A role for the extracellular matrix in retinal neurogenesis in vitro

Conditioned media from AICAR-treated skeletal muscle cells increases neuronal differentiation of adult neural progenitor cells

Exercise has profound benefits for brain function in animals and humans. In rodents, voluntary wheel running increases the production of new neurons and upregulates neurotrophin levels in the hippocampus, as well as improving synaptic plasticity, memory function and mood. The underlying cellular mechanisms, however, remain unresolved. Recent research indicates that peripheral organs such as skeletal muscle, liver and adipose tissue secrete factors during physical activity that may influence neuronal function. Here we used an in vitro cell assay and proteomic analysis to investigate the effects of proteins secreted from skeletal muscle cells on adult hippocampal neural progenitor cell (aNPC) differentiation. We also sought to identify the relevant molecules driving these effects. Specifically, we treated rat L6 skeletal muscle cells with the AMP-kinase (AMPK) agonist 5-aminoimidazole-4-carboxamide-1-β-d-ribofuranoside (AICAR) or vehicle (distilled water). We then collected the conditioned media (CM) and fractionated it using high-performance liquid chromatography (HPLC). Treatment of aNPCs with a specific fraction of the AICAR-CM upregulated expression of doublecortin (DCX) and Tuj1, markers of immature neurons. Proteomic analysis of this fraction identified proteins known to be involved in energy metabolism, cell migration, adhesion and neurogenesis. Culturing differentiating aNPCs in the presence of one of the factors, glycolytic enzyme glucose-6-phosphate isomerase (GPI), or AICAR-CM, increased the proportion of neuronal (Tuj1⁺) and astrocytic, glial fibrillary acidic protein (GFAP⁺) cells. Our study provides further evidence that proteins secreted from skeletal muscle cells may serve as a critical communication link to the brain through factors that enhance neural differentiation.

Regenerative capacity of retinal cells and the maintenance of their differentiation

Mechanisms underlying cell type stability and the capacity of retinal cells for transdifferentiation are discussed. It is shown that cells of amphibian pigmented epithelium can be transformed into retina or lens cells depending on the inducing cell type: the influence of retina enables them to be transformed into retina, the influence of lens epithelium, to lens cells (lentoids or lenses). This led to an attempt to discover the molecular character of cell action by means of transfilter induction in early gastrula ectoderm of Xenopus laevis. The results show that the induced cell types correspond to the main inducing cell type, around which a range of neighbouring cell types is produced; this has been shown for five different cell types. The inducing factors involved seem to show qualitative differences. It is probable that they play a stabilizing role in the maintenance of the differentiated state of tissues, since temporary dissociation into cells leads eye tissues to transdifferentiate into other types. Such molecular factors can play a significant role in the maintenance of the type of differentiation and also in conversion into other cell types. These mechanisms of maintenance are not restricted to interactions between molecules and cells, since membranes on the surface of the retina and pigmented epithelium contribute to their shaping and consequently to the stability of the cell type.

Integrins stimulate phosphorylation of neurofilament NF-M subunit KSP repeats through activation of extracellular regulated-kinases (Erk1/Erk2) in cultured motoneurons and transfected NIH 3T3 cells

Integrin-mediated interactions of cells with components of the extracellular matrix (ECM) regulate cell survival, cell proliferation, cell differentiation and cell migration through activation of multiple intracellular signal transduction pathways. In this study, we have demonstrated that integrin-matrix interactions promote KSP tail-domain phosphorylation of neurofilament medium molecular weight subunits (NF-M) in cultured rat spinal cord motoneurons and NF-M transfected NIH 3T3 cells. We found that laminin and fibronectin induce NF-M tail-domain phosphorylation in motoneurons and NIH 3T3 cells transfected with NF-M, respectively. This phosphorylation was selectively inhibited by PD98059, a specific MEK1 inhibitor. This suggests that laminin and fibronectin-induced MEK1 activation and the downstream targets Erk1 and Erk2 are involved in NF-M KSP tail-domain phosphorylation. This pathway appears to represent one of the mechanisms whereby integrin-extracellular matrix interactions are involved in phosphorylation of the NF-M KSP tail domain.

