Expression of s-laminin and laminin in the developing rat central nervous system

The Cytoskeleton Effectors Rho-Kinase (ROCK) and Mammalian Diaphanous-Related (mDia) Formin Have Dynamic Roles in Tumor Microtube Formation in Invasive Glioblastoma Cells

Glioblastoma (GBM) is a progressive and lethal brain cancer. Malignant control of actin and microtubule cytoskeletal mechanics facilitates two major GBM therapeutic resistance strategies-diffuse invasion and tumor microtube network formation. Actin and microtubule reorganization is controlled by Rho-GTPases, which exert their effects through downstream effector protein activation, including Rho-associated kinases (ROCK) 1 and 2 and mammalian diaphanous-related (mDia) formins (mDia1, 2, and 3). Precise spatial and temporal balancing of the activity between these effectors dictates cell shape, adhesion turnover, and motility. Using small molecules targeting mDia, we demonstrated that global agonism (IMM02) was superior to antagonism (SMIFH2) as anti-invasion strategies in GBM spheroids. Here, we use IDH-wild-type GBM patient-derived cell models and a novel semi-adherent in vitro system to investigate the relationship between ROCK and mDia in invasion and tumor microtube networks. IMM02-mediated mDia agonism disrupts invasion in GBM patient-derived spheroid models, in part by inducing mDia expression loss and tumor microtube network collapse. Pharmacological disruption of ROCK prevented invasive cell-body movement away from GBM spheres, yet induced ultralong, phenotypically abnormal tumor microtube formation. Simultaneously targeting mDia and ROCK did not enhance the anti-invasive/-tumor microtube effects of IMM02. Our data reveal that targeting mDia is a viable GBM anti-invasion/-tumor microtube networking strategy, while ROCK inhibition is contraindicated.

Mechanisms of oligodendrocyte progenitor developmental migration

Oligodendrocytes, the myelinating cells of the central nervous system (CNS), develop from oligodendrocyte progenitor cells (OPCs) that must first migrate extensively throughout the developing brain and spinal cord. Specified at particular times from discrete regions in the developing CNS, OPCs are one of the most migratory of cell types and disperse rapidly. A variety of factors act on OPCs to trigger intracellular changes that regulate their migration. We will discuss factors that act as long-range guidance cues, those that act to regulate cellular motility, and those that are critical in determining the final positioning of OPCs. In addition, recent evidence has identified the vasculature as the physical substrate used by OPCs for their migration. Several new findings relating to this oligodendroglial-vascular signaling axis reveal new insight on the relationship between OPCs and blood vessels in the developing and adult brain.

Advancing models of neural development with biomaterials

Human pluripotent stem cells have emerged as a promising in vitro model system for studying the brain. Two-dimensional and three-dimensional cell culture paradigms have provided valuable insights into the pathogenesis of neuropsychiatric disorders, but they remain limited in their capacity to model certain features of human neural development. Specifically, current models do not efficiently incorporate extracellular matrix-derived biochemical and biophysical cues, facilitate multicellular spatio-temporal patterning, or achieve advanced functional maturation. Engineered biomaterials have the capacity to create increasingly biomimetic neural microenvironments, yet further refinement is needed before these approaches are widely implemented. This Review therefore highlights how continued progression and increased integration of engineered biomaterials may be well poised to address intractable challenges in recapitulating human neural development.

Laminin γ3 plays an important role in retinal lamination, photoreceptor organisation and ganglion cell differentiation

Laminins are heterotrimeric glycoproteins of the extracellular matrix. Eleven different laminin chains have been identified in vertebrates. They are ubiquitously expressed in the human body, with a distinct tissue distribution. Laminin expression in neural retina and their functional role during human retinogenesis is still unknown. This study investigated the laminin expression in human developing and adult retina, showing laminin α1, α5, β1, β2 and γ1 to be predominantly expressed in Bruch's membrane and the inner limiting membrane. Laminin-332 and laminin γ3 expression were mainly observed in the neural retina during retinal histogenesis. These expression patterns were largely conserved in pluripotent stem cell-derived retinal organoids. Blocking of laminin γ3 function in retinal organoids resulted in the disruption of laminar organisation and synapse formation, the loss of photoreceptor organisation and retinal ganglion cells. Our data demonstrate a unique temporal and spatial expression for laminins and reveal a novel role for laminin γ3 during human retinogenesis.

Connexin 30 controls astroglial polarization during postnatal brain development

Astrocytes undergo intense morphological maturation during development, changing from individual sparsely branched cells to polarized and tremendously ramified cells. Connexin 30, an astroglial gap-junction channel-forming protein expressed postnatally, regulates in situ the extension and ramification of astroglial processes. However, the involvement of connexin 30 in astroglial polarization, which is known to control cell morphology, remains unexplored. We found that connexin 30, independently of gap-junction-mediated intercellular biochemical coupling, alters the orientation of astrocyte protrusion, centrosome and Golgi apparatus during polarized migration in an in vitro wound-healing assay. Connexin 30 sets the orientation of astroglial motile protrusions via modulation of the laminin/β1 integrin/Cdc42 polarity pathway. Connexin 30 indeed reduces laminin levels, inhibits the redistribution of the β1-integrin extracellular matrix receptors, and inhibits the recruitment and activation of the small Rho GTPase Cdc42 at the leading edge of migrating astrocytes. In vivo, connexin 30, the expression of which is developmentally regulated, also contributes to the establishment of hippocampal astrocyte polarity during postnatal maturation. This study thus reveals that connexin 30 controls astroglial polarity during development.

Summary: Connexin 30 sets the orientation of astroglial motile protrusions during polarized migration in vitro and contributes in vivo to the establishment of hippocampal astrocyte polarity during postnatal maturation.

