Laminin γ3 Chain Binds to Nidogen and Is Located in Murine Basement Membranes

The role of extracellular matrix alterations in mediating astrocyte damage and pericyte dysfunction in Alzheimer's disease: A comprehensive review

The brain is a highly vascularized tissue protected by the blood-brain barrier (BBB), a complex structure allowing only necessary substances to pass through into the brain while limiting the entrance of harmful toxins. The BBB comprises several components, and the most prominent features are tight junctions between endothelial cells (ECs), which are further wrapped in a layer of pericytes. Pericytes are multitasked cells embedded in a thick basement membrane (BM) that consists of a fibrous extracellular matrix (ECM) and are surrounded by astrocytic endfeet. The primary function of astrocytes and pericytes is to provide essential blood supply and vital nutrients to the brain. In Alzheimer's disease (AD), long-term neuroinflammatory cascades associated with infiltration of harmful neurotoxic proteins may lead to BBB dysfunction and altered ECM components resulting in brain homeostatic imbalance, synaptic damage, and declined cognitive functions. Moreover, BBB structure and functional integrity may be lost due to induced ECM alterations, astrocyte damage, and pericytes dysfunction, leading to amyloid-beta (Aβ) hallmarks deposition in different brain regions. Herein, we highlight how BBB, ECM, astrocytes, and pericytes dysfunction can play a leading role in AD's pathogenesis and discuss their impact on brain functions.

Variants in LAMC3 Causes Occipital Cortical Malformation

Occipital cortical malformation (OCCM) is a disease caused by malformations of cortical development characterized by polymicrogyria and pachygyria of the occipital lobes and childhood-onset seizures. The recessive or complex heterozygous variants of the LAMC3 gene are identified as the cause of OCCM. In the present study, we identified novel complex heterozygous variants (c.470G > A and c.4030 + 1G > A) of the LAMC3 gene in a Chinese female with childhood-onset seizures. Cranial magnetic resonance imaging was normal. Functional experiments confirmed that both variant sites caused premature truncation of the laminin γ3 chain. Bioinformatics analysis predicted 10 genes interacted with LAMC3 with an interaction score of 0.4 (P value = 1.0e–16). The proteins encoded by these genes were mainly located in the basement membrane and extracellular matrix component. Furthermore, the biological processes and molecular functions from gene ontology analysis indicated that laminin γ3 chain and related proteins played an important role in structural support and cellular processes through protein-containing complex binding and signaling receptor binding. KEGG pathway enrichment predicted that the LAMC3 gene variant was most likely to participate in the occurrence and development of OCCM through extracellular matrix receptor interaction and PI3K-Akt signaling pathway.

Compound heterozygous variants in LAMC3 in association with posterior periventricular nodular heterotopia

BACKGROUND

Periventricular nodular heterotopia (PNH) is a malformation of cortical development characterized by nodules of abnormally migrated neurons. The cause of posteriorly placed PNH is not well characterised and we present a case that provides insights into the cause of posterior PNH.

CASE PRESENTATION

We report a fetus with extensive posterior PNH in association with biallelic variants in LAMC3. LAMC3 mutations have previously been shown to cause polymicrogyria and pachygyria in the occipital cortex, but not PNH. The occipital location of PNH in our case and the proposed function of LAMC3 in cortical development suggest that the identified LAMC3 variants may be causal of PNH in this fetus.

CONCLUSION

We hypothesise that this finding extends the cortical phenotype associated with LAMC3 and provides valuable insight into genetic cause of posterior PNH.

Screening of Integrin Heterodimers Expressed Functionally on the Undifferentiated Spermatogonial Stem Cells in the Outbred ICR Mice

Background and Objectives

Outbred mice are widely used in toxicology, pharmacology, and fundamental biomedical research. However, there have been no reports of in vitro culture systems for spermatogonial stem cells (SSCs) derived from these mice.

Methods

As a step towards constructing a non-cellular niche supporting the in vitro maintenance of outbred mouse SSC self-renewal, we systematically investigated the types of integrin heterodimers that are expressed transcriptionally, translationally, and functionally in SSCs derived from Imprinting Control Region (ICR) mice.