Integrin alpha(1) beta(1)-mediated activation of cyclin-dependent kinase 5 activity is involved in neurite outgrowth and human neurofilament protein H Lys-Ser-Pro tail domain phosphorylation

Cellular adhesion to the extracellular matrix is mediated by a diverse class of alpha/beta heterodimeric receptors known as integrins, which transduce signals to activate multiple intracellular signal transduction pathways within the cells. The signaling pathway linking integrins to mediate neuronal process outgrowth is not well understood. Here, we have provided evidence that intracellular signaling by the alpha(1)beta(1) integrin-induced activation of cyclin-dependent kinase 5 (cdk5) is involved in neurite outgrowth and human neurofilament protein H (hNF-H) Lys-Ser-Pro (KSP) tail domain phosphorylation in differentiated human SH-SY5Y cells. The integrin alpha(1) and beta(1) monoclonal antibodies and BL-1, a specific cdk5 inhibitor, inhibited these effects. We also demonstrated that cdk5 activity and hNF-H KSP tail domain phosphorylation were increased in cdk5/p35 and hNF-H tail domain co-transfected HEK293 cells grown on laminin. This increased hNF-H tail domain phosphorylation was triggered by cdk5 activation. Taken together, these results indicated that cdk5 may play an important role in promoting neurite outgrowth and hNF-H tail KSP domain phosphorylation through the integrin alpha(1)beta(1) signaling pathway.

A developmental time line in a retinal slice from rainbow trout

The retina in teleost fish continues to grow throughout much of the life of the animal, in part by the continuing differentiation of new tissue at the retinal margin, an area termed the peripheral growth zone (PGZ) (Lyall, Q J Micros Sci, 1957:98:101-110). We have developed a retinal slice preparation--including the PGZ--from juvenile rainbow trout (Onchorynchus mykiss), a species in which retinal growth is rapid and the PGZ is correspondingly pronounced. The PGZ slice preparation contains a time line of retinal development, with cells at different stages of maturation present side by side. We present evidence that the birth sequence of the various retinal cell types in the PGZ recapitulates the sequence during embryonic development. We also report data on the rate of growth of the PGZ in juvenile trout in vivo. Finally, we have used the PGZ slice preparation to make whole-cell voltage clamp recordings from individual retinal GCs at both early and late stages of maturation. We report that the amplitude of delayed rectifier and A-type potassium currents increases during GC maturation.

Postnatal development of parvalbumin immunoreactive amacrine cells in the rabbit retina

In the adult rabbit, rat and cat retina, parvalbumin (PV) immunoreactivity is primarily localized to a population of narrow-field, bistratified amacrine cells, the AII amacrine cells-major interneurons of the rod pathway. This investigation examines the postnatal development of PV immunoreactivity in order to better understand the ontogeny of the AII amacrine cell population and the formation of the rod pathway. Rabbit retinas at various postnatal ages were processed for immunohistochemistry using a monoclonal antibody directed to PV and analyzed morphometrically. On the day of birth, PV immunoreactive cell bodies are numerous in the proximal inner nuclear layer (INL) in all retinal regions. These cells have a primary process directed towards the inner plexiform layer (IPL). At postnatal day (PND) 2, a few faint immunoreactive processes are observed in the IPL. At PND 4, well-stained processes are observed to ramify mainly in the proximal IPL. At PND 6, strongly immunoreactive processes are present in both the distal and proximal IPL, and at PND 10 they form a continuous, dense plexus in both levels of the IPL. By PND 10, the morphology of PV immunoreactive cells is similar to PV immunoreactive cells in adult retinas. The density of PV immunoreactive cells in the proximal INL increases from PND 2 to PND 5, then it gradually decreases to adult values, while the total number of PV immunoreactive cell bodies increases until PND 10. PV immunoreactive amacrine cells at PND 2, as in the adult, are nonrandomly distributed across the retinal surface. These studies show that PV immunoreactive amacrine cells have a developmental profile that is similar to several other amacrine cell types. This includes the elaboration of processes in the IPL during the first postnatal week and a mature appearance towards the end of the second week of life, about the time of eye opening. These observations indicate that the AII amacrine cell may participate in the processing of visual information at eye opening.

