Extracellular matrix and neurite outgrowth

Human platelet lysate stimulates neurotrophic properties of human adipose-derived stem cells better than Schwann cell-like cells

BACKGROUND

Trauma-associated peripheral nerve injury is a widespread clinical problem causing sensory and motor disabilities. Schwann cells (SCs) contribute to nerve regeneration, mainly by secreting nerve growth factor (NGF) and brain-derived neurotrophic factor. In the last years, adipose-derived stem cells (ASCs) differentiated into SCs (SC-ASCs) were considered as promising cell therapy. However, the cell trans-differentiation process has not been effectively showed and presents several drawbacks, thus an alternative approach for increasing ASCs neurotrophic properties is highly demanded. In the context of human cell-based therapies, Good Manufacturing Practice directions indicate that FBS should be substituted with a xenogeneic-free supplement, such as Human Platelet Lysate (HPL). Previously, we demonstrated that neurotrophic properties of HPL-cultured ASCs were superior compared to undifferentiated FBS-cultured ASCs. Therefore, as following step, here we compared the neurotrophic properties of differentiated SC-like ASCs and HPL-cultured ASCs.

METHODS

Both cell groups were investigated for gene expression level of neurotrophic factors, their receptors and neuronal markers. Moreover, the expression of nestin was quantitatively evaluated by flow cytometry. The commitment toward the SC phenotype was assessed with immunofluorescence pictures. Proteomics analysis was performed on both cells and their conditioned media to compare the differential protein profile. Finally, neurotrophic abilities of both groups were evaluated with a functional co-culture assay, assessing dorsal root ganglia survival and neurite outgrowth.

RESULTS

HPL-cultured ASCs demonstrated higher gene expression of NGF and lower expression of S100B. Moreover, nestin was present in almost all HPL-cultured ASCs and only in one quarter of SC-ASCs. Immunofluorescence confirmed that S100B was not present in HPL-cultured ASCs. Proteomics analysis validated the higher expression of nestin and the increase in cytoskeletal and ECM proteins involved in neural regeneration processes. The co-culture assay highlighted that neurite outgrowth was higher in the presence of HPL-ASCs or their conditioned medium compared to SC-ASCs.

CONCLUSIONS

All together, our results show that HPL-ASCs were more neurotrophic than SC-ASCs. We highlighted that the HPL triggers an immature neuro-induction state of ASCs, while keeping their stem properties, paving the way for innovative therapies for nerve regeneration.

Extracellular Matrix Regulation in Physiology and in Brain Disease

The extracellular matrix (ECM) surrounds cells in the brain, providing structural and functional support. Emerging studies demonstrate that the ECM plays important roles during development, in the healthy adult brain, and in brain diseases. The aim of this review is to briefly discuss the physiological roles of the ECM and its contribution to the pathogenesis of brain disease, highlighting the gene expression changes, transcriptional factors involved, and a role for microglia in ECM regulation. Much of the research conducted thus far on disease states has focused on "omic" approaches that reveal differences in gene expression related to the ECM. Here, we review recent findings on alterations in the expression of ECM-associated genes in seizure, neuropathic pain, cerebellar ataxia, and age-related neurodegenerative disorders. Next, we discuss evidence implicating the transcription factor hypoxia-inducible factor 1 (HIF-1) in regulating the expression of ECM genes. HIF-1 is induced in response to hypoxia, and also targets genes involved in ECM remodeling, suggesting that hypoxia could contribute to ECM remodeling in disease conditions. We conclude by discussing the role microglia play in the regulation of the perineuronal nets (PNNs), a specialized form of ECM in the central nervous system. We show evidence that microglia can modulate PNNs in healthy and diseased brain states. Altogether, these findings suggest that ECM regulation is altered in brain disease, and highlight the role of HIF-1 and microglia in ECM remodeling.

Extracellular matrix and synapse formation

The extracellular matrix (ECM) is a complex molecular network distributed throughout the extracellular space of different tissues as well as the neuronal system. Previous studies have identified various ECM components that play important roles in neuronal maturation and signal transduction. ECM components are reported to be involved in neurogenesis, neuronal migration, and axonal growth by interacting or binding to specific receptors. In addition, the ECM is found to regulate synapse formation, the stability of the synaptic structure, and synaptic plasticity. Here, we mainly reviewed the effects of various ECM components on synapse formation and briefly described the related diseases caused by the abnormality of several ECM components.

Glycosylated clusterin species facilitate Aβ toxicity in human neurons

Clusterin (CLU) is one of the most significant genetic risk factors for late onset Alzheimer's disease (AD). However, the mechanisms by which CLU contributes to AD development and pathogenesis remain unclear. Studies have demonstrated that the trafficking and localisation of glycosylated CLU proteins is altered by CLU-AD mutations and amyloid-β (Aβ), which may contribute to AD pathogenesis. However, the roles of non-glycosylated and glycosylated CLU proteins in mediating Aβ toxicity have not been studied in human neurons. iPSCs with altered CLU trafficking were generated following the removal of CLU exon 2 by CRISPR/Cas9 gene editing. Neurons were generated from control (CTR) and exon 2 -/- edited iPSCs and were incubated with aggregated Aβ peptides. Aβ induced changes in cell death and neurite length were quantified to determine if altered CLU protein trafficking influenced neuronal sensitivity to Aβ. Finally, RNA-Seq analysis was performed to identify key transcriptomic differences between CLU exon 2  -/- and CTR neurons. The removal of CLU exon 2, and the endoplasmic reticulum (ER)-signal peptide located within, abolished the presence of glycosylated CLU and increased the abundance of intracellular, non-glycosylated CLU. While non-glycosylated CLU levels were unaltered by Aβ_25-35 treatment, the trafficking of glycosylated CLU was altered in control but not exon 2  -/- neurons. The latter also displayed partial protection against Aβ-induced cell death and neurite retraction. Transcriptome analysis identified downregulation of multiple extracellular matrix (ECM) related genes in exon 2  -/- neurons, potentially contributing to their reduced sensitivity to Aβ toxicity. This study identifies a crucial role of glycosylated CLU in facilitating Aβ toxicity in human neurons. The loss of these proteins reduced both, cell death and neurite damage, two key consequences of Aβ toxicity identified in the AD brain. Strikingly, transcriptomic differences between exon 2  -/- and control neurons were small, but a significant and consistent downregulation of ECM genes and pathways was identified in exon 2  -/- neurons. This may contribute to the reduced sensitivity of these neurons to Aβ, providing new mechanistic insights into Aβ pathologies and therapeutic targets for AD.