Results

Among the genes encoding 25 integrin subunits, integrin α₁, α₅, α₆, α₉, α_V, and α_E, and integrin β₁ and β₅ had significantly higher transcriptional levels than the other subunits. Furthermore, at the translational level, integrin α₅, α₆, α₉, α_V, α_E, and β₁ were localized on the surface of SSCs, but integrin α₁ and β₅ not. Moreover, significantly stronger translational expression than integrin α₉ and α_E was observed in integrin α₅, α₆, α_V, and β₁. SSCs showed significantly increased adhesion to fibronectin, laminin, tenascin C and vitronectin, and functional blocking of integrin α₅β₁, α₆β₁, α₉β₁ or α_Vβ₁ significantly inhibited adhesion to these molecules.

Conclusions

We confirmed that integrin α₅β₁, α₆β₁, α₉β₁ and α_Vβ₁ actively function on the surface of undifferentiated SSCs derived from outbred ICR mice.

The extracellular matrix of the blood-brain barrier: structural and functional roles in health, aging, and Alzheimer's disease

There is increasing interest in defining the location, content, and role of extracellular matrix (ECM) components in brain structure and function during development, aging, injury, and neurodegeneration. Studies in vivo confirm brain ECM has a dynamic composition with constitutive and induced alterations that impact subsequent cell-cell and cell-matrix interactions. Moreover, it is clear that for any given ECM component, the brain region, and cell type within that location, determines the direction, magnitude, and composition of those changes. This review will examine the ECM at the neurovascular unit (NVU) and the blood-brain barrier (BBB) within the NVU. The discussion will begin at the glycocalyx ECM on the luminal surface of the vasculature, and progress to the abluminal side with a focus on changes in basement membrane ECM during aging and neurodegeneration.

Laminins and their receptors in the CNS

Laminin, an extracellular matrix protein, is widely expressed in the central nervous system (CNS). By interacting with integrin and non-integrin receptors, laminin exerts a large variety of important functions in the CNS in both physiological and pathological conditions. Due to the existence of many laminin isoforms and their differential expression in various cell types in the CNS, the exact functions of each individual laminin molecule in CNS development and homeostasis remain largely unclear. In this review, we first briefly introduce the structure and biochemistry of laminins and their receptors. Next, the dynamic expression of laminins and their receptors in the CNS during both development and in adulthood is summarized in a cell-type-specific manner, which allows appreciation of their functional redundancy/compensation. Furthermore, we discuss the biological functions of laminins and their receptors in CNS development, blood-brain barrier (BBB) maintenance, neurodegeneration, stroke, and neuroinflammation. Last, key challenges and potential future research directions are summarized and discussed. Our goals are to provide a synthetic review to stimulate future studies and promote the formation of new ideas/hypotheses and new lines of research in this field.

Basement membranes in the cornea and other organs that commonly develop fibrosis

Basement membranes are thin connective tissue structures composed of organ-specific assemblages of collagens, laminins, proteoglycan-like perlecan, nidogens, and other components. Traditionally, basement membranes are thought of as structures which primarily function to anchor epithelial, endothelial, or parenchymal cells to underlying connective tissues. While this role is important, other functions such as the modulation of growth factors and cytokines that regulate cell proliferation, migration, differentiation, and fibrosis are equally important. An example of this is the critical role of both the epithelial basement membrane and Descemet's basement membrane in the cornea in modulating myofibroblast development and fibrosis, as well as myofibroblast apoptosis and the resolution of fibrosis. This article compares the ultrastructure and functions of key basement membranes in several organs to illustrate the variability and importance of these structures in organs that commonly develop fibrosis.

Epidermolysis bullosa: Molecular pathology of connective tissue components in the cutaneous basement membrane zone

Epidermolysis bullosa (EB), a group of heritable skin fragility disorders, is characterized by blistering, erosions and chronic ulcers in the skin and mucous membranes. In some forms, the blistering phenotype is associated with extensive mutilating scarring and development of aggressive squamous cell carcinomas. The skin findings can be associated with extracutaneous manifestations in the ocular as well as gastrointestinal and vesico-urinary tracts. The phenotypic heterogeneity reflects the presence of mutations in as many as 20 different genes expressed in the cutaneous basement membrane zone, and the types and combinations of the mutations and their consequences at the mRNA and protein levels contribute to the spectrum of severity encountered in different subtypes of EB. This overview highlights the molecular genetics of EB based on mutations in the genes encoding type VII and XVII collagens as well as laminin-332. The mutations identified in these protein components of the extracellular matrix attest to their critical importance in providing stability to the cutaneous basement membrane zone, with implications for heritable and acquired diseases.