Collagen type IV promotes the differentiation of neuronal progenitors and inhibits astroglial differentiation in cortical cell cultures

In an effort to elucidate the interactions between cells in the developing cortex and their microenvironment, we have employed dissociated cell cultures and immunocytochemistry to analyze the effect of collagen type IV (COL) on the proliferation and differentiation of rat cortical progenitor cells during the period of corticogenesis. COL, present in the proliferative zones throughout the period of neurogenesis, belongs to a group of macromolecular proteins that make up a considerable portion of the extracellular matrix (ECM). We have shown that this ECM molecule inhibits cell proliferation and glial cell differentiation while promoting neuronal differentiation. We have also demonstrated that COL, when applied to the cultures with basic fibroblast growth factor (bFGF), induces glial cell differentiation while continuing to promote neuronal differentiation. These results indicate that cortical progenitor cells respond differentially to local environmental signals, and that components of the ECM are involved in the regulation of corticogenesis.

Disruption of the retinal basal lamina during early embryonic development leads to a retraction of vitreal end feet, an increased number of ganglion cells, and aberrant axonal outgrowth

Bacterial collagenase was injected into the vitreous of the eye of chick and quail embryos. Immunocytochemical and ultrastructural studies revealed that the collagenase dissolved the retinal basal lamina of the injected eye. The basal lamina disruption was first detectable 1 hour after enzyme injection and was complete within 3 hours. With further development, the retinal basal lamina was not reestablished; newly developing neuroepithelium in the peripheral retina, however, generated an intact basal lamina. Western blot analysis showed that Clostridial collagenase degraded various collagens but spared noncollagenous proteins. Basal lamina disruption of embryonic day 3 to 6 retinae led to the retraction of the end feet of the neuroepithelial cells, caused an increase in the number of Islet-1+ cells (most likely ganglion cells), an increase in the thickness of the optic fiber layer, and aberrant growth of optic axons on their way toward the optic disc. None of these changes were observed when retinal basal laminae were disrupted at later stages of development. The present data demonstrate that the retinal basal lamina, by anchoring the neuroepithelial cells to the pial surface of the retina, has an important function in the development of the normal cytoarchitecture of this structure. It is proposed that the altered extracellular environment in the vitreal part of the retina, resulting in the retraction of the neuroepithelial end feet, is responsible for the increased number of Islet-1+ cells and the aberrant axonal navigation.

The retinal pigmented epithelium is required for development and maintenance of the mouse neural retina

BACKGROUND

During development of the vertebrate eye, there is a series of reciprocal cellular interactions that determine the fate of the eye components. Although evidence from organ culture suggests that the retinal pigmented epithelium (RPE) organizes the laminar structure of the differentiated neural retina, no role has been identified for the RPE in early eye development, nor has the later function of RPE been demonstrated in vivo.

RESULTS

To investigate the role of RPE cells in eye development, we generated transgenic mice that carry the attenuated diphtheria toxin-A gene; this transgene was driven by the promoter of the gene encoding the tyrosinase-related protein-1, which is specifically expressed in pigment cells. Depending on the expression level of the transgene, the retinal epithelium was ablated before or after its differentiation into a pigmented cell layer. We show that an early ablation (embryonic day E10-11) resulted in disorganization of the retinal layer, immediate arrest of eye growth and subsequent eye resorption. A later ablation (E11.5-12.5) allowed the eye to be maintained during embryogenesis, but the laminar structure of the retina became disrupted by the end of gestation, the vitreous failed to accumulate the adults were anophthalmic or severely microphthalmic. In some microphthalmic eyes, a number of RPE cells escaped ablation and formed patches of pigmented cells; the laminar structure of the retina was maintained immediately adjacent to such pigmented areas but disrupted elsewhere. In both cases--early or late ablation of the RPE--the retina appears to be the primary affected tissue.

CONCLUSIONS

We conclude that presence of the RPE is required for the normal development of the eye in vivo. Its presence early in development is necessary for the correct morphogenesis of the neural retina. After the neural retina has started to differentiate, the RPE is still necessary, either directly or indirectly, to maintain the organization of the retinal lamina.