The role of laminins in the organization and function of neuromuscular junctions

The synapse between motor neurons and skeletal muscle is known as the neuromuscular junction (NMJ). Proper alignment of presynaptic and post-synaptic structures of motor neurons and muscle fibers, respectively, is essential for efficient motor control of skeletal muscles. The synaptic cleft between these two cells is filled with basal lamina. Laminins are heterotrimer extracellular matrix molecules that are key members of the basal lamina. Laminin α4, α5, and β2 chains specifically localize to NMJs, and these laminin isoforms play a critical role in maintenance of NMJs and organization of synaptic vesicle release sites known as active zones. These individual laminin chains exert their role in organizing NMJs by binding to their receptors including integrins, dystroglycan, and voltage-gated calcium channels (VGCCs). Disruption of these laminins or the laminin-receptor interaction occurs in neuromuscular diseases including Pierson syndrome and Lambert-Eaton myasthenic syndrome (LEMS). Interventions to maintain proper level of laminins and their receptor interactions may be insightful in treating neuromuscular diseases and aging related degeneration of NMJs.

The Cerebrovascular Basement Membrane: Role in the Clearance of β-amyloid and Cerebral Amyloid Angiopathy

Cerebral amyloid angiopathy (CAA), the accumulation of β-amyloid (Aβ) peptides in the walls of cerebral blood vessels, is observed in the majority of Alzheimer’s disease (AD) brains and is thought to be due to a failure of the aging brain to clear Aβ. Perivascular drainage of Aβ along cerebrovascular basement membranes (CVBMs) is one of the mechanisms by which Aβ is removed from the brain. CVBMs are specialized sheets of extracellular matrix that provide structural and functional support for cerebral blood vessels. Changes in CVBM composition and structure are observed in the aged and AD brain and may contribute to the development and progression of CAA. This review summarizes the properties of the CVBM, its role in mediating clearance of interstitial fluids and solutes from the brain, and evidence supporting a role for CVBM in the etiology of CAA.

G-protein coupled receptor 56 promotes myoblast fusion through serum response factor- and nuclear factor of activated T-cell-mediated signalling but is not essential for muscle development in vivo

Mammalian muscle cell differentiation is a complex process of multiple steps for which many of the factors involved have not yet been defined. In a screen to identify the regulators of myogenic cell fusion, we found that the gene for G-protein coupled receptor 56 (GPR56) was transiently up-regulated during the early fusion of human myoblasts. Human mutations in the gene for GPR56 cause the disease bilateral frontoparietal polymicrogyria; however, the consequences of receptor dysfunction on muscle development have not been explored. Using knockout mice, we defined the role of GPR56 in skeletal muscle. GPR56(-/-) myoblasts have decreased fusion and smaller myotube sizes in culture. In addition, a loss of GPR56 expression in muscle cells results in decreases or delays in the expression of myogenic differentiation 1, myogenin and nuclear factor of activated T-cell (NFAT)c2. Our data suggest that these abnormalities result from decreased GPR56-mediated serum response element and NFAT signalling. Despite these changes, no overt differences in phenotype were identified in the muscle of GPR56 knockout mice, which presented only a mild but statistically significant elevation of serum creatine kinase compared to wild-type. In agreement with these findings, clinical data from 13 bilateral frontoparietal polymicrogyria patients revealed mild serum creatine kinase increase in only two patients. In summary, targeted disruption of GPR56 in mice results in myoblast abnormalities. The absence of a severe muscle phenotype in GPR56 knockout mice and human patients suggests that other factors may compensate for the lack of this G-protein coupled receptor during muscle development and that the motor delay observed in these patients is likely not a result of primary muscle abnormalities.

Polylaminin recognition by retinal cells

Polylaminin (polyLM) is a flat biomimetic polymer of laminin capable of promoting axonal growth both in vitro and in vivo. It is assembled in a cell-free system when laminin 111 is incubated in acidic pH, whereas incubation in neutral buffer leads to the formation of bulky and irregular polymers (LM). In the present work, we compared the behaviors of cells isolated from the P1 rat retina on polyLM and LM. PolyLM induced cellular spreading and the outgrowth of neurites in contact with the substrate, whereas LM led to the formation of large clusters of cells, with neurites growing only inward. After 24 hr in culture, the number of cells on polyLM increased threefold, and this increase was inhibited by 60% in the presence of the PKA inhibitor H89 and by 41% in the presence of the PKC inhibitor chelerythrine chloride, whereas both inhibitors abolished neuritogenesis. Neither the cell number nor the outgrowth of neurites was affected by the ERK1/2 inhibitor PD98059 on polyLM. On the other hand, PD98059 was able to reduce the cell number on LM, whereas the other inhibitors were not. Immunostaining of P1 retina with an antilaminin antibody revealed that the protein was expressed not only at its inner surface but also within the neuroblast layer in close contact with individual cells. Our results indicate that, when provided in its active polymerized form, laminin can influence both neuritogenesis and proliferation of retinal cells.

Lessons from the embryonic neural stem cell niche for neural lineage differentiation of pluripotent stem cells

Pluripotent stem cells offer an abundant and malleable source for the generation of differentiated cells for transplantation as well as for in vitro screens. Patterning and differentiation protocols have been developed to generate neural progeny from human embryonic or induced pluripotent stem cells. However, continued refinement is required to enhance efficiency and to prevent the generation of unwanted cell types. We summarize and interpret insights gained from studies of embryonic neuroepithelium. A multitude of factors including soluble molecules, interactions with the extracellular matrix and neighboring cells cooperate to control neural stem cell self-renewal versus differentiation. Applying these findings and concepts to human stem cell systems in vitro may yield more appropriately patterned cell types for biomedical applications.

Sphingosine 1-phosphate-primed astrocytes enhance differentiation of neuronal progenitor cells

Sphingosine 1-phosphate (S1P) is a bioactive signaling lysophospholipid. Effects of S1P on proliferation, survival, migration, and differentiation have already been described; however, its role as a mediator of interactions between neurons and glial cells has been poorly explored. Here we describe effects of S1P, via the activation of its receptors in astrocytes, on the differentiation of neural progenitor cells (NPC) derived from either embryonic stem cells or the developing cerebral cortex. S1P added directly to NPC induced their differentiation, but S1P-primed astrocytes were able to promote even more pronounced changes in maturation, neurite outgrowth, and arborization in NPC. An increase in laminin by astrocytes was observed after S1P treatment. The effects of S1P-primed astrocytes on neural precursor cells were abrogated by antibodies against laminin. Together, our data indicate that S1P-treated astrocytes are able to induce neuronal differentiation of NPC by increasing the levels of laminin. These results implicate S1P signaling pathways as new targets for understanding neuroglial interactions within the central nervous system.

