Laminin and the mechanism of neuronal outgrowth

This review summarizes the structure of the laminin molecule and the role it plays in development, pathfinding and regeneration in the vertebrate nervous system. Laminin has proven to be an influential glycoprotein of the extracellular matrix which guides and promotes the differentiation and growth of neurons. Its numerous domains, its association with carbohydrate moieties, and its many isoforms associated with specific sites and stages will be important in elucidating its function. How laminin's signals become translated into changes in the behavior of cells remains one of the thorniest issues facing scientists working at the interface between neuronal growth cone and extracellular matrix. New approaches using molecular biological tools and immunological tools for dissecting the laminin molecule have provided hints of intramolecular shifts in laminin's properties which influence cell behavior. These shifts occur in response to other molecules in the extracellular matrix such as carbohydrates, or in response to moieties on the cell surface itself. Thus, reduction of laminin's structure to fragments and ultimately polypeptide sequences is leading to renewed significance of laminin's tertiary and quaternary structure with respect to laminin's biological interactions. Such insights about laminin's structure are providing new tools for probing growth cone behavior, tools that need to be coupled with equally sophisticated analyses of growth cone behavior using biophysical and biochemical measures at a biological level suitable for analyzing responses induced by the probes.

Nerve compression syndromes as models for research on osteopathic manipulative treatment

Experimental and clinical studies of nerve compression syndromes show that ischemia or edema, singly or combined, causes responses in nerves that lead to alterations in impulse conduction and to commonly observed clinical signs. Because osteopathic manipulative treatment (OMT) is thought to affect microcirculation and anatomic positioning of structures, nerve compression syndromes appear ideal as models for studying how OMT accomplishes results. We recommend that researchers develop experimental protocols or clinical studies of nerve compression syndromes that will use anatomic, histologic, and physiologic criteria to monitor the effects of OMT. Techniques such as soft tissue, muscle energy, counterstrain, or myofascial release are appropriate for study in nerve compression syndromes. Such studies are necessary to understand the biologic basis of OMT.

Localization of the 110 kDa receptor for laminin in brains of embryonic and postnatal mice

Laminin, a large glycoprotein of the basement membrane that promotes the growth of nerve cell processes in vitro has also been detected in the brains of developing embryos in situ where it is postulated to promote or guide neural outgrowth. We have investigated the histological and developmental patterns of a receptor to a specific pentapeptide sequence in the A chain of the laminin molecule (PA22-2 or IKVAV) that has been identified as a neuron growth-promoting sequence. Standard immunocytochemical procedures were used to localize the receptor by means of a polyclonal antibody to affinity-purified receptor (MR = 110 kDa) from mouse brains. Results for postnatal stages (P) stages (P 1,7,8,25,30,and adult) show that the 110 kDa receptor is localized in fibers in the cortex and hippocampus, in astroglial cells at the surface of the cortex, and in neuronal cell bodies in the hippocampus. In contrast, the A-chain ligand is localized in cell bodies in the same regions at P stages. For embryonic stages (E) (E 14 and E 16) the receptor is localized in bundles of fibers in the superficial and deep cortical layers, and in cell bodies in these regions at E 14 only. Staining for the A chain ligand of the receptor was first seen postnatally. We speculate that the inverse histological pattern of receptor and ligand with respect to cell bodies and fibers may reflect a role in controlling axon guidance during development or repair during regeneration.

Characterization of a type IV collagen major cell binding site with affinity to the alpha 1 beta 1 and the alpha 2 beta 1 integrins