Target preference of embryonic retina cells and retinal cell lines is cell-autonomous, position-specific, early determined and heritable

Retinal ganglion cells (RGCs) form the topographic connection between retina and optic tectum in the developing avian embryo. In vitro, neurons with the morphological traits and marker expression of RGCs were found both in single-cell cultures from embryonic day (E) 6 chick retina and in retinal cell lines derived from E3.5 quail retina. Rapid and substantial differentiation of RGC-like cells could be induced in the lines by addition of fibroblast growth factor aFGF or bFGF. RGC-like cells were examined with respect to their target discrimination properties as single cells in the stripe carpet assay. In this assay system, alternating stripes of membrane vesicles prepared from the anterior and posterior tectum are offered to growing axonal processes as a substrate. Temporal RGC-like cells, both primary cells prepared from the temporal retina and immortalized cells of those retinal lines derived from the temporal retina, avoid stripes of membrane vesicles from posterior tectum; they prefer to grow on membrane vesicles from the anterior tectum, which is their in vivo target. Nasal RGC-like cells did not exhibit a target preference, in accordance with previous findings. Together the experiments show that target preference of RGCs is a cell-autonomous and heritable mechanism that is determined early and is position-dependent.

Co-transplantation of embryonic retina and retinal pigment epithelial cells to rabbit retina

The retinal pigment epithelium (RPE) is important for normal development of the neural retina. We sought to investigate whether cografting RPE cells affected the differentiation and survival of retinal grafts. Pigmented embryonic day 16 (E16) rabbit retina was dissected either with or without attached RPE and injected into a lesion site in retinas of young adult rabbit hosts. Each host obtained a pure retina graft in one eye and a retina/RPE cograft in the other. Animals were sacrificed after 4, 8 and 12 weeks. After 4 weeks, grafts (1-2 mm in diameter) were seen in both experimental groups at the lesion site or in the subretinal space. However, 8 and 12 weeks after transplantation, the graft survival rate decreased. The grafts developed cell layers in folded sheets and many rosettes (a rosette consists of photoreceptors and cells of other retinal layers around a central lumen defined by an outer limiting membrane). Cografts of retina with RPE had areas of more distinct cell lamination than transplants of pure retina. Grafted RPE cells were organized in clusters of cells surrounded by extracellular matrix and often associated with blood vessels. If the extracellular matrix of RPE cell clusters was outside the rosettes close to inner retinal layers in the graft, transplant Müller cell endfeet developed an inner limiting membrane. Müller cell endfeet could also be observed in subretinal transplants attached to the denuded Bruch's membrane of the host. In 12-week grafts, when RPE cell clusters were inside rosettes, the surrounded photoreceptors survived better. No RPE effect could be seen if single RPE cells were dispersed among retinal donor cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Basic fibroblast growth factor promotes adhesive interactions of neuroepithelial cells from chick neural tube with extracellular matrix proteins in culture

Fibroblast growth factors have been increasingly assigned mitogenic and trophic roles in embryonic and postnatal development of the nervous system. Little is known, however, of their functional roles in early embryonic neural development at the neural tube stage. We have examined the effect of basic fibroblast growth factor (bFGF) on the adhesive behavior in culture of dissociated brachio-thoracic neural tube cells from 26- to 30-somite stage chick embryos. Cells plated on collagen-coated substratum at a low density attach to the substratum but show poor cell spreading. Addition of bFGF markedly promotes cell spreading, yielding an epithelial morphology. This effect becomes discernible 6–8 hours after cell plating with bFGF and is completed by 24 hours, with half-maximal and maximal effects attained at around 0.4 and 10 ng/ml, respectively. The number of cells remain largely constant up to 24 hours, and then cell survival and/or mitogenic effects of bFGF become apparent. The cell spreading effect is abolished by cycloheximide treatment, inhibited by the anti-beta 1-integrin antibody CSAT, and accompanied by about twofold increases in the expression of beta 1-integrin and vinculin, components of focal adhesion complexes. Cells cultured with bFGF for 24 hours exhibit enhanced cell attachment and cell spreading with little time lag following cell plating. In earlier embryonic stages, developmentally less mature cells depend much more on bFGF for their cell spreading and survival, while in later stages the cell spreading response to bFGF becomes undetectable as neural tube develops to spinal cord. The cell spreading effect of bFGF is realized on specific extracellular matrix proteins including laminin, fibronectin and collagen, but not on vitronectin, arg-gly-asp peptide (PepTite-2000), poly-L-ornithine or others. These results suggest that, in an early stage of neural tube development, bFGF is involved in the developmental regulation of adhesive interactions between neuroepithelial cells and the extracellular matrix, thereby controlling their proliferation, migration and differentiation.