Feasibility and application of polygenic score analysis to the morphology of human-induced pluripotent stem cells

Genome-wide association studies have identified thousands of significant associations between genetic variants and complex traits. Inferring biological insights from these associations has been challenging. One approach attempted has been to examine the effects of individual variants in cellular models. Here, I demonstrate the feasibility of examining the aggregate effect of many variants on cellular phenotypes. I examine the effects of polygenic scores for cross-psychiatric disorder risk, schizophrenia, body mass index and height on cellular morphology, using 1.5 million induced pluripotent stem cells (iPSC) from 60 European-ancestry donors from the Human iPSC Initiative dataset. I show that measuring multiple cells per donor provides sufficient power for polygenic score analyses, and that cross-psychiatric disorder risk is associated with cell area (p = 0.004). Combined with emerging methods of high-throughput iPSC phenotyping, cellular polygenic scoring is a promising method for understanding potential biological effects of the polygenic component of complex traits.

How the extracellular matrix shapes neural development

During development, both cells and tissues must acquire the correct shape to allow their proper function. This is especially relevant in the nervous system, where the shape of individual cell processes, such as the axons and dendrites, and the shape of entire tissues, such as the folding of the neocortex, are highly specialized. While many aspects of neural development have been uncovered, there are still several open questions concerning the mechanisms governing cell and tissue shape. In this review, we discuss the role of the extracellular matrix (ECM) in these processes. In particular, we consider how the ECM regulates cell shape, proliferation, differentiation and migration, and more recent work highlighting a key role of ECM in the morphogenesis of neural tissues.

Co-culture of osteocytes and neurons on a unique patterned surface

Neural and skeletal communication is essential for the maintenance of bone mass and transmission of pain, yet the mechanism(s) of signal transduction between these tissues is unknown. The authors established a novel system to co-culture murine long bone osteocyte-like cells (MLO-Y4) and primary murine dorsal root ganglia (DRG) neurons. Assessment of morphology and maturation marker expression on perlecan domain IV peptide (PlnDIV) and collagen type-1 (Col1) demonstrated that PlnDIV was an optimal matrix for MLO-Y4 culture. A novel matrix-specificity competition assay was developed to expose these cells to several extracellular matrix proteins such as PlnDIV, Col1, and laminin (Ln). The competition assay showed that approximately 70% of MLO-Y4 cells preferred either PlnDIV or Col1 to Ln. To co-culture MLO-Y4 and DRG, we developed patterned surfaces using micro-contact printing to create 40 μm × 1 cm alternating stripes of PlnDIV and Ln or PlnDIV and Col1. Co-culture on PlnDIV/Ln surfaces demonstrated that these matrix molecules provided unique cues for each cell type, with MLO-Y4 preferentially attaching to the PlnDIV lanes and DRG neurons to the Ln lanes. Approximately 80% of DRG were localized to Ln. Cellular processes from MLO-Y4 were closely associated with axonal extensions of DRG neurons. Approximately 57% of neuronal processes were in close proximity to nearby MLO-Y4 cells at the PlnDIV-Ln interface. The surfaces in this new assay provided a unique model system with which to study the communication between osteocyte-like cells and neurons in an in vitro environment.

Characterization of chondroitin sulfate from deer tip antler and osteogenic properties

Deer antler is a highly regenerative tissue that involves cellular differentiation, osteogenesis and ossification processes. Chondroitin sulfate is the major glycosaminoglycan contained in antler connective tissue and has been isolated from cartilaginous antler by 4 M GuHCl extraction, gradient ultracentrifugation and chromatography techniques. We examined the disaccharide composition by 2-AB labeling and anion exchange HPLC analysis of the three resultant fractions (high, medium and low density fractions). The high density fraction consists of A-unit and D-unit disaccharide in the ratio of 1:1, whereas, the CS disaccharide composition ratio of A- unit:C-unit:D-Unit:E-unit contained in medium and low density fractions are 3:4:3:1 and 2:2:2:1, respectively. The only intact CS oligosaccharides of the medium density fraction upregulated gene expression of bone-specific proteins of a human osteoblastic cell line (hFOB1.19). Thus, CS oligosaccharides from cartilaginous deer antler, with their oversulfated chondroitin sulfate composition, demonstrated the physiological properties and may be good candidates for osteogenetic agents in humans.

Two related but distinct chondroitin sulfate mimetope octasaccharide sequences recognized by monoclonal antibody WF6

Chondroitin sulfate (CS) proteoglycans are major components of cartilage and other connective tissues. The monoclonal antibody WF6, developed against embryonic shark cartilage CS, recognizes an epitope in CS chains, which is expressed in ovarian cancer and variably in joint diseases. To elucidate the structure of the epitope, we isolated oligosaccharide fractions from a partial chondroitinase ABC digest of shark cartilage CS-C and established their chain length, disaccharide composition, sulfate content, and sulfation pattern. These structurally defined oligosaccharide fractions were characterized for binding to WF6 by enzyme-linked immunosorbent assay using an oligosaccharide microarray prepared with CS oligosaccharides derivatized with a fluorescent aminolipid. The lowest molecular weight fraction recognized by WF6 contained octasaccharides, which were split into five subfractions. The most reactive subfraction contained several distinct octasaccharide sequences. Two octasaccharides, DeltaD-C-C-C and DeltaC-C-A-D (where A represents GlcUAbeta1-3GalNAc(4-O-sulfate), C is GlcUAbeta1-3Gal-NAc(6-O-sulfate), D is GlcUA(2-O-sulfate)beta1-3GalNAc(6-O-sulfate), DeltaCis Delta(4,5)HexUAalpha1-3GalNAc(6-O-sulfate), and DeltaDis Delta(4,5)HexUA(2-O-sulfate)alpha1-3GalNAc(6-O-sulfate)), were recognized by WF6, but other related octasaccharides, DeltaC-A-D-C and DeltaC-C-C-C, were not. The structure and sequences of both the binding and nonbinding octasaccharides were compared by computer modeling, which revealed a remarkable similarity between the shape and distribution of the electrostatic potential in the two different octasaccharide sequences that bound to WF6 and that differed from the nonbinding octasaccharides. The strong similarity in structure predicted for the two binding CS octasaccharides (DeltaD-C-C-C and DeltaC-C-A-D) provided a possible explanation for their similar affinity for WF6, although they differed in sequence and thus form two specific mimetopes for the antibody.