The aim of this investigation was to identify the domains of type IV collagen participating in cell binding and the cell surface receptor involved. A major cell binding site was found in the trimeric cyanogen bromide-derived fragment CB3, located 100 nm away from the NH2 terminus of the molecule, in which the triple-helical conformation is stabilized by interchain disulfide bridges. Cell attachment assays with type IV collagen and CB3 revealed comparable cell binding activities. Antibodies against CB3 inhibited attachment on fragment CB3 completely and on type IV collagen to 80%. The ability to bind cells was strictly conformation dependent. Four trypsin derived fragments of CB3 allowed a closer investigation of the binding site. The smallest, fully active triple-helical fragment was (150)3-amino acid residues long. It contained segments of 27 and 37 residues, respectively, at the NH2 and COOH terminus, which proved to be essential for cell binding. By affinity chromatography on Sepharose-immobilized CB3, two receptor molecules of the integrin family, alpha 1 beta 1 and alpha 2 beta 1, were isolated. Their subunits were identified by sequencing the NH2 termini or by immunoblotting. The availability of fragment CB3 will allow for a more in-depth study of the molecular interaction of a short, well defined triple-helical ligand with collagen receptors alpha 1 beta 1 and alpha 2 beta 1.

Quantitative distribution of chick neural crest cells during gangliogenesis

We have quantitated the distribution of chick neural crest cells after they have completed early migration and are aggregating into ganglia. Variables tested for an influence on the distribution of cells include stage, level of somites, position in each of the primary body axes, and individual embryo. The 11th-15th cervical somites of embryos at stages 30, 35, and 40 somites (s) incubated for 2.5, 3.0, and 3.5 days were labeled with antibody to HNK-1 to detect neural crest cells, and doubly labeled with antibody to HNK-1 and to the 150 kD neurofilament subunit to detect neural crest-derived neurons. Significantly more neural crest cells appear at older stages, but cells are uniformly distributed among the 11th-15th somites at any given stage. Significant differences in the total number of neural crest cells among three embryos sampled at the same stage indicate that the number of cells is independent of the staging series used. As early as the 35 s stage about one-third of the neural crest cells throughout the somite exhibit NF staining. At the 40 s stage, doubly labeled NF cells, as well as HNK-1 labeled cells, aggregate in a circumscribed portion of the mediolateral axis to form presumptive sensory ganglia in the dorsal region of the somites. Also at 40 s a wave of cell aggregation into sympathetic ganglia proceeds anteroposteriorly along the ventral border of the somitic mesenchyme. The results show a sequence of phenotypic expression beginning with neurofilament antigen, then ganglionic aggregation, and finally, in the case of sympathetic neurons, catecholamine transmitter.

Effect of cytochalasin D on the adhesion of a neuroblastoma x glioma cell line (NG108-15) to laminin and plastic substrates

Adhesion of the neuronal cell surface to its underlying substrate plays an important role in neurite outgrowth in vitro. I have investigated the adhesive basis for neurite outgrowth in the presence of cytochalasin D, a disruptor of actin-containing microfilaments, and in the presence of vinblastine, a depolymerizer of microtubules. Scanning electron microscopy shows that cytochalasin D does not alter the branching configuration of filopodia on a laminin substrate, although processes are shorter and tapered distally in the presence of the drug. Using a standard attachment assay for the neuroblastoma x glioma cell line (NG108-15) I show that vinblastine does not influence attachment of NG108-15 cells to either plastic or laminin. Cytochalasin D-treated cells normally attach to high concentrations of a laminin substrate (20 micrograms/ml). However, when cell are seeded on a laminin substrate at lower concentrations (0.001-10 micrograms/ml), or on YIGSR, a fragment of laminin, cytochalasin D increases cell attachment. Cytochalasin D increases attachment in a dose-dependent manner when cells are seeded on plain polystyrene plastic, so that the number of cells attached to plastic in 1 microM cytochalasin D is similar to the number attached to laminin (20 micrograms/ml). Combining low concentrations of cytochalasin D and laminin results in greater attachment than with either agent alone. Mild trypsinization of the cell surface reduces the CD-enhanced attachment to plastic, indicating that a protein on the cell surface may be involved. The effect of cytochalasin D appears to be cell specific since cytochalasin D does not affect the attachment of a fibroblast cell line (NIH 3T3) to laminin and plastic.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of hyaluronic acid on the emergence of neural crest cells from the neural tube of the quail, Coturnix coturnix japonica