Position, guidance, and mapping in the developing visual system

Positional identity in the visual system affects the topographic projection of the retina onto its central targets. In this review we discuss gradients and positional information in the retina, when and how they arise, and their functional significance in development. When the axons of retinal ganglion cells leave the eye, they navigate through territory in the central nervous system that is rich in positional information. We review studies that explore the navigational cues that the growth cones of retinal axons use to orient towards their target and organize themselves as they make this journey. Finally, these axons arrive at their central targets and make a precise topographic map of visual space that is crucial for adaptive visual behavior. In the last section of this review, we examine the topographic cues in the tectum, what they are, when, and how they arise, and how retinal axons respond to them. We also touch on the role of neural activity in the refinement of this topography.

Proportion of proliferative cells in the tadpole retina is increased after embryonic lesion

Little is known about the cellular mechanisms that cause some cells to stop dividing while leaving neighboring cells free to continue dividing. Such events occur during development of the Xenopus retina; all cells of the embryonic eyebud are mitotic, but by stage 37 (St 37), only cells at the ciliary margin continue to proliferate as neighboring cells become post-mitotic. The mechanisms that control these different proliferative fates remain unknown. One possibility is that total cell number regulates the initial number of proliferative cells at the ciliary margin. To test this hypothesis, we reduced the cell number by surgically removing a portion of the embryonic eyebud, including part of the prospective proliferative zone. Cell counts confirmed that the numbers of both the mitotic, undifferentiated cells and the post-mitotic, differentiated cells were reduced following the partial ablation. A regression analysis suggested that the initial number of undifferentiated cells was a fixed proportion of the total number, but that this proportion was increased by the partial ablation. This increase occurred for all stages that the partial ablation was performed, from early optic vesicle to mid optic cup stages. The proportion of undifferentiated cells was normal in sham-operated retinas, indicating that the increase in partially ablated retinas was induced by tissue removal and not by wound healing. Analyses of clones derived from single precursors, labeled with a fluorescent lineage tracer, indicated that the rate of proliferation was the same in partially ablated and sham-operated retinas. Measurements of bromodeoxyuridine incorporation directly confirmed that at the ciliary margin cell division time was unchanged after partial ablation. Our observations are most consistent with the hypothesis that the proportion of undifferentiated cells was increased because cells that would have become post-mitotic remained proliferative after the partial ablation. Furthermore, cell-cell interactions most likely play a major role in controlling the initial number of proliferative cells in the tadpole retina.

Regulation of NCAM by growth factors in serum-free myotube cultures

Regulation of the neural cell adhesion molecule (NCAM) was examined in primary cultures of chick skeletal muscle grown in serum-free defined medium. Relative levels of NCAM (per microgram protein) increased 20-30% in myotubes grown on Matrigel, a reconstituted basement membrane preparation, compared to those grown on collagen; total NCAM levels on Matrigel were increased 40-55% due to the additional increase in total protein. A dose dependent increase in relative NCAM levels in myotubes grown on Matrigel in defined medium was observed with the addition of adsorbed horse serum, while relative NCAM levels in myotubes grown on collagen were unaffected by altering the serum concentration. Thus, extracellular matrix molecules and soluble factors exert trophic effects on myotube NCAM expression. Similar developmental changes in the expression of the different molecular size forms of NCAM occurred in myotubes grown on collagen and Matrigel: levels of 150K and 135K Mr forms decreased during development, while 125K remained prominent in older myotubes. Relative NCAM levels were specifically enhanced 11-26% by several factors: nerve growth factor, thyroxine, insulin-like growth factor II, dibutyryl cyclic AMP, veratridine (a sodium ion channel agonist), and nisoldipine (a calcium ion channel agonist). Total protein and overall myotube development in serum-free cultures were enhanced by fetuin, insulin-like growth factor II, acidic fibroblast growth factor, calcitonin gene-related peptide, dibutyryl cyclic AMP, and veratridine. Thus, changes in extracellular matrix, intracellular calcium, and sodium ions, as well as extracellular trophic factors, such as nerve growth factor, thyroxine, and insulin-like growth factor II, may regulate muscle NCAM expression during embryonic development.