Autocrine netrin function inhibits glioma cell motility and promotes focal adhesion formation

Deregulation of mechanisms that control cell motility plays a key role in tumor progression by promoting tumor cell dissemination. Secreted netrins and their receptors, Deleted in Colorectal Cancer (DCC), neogenin, and the UNC5 homologues, regulate cell and axon migration, cell adhesion, and tissue morphogenesis. Netrin and netrin receptor expression have previously been shown to be disrupted in invasive tumors, including glioblastoma. We determined that the human glioblastoma cell lines U87, U343, and U373 all express neogenin, UNC5 homologues, and netrin-1 or netrin-3, but only U87 cells express DCC. Using transfilter migration assays, we demonstrate DCC-dependent chemoattractant migration of U87 cells up a gradient of netrin-1. In contrast, U343 and U373 cells, which do not express DCC, were neither attracted nor repelled. Ectopic expression of DCC by U343 and U373 cells resulted in these cells becoming competent to respond to a gradient of netrin-1 as a chemoattractant, and also slowed their rate of spontaneous migration. Here, in addition to netrins' well-characterized chemotropic activity, we demonstrate an autocrine function for netrin-1 and netrin-3 in U87 and U373 cells that slows migration. We provide evidence that netrins promote the maturation of focal complexes, structures associated with cell movement, into focal adhesions. Consistent with this, netrin, DCC, and UNC5 homologues were associated with focal adhesions, but not focal complexes. Disrupting netrin or DCC function did not alter cell proliferation or survival. Our findings provide evidence that DCC can slow cell migration, and that neogenin and UNC5 homologues are not sufficient to substitute for DCC function in these cells. Furthermore, we identify a role for netrins as autocrine inhibitors of cell motility that promote focal adhesion formation. These findings suggest that disruption of netrin signalling may disable a mechanism that normally restrains inappropriate cell migration.

Gene expression analysis of the embryonic subplate

The subplate layer of the cerebral cortex is comprised of a heterogeneous population of cells and contains some of the earliest-generated neurons. In the embryonic brain, subplate cells contribute to the guidance and areal targeting of thalamocortical axons. At later developmental stages, they are predominantly involved in the maturation and plasticity of the cortical circuitry and the establishment of functional modules. We aimed to further characterize the embryonic murine subplate population by establishing a gene expression profile at embryonic day (E) 15.5 using laser capture microdissection and microarrays. The microarray identified over 300 transcripts with higher expression in the subplate compared with the cortical plate at this stage. Using quantitative reverse transcription-polymerase chain reaction, in situ hybridization (ISH), and immunohistochemistry (IHC), we have confirmed specific expression in the E15.5 subplate for 13 selected genes, which have not been previously associated with this compartment (Abca8a, Cdh10, Cdh18, Csmd3, Gabra5, Kcnt2, Ogfrl1, Pls3, Rcan2, Sv2b, Slc8a2, Unc5c, and Zdhhc2). In the reeler mutant, the expression of the majority of these genes (9 of 13) was shifted in accordance with the altered position of subplate. These genes belong to several functional groups and likely contribute to synapse formation and axonal growth and guidance in subplate cells.

Tissue distribution of the laminin beta1 and beta2 chain during embryonic and fetal human development

Laminins are the major glycoproteins present in all basement membranes. Previously, we showed that perlecan is present during human development. Although an overview of mRNA-expression of the laminin β1 and β2 chains in various developing fetal organs is already available, a systematic localization of the laminin β1 and β2 chains on the protein level during embryonic and fetal human development is missing. Therefore, we studied the immunohistochemical expression and tissue distribution of the laminin β1 and β2 chains in various developing embryonic and fetal human organs between gestational weeks 8 and 12. The laminin β1 chain was ubiquitously expressed in the basement membrane zones of the brain, ganglia, blood vessels, liver, kidney, skin, pancreas, intestine, heart and skeletal system. Furthermore, the laminin β2 chain was present in the basement membrane zones of the brain, ganglia, skin, heart and skeletal system. The findings of this study support and expand upon the theory that these two laminin chains are important during human development.

Neuroprotective effects of laminin and its KDI domain

Successful treatment of neurodegenerative diseases and CNS trauma are the most intractable problems in modern medicine. Numerous reports have shown the strong role that laminins have on the survival, regeneration and development of various types of cells, including neural cells. It would be desirable to take advantage of laminin activities for therapeutic purposes. However, there are at least ten laminin variants and the trimeric molecules are of the order of 800,000 molecular weight. Furthermore, human laminins are not available in quantity. Therefore, we and others have taken the approach of determining which domains of the laminin molecules are functional in the CNS, and whether short peptides from these regions exhibit biological activities with the intent of testing their potential for therapeutic use. Understanding the role of laminins and their small biologically active peptide domains, such as the KDI (lysine–aspartic acid–isoleucine) peptide from γ1 laminin, in neuronal development, CNS trauma (spinal cord injury and stroke) and neurodegenerative disorders (amyotrophic lateral sclerosis, Alzheimer’s disease and Parkinson’s disease) may help to develop clinically applicable methods to treat the presently untreatable CNS diseases and trauma even in the near future.

Modulation of neuritogenesis by astrocyte muscarinic receptors

Astrocytes have been shown to release factors that have promoting or inhibiting effects on neuronal development. However, mechanisms controlling the release of such factors from astrocytes are not well established. Astrocytes express muscarinic receptors whose activation stimulates a robust intracellular signaling, although the role of these receptors in glial cells is not well understood. Acetylcholine and acetylcholine receptors are present in the brain before synaptogenesis occurs and are believed to be involved in neuronal maturation. The present study was undertaken to investigate whether stimulation of muscarinic receptors in astrocytes would modulate neurite outgrowth in hippocampal neurons. Rat hippocampal neurons, co-cultured with rat cortical astrocytes previously exposed to the cholinergic agonist carbachol, displayed longer neurites. The effect of carbachol in astrocytes was due to the activation of M3 muscarinic receptors. Exposure of astrocytes to carbachol increased the expression of the extracellular matrix proteins fibronectin and laminin-1 in these cells. This effect was mediated in part by an increase in laminin-1 and fibronectin mRNA levels and in part by the up-regulation of the production and release of plasminogen activator inhibitor-1, an inhibitor of the proteolytic degradation of the extracellular matrix. The inhibition of fibronectin activity strongly reduced the effect of carbachol on the elongation of all the neurites, whereas inhibition of laminin-1 activity reduced the elongation of minor neurites only. Plasminogen activator inhibitor-1 also induced neurite elongation through a direct effect on neurons. Taken together, these results demonstrate that cholinergic muscarinic stimulation of astrocytes induces the release of permissive factors that accelerate neuronal development.