Hyaluronic acid (HA) added to the medium of quail neural tubes explanted in vitro influences the number of migratory neural crest cells that emerge, compared with controls. Neural crest cells were counted with an ocular grid after 20 h of migration into 0.1 mm wide areas or 'bins' lying parallel to the neural tube, and the results were analyzed by linear regression. A low concentration of HA (5 micrograms/ml) significantly decreased the total number of neural crest cells in all bins adjacent to the neural tube, whereas several high concentrations of HA (250, 500, and 1000 micrograms/ml) significantly increased the number of neural crest cells. Intermediate concentrations of HA (50 and 100 micrograms/ml) did not differ from that of controls. Linear regressions of number of cells versus distance from the tube showed no significant differences among the slopes of control, low HA, and high HA treatments, providing evidence that HA does not influence the rate of cell migration. Scanning electron microscopy showed that cells in neuroepithelia exposed to low HA (5 micrograms/ml) appeared in tighter contact, while cells of neuroepithelia in high HA (500 micrograms/ml) appeared more loosely organized, compared with controls. Cells in tight contact could be restrained from leaving the neuroepithelium, whereas cells in loose contact could more readily move out of the neural tube, thus explaining the differences in cell numbers in low HA and high HA, respectively. We conclude that HA can be a factor in the differential adhesivity among neuroepithelial cells and may be important in the initial separation of the neural crest from the neural tube.

Effect of laminin and cytoskeletal agents on neurite formation by NG108-15 cells

Laminin promotes attachment and process formation in the neuroblastoma X glioma hybrid cell line NG108-15. As cells attached to laminin, they flattened and remained dispersed rather than associated in clumps. Process formation was observed within 1 hr after exposure to laminin and was dose dependent. Cycloheximide, an inhibitor of protein synthesis, did not block laminin-mediated attachment and neurite formation. Addition of drugs that depolymerize the cytoskeleton led to different behaviors for cells grown on plastic compared with those in the presence of laminin. Cells on plastic treated with either vinblastine or cytochalasin neither flattened nor grew processes. Cells plus laminin and vinblastine retracted processes, but remained flat, suggesting that laminin-induced processes can be destabilized by disrupting microtubules. Cells sequentially treated with laminin and cytochalasin produced processes that were thin and highly branched. Cells in high concentrations of cytochalasin on a laminin substrate formed aberrant processes even when their soma did not flatten. Since laminin counteracted the effect of cytochalasin on process outgrowth but did not alter the effect of cytochalasin on flattening of the cell body, different mechanisms mediated by microfilaments may be involved in cell flattening and in process formation.

Laminin receptors for neurite formation

Laminin, a basement membrane glycoprotein promotes both cell attachment and neurite outgrowth. Separate domains on laminin elicit these responses, suggesting that distinct receptors occur on the surface of cells. NG108-15 neuroblastoma-glioma cells rapidly extend long processes in the presence of laminin. We report here that 125I-labeled laminin specifically binds to these cells and to three membrane proteins of 67, 110, and 180 kDa. These proteins were isolated by affinity chromatography on laminin-Sepharose. The 67-kDa protein reacted with antibody to the previously characterized receptor for cell attachment to laminin. Antibodies to the 110-kDa and 180-kDa bands demonstrated that the 110-kDa protein was found in a variety of epithelial cell lines and in brain, whereas the 180-kDa protein was neural specific. Antibodies prepared against the 110-kDa and 180-kDa proteins inhibited neurite outgrowth induced by the neurite-promoting domain of laminin, whereas antibodies to the 67-kDa laminin receptor had no effect on neurite outgrowth. We conclude that neuronal cells have multiple cell-surface laminin receptors and that the 110-kDa and 180-kDa proteins are involved in neurite formation.

Role of basement membranes in cell differentiation

Extracellular matrices have diverse biological effects, including promoting the growth and differentiation of various cells of epithelial origin. The components of one of these matrices, the basement membrane, are discussed, as well as studies using these components alone or in combination with cells in culture. The particular response observed varies with the cell type examined and appears to be dependent on multiple interactions with components of the matrix. Potential uses for a basement membrane-derived matrix in vitro and in vivo are being developed.