Laminin in neural development

This short and selective review of the role of laminin in neural development discusses emerging concepts about the way that elements of the extracellular matrix control the differentiation of embryonic neurons. New laminin isoforms have recently been discovered, discoveries which now reveal the very great heterology of basement membranes in different regions of the nervous system, at different stages of development. The problems of identifying true, neuronal-specific laminin receptors are also discussed, particularly with reference to neuronal pathway formation.

Cellular interactions determine neuronal phenotypes in rodent retinal cultures

Progenitor cells isolated from early rat embryo retinas differentiate into phenotypes normally generated early in retinal development (e.g., ganglion cells), whereas progenitors isolated from postnatal retinas differentiate into later-generated retinal cell types (e.g., rod photoreceptors; Reh and Kljavin, J. Neurosci. 9:4179-4189; 1989; Adler and Hatlee, 1989; Science 243:391-393; Sparrow, Hicks, and Barnstable, 1990, Dev. Brain Res. 51:69-84). To determine whether this change in committment is intrinsic to the progenitor cells, or alternatively can be modified by interactions with their developing environment, I co-cultured mouse and rat retinal cells, from different developmental stages, and identified the resulting phenotypes with species-specific and cell class-specific antibodies. I found that the phenotypes into which mouse neuroepithelial cells differentiate depends on the phenotypes of the rat cells that surround them. Retinal precursor cells from embryonic day (E) 10-12 will adopt the rod photoreceptor phenotype only when close to cells expressing this phenotype. By contrast, when the E10-12 retinal progenitor cells are cultured with cells from the cerebral cortex, they differentiate primarily into large multipolar neurons, similar in their morphology and antigen expression to retinal ganglion cells. These results indicate that interactions among the cells of the developing retina are important in the determination of cell fate.

Effects of TGF beta 1 on the proliferation and differentiation of an immortalized astrocyte cell line: relationship with extracellular matrix

The astrocyte cell line (C.LT.T.1.1.), which is immortalized and has retained a normal density-dependent regulation of growth, is a suitable model for studying the relationships between proliferation, differentiation, and the production of extracellular matrix. The growth factor TGF beta 1 was used to modulate these processes. When added to proliferative cells, it inhibited growth and caused morphological changes. It also suppressed the growth arrest at confluence, so that the cells formed multilayers of parallel spindle-shaped cells. Whereas untreated control cells expressed progressively the glial fibrillary acidic protein (GFAP) after arrest of multiplication, the addition of TGF beta 1 to proliferative cells prevented GFAP expression and accumulation of its mRNA. Concomitantly, it increased the amounts of laminin, fibronectin, and collagens synthesized during the growth phase and greatly altered the composition and the structure of the matrix deposited at confluence. In contrast, when added after cell differentiation had begun, TGF beta 1 did not alter the appearance of the matrix whereas it still stimulated, but to a lesser extent, extracellular matrix components production. The results show that TGF beta 1 prevents the transition from the proliferating to the differentiating state and correlatively alters the composition and structure of the extracellular matrix.

Matrigel enhances myotube development in a serum-free defined medium

Previously reported serum-free defined media for muscle cell culture require supplementation with hormones, purified growth factors or attachment factors. This report describes a culture system that enhances embryonic chick, skeletal muscle cell growth and differentiation in a serum-free defined medium, without added specialized trophic factors. Myoblasts adhered more to and proliferated more rapidly on a reconstituted basement membrane substrate, Matrigel, than on rat-tail collagen. Matrigel contains several basement membrane attachment molecules which apparently obviate the need for added purified attachment factors. Matrigel also appeared to play a trophic role in subsequent development by enabling the serum-free growth of myotubes which suggests that Matrigel mediates the cellular interaction of growth or attachment factors. Collagen, on the other hand, did not support serum-free myotube growth. Supplementation of defined medium with increasing levels of horse serum enhanced total protein in myotubes grown on both substrates; protein was higher in Matrigel cultures for each medium tested. The serum-free defined medium supported complete morphological differentiation of myotubes grown on Matrigel and maintained myotube cultures up to 22 days. Fibroblast proliferation was higher in cultures on collagen in defined medium with high serum levels, but was virtually eliminated in cultures on Matrigel in serum-free defined medium. The culture system described supports the differentiation of embryonic muscle cells in a simple, serum-free defined medium, thus providing an in vitro model of developing myotubes which should be particularly useful for studies of regulation mediated by extracellular factors.