Neurite outgrowth and in vivo sensory innervation mediated by a Ca(V)2.2-laminin beta 2 stop signal

Axons and dendrites of developing neurons establish distributed innervation patterns enabling precise discrimination in sensory systems. We describe the role of the extracellular matrix molecule, laminin beta2, interacting with the Ca(V)2.2 calcium channel in establishing appropriate sensory innervation. In vivo, Ca(V)2.2 is expressed on the growth cones of Xenopus laevis sensory neurites and laminin beta2 is expressed in the skin. Culturing neurons on a laminin beta2 substrate inhibits neurite outgrowth in a specific and calcium-dependent manner. Blocking signaling between laminin beta2 and Ca(V)2.2 leads to increased numbers of sensory terminals in vivo. These findings suggest that interactions between extracellular matrix molecules and calcium channels regulate connectivity in the developing nervous system.

Involvement of Gq/11 in both integrin signal-dependent and -independent pathways regulating endothelin-induced neural progenitor proliferation

We have previously shown that endothelin-B receptor stimulation increases neural progenitor proliferation, partly in G(i) and extracellular matrix molecule-dependent manner. In the present study, we investigated whether G(q/11) is also involved in this response and how G(i) and G(q/11) might regulate the extracellular signal-regulated kinase (ERK) pathway and integrin signaling. Endothelin-induced ERK phosphorylation was independent of integrin ligands, and an inhibitor of G(q/11), YM-254890, as well as pertussis toxin, partially inhibited endothelin-stimulated phosphorylation of Raf-1 and ERK. Endothelin-stimulated protein kinase C (PKC) was partially inhibited by both YM-254890 and pertussis toxin, while only pertussis toxin attenuated endothelin-induced Ras activation. In contrast, endothelin increased tyrosine phosphorylation of focal adhesion kinase (FAK) and paxillin in an integrin ligand-dependent manner. Both YM-254890 and pertussis toxin partially inhibited endothelin-stimulated phosphorylation of these proteins. A PKC inhibitor and down-regulation of PKC prevented endothelin-induced phosphorylation of paxillin and ERK. In addition, endothelin-induced proliferation and DNA synthesis were partially inhibited by YM-254890 and pertussis toxin. Taken together, the results indicate that endothelin activates PKC via G(q/11) and G(i), and consequently stimulates the ERK cascade in cooperation with Ras signaling stimulated by G(i). PKC appears to increase tyrosine phosphorylation of paxillin to enhance integrin signaling, which further increases DNA synthesis and proliferation.

Proteolysis and membrane capture of F-spondin generates combinatorial guidance cues from a single molecule

The formation of neuronal networks is governed by a limited number of guidance molecules, yet it is immensely complex. The complexity of guidance cues is augmented by posttranslational modification of guidance molecules and their receptors. We report here that cleavage of the floor plate guidance molecule F-spondin generates two functionally opposing fragments: a short-range repellent protein deposited in the membrane of floor plate cells and an adhesive protein that accumulates at the basement membrane. Their coordinated activity, acting respectively as a short-range repellant and a permissive short-range attractant, constricts commissural axons to the basement membrane beneath the floor plate cells. We further demonstrate that the repulsive activity of the inhibitory fragment of F-spondin requires its presentation by the lipoprotein receptor–related protein (LRP) receptors apolipoprotein E receptor 2, LRP2/megalin, and LRP4, which are expressed in the floor plate. Thus, proteolysis and membrane interaction coordinate combinatorial guidance signaling originating from a single guidance cue.

Neurodevelopmental deficits in Pierson (microcoria-congenital nephrosis) syndrome

Pierson syndrome is an autosomal recessive disorder comprising congenital nephrotic syndrome with diffuse mesangial sclerosis and distinct eye abnormalities with microcoria reported as the most prominent clinical feature. LAMB2 mutations leading to lack of laminin beta2 were identified as the molecular cause underlying Pierson syndrome. Although LAMB2 is known to be expressed in the neuromuscular system, and defects of the neuromuscular junctions had been found in laminin beta2-deficient mice, no consistent neurological phenotype has been described clinically in murine or human laminin beta2-deficiency before. This is likely due to the early lethality from renal failure. Here we provide a detailed description of neurological manifestations and development in four patients affected by Pierson syndrome, who survived until the age of 1.3-4.8 years owing to renal replacement therapy. Severe muscular hypotonia, psychomotor retardation, and blindness were present in three patients harboring truncating mutations on both LAMB2 alleles. These symptoms were not attributable to complications of chronic renal failure, thus representing a primary feature of the genetic disorder. Alterations in skeletal muscle tissue from one case were compatible with a chronic denervating process. One affected girl, however, exhibited a milder course of renal disease, normal development, and preserved vision, presumably owing to some residual LAMB2 function. Our findings indicate that severe neurodevelopmental deficits have to be considered as part of Pierson syndrome, at least in the presence of biallelic functional null mutations (complete lack of laminin beta2). This is an important issue in the counseling of parents of an affected newborn or infant.

Laminins containing the beta2 chain modulate the precise organization of CNS synapses

Synapses are formed and stabilized by concerted interactions of pre-, intra-, and post-synaptic components; however, the precise nature of the intrasynaptic components in the CNS remains obscure. Potential intrasynaptic components include extracellular matrix molecules such as laminins; here, we isolate beta2-containing laminins, including perhaps laminins 13 (alpha3beta2gamma3) and 14 (alpha4beta2gamma3), from CNS synaptosomes suggesting a role for these molecules in synaptic organization. Indeed, hippocampal synapses that form in vivo in the absence of these laminins are malformed at the ultrastructural level and this malformation is replicated in synapses formed in vitro, where laminins are provided largely by the post-synaptic neuron. This recapitulation of the in vivo function of laminins in vitro suggests that the malformations are a direct consequence of the removal of laminins from the synapse. Together, these results support a role for neuronal laminins in the structural integrity of central synapses.