Interaction of Cochlear Nucleus Explants With Semiconductor Materials

OBJECTIVE/HYPOTHESIS

Implantable hearing devices such as cochlear implants and auditory brainstem implants deliver auditory information through electrical stimulation of auditory neurons. The combination of microelectronic electrodes with auditory nerve cells may lead to further improvement of the hearing quality with these devices. Whereas several kinds of neurons are known to grow on semiconductor substrates, interactions of cochlear nucleus (CN) neurons with such materials have yet to be described.

MATERIALS AND METHODS

To investigate survival and growth behavior of CN neurons on different semiconductor materials. CN explants from postnatal day 10 Sprague-Dawley rats were cultured for 96 hours in Neurobasal medium on polished and unpolished silicon wafers (p-type Si [100] and p-type Si3N4[100]) as well as plastic surface. These surfaces had been coated with poly-L-lysine and laminin. Neuronal outgrowth was examined using image analysis software after immunohistologic staining for neurofilament. Neurite length and directional changes were quantified. Additionally, neurite morphology and adhesion to the semiconductor material was evaluated by scanning electron microscopy.

RESULTS

Although proper adhesion of CN explants was seen, no neurite growth could be detected on unpolished silicon wafers (Si and Si3N4). Compared with the other test conditions, polished, laminin-coated Si3N4 wafers showed best biocompatibility regarding neurite length and number per explant. CN explants developed a mean of eight neurons with an average length of 236 mum in 96 hours of culture on these wafers.

CONCLUSION

The results of this study demonstrate the general possibility of CN neuron growth in culture on semiconductors in vitro. The differences in neuron length and number per explant indicate that the growth of CN neurons is influenced by the semiconductor substrate as well as extracellular matrix proteins, with laminin-coated p-type Si3N4[100] being a preferable material for future hybrid experiments on auditory-neuron semiconductor chips.

Roles of Eph receptors and ephrins in the normal and damaged adult CNS

Injury to the central nervous system (CNS) usually results in very limited regeneration of lesioned axons, which are inhibited by the environment of the injury site. Factors that have been implicated in inhibition of axonal regeneration include myelin proteins, astrocytic gliosis and cell surface molecules that are involved in axon guidance during development. This review examines the contribution of one such family of developmental guidance molecules, the Eph receptor tyrosine kinases and their ligands, the ephrins in normal adult CNS and following injury or disease. Eph/ephrin signaling regulates axon guidance through contact repulsion during development of the CNS, inducing collapse of neuronal growth cones. Eph receptors and ephrins continue to be expressed in the adult CNS, although usually at lower levels, but are upregulated following neural injury on different cell types, including reactive astrocytes, neurons and oligodendrocytes. This upregulated expression may directly inhibit regrowth of regenerating axons; however, in addition, Eph expression also regulates astrocytic gliosis and formation of the glial scar. Therefore, Eph/ephrin signaling may inhibit regeneration by more than one mechanism and modulation of Eph receptor expression or signaling could prove pivotal in determining the outcome of injury in the adult CNS.

The stop signal revised: immature cerebellar granule neurons in the external germinal layer arrest pontine mossy fiber growth

During the formation of neuronal circuits, afferent axons often enter target regions before their target cells are mature and then make temporary contacts with nonspecific targets before forming synapses on specific target cells. The regulation of these different steps of afferent-target interactions is poorly understood. The cerebellum is a good model for addressing these aspects, because cerebellar development is well defined and identified neurons in the circuitry can be purified and combined in vitro. Previous reports from our laboratory showed that cultured granule neurons specifically arrest the extension of their pontine mossy fiber afferents, leading us to propose that granule cells arrested growth of their afferents as a prelude to synaptogenesis. However, we knew little about the differentiation state of the cultured granule cells that mediate afferent arrest. In this study, we better define the purified granule cell fraction by marker expression and morphology, and demonstrate that only freshly plated granule cells in the precursor and premigratory state arrest mossy fiber outgrowth. Mature granule cells, in contrast, support extension, defasciculation, and synapse formation, as in vivo. In addition, axonal tracing in vivo during the first postnatal week indicates that immature mossy fibers extend into the Purkinje cell layer but never into the external germinal layer (EGL), where precursors of granule cell targets reside. We found that the stop-growing signals are dependent on heparin-binding factors, and we propose that such signals in the EGL restrict the extension of mossy fiber afferents and prevent invasion of proliferative regions.

Atypical presentation of a patient with both kallmann syndrome and a craniopharyngioma: case report and literature review

OBJECTIVE

To describe an unusual presentation of a patient with Kallmann syndrome, without the typical eunuchoid features, who had additional hormonal abnormalities caused by a craniopharyngioma.

METHODS

This patient's clinical features, endocrine evaluation, and treatment are described, and the literature regarding Kallmann syndrome is reviewed. The expected phenotype of Kallmann syndrome is contrasted with this case presentation. A literature search was also performed to determine whether the combination of craniopharyngioma and Kallmann syndrome had been described previously.

RESULTS

A 23-year-old man had a suprasellar tumor in conjunction with hypogonadotropic hypogonadism and growth hormone deficiency. Subsequently, he was also noted to have anosmia, a cleft palate, and bilateral olfactory bulb hypoplasia. His height was less than his calculated midparental height and exceeded his arm span. Defective neuronal migration in Kallmann syndrome is caused by absence of adhesion proteins needed for cellular, neuronal, and axonal guidance. This results in failure of olfactory and gonadotropin-releasing hormone neurons to complete normal migration. Defective migration can also cause midline craniofacial abnormalities, renal agenesis, and cardiovascular defects. Arachnoid cysts have been reported in two patients with Kallmann syndrome, although whether a migration defect underlies their occurrence is speculative. No prior reports of craniopharyngioma in a patient with Kallmann syndrome could be identified.

CONCLUSION

It is postulated that although this patient had Kallmann syndrome, he did not present with a eunuchoid body habitus because of concomitant growth hormone deficiency caused by his craniopharyngioma. Although midline craniofacial abnormalities have been seen in patients with Kallmann syndrome, this patient's craniopharyngioma seems more likely to be coincidental, rather than being one of the developmental anomalies that are part of the spectrum of this syndrome.