Epidermal growth factor-induced survival and proliferation of neuronal precursor cells from embryonic rat mesencephalon

Neuronal and glial precursor cells were isolated from primary cultures of embryonic rat mesencephalon. The separation of precursor cells from the neurons was accomplished by the resuspension of the primary cells by trypsinization, followed by replating. This procedure resulted in the death of differentiated neurons and the survival of precursor cells. The survival and proliferation of the replated precursor cells required the presence of epidermal growth factor (EGF) in the culture medium. The precursor cells differentiated into neurons and astrocytes, as determined by immunocytochemical staining with antibodies to neuron specific enolase (NSE) and tau protein or glial fibrillary acidic protein (GFAP) respectively.

Basic fibroblast growth factor upregulates steady-state levels of laminin B1 and B2 chain mRNA in cultured neuroepithelial cells

The growth of purified populations of murine neuroepithelial cells isolated from 10 day embryonic (E10) telencephalon and mesencephalon can be specifically enhanced by supplementing growth culture media with basic fibroblast growth factor (bFGF). One effect of bFGF on cultured neuroepithelial cells was to enhance the amount of laminin expressed at the protein level as detected by immunofluorescence. This was correlated with significant upregulation of steady-state levels of laminin B1 and B2 chain expression as analyzed at the mRNA level. When E12 neuroepithelial cells were split into precursor neuronal or glial subpopulations on the basis of differential expression of major histocompatibility class-1 antigens, only the glial progenitor fraction was found to be capable of detectable laminin synthesis. It is thus possible that a primary action of FGF is to increase the synthesis and release of extracellular matrix molecules from neural cells which act back in a paracrine manner to stimulate differentiation.

A method for the isolation of purified murine neuroepithelial cells from the developing mouse brain

The adult mammalian central nervous system develops from the pseudostratified neuroepithelium of the neural tube. In order to study, in vitro, the differentiation of the neuroepithelial cells in detail and to identify factors that may influence this process, an uncontaminated, viable population of neuroepithelial cells, that still retains full developmental potential, is required. In this paper we describe a highly efficient method, involving differential trypsinization and micro-dissection, to cleanly separate the neuroepithelium from surrounding mesenchyme and ectoderm. The purity of isolated neuroepithelium has been assessed by monitoring for the presence of endothelial cells using an anti-endothelial antibody, MTS-12, and found to contain no significant level of contamination. Neuroepithelial cells prepared by this method have been demonstrated to divide and differentiate in tissue culture, to act as target cells for immortalization by proto-oncogenes and to differentiate into neurons in neural transplantation studies.

Neuronal determination without cell division in Xenopus embryos

Cell division in the Xenopus CNS was blocked by incubating embryos in a mixture of the DNA synthesis inhibitors hydroxyurea and aphidicolin. Surprisingly, embryos treated at the beginning of gastrulation proceeded normally through neurulation, neural tube closure, and CNS subdivision. Thus, cell division is not critical for neural induction or early morphogenetic events in the CNS. Neuroblasts in treated embryos differentiated into neurons of many classes, indicating that cellular determination in the CNS can be dissociated from lineage and birth date. Axonal tracts and embryonic reflexes also developed. The remarkable amount of normal CNS development that occurs in these animals may be explained by a series of sequential inductions that are largely independent of cell proliferation.

Thin slices of teleost retina continue to grow in culture

Thin slices of differentiated fish retinas were maintained up to 5 days in culture conditions where they exhibited properties essentially identical to those found in retinas of intact animals. Retinal slices were prepared by embedding eyecups from young fish in agarose and sectioning them on a vibratome. Phenotypic integrity of specific cell types was maintained, as demonstrated by specific antibody staining patterns. Stem cells in the retinal margin and presumptive rod progenitor cells in the outer nuclear layer continued to proliferate in vitro, just as they do in vivo. Some of these cells differentiated in vitro as demonstrated by labelling both cell division and cell phenotype. After several days in culture, some regeneration-like responses were observed, such as growth of neurites and swelling of cell bodies in the ganglion cell layer. This retinal slice preparation appears to offer a unique opportunity for studying the interactions among developing retinal cells.