Developmental and injury-induced expression of alpha1beta1 and alpha6beta1 integrins in the rat spinal cord

Loss and damage to blood vessels are thought to contribute to secondary tissue loss after spinal cord injury. Integrins might be therapeutic targets to protect the vasculature and/or promote angiogenesis, as their activation can promote tubule formation and survival of endothelial cells in vitro. Here, we show that immunostaining with an antibody against the alpha1beta1 integrin heterodimer is present only in blood vessels from postnatal day 1 (P1) through adulthood in Sprague-Dawley rats. After a spinal cord contusion at T9 in adults, the area of alpha1beta1 integrin positive blood vessels increases within 11 mm from the injury site at 3 days post-injury and remains prominent within the injured core only at 7 days. Staining for the alpha6beta1 integrin heterodimer increases in blood vessels between P10 and adulthood and is present in preganglionic neurons of the intermediolateral cell column (IML) at all ages. The alpha6beta1 integrin is also expressed by motor neurons postnatally, and oligodendrocyte precursors (OPCs), as previously reported. After the contusion, the area of alpha6beta1-stained blood vessels is increased at 3 days and most prominently, 1 mm from the injury site, followed by a significant reduction at 7 days, when alpha6beta1 integrin staining is most prominent around the injured core. Staining is also present in a subset of microglia and/or macrophages. These results raise the possibility that alpha1beta1 and alpha6beta1 integrins in blood vessels might be targeted to reduce blood vessel loss and promote angiogenesis, which may promote tissue sparing after spinal cord injury.

Temporally restricted substrate interactions direct fate and specification of neural precursors derived from embryonic stem cells

It was, until now, not entirely clear how the nervous system attains its cellular phenotypic diversity and wired complexity during development. Here we describe how environmental interactions alone can modify the development of neurogenic precursor cells. Upon evaluating distinct growth-permissive substrates in an embryonic stem cell-neurogenesis assay, we found that laminin, fibronectin, and gelatin instruct neural fate and alter the functional specification of neurons when applied at distinct stages of development. Changes in phenotypic, electrophysiological, and molecular characteristics could resemble cellular events and interactions in the early embryonic brain and may explain why these extracellular matrix components transiently demarcate certain developing brain structures.

Prenatal findings in four consecutive pregnancies with fetal Pierson syndrome, a newly defined congenital nephrosis syndrome

OBJECTIVE

To describe the prenatal findings in Pierson syndrome, a newly defined autosomal recessive entity, comprising congenital nephrotic syndrome (CNS) with diffuse mesangial sclerosis and distinct eye abnormalities due to LAMB2 mutations.

METHODS

Serial prenatal ultrasound examinations were performed in four consecutive pregnancies affected by Pierson syndrome in the same family. LAMB2 mutations were demonstrated in retrospect by direct sequencing of the gene in the newborn index patient and three abortuses.

RESULTS

Fetal ultrasound consistently revealed marked renal hyperechogenicity associated with variable degree of pyelectasis. These features were detectable by 15 weeks of gestation in all fetuses. Hydrops fetalis due to severe hypalbuminemia demonstrated by chordocentesis occurred in one fetus. Placentas were significantly enlarged. Development of oligohydramnios indicated prenatal decline of renal excretory function. Anencephaly was detected in another fetus with molecularly proven Pierson syndrome at 12 weeks of gestation.

CONCLUSION

We conclude that Pierson syndrome has to be considered in the differential diagnosis of nephrotic disorders with prenatal onset. Ultrasound criteria for differentiation from the most common type of CNS-congenital nephrosis of the Finnish type (CNF)-are discussed. Because of its prognostic relevance, we advocate molecular genetic testing of LAMB2 in any case of prenatally detected nephrotic syndrome with negative results of NPHS1 mutational screening, especially in the presence of the typical sonomorphologic findings of the kidneys and the development of oligohydramnios.

Perinatal subplate neuron injury: implications for cortical development and plasticity

Perinatal brain injury may result in widespread deficits in visual, motor and cognitive systems suggesting disrupted brain development. Neurosensory and cognitive impairment are observed at increasing frequency with decreasing gestational ages, suggesting a unique vulnerability of the developing brain. The peak of human subplate neuron development coincides with the gestational ages of highest vulnerability to perinatal brain injury in the premature infant. At the same time, human thalamocortical connections are forming and being refined by activity-dependent mechanisms during critical periods. Subplate neurons are the first cortical neurons to mature and are selectively vulnerable to early hypoxic-ischemic brain injury in animal models. Timing of subplate neuron death determines the resulting defect in thalamocortical development: very early excitotoxic subplate neuron death results in failure of thalamocortical innervation, while later subplate neuron death interferes with the refinement of thalamocortical connections into mature circuits. We suggest that subplate neuron injury may be a central component of perinatal brain injury resulting in specific neurodevelopmental consequences.

Human diseases reveal novel roles for neural laminins

Extracellular matrix molecules such as laminins have a central role in regulating cell behaviour. However, our understanding of their functions in the mammalian nervous system is incomplete. It is important to establish these functions, both for an understanding of normal development and to devise strategies to enhance repair. Here, we review how insights gained from human diseases caused by genetic mutations in laminins or their receptors have revealed significant and sometimes unexpected roles for laminins in neural stem cells, migrating neurons and myelinating glia, in both the PNS and CNS.