Shaping Cell Fate: Influence of Topographical Substratum Properties on Embryonic Stem Cells

Development of multicellular organisms is a highly orchestrated process, with cells responding to factors and features present in the extracellular milieu. Changes in the surrounding environment help decide the fate of cells at various stages of development. This review highlights recent research that details the effects of mechanical properties of the surrounding environment and extracellular matrix and the underlying molecular mechanisms that regulate the behavior of embryonic stem cells (ESCs). In this study, we review the role of mechanical properties during embryogenesis and discuss the effect of engineered microtopographies on ESC pluripotency.

Knockdown of Laminin gamma-3 (Lamc3) impairs motoneuron guidance in the zebrafish embryo

Background: Previous work in the zebrafish embryo has shown that laminin γ-3 ( lamc3) is enriched in endothelial cells marked by expression of fli1a, but the role of Lamc3 has been unknown. Methods: We use antisense morpholino oligonucleotides, and CRISPR/Cas9 mutagenesis of F0 embryos, to create zebrafish embryos in which lamc3 expression is compromised. Transgenic imaging, immunofluorescence, and in situ hybridisation reveal that Lamc3 loss-of-function affects the development of muscle pioneers, endothelial cells, and motoneurons. Results:  Lamc3 is enriched in endothelial cells during zebrafish development, but it is also expressed by other tissues. Depletion of Lamc3 by use of antisense morpholino oligonucleotides perturbs formation of the parachordal chain and subsequently the thoracic duct, but Lamc3 is not required for sprouting of the cardinal vein. F0 embryos in which lamc3 expression is perturbed by a CRISPR/Cas9 approach also fail to form a parachordal chain, but we were unable to establish a stable lamc3 null line. Lamc3 is dispensable for muscle pioneer specification and for the expression of netrin-1a in these cells. Lamc3 knockdown causes netrin-1a up-regulation in the neural tube and there is increased Netrin-1 protein throughout the trunk of the embryo. Axonal guidance of rostral primary motoneurons is defective in Lamc3 knockdown embryos. Conclusions: We suggest that knockdown of Lamc3 perturbs migration of rostral primary motoneurons at the level of the horizontal myoseptum, indicating that laminin γ3 plays a role in motoneuron guidance.

Regulation of the Immune System by Laminins

Laminins are trimeric proteins that are major components of the basement membranes that separate endothelia and epithelia from the underlying tissue. Sixteen laminin isoforms have been described, each with distinct tissue expression patterns and functions. While laminins have a critical structural role, recent evidence also indicates that they also impact the migration and functions of immune cells. Laminins are differentially expressed upon immunity or tolerance and orientate the immune response. This review will summarize the structure of laminins, the modulation of their expression, and their interactions with the immune system. Finally, the role of the laminins in autoimmune diseases and transplantation will be discussed.

Endothelial basement membrane laminin 511 is essential for shear stress response

Shear detection and mechanotransduction by arterial endothelium requires junctional complexes containing PECAM-1 and VE-cadherin, as well as firm anchorage to the underlying basement membrane. While considerable information is available for junctional complexes in these processes, gained largely from in vitro studies, little is known about the contribution of the endothelial basement membrane. Using resistance artery explants, we show that the integral endothelial basement membrane component, laminin 511 (laminin α5), is central to shear detection and mechanotransduction and its elimination at this site results in ablation of dilation in response to increased shear stress. Loss of endothelial laminin 511 correlates with reduced cortical stiffness of arterial endothelium in vivo, smaller integrin β1-positive/vinculin-positive focal adhesions, and reduced junctional association of actin-myosin II In vitro assays reveal that β1 integrin-mediated interaction with laminin 511 results in high strengths of adhesion, which promotes p120 catenin association with VE-cadherin, stabilizing it at cell junctions and increasing cell-cell adhesion strength. This highlights the importance of endothelial laminin 511 in shear response in the physiologically relevant context of resistance arteries.