Laminin through its long arm E8 fragment promotes the proliferation and differentiation of murine neuroepithelial cells in vitro

The epigenetic factors involved in regulating the proliferation and differentiation of cells of the developing mammalian central nervous system are largely unknown. In this study, laminin, a molecule which is present in the basal lamina from the earliest stage of neural tube formation, has been examined in vitro for its possible regulatory role in mammalian neural development. Purified populations of murine neuroepithelial (NEP) cells isolated from the 10-day embryonic telencephalon and mesencephalon respond in vitro to laminin by undergoing aggregation, proliferation, and extensive neurite elaboration. The proliferation and differentiation of NEP cells induced by the interaction with laminin were dependent upon an early cell aggregation, since precoating of wells with poly-L-ornithine, a procedure which prevented such aggregation, completely blocked these responses. The previously reported proliferative effect of acidic fibroblast growth factor (FGF) on NEP cells was found to be synergistic with that of laminin. This observation is consistent with the idea that laminin may regulate cell responses in several ways: by direct stimulation via laminin receptors; by optimal presentation of FGF molecules to neural cells; and finally by upregulation of FGF receptor numbers on responsive cells. The in vitro response of laminin is mimicked by its long arm elastase digestion fragment, E8, whereas the cross arm fragment of laminin, E1-4, had no effect. In addition, antibodies specific for epitopes on the long arm blocked the effect seen with the whole laminin molecule. Binding studies of 125I-labeled laminin and its fragment performed on freshly isolated NEP cells confirmed the specificity of the in vitro observations: whole laminin and the E8 fragment bound to the NEP cell surface whereas the E1-4 fragment did not. These studies demonstrate mechanisms by which laminin, specifically through its long arm fragment, may assert a regulatory function during development of the mammalian central nervous system.

Specific effects of ethanol on neurite-promoting proteoglycans of neuronal origin

Quantitative analysis of proteoglycan synthesis and release by neurons indicated that of the total incorporation of 35SO4 and [3H]glucosamine into proteoglycan, approximately 75% was chondroitin sulphate while approximately 25% was heparan sulphate. Using a biological assay it has been shown that heparan sulphate proteoglycans (HSPGs) in conditioned medium promote neurite outgrowth from sensory neurons when complexed to a laminin substrate. Culture media conditioned in the presence of ethanol did not enhance neurite formation over control levels. Co-incubation of neurons with beta-D-xyloside, an inhibitor of proteoglycan synthesis, reduced neurite outgrowth after 20 h in culture and the combination of ethanol and beta-D-xyloside produced no further inhibition than with either ethanol or beta-D-xyloside used alone. If the laminin substrate was coated with medium conditioned by neurons, the direct inhibitory effects on process formation seen when ethanol was co-incubated with neurons were no longer observed. Ethanol inhibited the incorporation of 35SO4 and [3H]glucosamine into HSPG by neurons while having little or no effect on incorporation into chondroitin sulphate. These results suggest that inhibition of neuronal synthesis of HSPGs by ethanol is responsible for the decrease in neurite promoting activity of medium conditioned in the presence of ethanol.

Extracellular matrix of the superior olivary nuclei in the dog

The extracellular matrix around nerve cell bodies in canine lateral and medial superior olivary nuclei was examined by conventional electron microscopy, Golgi impregnation and histochemical techniques. Each neuron is surrounded by a region of myelin-free neuropil embedded amongst the myelinated fibres of the trapezoid body. In the myelin-free neuropil there are astrocytes, axons, synaptic boutons and extracellular matrix. The extracellular matrix fills the spaces between slender axons near the terminals, synaptic boutons and glial processes, but not the synaptic cleft. Golgi impregnation selectively stains the perineuronal nets which cover some of all of the nerve cell bodies and dendrites. The Golgi-EM method revealed that the impregnated profiles of the nets are restricted to the extracellular matrix. Synaptic boutons are situated in the holes of the perineuronal nets. Peanut (PNA) and soybean (SBA) agglutinins bound the extracellular matrix but not the synaptic boutons, glial processes, nerve cell bodies or basal lamina of blood capillaries. Light microscopic immunohistochemistry of the glial fibrillary acidic protein (GFAP) and S-100 protein did not stain a layer corresponding to the extracellular matrix and synapses but showed an intensely positive reaction immediately outside this layer. These data suggest the existence of a unique microenvironments associated with glycoconjugates around nerve cell bodies in canine superior olivary nuclei.