Sequence of oligodendrocyte development in the human fetal telencephalon

Oligodendrocytes (OL), cells that myelinate axons in the CNS, differentiate from early to late oligodendrocyte progenitor cells (OPC) to become mature OL. Unlike the case in the rodent brain, myelin formation starts prenatally in the human brain, but the sequence of OL development and the onset of myelination are not well understood. We studied the human fetal forebrain at midgestation (17-23 gestational weeks, g.w.) using OL lineage-specific antibodies and mRNA probes. Early OPC were present in a gradient from the subventricular zone to the cortical plate. Their close apposition to radial glia fibers suggests a possible role of these fibers in OPC migration. Late OPC reached peak density in the subplate layer, whereas multipolar cells with the morphology of mature OL were restricted to the emerging white matter. At 20 g.w., myelinated axons were observed in the diencephalon, but not in the telencephalon, consistent with caudal-to-rostral progression of myelination. Interestingly, in organotypic slice cultures of the same gestational ages, the subventricular zone contained a considerably greater number of the mature OL cells, suggesting the presence of inhibitory signals in vivo. Overall, in addition to considerable similarities with rodents, important differences in temporal and spatial distribution and regulatory signals for OL differentiation exist in the human brain.

Human laminin beta2 deficiency causes congenital nephrosis with mesangial sclerosis and distinct eye abnormalities

Congenital nephrotic syndrome (CNS) is clinically and genetically heterogeneous, with mutations in WT1, NPHS1 and NPHS2 accounting for part of cases. We recently delineated a new autosomal recessive entity comprising CNS with diffuse mesangial sclerosis and distinct ocular anomalies with microcoria as the leading clinical feature (Pierson syndrome). On the basis of homozygosity mapping to markers on chromosome 3p14-p22, we identified homozygous or compound heterozygous mutations of LAMB2 in patients from five unrelated families. Most disease-associated alleles were truncating mutations. Using immunohistochemistry and western blotting we could demonstrate that the respective LAMB2 mutations lead to loss of laminin beta2 expression in kidney and other tissues studied. Laminin beta2 is known to be abundantly expressed in the glomerular basement membrane (GBM) where it is thought to play a key role in anchoring as well as differentiation of podocyte foot processes. Lamb2 knockout mice were reported to exhibit congenital nephrosis in association with anomalies of retina and neuromuscular junctions. By studying ocular laminin beta2 expression in unaffected controls, we detected the strongest expression in the intraocular muscles corresponding well to the characteristic hypoplasia of ciliary and pupillary muscles observed in patients. Moreover, we present first clinical evidence of severe impairment of vision and neurodevelopment due to LAMB2 defects. Our current data suggest that human laminin beta2 deficiency is consistently and specifically associated with this particular oculorenal syndrome. In addition, components of the molecular interface between GBM and podocyte foot processes come in the focus as potential candidates for isolated and syndromic CNS.

Oligodendrocyte precursors on the move: mechanisms directing migration

Oligodendrocyte precursor cells traverse long distances to reach their axonal targets. The molecules that influence their migration include a combination of short-range attractants and repellents and long-range chemoattractants and chemorepellents. Here, the authors review mechanisms that direct oligodendrocyte precursor cells as they migrate throughout the developing CNS.

Basement membrane assembly, stability and activities observed through a developmental lens

Basement membranes are cell surface associated extracellular matrices containing laminins, type IV collagens, nidogens, perlecan, agrin, and other macromolecules. Biochemical and ultrastructural studies have suggested that basement membrane assembly and integrity is provided through multiple component interactions consisting of self-polymerizations, inter-component binding, and cell surface adhesions. Mutagenesis in vertebrate embryos and embryoid bodies have led to revisions of this model, providing evidence that laminins are essential for the formation of an initial polymeric scaffold of cell-attached matrix which matures in stability, ligand diversity, and functional complexity as additional matrix components are integrated into the scaffold. These studies also demonstrate that basement membrane components differentially promote cell polarization, organize and compartmentalize developing tissues, and maintain adult tissue function.

Disappearance of the post-lesional laminin immunopositivity of brain vessels is parallel with the formation of gliovascular junctions and common basal lamina. A double-labelling immunohistochemical study

Previous studies revealed that during development the laminin immunopositivity gradually disappeared from the brain vessels, but temporarily re-appeared in them around lesions. The question of the present study was the correlation between the post-lesional vascular immunopositivity to laminin and the glial reaction. Following stab wounds, double fluorescent immunohistochemical labelling was performed against laminin (using a polyclonal antiserum against laminin 1) and glial fibrillary acidic protein. A number of vessels exhibited intense immunopositivity to laminin within the lesioned tissue. Where these laminin immunopositive vessels entered the perilesional brain substance, the astroglia formed contacts on them, and the separate vascular and glial basal laminae fused. The disappearance of the post-lesional laminin immunopositivity seemed to coincide with these phenomena. When monoclonal antibodies were applied against the beta1 and gamma1 laminin chains, vessels proved to be immunopositive at the lesion, but none in the intact brain tissue. No immunoreactivity was detected in the cases of alpha2 and beta2 chains. The results suggest that the disappearance of laminin immunopositivity may be attributed to that the epitopes become inaccessible for antibodies owing to the formation of gliovascular junctions and common basal lamina between astroglia and vessel. The possible role of an alteration in the laminin composition and the effect of fixation are discussed.

Expression of laminin chains by central neurons: analysis with gene and protein trapping techniques

Laminins exert numerous effects on neurons in vitro, but expression of laminin subunit genes by neurons in vivo remains controversial. To reexamine this issue, we generated mice from ES cells in which the laminin alpha1, alpha5, beta1, and gamma1 genes had been "trapped" by insertion of a histochemically detectable selectable marker, betageo (beta-galactosidase fused to neomycin phosphotransferase). The presence of laminin-betageo fusion proteins was assayed histochemically and immunochemically, revealing expression of laminin beta1 and gamma1 genes, but not alpha chain genes, by defined subsets of neurons in brain and retina. We also used the gene traps in a novel way to assay expression of endogenous laminin subunits, which were barely detectable by ordinary immunohistochemical methods. The trapping vector included a transmembrane domain that anchors proteins otherwise destined for secretion. Laminin alpha/beta/gamma heterotrimers are assembled intracellularly, and we show that the trapped laminin gamma1 fusion protein "co-trapped" endogenous beta1 intracellularly. The laminin gamma1 fusion was also able to co-trap transgene-derived alpha chains, but we detected no co-trapped endogenous alpha chains. The co-trapping method may be generally useful for identifying proteins or isolating protein complexes associated with trapped gene products.