A discoidin domain receptor 1 knock-out mouse as a novel model for osteoarthritis of the temporomandibular joint

Discoidin domain receptor 1 (DDR-1)-deficient mice exhibited a high incidence of osteoarthritis (OA) in the temporomandibular joint (TMJ) as early as 9 weeks of age. They showed typical histological signs of OA, including surface fissures, loss of proteoglycans, chondrocyte cluster formation, collagen type I upregulation, and atypical collagen fibril arrangements. Chondrocytes isolated from the TMJs of DDR-1-deficient mice maintained their osteoarthritic characteristics when placed in culture. They expressed high levels of runx-2 and collagen type I, as well as low levels of sox-9 and aggrecan. The expression of DDR-2, a key factor in OA, was increased. DDR-1-deficient chondrocytes from the TMJ were positively influenced towards chondrogenesis by a three-dimensional matrix combined with a runx-2 knockdown or stimulation with extracellular matrix components, such as nidogen-2. Therefore, the DDR-1 knock-out mouse can serve as a novel model for temporomandibular disorders, such as OA of the TMJ, and will help to develop new treatment options, particularly those involving tissue regeneration.

Skin basement membrane: the foundation of epidermal integrity--BM functions and diverse roles of bridging molecules nidogen and perlecan

The epidermis functions in skin as first defense line or barrier against environmental impacts, resting on extracellular matrix (ECM) of the dermis underneath. Both compartments are connected by the basement membrane (BM), composed of a set of distinct glycoproteins and proteoglycans. Herein we are reviewing molecular aspects of BM structure, composition, and function regarding not only (i) the dermoepidermal interface but also (ii) the resident microvasculature, primarily focusing on the per se nonscaffold forming components perlecan and nidogen-1 and nidogen-2. Depletion or functional deficiencies of any BM component are lethal at some stage of development or around birth, though BM defects vary between organs and tissues. Lethality problems were overcome by developmental stage- and skin-specific gene targeting or by cell grafting and organotypic (3D) cocultures of normal or defective cells, which allows recapitulating BM formation de novo. Thus, evidence is accumulating that BM assembly and turnover rely on mechanical properties and composition of the adjacent ECM and the dynamics of molecular assembly, including further "minor" local components, nidogens largely functioning as catalysts or molecular adaptors and perlecan as bridging stabilizer. Collectively, orchestration of BM assembly, remodeling, and the role of individual players herein are determined by the developmental, tissue-specific, or functional context.

The laminin family

Laminins are large molecular weight glycoproteins constituted by the assembly of three disulfide-linked polypeptides, the α, β and γ chains. The human genome encodes 11 genetically distinct laminin chains. Structurally, laminin chains differ by the number, size and organization of a few constitutive domains, endowing the various members of the laminin family with common and unique important functions. In particular, laminins are indispensable building blocks for cellular networks physically bridging the intracellular and extracellular compartments and relaying signals critical for cellular behavior, and for extracellular polymers determining the architecture and the physiology of basement membranes.

Laminin and integrin expression in the ventral ectodermal ridge of the mouse embryo: implications for regulation of BMP signalling

BACKGROUND

The ventral ectodermal ridge (VER) is an important signalling centre in the mouse tail-bud following completion of gastrulation. BMP regulation is essential for VER function, but how these signals are transmitted between adjacent tissues is unclear.

RESULTS

We investigated the idea that extracellular matrix components might be involved, using immunohistochemistry and in situ hybridisation to detect all known α, β, and γ laminin chains and their mRNAs in the early tail bud. We identified an apparently novel laminin variant, comprising α5, β3 and γ2 chains, as a major component of the VER basement membrane at E9.5. Strikingly, only the mRNAs for these chains were co-expressed in VER cells, suggesting that lamin532 may be the sole basement membrane laminin at this stage. Since α6 integrin was also expressed in VER cells, this raises the possibility of cell-matrix interactions regulating BMP signalling at this site of caudal morphogenesis.

CONCLUSIONS

Laminin532 could interact with α6-containing integrin to direct differentiation of the specialised VER cells from surface ectoderm.

Cell-matrix interactions in muscle disease

The extracellular matrix (ECM) provides a solid scaffold and signals to cells through ECM receptors. The cell-matrix interactions are crucial for normal biological processes and when disrupted they may lead to pathological processes. In particular, the biological importance of ECM-cell membrane-cytoskeleton interactions in skeletal muscle is accentuated by the number of inherited muscle diseases caused by mutations in proteins conferring these interactions. In this review we introduce laminins, collagens, dystroglycan, integrins, dystrophin and sarcoglycans. Mutations in corresponding genes cause various forms of muscular dystrophy. The muscle disorders are presented as well as advances toward the development of treatment.

