that is unique to the developing nervous system and expressed specifically during neuronal differentiation

Heparan sulfate proteoglycans (HSPGs) are found on the surface of all adherent cells and participate in the binding of growth factors, extracellular matrix glycoproteins, cell adhesion molecules, and proteases and antiproteases. We report here the cloning and pattern of expression of cerebroglycan, a glycosylphosphatidylinositol (GPI)-anchored HSPG that is found in the developing rat brain (previously referred to as HSPG M13; Herndon, M. E., and A. D. Lander. 1990. Neuron. 4:949-961). The cerebroglycan core protein has a predicted molecular mass of 58.6 kD and five potential heparan sulfate attachment sites. Together with glypican (David, G., V. Lories, B. Decock, P. Marynen, J.-J. Cassiman, and H. Van den Berghe. 1990. J. Cell Biol. 111:3165-3176), it defines a family of integral membrane HSPGs characterized by GPI linkage and conserved structural motifs, including a pattern of 14 cysteine residues that is absolutely conserved. Unlike other known integral membrane HSPGs, including glypican and members of the syndecan family of transmembrane proteoglycans, cerebroglycan is expressed in only one tissue: the nervous system. In situ hybridization experiments at several developmental stages strongly suggest that cerebroglycan message is widely and transiently expressed by immature neurons, appearing around the time of final mitosis and disappearing after cell migration and axon outgrowth have been completed. These results suggest that cerebroglycan may fulfill a function related to the motile behaviors of developing neurons.

Expression of janusin (J1-160/180) in the retina and optic nerve of the developing and adult mouse

We have analyzed the expression of the oligodendrocyte-derived extra-cellular matrix molecule janusin (previously termed J1-160/180) in the retina and optic nerve of developing and adult mice using indirect light and electron microscopic immunocytochemistry, immunoblot analysis, and enzyme-linked immunosorbent assay. In the optic nerve, janusin is not detectable in neonatal and only weakly detectable in 7-day-old animals. Expression is at a peak in 2- or 3-week-old animals and subsequently decreases with increasing age. In the retina, expression increases until the third postnatal week and then remains at a constant level. In immunocytochemical investigations at the light microscopic level, janusin was found in the myelinated regions of the nerve with spots of increased immunoreactivity possibly corresponding to an accumulation of the molecule at the nodes of Ranvier. At the electron microscopic level, contact sites between unmyelinated axons, between axons and glial cells, and between axons and processes of myelinating oligodendrocytes were immunoreactive. Cell surfaces of astrocytes at the periphery of the nerve and forming the glial-limiting membrane, in contrast, were only weakly immunopositive or negative. In cell cultures of young postnatal mouse or rat optic nerves, oligodendrocytes and type-2 astrocytes, but not type-1 astrocytes were stained by janusin antibodies. In the oligodendrocyte-free retina, janusin was detectable in association with neuronal cell surfaces, but not with cell surfaces of Müller cells or retinal astrocytes. Our observations indicate that expression of janusin in the optic nerve and in the retina is developmentally differentially regulated and that other cell types, in addition to oligodendrocytes, express the molecule. Since the time course of janusin expression in the optic nerve coincides with the appearance of oligodendrocytes and myelin and since janusin is associated with cell surfaces of oligodendrocytes and outer aspects of myelin sheaths and is concentrated at nodes of Ranvier, we suggest that janusin is functionally involved in the process of myelination.

X-linked Kallmann syndrome. A neuronal targeting defect in the olfactory system?

Kallmann syndrome is a human genetic disorder characterized by the association of hypogonadism with the inability to smell, and is due to defects in the olfactory system development (i.e. incomplete migration of olfactory axons and of gonadotropin-releasing hormone producing neurons from the olfactory epithelium to the forebrain; aplasia or hypoplasia of olfactory bulbs and tracts). The human X-linked Kallmann syndrome gene and its chicken homologue have been cloned. Their protein products contain fibronectin type III repeats and a 'four-disulfide-core' domain also found in molecules that are involved in neural development. Consistent with the human phenotype, the chicken Kallmann gene is expressed in the developing olfactory bulb. At present the molecular and cellular mechanism of action of the Kallmann syndrome gene product is unknown. Based on expression studies and the characteristics domains of the predicted protein, it is hypothesized that the protein may be involved in targeting olfactory axons to the bulb. Alternatively, the Kallmann protein could be an extracellular matrix component required for the proper formation of the multilayered structure of the olfactory bulb.

Development of the cortical dysplasia of type II lissencephaly

A detailed neuropathological study of five immature brains with type II lissencephaly is reported. The cases described include two pairs of siblings. One infant survived for 2 months after birth, the others died at 18, 20, 20 and 32 weeks of gestation. This series of cases demonstrates the sequence in which the malformation develops from mid-gestation to post-natal life and shows that type II lissencephaly is not an intracortical malformation but is the result of massive glial and neuronal ectopia in the leptomeninges. This results from a failure of arrest of neuronal migration due to defects in the integrity of the pial/glial barrier.