Use of extracellular matrix components for cell culture

Extracellular matrix components when used as a substratum in vitro can greatly influence cell behavior. The response observed is dependent on the type of cell and matrix used. Cells in vitro usually respond best to the matrix components with which they are normally in contact in vivo. More differentiated phenotypes are observed and cells generally survive longer on such matrices. In some cases, the presence of such matrices allows cells to be cultured in the absence of serum and growth factors. As more investigators try the matrices and matrix components described, as well as new components and combinations of them, it is anticipated that improvement in the culture of many cells can be expected.

Development of extracellular matrix in chick paravertebral sympathetic ganglia

Alcian blue staining coupled with enzyme digestion or critical electrolyte staining revealed differences in the development of extracellular matrix (ECM) within sympathetic ganglia compared with the surrounding capsule. On day 5 of chick development (Hamburger-Hamilton stage 26) only hyaluronic acid (HA) could be detected in the ECM surrounding condensing primary ganglia. By day 7 (st 30) the ganglionic capsule contained HA, as well as sulfated glycosaminoglycans (GAGs), and this pattern continued into the adult stage. During the later stages of embryonic life (st 41-45) satellite cells appear, showing fine structural characteristics that point to their role in the secretion of intraganglionic ECM. Only during these stages could ECM be detected histochemically within ganglia, the same stages (days 15-19) when routine electron microscopic methods reveal collagen fibrils embedded in a granular ground substance. Thus, the intraganglionic environment appears as a separate compartment free of detectable amounts of GAG until late embryonic stages when ECM is secreted around satellite cells. This developmental pattern could represent a role of ECM in the histological stabilization of ganglia during the late stages of differentiation, since the appearance of intraganglionic ECM is correlated with the appearance of small dense-cored vesicles characteristic of adult neurons. The developmental pattern of ECM in differentiating sympathetic ganglia is compared with that of other tissues that undergo condensation and morphogenesis.

Development of chick paravertebral sympathetic ganglia. I. Fine structure and correlative histofluorescence of catecholaminergic cells

Paravertebral sympathetic ganglia from the lumbosacral region of a series of chick embryos have been studied with electron microscopic methods, including aldehyde-osmium and permanganate fixatives, and correlative histofluorescence (Grillo et al, '74). Our purpose was to assess the differentiation of catecholaminergic (CA) cells during histogenesis in ovo. Examination of comparable adult ganglia as a baseline for differentiating stages confirmed that the principal sympathetic neuron (PN) is similar to those of other species in that it contains predominately small dense-cored vesicles (SDCV) preserved only by permanganate, and does not histofluoresce following the method of Grillo et al. ('74). At embryonic day (E) 7--8, when ganglia have just formed, areas fluorescing bright yellow-green are correlated with two types of cells: 1) Neuroblasts with vesicular nuclei and large dense-cored vesicles (LDCV) are common. As the neuroblasts grow and differentiate, LDCV move away from perikaryal cytoplasm into developing processes. Around E13-15, LDCV appear in the neuroblasts which continue to develop until they resemble miniature adult PN in late embryos and hatchlings. 2) Granule (GR) cells with clumped chromatin and sparse cytoplasm are clustered in te ganglionic periphery at E7-8, but are rare. The GR cells increase somewhat in size and numbers by E11, but retail essentially the same characteristics as at earlier stages. Neither bright fluorescence nor GR cells appear later than stages E13-15. These results are interpreted to mean that when chick sympathetic stem cells have migrated from the primary ganglia into the paravertebral ganglia, they give rise to two separate lines of CA cells, one of which is not maintained and subsequently disappears. The results are significant as a basis for understanding how a mixed population of CA cells might arise within sympathetic ganglia in situ.