The γ3 chain of laminin is widely but differentially expressed in murine basement membranes: expression and functional studies

Laminins are heterotrimeric extracellular glycoproteins found in, but not confined to, basement membranes (BMs). They are important components in formation of the molecular networks of BMs as well as in cell polarity, cell differentiation and tissue morphogenesis. Each laminin is composed by an α, a β and a γ chain. Previous studies have shown that the γ3 chain is partnered with either the β1 chain (in placenta) or β2 chain (in the CNS) (Libby et al., 2000). Several studies, including our own, suggested that the γ3 chain is expressed in both apical and basal compartments (Koch et al., 1999; Gersdorff et al., 2005; Yan and Cheng, 2006). This study investigates the expression pattern of the γ3 chain in mouse. We developed three new γ3-reactive antibodies, and we show that the γ3 chain is present in BMs. The distribution pattern is considerably more restricted than that of the γ1 chain and within any tissue there is differential deposition into BM compartments. This is particularly true in the retina and brain, where γ3 is uniquely expressed in a subset of the vascular basement membranes and the pial surface. We used conventional genetic ablation techniques to remove the γ3 chain in mice; unlike other laminin null mice (α5, β2, γ1 nulls), these mice live a normal lifespan and have only minor abnormalities, the most striking of which are ectopic granule cells in the cerebellum and an apparent increase in capillary branching in the outer retina. These data support the suggestion that the γ3 chain is deposited in BMs and contributes some unique properties to their function, particularly in the nervous system.

Recessive LAMC3 mutations cause malformations of occipital cortical development

The biological basis for regional and inter-species differences in cerebral cortical morphology is poorly understood. We focused on consanguineous Turkish families with a single affected member with complex bilateral occipital cortical gyration abnormalities. By using whole-exome sequencing, we initially identified a homozygous 2-bp deletion in LAMC3, the laminin γ3 gene, leading to an immediate premature termination codon. In two other affected individuals with nearly identical phenotypes, we identified a homozygous nonsense mutation and a compound heterozygous mutation. In human but not mouse fetal brain, LAMC3 is enriched in postmitotic cortical plate neurons, localizing primarily to the somatodendritic compartment. LAMC3 expression peaks between late gestation and late infancy, paralleling the expression of molecules that are important in dendritogenesis and synapse formation. The discovery of the molecular basis of this unusual occipital malformation furthers our understanding of the complex biology underlying the formation of cortical gyrations.

Regional differences in the expression of laminin isoforms during mouse neural tube development

Many significant human birth defects originate around the time of neural tube closure or early during post-closure nervous system development. For example, failure of the neural tube to close generates anencephaly and spina bifida, faulty cell cycle progression is implicated in primary microcephaly, while defective migration of neuroblasts can lead to neuronal migration disorders such as lissencephaly. At the stage of neural tube closure, basement membranes are becoming organised around the neuroepithelium, and beneath the adjacent non-neural surface ectoderm. While there is circumstantial evidence to implicate basement membrane dynamics in neural tube and surface ectodermal development, we have an incomplete understanding of the molecular composition of basement membranes at this stage. In the present study, we examined the developing basement membranes of the mouse embryo at mid-gestation (embryonic day 9.5), with particular reference to laminin composition. We performed in situ hybridization to detect the mRNAs of all eleven individual laminin chains, and immunohistochemistry to identify which laminin chains are present in the basement membranes. From this information, we inferred the likely laminin variants and their tissues of origin: that is, whether a given basement membrane laminin is contributed by epithelium, mesenchyme, or both. Our findings reveal major differences in basement composition along the body axis, with the rostral neural tube (at mandibular arch and heart levels) exhibiting many distinct laminin variants, while the lumbar level where the neural tube is just closing shows a much simpler laminin profile. Moreover, there appears to be a marked difference in the extent to which the mesenchyme contributes laminin variants to the basement membrane, with potential contribution of several laminins rostrally, but no contribution caudally. This information paves the way towards a mechanistic analysis of basement membrane laminin function during early neural tube development in mammals.