Gamma 1 laminin and its biologically active KDI-domain may guide axons in the floor plate of human embryonic spinal cord

Immunocytochemistry, in situ hybridization and Matrigel-embedded cultures were used to investigate the distribution of laminins during development of the human embryonic spinal cord (7-11 weeks). Our results indicate that alpha 1, beta 1, beta 3 and gamma 1 laminins localize as punctate deposits in the floor plate region in association with commissural fibers crossing the ventral midline. In addition, the neurite outgrowth domain of gamma 1 laminin accumulates heavily in the floor plate region, in the notochord and in GFAP-immunoreactive glial fibers of the embryonic spinal cord. In culture experiments, the biologically active KDI-domain of gamma 1 laminin selectively attracted directional outgrowth of neurites from explants of the dorsal spinal cord. The spatial and temporal colocalization of punctate deposits of laminins with nerve fibers crossing the ventral midline, and the guidance of neurites by the KDI-peptide domain, indicate that laminins, specifically the gamma 1 laminin, may be involved in guidance of axons during embryonic development of the human spinal cord.

The extracellular matrix in axon regeneration

This review of ECM molecules shows quite clearly the function of the ECM in development but more importantly in the mature CNS after injury. Most of the proteoglycans, especially the large CS-PGs, are able to inhibit neurite outgrowth and in vivo experiments are now in progress to specifically inhibit these important molecules. The nature of growth promoter ECM molecules in the CNS after injury, either within or distant from the injury is now becoming better appreciated and we suggest that the laminin family should be important targets for exploration. Indeed, a better understanding of the interaction of laminin with those ECM components that are inhibitory is a clear goal for the future. Our ultimate aim must be to change the balance of factors at lesion sites to allow the more permissive environment after CNS injury to predominate.

Structure of laminin substrate modulates cellular signaling for neuritogenesis

Laminin, a major component of basement membranes, can self-assemble in vitro into a typical mesh-like structure, according to a mass-action-driven process. Previously, we showed that pH acidification dramatically increased the efficiency of laminin self-assembly, practically abolishing the necessity for a minimal protein concentration. Here we have characterized the morphologies of laminin matrices produced in either neutral or acidic conditions and compared their capacities to induce neuritogenesis of rat embryonic cortical neurons. Although laminin matrices formed in neutral buffer presented aggregates of heterogeneous morphology, the acidic matrix consisted of a homogeneous hexagonal sheet-like structure. The latter was comparable to the matrix assembled in vivo at the inner limiting membrane of the retina in newborn rats, shown here, and to matrices secreted by cultivated cells, shown elsewhere. The average neurite length of cortical neurons plated on acidic matrices was 244.9 micro m, whereas on neutral matrices this value dropped to 104.1 micro m. Increased neuritogenesis on the acidic matrix seemed to be associated with a higher degree of neuronal differentiation, since cell proliferation was immediately arrested upon plating, whereas on neutral matrices, the cell number increased six-fold within 24 hours. Investigation of the mechanisms mediating neurite outgrowth on each condition revealed that the extensive neuritogenesis observed on the acidic matrix involved activation of protein kinase A, whereas moderate neuritogenesis on neutral laminin was mediated by activation of protein kinase C and/or myosin light-chain kinase. Explants of cerebral cortex from P2 rats did not grow on the neutral laminin substrate but presented extensive cell migration and neurite outgrowth on the acidic laminin matrix. We propose that laminin can self-assemble independently of cell contact and that the assembling mode differentially modulates neuritogenesis and neuroplasticity.

Modulation of glial glutamate transport through cell interactions with the extracellular matrix

Glial glutamate transport plays a pivotal role in maintaining glutamate homeostasis in the central nervous system. Expression of glutamate transporters is highly regulated during brain development, and a number of pathological conditions are associated with deficits in expression and/or function of glutamate transports. While several soluble factors have been shown to regulate the expression of glutamate transporter, the contribution of cell-cell interaction and cell-environmental interaction in the regulation of glutamate transport is unknown. Extracellular matrix (ECM) molecules are essential components in cell-cell and cell-environmental interactions, and the ECM has been shown to play critical role in normal development and during brain pathogenesis. We, therefore, investigated the possibility that ECM molecules may regulate astrocytic glutamate transport. Therefore, we cultured rat cortical astrocytes with different ECMs and determined expression levels of the two astrocytic glutamate transporters GLT-1 and GLAST by Western Blot and determined transporter activity through measurements of 3H-D-aspartate uptake. Astrocytes grown on poly-ornithine or poly-D/L-lysine showed approximately two-fold higher GLT-1 expression than sister cells grown on plastic dishes without ECM. Naturally occurring ECM's, including laminin and collagen, showed a dose-dependent regulation of GLT-1 protein expression. These effects were specific for GLT-1 as GLAST expression was unaffected by different ECMs. Surprisingly, however, none of the examined ECMs altered the apparent glutamate uptake activity. In probing blots side-by-side for expression of Na(+)/K(+)-ATPase, we found that ECMs affected expression of Na(+)/K(+)-ATPase and GLT-1 in a reciprocal fashion. Poly-ornithine, for example, enhanced GLT-1 expression, but reduced expression of Na(+)/K(+)-ATPase. Na(+) transport may, thus, be a limiting factor for glutamate uptake.

Laminets: laminin- and netrin-related genes expressed in distinct neuronal subsets

Laminins and netrins are families of related secreted proteins known to play critical roles in guiding the growth of peripheral and central axons, respectively. Here we report the identification of two novel cell surface glycoproteins that we name laminets because they resemble both laminins and netrins. Laminet-1 and -2 are selectively expressed in neurons, each in a distinct subset that includes populations in forebrain, midbrain, hindbrain, spinal cord, and spinal ganglia. In several forebrain regions, including main relays of the central olfactory pathway, laminet-1 and -2 are expressed in nonoverlapping neuronal subsets. Both laminets are subject to alternative splicing which, in the case of laminet-1, generates at least 10 distinct isoforms, each of which contains a unique combination of potential binding sites for ligands or counterreceptors. Their complex patterns of distribution and isoform diversity, along with their homology to known axon guidance molecules, suggest that laminets contribute to the patterning of neuronal connections.