Differential functions of the C. elegans FGF receptor in axon outgrowth and maintenance of axon position

Wiring of the nervous system requires that axons navigate to their targets and maintain their correct positions in axon fascicles after termination of axon outgrowth. We show here that the C. elegans fibroblast growth factor receptor (FGFR), EGL-15, affects both processes in fundamentally distinct manners. FGF-dependent activation of the EGL-15 tyrosine kinase and subsequently the GTPase LET-60/ras is required within epidermal cells, the substratum for most outgrowing axon, for appropriate outgrowth of specific axon classes to their target area. In contrast, genetic elimination of the FGFR isoform EGL-15(5A), defined by the inclusion of an alternative extracellular interimmunoglobulin domain, has no consequence for axon outgrowth but leads to a failure to postembryonically maintain axon position within defined axon fascicles. An engineered, secreted form of EGL-15(5A) containing only its ectodomain is sufficient for maintenance of axon position, thus providing novel insights into receptor tyrosine kinase function and the process of maintaining axon position.

Differential sulfations and epimerization define heparan sulfate specificity in nervous system development

Heparan sulfate proteoglycans (HSPG) are components of the extracellular matrix through which axons navigate to reach their targets. The heparan sulfate (HS) side chains of HSPGs show complex and differentially regulated patterns of secondary modifications, including sulfations of distinct hydroxyl groups and epimerization of an asymmetric carbon atom. These modifications endow the HSPG-containing extracellular matrix with the potential to code for an enormous molecular diversity. Attempting to decode this diversity, we analyzed C. elegans animals lacking three HS-modifying enzymes, glucuronyl C5-epimerase, heparan 6O-sulfotransferase, and 2O-sulfotransferase. Each of the mutant animals exhibit distinct as well as overlapping axonal and cellular guidance defects in specific neuron classes. We have linked individual HS modifications to two specific guidance systems, the sax-3/Robo and kal-1/Anosmin-1 systems, whose activity is dependent on different HS modifications in different cellular contexts. Our results demonstrate that the molecular diversity in HS encodes information that is crucial for different aspects of neuronal development.

In vitro reconstitution of signal transmission from a hair cell to the growth cone of a chick vestibular ganglion cell

Signal transmission from a chick hair cell to the growth cone of a vestibular ganglion cell was examined by placing an acutely dissociated hair cell on the growth cone of a cultured vestibular ganglion cell. Electrical stimuli were applied to the hair cell while monitoring the intracellular Ca(2+) concentration ([Ca(2+)](i)) at the growth cone or recording whole-cell currents from the vestibular ganglion cell. Electrical stimulation of the hair cell induced [Ca(2+)](i) increases at the growth cone and inward currents in the vestibular ganglion cell. The [Ca(2+)](i) increase was blocked by 6-cyano-7-nitroquinoxaline (CNQX) (10 microM) but not by 2-amino-5-phosphonovaleric acid (APV; 50 microM). Glutamate (100 nM-300 microM) applied to the vestibular ganglion cell by the Y-tube method induced inward currents which were also antagonized by CNQX, but not by APV. These results indicate that the electrical stimulation of a hair cell induced glutamate or glutamate like agent release from the hair cell, which activated non-N-methyl-D-aspartate receptors at the growth cone of the vestibular ganglion cell, followed by action potentials and [Ca(2+)](i) elevation in the vestibular ganglion cell. This is the first demonstration of in vitro reconstitution of functional signal transmission from a hair cell to a vestibular ganglion cell.

Facilitation of learning and modulation of frontal cortex acetylcholine by ventral pallidal injection of heparin glucosaminoglycan

We examined the effects of heparin on learning and frontal cortex acetylcholine parameters following injection of the glucosaminoglycan into the ventral pallidum. In Experiment 1, possible mnemoactive effects of intrapallidal heparin injection were assessed. Rats with chronically implanted cannulae were administered heparin (0.1, 1.0, 10 ng) or vehicle (0.5 microl) and were tested on a one-trial step-through avoidance task. Two retention tests were carried out in each animal, one at 1.5 h after training to measure short-term memory and another at 24 h to measure long-term memory. Post-trial intrapallidal injection of 1.0 ng heparin improved both short- and long-term retention of the task, whereas the lower and the higher dose of the glucosaminoglycan had no effect. When the effective dose of heparin was injected 5 h, rather than immediately after training, it no longer facilitated long-term retention of the conditioned avoidance response. In Experiment 2, the effects of ventral pallidal heparin injection on frontal cortex acetylcholine and choline concentrations were investigated with in vivo microdialysis in anaesthetized rats. Heparin, administered in the dose of 1.0 ng, which was effective in facilitating avoidance performance, produced a delayed increase in cortical acetylcholine levels ipsi- and contralaterally to the side of intrabasalis injection, resembling the known neurochemical effects obtained for another glycosaminoglycan, chondroitin sulfate, which recently was shown to facilitate inhibitory avoidance learning and to increase frontal cortex acetylcholine. The present findings indicate that heparin, like other extracellular matrix proteoglycans, can exert beneficial effects on memory and strengthen the presumptive relationship between such promnestic effects of proteoglycans and basal forebrain cholinergic mechanisms. The data are discussed with respect to the presumed roles of matrix molecules in extrasynaptic volume transmission and in the 'cross-talk' between synapses.

Development of the facial midline

"Intellectual excellence lies in having faith in the observation of apparently nontranscendental and unimportant facts. To observe an anatomic element calmly, with an open, analytical spirit, and with spiritual freedom, can lead to an explosive vortex of new knowledge."-Miguel Orticochea, M.D.(1) Traditional descriptive embryology based upon the interaction of frontonasal, lateral nasal, and medial nasal prominences is incapable of explaining the three-dimensional development of the facial midline. The internal structure of the nose and that of the oronasal midline can best be explained by the presence of paired A fields originating from the prechordal mesendoderm, associated with the nasal and optic placodes, supplied by the internal carotid artery, and sharing a common genetic coding with the prosomeres of the forebrain. Mesial drift of these fields leads to fusion of their medial walls; this in turn provides bilateral functional matrics within which form the orbits ethmoids, lacrimals, turbinates, premaxillae, vomerine bones, and the cartilages of the nose. This two-part paper reports six lines of evidence supporting the field theory model of facial development: (1) An apparent watershed exists in the midline of the base between the territories of the internal and external carotid systems. Isolation of the ICA in injected fetal specimens confirmed that the demarcation was distinct and restricted to the embryonic nasal capsule. (2) Field theory explains the developmental anatomy of the contents of the nasal capsule. (3) The neuromeric model of CNS development provides a genetic basis for the anatomy and behavior of fields. (4) Mutants for the Dlx5 gene demonstrate A field deletion patterns. These experiments relate the nasal placode to the structures of the A fields. (5) Separate regions of the original nasal placodes give rise to neurons, which are dedicated to separate sensory and endocrine systems. The A fields constitute the pathways by which these neurons reach the brain. (6) Non-cleft lip-related cleft palate, holoprosencephaly, and the Kallmann syndrome are clinical models that demonstrate the effects of anatomic disturbances within the A fields.