Basement membranes: cell scaffoldings and signaling platforms

Basement membranes are widely distributed extracellular matrices that coat the basal aspect of epithelial and endothelial cells and surround muscle, fat, and Schwann cells. These extracellular matrices, first expressed in early embryogenesis, are self-assembled on competent cell surfaces through binding interactions among laminins, type IV collagens, nidogens, and proteoglycans. They form stabilizing extensions of the plasma membrane that provide cell adhesion and that act as solid-phase agonists. Basement membranes play a role in tissue and organ morphogenesis and help maintain function in the adult. Mutations adversely affecting expression of the different structural components are associated with developmental arrest at different stages as well as postnatal diseases of muscle, nerve, brain, eye, skin, vasculature, and kidney.

Basement membrane deposition of nidogen 1 but not nidogen 2 requires the nidogen binding module of the laminin gamma1 chain

The nidogen-laminin interaction is proposed to play a key role in basement membrane (BM) assembly. However, though there are similarities, the phenotypes in mice lacking nidogen 1 and 2 (nidogen double null) differ to those of mice lacking the nidogen binding module (γ1III4) of the laminin γ1 chain. This indicates different cell- and tissue-specific functions for nidogens and their interaction with laminin and poses the question of whether the phenotypes in nidogen double null mice are caused by the loss of the laminin-nidogen interaction or rather by other unknown nidogen functions. To investigate this, we analyzed BMs, in particular those in the skin of mice lacking the nidogen binding module. In contrast to nidogen double null mice, all skin BMs in γ1III4-deficient mice appeared normal. Furthermore, although nidogen 1 deposition was strongly reduced, nidogen 2 appeared unchanged. Mice with additional deletion of the laminin γ3 chain, which contains a γ1-like nidogen binding module, showed a further reduction of nidogen 1 in the dermoepidermal BM; however, this again did not affect nidogen 2. This demonstrates that in vivo only nidogen 1 deposition is critically dependent on the nidogen binding modules of the laminin γ1 and γ3 chains, whereas nidogen 2 is independently recruited either by binding to an alternative site on laminin or to other BM proteins.

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.

Laminin-121--recombinant expression and interactions with integrins

Laminin-121, previously referred as to laminin-3, was expressed recombinantly in human embryonic kidney (HEK) 293 cells by triple transfection of full-length cDNAs encoding mouse laminin α1, β2 and γ1 chains. The recombinant laminin-121 was purified using Heparin-Sepharose followed by molecular sieve chromatography and shown to be correctly folded by electron microscopy and circular dichroism (CD). The CD spectra of recombinant laminin-121 were very similar to those of laminin-111 isolated from Engelbreth-Holm-Swarm tumor (EHS-laminin) but its T(m) value was smaller than EHS-laminin and recombinant lamnin-111 suggesting that the replacement of the β chain reduced the stability of the coiled-coil structure of laminin-121. Its binding to integrins was compared with EHS-laminin, laminin-3A32 purified from murine epidermal cell line and recombinantly expressed laminins-111, -211 and -221. Laminin-121 showed the highest affinity to α6β1 and α7β1 integrins and furthermore, laminin-121 most effectively supported neurite outgrowth. Together, this suggests that the β2 laminins have higher affinity for integrins than the β1 laminins.

Migratory chondrogenic progenitor cells from repair tissue during the later stages of human osteoarthritis

The regeneration of diseased hyaline cartilage continues to be a great challenge, mainly because degeneration--caused either by major injury or by age-related processes--can overextend the tissue's self-renewal capacity. We show that repair tissue from human articular cartilage during the late stages of osteoarthritis harbors a unique progenitor cell population, termed chondrogenic progenitor cells (CPCs). These exhibit stem cell characteristics such as clonogenicity, multipotency, and migratory activity. The isolated CPCs, which exhibit a high chondrogenic potential, were shown to populate diseased tissue ex vivo. Moreover, downregulation of the osteogenic transcription factor runx-2 enhanced the expression of the chondrogenic transcription factor sox-9. This, in turn, increased the matrix synthesis potential of the CPCs without altering their migratory capacity. Our results offer new insights into the biology of progenitor cells in the context of diseased cartilage tissue. Our work may be relevant in the development of novel therapeutics for the later stages of osteoarthritis.