Fine structure of initial outgrowth of processes induced in a pheochromocytoma cell line (PC12) by nerve growth factor

Cells of the PC12 line (which is derived froma rat pheochromocytoma) develop neuron-like processes upon exposure to nerve growth factor (NGF), and thus provide an opportunity to study this phenomenon de novo. We have used the transmission electron microscope to analyse the early stages of process outgrowth (1, 2, 3 and 7 days) to determine what organelles are involved and in what sequence they appear during development. Despite the non-synchronous response to NGF, we can derive three main stages in early process formation. (1) NGF-treated cells develop conical extensions similar to, but larger and more numerous than those of controls. Extensions terminate in bulbous expansions that contain large number of chromaffin-like granules and bear microspikes filled with microfilaments. (2) The extensions of NGF-treated cells then acquire membranous organelles indicative of transmitter packaging and/or recycling of cytoplasmic membranes, for example, tubular reticulum, clear and dense-cored vesicles, multivesicular bodies, and lysosomes. (3) As processes elongate, they develop a shaft that contains an array of microtubules and fine tubular reticulum dispersed in a filamentous matrix, and varicosities that exhibit the same organelles seen in stage 2. The discussion stresses the similarities in the outgrowth of processes in PC12 cells and neurons, and speculates that NGF causes a change in organization and/or quantity or organelles that already exist in non-treated control cells.

Effects of eye removal on receptors of alpha-bungarotoxin in the optic lobes of chick brain

The existence of receptors with high affinity for alpha-bungarotoxin and the pharmacologic properties of a nicotinic ACh receptor has been shown in the optic tectum of chick brain. In the present study eyes were removed from chicks at embryonic day 3 (E3), or at post-hatching day 3 (P3). In both cases, the total number of receptors for I125-alphaBT which developed in the deafferented optic lobe was about 50% of the number in normal lobes.

Effects of neurotoxic industrial solvents on cultured neuroblastoma cells: methyl n-butyl ketone, n-hexane and derivatives

The neurotoxic effects of the commercial organic solvents n-hexane and methyl n-butyl ketone (MBK), recently discovered to cause profound peripheral neuropathy in man, were studied in neuronal-like cells in tissue culture. These agents are known to induce marked proliferation of 10nm neurofilaments in peripheral and central axons of both humans and rats. In a murine neuroblastoma cell line, previously reported to show filamentous hyperplasia when exposed to aluminum ions, both MBK and n-hexane induced a highly reproducible series of cytotoxic effects at the light and electron microscopic levels and caused dose-dependent inhibition of cellular proliferation. In contrast, two closely related but clinically non-toxic solvents, methyl isobutyl ketone and methyl ethyl ketone, caused little or no cytopathological or growth inhibiting effects. MBK and its major water soluble derivative, 2,5-hexane dione (HD), produced identical cytotoxic changes in vitro, supporting the postulate that HD is the toxically active agent in victims exposed to MBK. Although MBKlthought MBK and n-hexand adversely affected the extension of maintenance of neuritic processes, electron microscopy and immunofluorescent reaction failed to reveal any proliferation of 10 nm cytoplasmic filaments in the intoxicated cells. Also, these agents had no deleterious effect on in vitro brain microtubule polymerization. In contrast, aluminum ions produced a doserelated inhibition of neurotubule assembly, similar to that seen with the filament-inducing agents colchicine and vinblastine. The results suggest that the fibrous cytoskeleton may not be the primary or essential target of MBK n-hexane and related human neurotoxins.

Retinotectal projection of the adult winter flounder (Pseudopleuronectes americanus)

The winter flounder shifts the orinetation of its body 90 degrees at metamorphosis so that its left side is functionally ventral and its right side functionally dorsal. Concomitantly the left eye migrates onto the right side. The net result of these complex metamorphic changes is that the dorsoventral axes of the visual fields are perpendicular to the body rather than parallel as in most other teleosts. The developing flatfish may provide a resource for studying the formation of neural connections, for the change in orientation may necessitate some shift in connections in visuomotor pathways. As a baseline for developmental studies, we have established the retinotectal projection in adult winter flounder by means of anatomical tracing techniques (autoradiography and degeneration staining) and electrophysiological mapping techniques. The histological pattern of retinal afferents to the tectum is similar to that of other teleosts; afferents are confined to the superficial white and gray zone, with a few fibers coursing in the deep white zone. Electrophysiological mapping shows that the visuotectal projection is complete over the entire extent of the tectum, symmetrical for right and left fields and patterned normally.