Fibronectin and laminin elicit differential behaviors from SH-SY5Y growth cones contacting inhibitory chondroitin sulfate proteoglycans

Neuronal growth cones integrate signals from outgrowth-promoting molecules, e.g., laminin (LN) or fibronectin (FN), and outgrowth-inhibiting molecules, e.g., chondroitin sulfate proteoglycans (CSPGs), to navigate through extracellular matrix (ECM). Sensory neurons on LN typically turn to avoid areas rich in inhibitory CSPGs, whereas neuron-like cells of human origin (SH-SY5Y) preferentially stop/stall. These different behaviors may reflect differences in neuron type, response to outgrowth-promoters, or the mechanisms involved in outgrowth vs. inhibition. We used image analysis to determine the effects of different outgrowth promoters on the response of SH-SY5Y cells to inhibitory CSPGs. LN increased neurite initiation and elongation compared to cells plated either on endogenous matrix or FN. On a patterned substratum consisting of alternating stripes of FN and CSPGs, 59.6 +/- 9.3% of SH-SY5Y growth cones turned upon CSPG contact, whereas only 31.9 +/- 8.2% of growth cones turned at a LN/CSPG border. Growth cones on LN spread more upon contact with CSPG than growth cones on FN, whereas growth cones on LN or FN not contacting CSPGs were morphologically similar. Because it is known that integrins are involved in outgrowth on promoters, we analyzed integrin expression in response to inhibitory CSPGs in a choice assay. CSPGs did not induce increases or redistribution of several integrin subunits in SH-SY5Y cells. Furthermore, an anti-beta1 integrin function-blocking antibody did not alter growth cone behavior at a CSPG border. These results indicate that significant mechanistic differences may exist between outgrowth on homogenous outgrowth promoters and growth cone turning at inhibitory molecules.

Factors controlling axonal and dendritic arbors

The sculpting and maintenance of axonal and dendritic arbors is largely under the control of molecules external to the cell. These factors include both substratum-associated and soluble factors that can enhance or inhibit the outgrowth of axons and dendrites. A large number of factors that modulate axonal outgrowth have been identified, and the first stages of the intracellular signaling pathways by which they modify process outgrowth have been characterized. Relatively fewer factors and pathways that affect dendritic outgrowth have been described. The factors that affect axonal arbors form an incompletely overlapping set with those that affect dendritic arbors, allowing selective control of the development and maintenance of these critical aspects of neuronal morphology.

Inactivation of the glial fibrillary acidic protein gene, but not that of vimentin, improves neuronal survival and neurite growth by modifying adhesion molecule expression

Intermediate filaments (IFs) are a major component of the cytoskeleton in astrocytes. Their role is far from being completely understood. Immature astrocytes play a major role in neuronal migration and neuritogenesis, and their IFs are mainly composed of vimentin. In mature differentiated astrocytes, vimentin is replaced by the IF protein glial fibrillary acidic protein (GFAP). In response to injury of the CNS in the adult, astrocytes become reactive, upregulate the expression of GFAP, and reexpress vimentin. These modifications contribute to the formation of a glial scar that is obstructive to axonal regeneration. Nevertheless, astrocytes in vitro are considered to be the ideal substratum for the growth of embryonic CNS axons. In the present study, we have examined the potential role of these two major IF proteins in both neuronal survival and neurite growth. For this purpose, we cocultured wild-type neurons on astrocytes from three types of knock-out (KO) mice for GFAP or/and vimentin in a neuron-astrocyte coculture model. We show that the double KO astrocytes present many features of immaturity and greatly improve survival and neurite growth of cocultured neurons by increasing cell-cell contact and secreting diffusible factors. Moreover, our data suggest that the absence of vimentin is not a key element in the permissivity of the mutant astrocytes. Finally, we show that only the absence of GFAP is associated with an increased expression of some extracellular matrix and adhesion molecules. To conclude, our results suggest that GFAP expression is able to modulate key biochemical properties of astrocytes that are implicated in their permissivity.

Developmental regulation of alphav integrins produces functional changes in astrocyte behavior

To examine the role of the extracellular matrix in regulating astrocyte behavior we previously characterized alphav integrin expression on postnatal astrocytes in vitro and found that they express alphavbeta5 and alphavbeta8. Here we show that differentiation of immature cells into astrocytes is accompanied by developmental regulation of alphav integrins, downregulation of alphavbeta1 and alphavbeta8, and upregulation of alphavbeta5. In addition, using two previously described astrocyte cell lines, we found that the neurite-permissive A7 cell line expressed high levels of alphavbeta1 in addition to alphavbeta5 and alphavbeta8, while the neurite-inhibitory Neu7 cell line expressed only alphavbeta5. To examine integrin function we generated clones of the Neu7 cell line expressing alphavbeta1 or alphavbeta3 in addition to alphavbeta5. This showed that the parent Neu7 cells migrated more slowly than the A7 cells on fibronectin and vitronectin, but that Neu7 cells expressing alphavbeta1 or alphavbeta3 integrins showed enhanced migration on fibronectin and vitronectin, respectively. These results show that alphav integrin expression is regulated during astrocyte development and confirm an instructive role in cell migration for alphavbeta1 in embryonic cells and alphavbeta3 in astroglial tumors.

Impaired axonal regeneration in alpha7 integrin-deficient mice

The interplay between growing axons and the extracellular substrate is pivotal for directing axonal outgrowth during development and regeneration. Here we show an important role for the neuronal cell adhesion molecule alpha7beta1 integrin during peripheral nerve regeneration. Axotomy led to a strong increase of this integrin on regenerating motor and sensory neurons, but not on the normally nonregenerating CNS neurons. alpha7 and beta1 subunits were present on the axons and their growth cones in the regenerating facial nerve. Transgenic deletion of the alpha7 subunit caused a significant reduction of axonal elongation. The associated delay in the reinnervation of the whiskerpad, a peripheral target of the facial motor neurons, points to an important role for this integrin in the successful execution of axonal regeneration.