A gene expression profile of Alzheimer's disease

Postmortem analysis of brains of patients with Alzheimer's disease (AD) has led to diverse theories about the causes of the pathology, suggesting that this complex disease involves multiple physiological changes. In an effort to better understand the variety and integration of these changes, we generated a gene expression profile for AD brain. Comparing affected and unaffected brain regions in nine controls and six AD cases, we showed that 118 of the 7050 sequences on a broadly representative cDNA microarray were differentially expressed in the amygdala and cingulate cortex, two regions affected early in the disease. The identity of these genes suggests the most prominent upregulated physiological correlates of pathology involve chronic inflammation, cell adhesion, cell proliferation, and protein synthesis (31 upregulated genes). Conversely, downregulated correlates of pathology involve signal transduction, energy metabolism, stress response, synaptic vesicle synthesis and function, calcium binding, and cytoskeleton (87 downregulated genes). The results support several separate theories of the causes of AD pathology, as well as add to the list of genes associated with AD. In addition, approximately 10 genes of unknown function were found to correlate with the pathology.

Sensory axon response to substrate-bound Slit2 is modulated by laminin and cyclic GMP

In vertebrates, Slit2 is a chemorepellent for some developing axons but stimulates axonal elongation and branching of sensory axons. In vivo, Slit2 is cleaved into 140-kDa N-terminal (Slit2-N) and 55- to 60-kDa C-terminal fragments, but the uncleaved/full-length form can also be isolated from brain extracts. As Slit2-N and full-length Slit2 bind tightly to cell membranes, we decided to explore the response of rat dorsal root ganglia (DRG) axons to substrate-bound Slit2 fragments in the stripe assay. Slit2 fragments were avoided by DRG axons when expressed on membranes or coated as stripes on laminin. However, when the Slit2 stripes were coated on fibronectin, DRG axons still avoided full-length Slit2 but grew preferentially on Slit2-N. DRG axon response to Slit2 fragments could be modulated by cGMP and by a laminin-1 peptide. These results strongly support the idea that extracellular matrix proteins modulate the response of growth cones to chemotropic molecules by modulating cyclic nucleotide levels.

Tenascin and laminin function in target recognition and central synaptic differentiation

The influence of the target cell-issued extracellular molecules tenascin-C and laminin on synaptogenesis was studied in mixed primary cultures of pituitary melanotrophs and hypothalamic neurons. We could demonstrate in this neuron-target co-culture system a new role for tenascin-C, which appeared to be expressed as an early and transitory signal of target recognition for selective afferent fibers. Tenascin-C expression disappeared from the melanotrophs soon after the establishment of neural contacts. Concomitantly, the melanotrophs became immunoreactive for laminins, and more specifically for the synaptic isoform beta2 chain-containing laminin. The laminin signal appeared to be involved in the induction of synaptic differentiation, selectively with fibers containing both dopamine and GABA, like those innervating the melanotrophs in situ.

Neurons and glial cells of the embryonic human brain and spinal cord express multiple and distinct isoforms of laminin

We have identified by immunocytochemistry, Western blotting, and RT-PCR the isoforms of laminin expressed by glial cells and neurons cultured from human embryonic brain and spinal cord. We show that most of the known laminins are present in human neurons and glial cells. Importantly, Western analysis demonstrates that the isoforms of laminin present in embryonic human brain differ from those expressed in human spinal cord. Neurons of the brain and spinal cord also express their distinct and characteristic isoforms of laminin compared to the glial cells of the same CNS regions. These results suggest that, in addition to the known laminins, several novel isoforms may exist in the human embryonic CNS. The observed differences between the isoforms of laminin in brain and spinal cord neurons and glial cells may result from primary structural changes or from posttranslational modifications, e.g., variations in glycosylation. Thus, identification of these novel laminins and determination of their function(s) should further our understanding of the mechanisms of aging, disease, and trauma in the human CNS.

Differential mRNA expression of the related extracellular matrix glycoproteins SC1 and SPARC in the rat embryonic nervous system and skeletal structure

SPARC is a multifunctional extracellular matrix glycoprotein that shares partial sequence homology with SC1. These extracellular matrix molecules are thought to play important roles in modulating cellular interactions. In vitro, SPARC has been shown to exhibit anti-adhesive activity. In the present investigation, in situ hybridization is used to compare the expression patterns of SC1 and SPARC mRNA in the rat embryo. Results show that SC1 and SPARC expression is spatially and temporally regulated. SC1 mRNA is strongly expressed in the embryonic brain and spinal cord, whereas SPARC mRNA is enriched in craniofacial cartilage and skeletal structures. This differential expression pattern in the rat embryo suggests that SC1 plays an important role in the developing nervous system, whereas SPARC participates primarily in events associated with skeletal development. However at embryonic day 17, SC1 and SPARC mRNA show parallel expression patterns in areas of the cerebellum undergoing cell migratory events.

Laminins and human disease

The laminin protein family has diverse tissue expression patterns and is involved in the pathology of a number of organs, including skin, muscle, and nerve. In the skin, laminins 5 and 6 contribute to dermal-epidermal cohesion, and mutations in the constituent chains result in the blistering phenotype observed in patients with junctional epidermolysis bullosa (JEB). Allelic heterogeneity is observed in patients with JEB: mutations that results in premature stop codons produce a more severe phenotype than do missense mutations. Gene therapy approaches are currently being studied in the treatment of this disease. A blistering phenotype is also observed in patients with acquired cicatricial pemphigoid (CP). Autoantibodies targeted against laminins 5 and 6 destabilize epithelial adhesion and are pathogenic. In muscle cells, laminin alpha 2 is a component of the bridge that links the actin cytoskeleton to the extracellular matrix. In patients with laminin alpha 2 mutations, the bridge is disrupted and mature muscle cells apoptose. Congenital muscular dystrophy (CMD) results. The role of laminin in diseases of the nervous system is less well defined, but the extracellular protein has been shown to serve an important role in peripheral nerve regeneration. The adhesive molecule influences neurite outgrowth, neural differentiation, and synapse formation. The broad spatial distribution of laminin gene products suggests that laminin may be involved in a number of diseases for which pathogenic mechanisms are still being unraveled.