Amyloid beta-protein as a substrate interacts with extracellular matrix to promote neurite outgrowth

Progressive deposition of amyloid beta-protein (A beta) in brain parenchyma and blood vessels is a characteristic feature of Alzheimer disease. Recent evidence suggests that addition of solubilized synthetic A beta to medium may produce toxic or trophic effects on cultured hippocampal neurons. Because soluble A beta may not accumulate in significant quantities in brain, we asked whether immobilized A beta peptide as a substrate alters neurite outgrowth from cultured rat peripheral sensory neurons. This paradigm may closely mimic the conditions in Alzheimer disease brain tissue, in which neurites contact insoluble, extracellular aggregates of beta-amyloid. We detected no detrimental effects of A beta substrate on neurite outgrowth. Rather, A beta in combination with low doses of laminin or fibronectin enhanced neurite out-growth from these neuronal explants. Our results suggest that insoluble A beta in the cerebral neuropil may serve as a neurite-promoting matrix, perhaps explaining the apparent regenerative response of neurites observed around amyloid plaques in Alzheimer disease. Moreover, in concert with the recent discovery of A beta production by cultured neurons, our data suggest that A beta plays a normal physiological role in brain by complexing with the extracellular matrix.

Expression pattern of the Kallmann syndrome gene in the olfactory system suggests a role in neuronal targeting

Kallmann syndrome is a genetic disorder characterized by a defect in olfactory system development, which appears to be due to an abnormality in the migration of olfactory axons and gonadotropin releasing hormone (Gn-RH) producing neurons. The X-linked Kallmann syndrome gene shares significant similarities with molecules involved in neural development. We have now isolated the evolutionarily conserved chicken homologue of the Kallmann gene. In the developing and adult chicken, high levels of expression were found in the mitral cells of the olfactory bulb (the target of olfactory axons) and in the Purkinje cells of the cerebellar cortex, both areas affected in patients with Kallmann syndrome. We propose a model in which the Kallmann syndrome gene product is a signal molecule required for neuronal targeting throughout life.

Isolation of sympathonectin; a substrate-bound protein which induces preferential growth of sympathetic fibers in vitro

A protein named 'sympathonectin', was purified from chick heart cell-conditioned medium (HCM), on the basis of its ability to direct the neurite outgrowth of cultured sympathetic neurons. The most purified fraction showed a doublet band on SDS-PAGE with an apparent molecular weight of 370 kDa. The biological activity of sympathonectin was over 100 times higher than that of laminin. Immunoblotting with anti-sympathonectin of the 100,000 x g pellet (particulate) fraction of HCM identified a distinct 370 kDa band; this molecule did not react to the anti-laminin serum. The immunohistochemical analysis showed that the antibody against sympathonectin stained heart tissue but not skeletal muscle tissue, whereas anti-laminin serum stained both tissues. These results suggest that sympathonectin may play a role during sympathetic innervation of target organs.

Guidance and topographic stabilization of nasal chick retinal axons on target-derived components in vitro

We studied mechanisms underlying the generation of topographic order within the developing chick retinotectal connection by combining the recently introduced stripe assay with a novel membrane protein fractionation technique. Our experiments show a preference of temporal and nasal retinal fibers for growing on cell membranes prepared from their proper target area. In addition, membrane preparations from posterior tectum were found to prolong substantially the survival of nasal neurites in vitro. We conclude that tropic as well as trophic interactions contribute to the generation of topographic maps during embryogenesis, in our case to the homing of nasal axons within the posterior tectum.

Synaptic organization and development of the antennal lobe in insects

Many insects possess a highly developed sense of smell. This paper summarizes the cellular and synaptic organization of the antennal (olfactory) lobe of the insect brain and then reviews morphological and fine-structural aspects of the development of the lobe. Visualization of synapses between classes of neurons identified by physiological, morphological, or transmitter-cytochemical properties has provided insights into arrangements of contacts and their possible roles in information processing. Studies of development have revealed the requirement for afferent axons from the antenna for the formation of olfactory glomeruli, where virtually all of the synapses in the lobe occur, and have suggested the possibility that glial cells play a role in the instructive influence of the axons on their target neurons in the lobe. The findings reviewed in this paper are primarily from one representative hemimetabolous insect, the American cockroach, and one representative holometabolous insect, a hawkmoth, and comparisons are made with vertebrate systems when appropriate.