Integrin family of cell adhesion molecules in the injured brain: regulation and cellular localization in the normal and regenerating mouse facial motor nucleus

Integrins are a large family of heterodimeric glycoproteins that play a crucial role in cell adhesion during development, inflammation, and tissue repair. In the current study, we investigated the localization of different integrin subunits in the mouse facial motor nucleus and their regulation after transection of the facial nerve. In the normal mouse brain, there was clear immunoreactivity for alpha5-, alpha6-, and beta1-integrin subunits on blood vessel endothelia and for alphaM- and beta2-subunits on resting parenchymal microglia. Facial nerve transection led to an up-regulation of the beta1-subunit on the axotomized neurons and an increase in the alpha4-, alpha5-, alpha6-, beta1-, alphaM-, alphaX-, and beta2-subunits on the adjacent, activated microglia. Quantification of the microglial integrins revealed two different expression patterns. The subunits alpha5 and alpha6 showed a monophasic increase with a maximum at day 4, the alphaM-subunit a biphasic regulation, with an early peak at day 1 and an elevated plateau between day 14 and 42. At day 14, there was also an influx of lymphocytes immunoreactive for the alpha4beta1- and alphaLbeta2-integrins, which aggregated at sites of neural debris and phagocytotic microglia. This finding was accompanied by a significant increase of the alpha5beta1-integrin on blood vessel endothelia. In summary, facial axotomy is followed by a strong and cell-type-specific expression of integrins on the affected neurons and on surrounding microglia, lymphocytes, and vascular endothelia. The presence of several, strikingly different temporal patterns suggests a selective involvement of these molecules in the different adhesive events during regeneration in the central nervous system.

The DSD-1 carbohydrate epitope depends on sulfation, correlates with chondroitin sulfate D motifs, and is sufficient to promote neurite outgrowth

The neural chondroitin sulfate (CS) proteoglycan (PG) DSD-1-PG was originally identified with the monoclonal antibody (mAb) 473HD. It promotes neurite outgrowth of hippocampal neurons when coated as a substrate in the presence of polycations. This effect is inhibited by mAb 473HD that specifically recognizes the DSD-1 epitope. The DSD-1 epitope is also detectable in CS-C and CS-D preparations from shark cartilage but not in other chondroitin sulfates that are structurally related and differ in their sulfation patterns. Non-sulfated DSD-1-PG and chemically desulfated CS-D were not recognized by mAb 473HD, suggesting that the DSD-1 epitope depends on sulfation. It was possible to enrich DSD-1 epitope-bearing carbohydrates and D disaccharide units from CS-C and CS-D preparations on a mAb 473HD affinity matrix. This indicates that the DSD-1 epitope represents a distinct glycosaminoglycan structure containing D units. The analysis of glycosaminoglycan digestion products by high pressure liquid chromatography revealed that DSD-1-PG preparations contain a unique D disaccharide unit as well as an A, a C, and a non-sulfated disaccharide unit. In neurite outgrowth assays with hippocampal neurons, substrate-bound CS-D promoted neurite outgrowth, whereas CS-A, CS-B, or CS-C did not. This effect of CS-D was inhibited by mAb 473HD. DSD-1 epitope-enriched fractions obtained from CS-D and CS-C promoted neurite outgrowth, whereas CS-C had no such effect prior to enrichment on the mAb 473HD matrix. Based on these findings we conclude that the DSD-1 epitope by itself is sufficient to promote neurite outgrowth and that this activity is possibly associated with D motifs.

Beta1 integrin deficiency impairs migration and differentiation of mouse embryonic stem cell derived neurons

Cell-matrix interaction plays an important role during neuronal development, which is demonstrated by comparing wild type (D3)- and beta1 integrin-deficient (G201) embryonic stem cell derived neurons. In D3 preparations complex networks of functionally coupled neurons with bi- and multipolar morphologies develop. In contrast, neuronal differentiation is retarded in G201 derived neurons, recognised by limited migration and restricted morphological differentiation. Furthermore, beta1 integrin deficiency causes a delay in expression of major neurotransmitters like GABA and glutamate as well as of synaptophysin. These findings indicate a prominent role of beta1 integrin for both morphological and chemical differentiation.

Fine structure of extracellular matrix and basal laminae in two types of abnormal collagen production: L-proline analog-treated otocyst cultures and disproportionate micromelia (Dmm/Dmm) mutants

L-Azetidine-2-carboxylic acid (LACA), a naturally occurring vegetable imino acid, can be incorporated into mammalian proteins in place of proline, thereby eliciting an inhibitory effect on collagen secretion. Exposure of explants of the embryonic mouse inner ear to LACA reduces the number of collagen fibrils in the otic capsule, gives rise to a dose-dependent derangement of the basal lamina, and ultimately results in dysmorphogenesis and retarded differentiation of the inner ear. Disproportionate micromelia (Dmm) is an incomplete dominant form of dwarfism characterized by a reduced quantity of type II collagen in the cartilaginous extracellular matrix (ECM). Abnormal morphogenesis in homozygotic Dmm mice resembles the abnormal morphogenesis observed in LACA-exposed otic explants, resulting in malformed inner ears with a bulky cartilaginous capsule and a lack or reduction of defined perilymphatic spaces (Van De Water and Galinovic-Schwartz, 1987). In this study, we examined by ultrastructural analysis LACA-exposed otic explants and inner ears of Dmm/Dmm mouse embryos for abnormalities in the collagenous constituents of the basal laminae and capsular ECM. We demonstrate, in comparison to normal embryonic mouse inner ears, a reduction in collagen fibrils and irregular cytodifferentiation of chondrocytes in the ECM of LACA-exposed and Dmm/Dmm inner ears as well as in the basal laminae of LACA-exposed specimens. In addition, we provide evidence of dysmorphogenesis of the otic capsule and perilymphatic spaces in LACA-exposed explants. Moreover, while previous studies demonstrated the anomalous development of sensory structures in otocyst explants following LACA exposure, in this study we provide evidence of the normal morphogenesis of otic epithelial-derived sensory structures in homozygotic Dmm/Dmm mouse embryos.

Chondroitin/dermatan sulphate promotes the survival of neurons from rat embryonic neocortex

Recently we have shown that biglycan, a small chondroitin sulphate proteoglycan of the extracellular matrix, supports the survival of cultured neurons from the developing neocortex of embryonic day 15 rats. Here we investigate the structure-function relationship of this neurotrophic proteoglycan and show that chondroitin/dermatan sulphate chains are the active moieties supporting survival. Heparin, a highly sulphated glucosaminoglycan, is less active than the galactosaminoglycans (chondroitin-4-sulphate, chondroitin-6-sulphate and dermatan sulphate), whereas hyaluronic acid, an unsulphated glucosaminoglycan, does not support neuron survival. Galactosaminoglycans must be in direct contact with neurons to cause survival. Experiments with elevated potassium concentrations and antagonists of voltage-gated calcium channels exclude the involvement of membrane depolarization. However, genistein and an erbstatin analogue, which are inhibitors of tyrosine kinases with low specificity, abolished neuron survival in the presence of chondroitin/dermatan sulphate, whereas a selective inhibitor of neurotrophin receptor kinases (K252a) had no suppressive effect. Thus, yet unidentified tyrosine kinases are involved in the chondroitin/dermatan sulphate-dependent survival of neocortical neurons. In the embryonic stages of rat neocortical development chondroitin sulphate is mainly located in layers I, V and VI and the subplate. Chondroitin sulphate expression is maintained after birth, extends up to cortical layer IV on postnatal day 7, and is down-regulated until postnatal day 21 concomitant with the period of naturally occurring cell death. The latter observation is consistent with a putative role of chondroitin sulphate in the control of neuron survival during cortical histogenesis.

Cultured astrocytes express biglycan, a chondroitin/dermatan sulfate proteoglycan supporting the survival of neocortical neurons

Astrocyte-conditioned medium (ACM) supports the survival of rat E15 neocortical neurons. Using a microtiter assay for neuronal survival, we demonstrated that part of the survival activity is associated with a proteoglycan fraction obtained after two chromatographic steps: (1) preparative Q-Sepharose anion-exchange chromatography under non-denaturating conditions and (2) MonoQ chromatography in the presence of 8 M urea. Analytical SDS-polyacrylamide gradient gel electrophoresis of pooled active MonoQ-fractions (MQ-pool) revealed a broad proteoglycan band migrating with an apparent M(r) in the range of 150-400 kDa. Digestion of the MQ-pool with chondroitin-ABC-lyase yielded a major core protein of 50 kDa. In Western blots the high molecular weight (150-400 kDa) material as well as the 50 kDa core protein band were immunoreactive to chicken polyclonal antibodies raised against purified biglycan from rat meningeal fibroblasts. Northern blot analysis of total RNA prepared from highly enriched astrocyte cultures revealed a single 2.9 kb biglycan transcript. By using in situ hybridization we demonstrated that essentially all cells in these cultures expressed biglycan mRNA. Furthermore, highly purified biglycan from bovine cartilage was shown to markedly enhance survival of rat neocortical neurons. In conclusion, we have shown that astrocytes synthesize and release the small chondroitin/dermatan sulfate proteoglycan (CS/DSPG) biglycan, a molecule that was found to support survival of neocortical neurons in vitro.

Growth cone behavior in the presence of soluble chondroitin sulfate proteoglycan (CSPG), compared to behavior on CSPG bound to laminin or fibronectin

Proteoglycans (PGs) are complex macromolecules of the extracellular matrix (ECM) that have a wide variety of effects on developing and regenerating neurons in vivo and in vitro. One hypothesis regarding the mechanisms of PG regulation of neuronal behavior states that the conformation of PGs may be critical, and thus that ECM- or cell surface-bound PGs may operate differently than secreted (soluble) PGs. Therefore, this study examined differences between the effects of soluble chondroitin sulfate proteoglycan (CSPG) and substratum-bound CSPG on neuronal growth cone behavior. Dissociated chicken dorsal root ganglion (DRG) neurons were cultured on either laminin (LN) or fibronectin (FN), both sensory neurite outgrowth-promotin glycoproteins. CSPG (or chondroitin sulfate alone) was either bound to FN or LN, or was added to the culture media. Subsequently, using time lapse video microscopy and image analysis, this study measured: (1) neuronal attachment, (2) neurite outgrowth, (3) rate of neurite elongation, and (4) filopodial length and lifespan. To determine the site of CSPG action, DRG neurons were grown on either: CS-1, a FN peptide [Humphries M. J. et al. (1987) J. biol. Chem. 262, 6886-6892], or a recombinant FN protein, RFNIIIcs (Maejne, submitted), both of which permit DRG attachment and outgrowth but do not have recognized CSPG binding sites, and the resulting neuronal behavior was compared to that of DRG neurons grown on intact FN. The results of these studies confirm that the effect of CSPG on DRG neurons is concentration-, conformation- and substratum-dependent. On I.N, soluble CSPG had little to no effect on neurite initiation or outgrowth, while substratum-bound CSPG inhibited neurite outgrowth. In contrast, on FN, soluble CSPG inhibited neurite outgrowth and decreased the rate of neurite elongation. Soluble CSPG did not affect the length of sensory growth cone filopodia or filopodial lifespan on either LN or FN. From the FN fragment experiments, we found that: (1) soluble CSPG reduces neurite outgrowth on FN or FN fragments, but not on LN, up to 80%, and reduces elongation rate on FN up to 50%, and (2) soluble CSPG regulates neuronal behavior by binding directly to growth cones elongating on FN. Given that substratum-bound CSPG from a variety of sources is inhibitory to neurite outgrowth and to the rate of neurite elongation, while soluble CSPG often has different effects on growth cone behavior, the regulation of growth cone behavior by CSPGs may be dependent upon CSPG conformation. Further, CSPG may affect growth cone behavior by either binding to the substratum or by binding directly to growth cones.