Molecular and cellular properties of mammalian primary olfactory axons

How are the axonal projections of olfactory and vomeronasal receptor neurons to the olfactory bulb formed during development? How are the primary olfactory axonal connections functionally organized? With progress in molecular biological techniques and histochemical methods, it became possible to study cellular strategies and molecular mechanisms which guide the primary olfactory axons of the main and accessory olfactory systems to the target glomeruli in the bulb. In addition, new methodologies have begun to elucidate various subsets of the primary olfactory axons with distinctive central connections. The aim of the present paper is to review (1) the characteristic organization of the projection of the primary olfactory axons, (2) projection patterns of histochemically defined subsets of primary olfactory axons, and (3) information on molecules expressed by the surface membrane of the primary olfactory axons. This knowledge gives insight into the functional organization of the primary olfactory axon projection, which is indispensable for understanding signal processing in the olfactory system. This knowledge also underscores the notion that the primary olfactory axon projection provides an excellent model system in which to study axonal guidance and the formation of specific synaptic connections.

Neuronal cell cultures: a tool for investigations in developmental neurobiology

The aim of this review is to describe environmental requirements for survival of neuronal cells in culture, and secondly to survey the complex interplay between hormones, neurotrophic factors, transport- and extracellular matrix- proteins, which characterize the developmental program of differentiating neurons. An overall reconsideration of the literature in this vast field is above the limits of the present paper; since progress and refinement in the techniques of neuronal cell cultures have paralleled the advancement in Developmental Neurobiology, we will run instead through the main steps which form the conceptual framework of neuronal cell cultures.

Formation of the Drosophila larval photoreceptor organ and its neuronal differentiation require continuous Krüppel gene activity

The Drosophila segmentation gene Krüppel (Kr) is redeployed to play a critical role for the establishment of the larval visual system. Using reporter gene expression conducted by a specific Kr cis-acting element, we were able to trace back the origin of the larval photoreceptor organ, the Bolwig organ, to a single progenitor neuron and to examine Kr function in Bolwig organ development when Kr+ activity is absent from embryos due to specific mutations or reduced by neuron-specific and temporally restricted Kr antisense RNA expression. Our results show that Kr is required for neurons to differentiate into Bolwig organs, for fasciculation of the Bolwig nerve, and for this nerve to follow a specific pathway toward the synaptic targets in the larval brain. The transcription factor encoded by Kr is likely to regulate surface molecules necessary for neuronal cell adhesion and recognition in the developing larval visual system.

Plasticity of neuronal connections in developing brains of mammals

Although mature nervous systems show substantial malleability following various surgical or environmental manipulations, developing brains show far more prominent plasticity, particularly in terms of morphological features. Neuronal circuits, for example, can be dramatically rewired following neonatal but not adult brain lesions. It remains unknown why neuronal circuits in developing brains show such remarkable plasticity. A number of anatomical and physiological studies suggest that there are transient projections in developing brains and they are eliminated by cell death and/or collateral elimination as development proceeds. This raises a possibility that aberrant projections observed following various surgical or environmental manipulations such as partial denervation, results from retention or stabilization of transient projections. However, evidence suggests that cell death does not play an important role in developmental fine-tuning of neuronal projections. Furthermore, although the elimination of axon collaterals takes place, individual neurons appear to elaborate axonal arbors in appropriate target areas, resulting in a net increase in the size of axonal arbor emerging from individual neurons. In accord with these observations, the number of synapses appear to increase during the period when axonal elimination proceeds. Taken together, reinforcement of appropriate projections rather than elimination of excessive connections plays a major role in developmental specification of neuronal connections. Appearance of aberrant projections after partial denervation may not be a consequence of disordered axonal growth, since they form topographic maps which precisely mirrors those for normal projections. They may be induced due to reinforcement of pre-existing neuronal connections rather than to construction of novel pathways. Observations of axonal morphology in denervated areas indicate that lesion-induced enlargement of projections is due to transformation of axonal morphology, from simple and poorly branched to multiply branched. Perhaps such simple and poorly branched axons in inappropriate target areas may represent ones in the course of elimination but they may serve as a source of sprouting when denervated. In other words, after total elimination of axons any surgical or environmental manipulation cannot induce enlargement of projections. The mechanisms underlying such modifiability of neuronal connections remains unclarified but possible participation of an activity-dependent competitive mechanism is discussed.

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)

Identification of a 58-kDa antigen with increased immunoreactivity in the cerebella of multiple sclerosis patients

An increase in immunoreactivity associated with a 58-kDa antigen was found in a majority of MS cerebellar homogenates examined by Western blot analysis using antisera obtained by selective immunization of rabbits with autopsy cerebella. Two-dimensional immunoblotting demonstrated that the majority of the increased immunoreactivity observed in MS cerebella was associated with the highest apparent pI of three immunoreactive species at 58 kDa. Immuno-crossreaction with rat cerebellar homogenates demonstrated that the 58-kDa antigen was developmentally regulated, showing the greatest immunoreactivity at embryonic day 15. The 58-kDa cerebellar antigen may represent a membrane protein which is re-expressed as part of the onset of MS.