Pertussis toxin specifically inhibits growth cone guidance by a mechanism independent of direct G protein inactivation

An assay employing patterned laminin substrata was used to screen for compounds that disrupt neurite guidance. One molecule, pertussis toxin, caused neurites to wander from patterns that normally guided them, yet had no significant effect on rates of neurite outgrowth. Wandering was greatest on patterns requiring frequent guidance (e.g., laminin stripes with periodic gaps). Surprisingly, the B oligomer of pertussis toxin, which lacks the subunit that inactivates G proteins, was equipotent at disrupting neurite guidance. Pertussis toxin probably acts by binding cell surface carbohydrates, since neurites lacking complex-type N-linked oligosaccharides were insensitive to the effects of the toxin. The B oligomer also blocked growth cone collapse induced by a brain membrane-derived factor; such factors are thought to act as repulsive guidance cues in vivo. That a single reagent can inhibit neuronal responses to both attractive and repulsive guidance cues suggests that such cues may share signaling pathways.

The effects of lyotropic anions on electric field-induced guidance of cultured frog nerves

1. Dissociated Xenopus neurites turn cathodally in small applied electric fields. Increasing the external polycation concentration alters the direction and extent of field-induced orientation. A decrease in membrane surface charge may underlie these effects. 2. Lyotropic anions increase membrane surface charge and we have examined the effect of perchlorate (ClO4-), thiocyanate (SCN-) and sulphate (SO4(2-)) on galvanic nerve orientation. 3. Perchlorate and SCN- had no effect on field-induced cathodal turning, whereas incubation with SO4(2-) was inhibitory. In addition to its effects on surface charge, SO4(2-) increases production of the second messengers diacylglycerol and inositol trisphosphate. Interestingly, lithium (Li+), a blocker of polyphosphoinositide metabolism, had a similar effect to SO4(2-) on field-induced neurite orientation. 4. We conclude that increasing surface charge with lyotropic anions neither enhances galvanotropic orientation nor underlies the inhibitory effects of SO4(2-) and suggest that modulation of galvanotropism by SO4(2-) occurs owing to changes in the inositolphospholipid second messenger system.

Ultrastructure of an identified array of growth cones and possible substrates for guidance in the embryonic medicinal leech, Hirudo medicinalis

The oblique muscle organizer (Comb- or C-cell) in the embryonic medicinal leech, Hirudo medicinalis, provides an amenable situation to examine growth cone navigation in vivo. Each of the segmentally iterated C-cells extends an array of growth cones through the body wall along oblique trajectories. C-cell growth cones undergo an early, relatively slow period of extension followed by later, protracted and rapid directed outgrowth. During such transitions in extension, guidance might be mediated by a number of factors, including intrinsic constraints on polarity, spatially and temporally regulated cell and matrix interactions, physical constraints imposed by the environment, or guidance along particular cells in advance of the growth cones. Growth cones and their environment were examined by transmission electron microscopy to define those factors that might play a significant role in migration and guidance in this system. The ultrastructural examination has made the possibility very unlikely that simple, physical constraints play a prominent role in guiding C-cell growth cones. No anatomically defined paths or obliquely aligned channels were found in advance of these growth cones, and there were no identifiable physical boundaries, which might constrain young growth cones to a particular location in the body wall before rapid extension. There were diverse associations with many matrices and basement membranes located above, below, and within the layer in which growth cones appear to extend at the light level. Additionally, a preliminary examination of myocyte assembly upon processes proximal to the growth cones further implicates a role for matrix-associated interactions in muscle histogenesis as well as process outgrowth during embryonic development.

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.

Developmental expression in the rat cerebellum of SC1, a putative brain extracellular matrix glycoprotein related to SPARC

In the nervous system, extracellular matrix (ECM) molecules have been shown to have effects on cell migration, process outgrowth and the survival of neurons. Recently we have described the molecular cloning of SC1, a putative brain extracellular matrix glycoprotein, showing partial similarity to the ECM glycoprotein SPARC/osteonectin. We have now examined the expression of SC1 during the development of the rat cerebellum at both the protein and mRNA levels. Our results indicate that SC1 is both temporally and spatially regulated during this process. Bergmann glial cells express SC1 mRNA and the resultant protein is deposited along the length of their radial fibres during the process of granule cell migration in the developing cerebellum. SC1 mRNA and protein is also found in the adult cerebellum, concentrated in the Bergmann glial cells and their radial processes, indicating that this putative ECM molecule continues to play roles in the central nervous system after migration and proliferative events have ceased.

Axonal glycoproteins with immunoglobulin- and fibronectin type III-related domains in vertebrates: structural features, binding activities, and signal transduction

The L1- and F11-like axonal glycoproteins, implicated in neurite outgrowth and fasciculation, are members of the Ig superfamily comprising multiple fibronectin type III-like domains. Their Ig-like and fibronectin type III-related domains are likely to be composed of seven beta-strands arranged in two opposing beta-sheets of highly similar topology. Whereas the F11-like molecules lack a transmembrane sequence and are anchored in the plasma membrane by a glycosylphosphatidylinositol, the L1-like molecules comprise cytoplasmic domains with highly conserved sequence motifs. Most of the latter proteins occur in different isoforms generated by alternative pre-mRNA splicing, which has not been documented for molecules of the F11 subgroup. L1-like proteins undergo heterophilic as well as homophilic interactions, whereas only the former mode of binding was observed for F11-like proteins. Evidence is accumulating that these Ig superfamily molecules with fibronectin type III-like domains are interacting in a complex manner with each other and molecules of the extracellular matrix. Investigations assigning structure to function reveal that their individual extracellular domains serve distinct binding activities. Recent studies also suggest that L1 and NCAM are implicated in the transduction of transmembrane signals.

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.

Epidermal growth factor and transforming growth factor-alpha can induce neuronal differentiation of rat pheochromocytoma PC12 cells under particular culture conditions

In rat pheochromocytoma PC12 cells, NGF induces neuronal differentiation. Upon stimulation with NGF, Ras is activated to a GTP-bound form, and the activated Ras can induce neuronal differentiation. Recently, we and others observed that epidermal growth factor (EGF) and transforming growth factor-alpha (TGF-alpha) can also activate Ras in PC12 cells. This is puzzling since previous reports indicated that EGF stimulates proliferation rather than differentiation in PC12 cells. In this paper, we re-examined the biological effect of EGF and TGF-alpha, and found that these factors can also induce neuronal differentiation under particular culture conditions. Not only the outgrowth of long neurites, but the induction of neurofilament proteins and the metalloprotease transin was also observed in the EGF- and TGF-alpha-stimulated cells. These data clearly indicate that in addition to NGF, EGF and TGF-alpha can also induce the differentiation of PC12 cells under particular conditions.