Lack of laminin gamma1 in embryonic stem cell-derived cardiomyocytes causes inhomogeneous electrical spreading despite intact differentiation and function

Laminins form a large family of extracellular matrix (ECM) proteins, and their expression is a prerequisite for normal embryonic development. Herein we investigated the role of the laminin gamma1 chain for cardiac muscle differentiation and function using cardiomyocytes derived from embryonic stem cells deficient in the LAMC1 gene. Laminin gamma1 (-/-) cardiomyocytes lacked basement membranes (BM), whereas their sarcomeric organization was unaffected. Accordingly, electrical activity and hormonal regulation were found to be intact. However, the inadequate BM formation led to an increase of ECM deposits between adjacent cardiomyocytes, and this resulted in defects of the electrical signal propagation. Furthermore, we also found an increase in the number of pacemaker areas. Thus, although laminin and intact BM are not essential for cardiomyocyte development and differentiation per se, they are required for the normal deposition of matrix molecules and critical for intact electrical signal propagation.

A comprehensive survey of the laminins and collagens type IV expressed in mouse Leydig cells and their regulation by LH/hCG

Extracellular matrix (ECM) proteins have been shown to alter Leydig cell steroidogenesis in vitro, substantiating the hypothesis that Leydig cell steroidogenic activity and matrix environment are interdependent events. However, the nature of the ECM components synthesized by Leydig cells and their regulation by LH/human chorionic gonadotropin (hCG) remain unknown. Here, we examine the occurrence of the 11 laminin subunits and the 6 alpha chains of collagen IV (COL4A1-6) by RT-PCR in Leydig cells cultured with or without LH/hCG. Leydig cells were a tumor Leydig cell line (mLTC-1) or 8-week-old mice Leydig cells. Based on PCR data, it is suggested that normal Leydig cells may synthesize a maximum of 11 laminin heterotrimers and the 6 alpha chains of collagen IV. They also may synthesize various proteases and inhibitors of the metzincin family. The mLTC-1 cells have a limited repertoire as compared with normal Leydig cells. Interestingly, none of the ten proteases and inhibitors monitored is under LH-hCG regulation whereas every protease and inhibitor of the serine protease family yet identified in Leydig cells is under gonadotropin regulation. In addition, a few laminin and collagen subunit genes are regulated by LH/hCG. These are laminins alpha3 and gamma3 (Lama3 and Lamc3), Col4a3, and Col4a6, which are negatively regulated by LH/hCG in both Leydig cell types, and Col4a4, which was downregulated in primary cultures but not in mLTC-1 cells. Collectively, the present study suggests that Leydig cells modulate in a selective fashion their matrix environment in response to their trophic hormone. This may alter the steroidogenic outcome of Leydig cells.

Laminin isoforms containing the gamma3 chain are unable to bind to integrins due to the absence of the glutamic acid residue conserved in the C-terminal regions of the gamma1 and gamma2 chains

Laminins are the major cell adhesive proteins in basement membranes, and consist of three subunits termed alpha, beta, and gamma. Recently, we found that the Glu residue at the third position from the C termini of the gamma1 and gamma2 chains is critically involved in integrin binding by laminins. However, the gamma3 chain lacks this Glu residue, suggesting that laminin isoforms containing the gamma3 chain may be unable to bind to integrins. To address this possibility, we expressed the E8 fragment of laminin-213 and found that it was incapable of binding to integrins. Similarly, the E8 fragment of laminin-113 was expressed and also found to be inactive in binding to integrins, confirming the distinction between the integrin binding activities of gamma3 chain-containing isoforms and those containing the gamma1 or gamma2 chain. To further address the importance of the Glu residue, we swapped the C-terminal four amino acids of the gamma3 chain with the C-terminal nine amino acids of the gamma1 chain, which contain the Glu residue. The resulting chimeric E8 fragment of laminin-213 became fully active in integrin binding, whereas replacement with the nine amino acids of the gamma1 chain after substitution of Gln for the conserved Glu residue failed to restore the integrin binding activity. These results provide both loss-of-function and gain-of-function evidence that laminin isoforms containing the gamma3 chain are unable to bind to integrins due to the absence of the conserved Glu residue, which should play a critical role in integrin binding by laminins.

Gene expression and functional studies of the optic nerve head astrocyte transcriptome from normal African Americans and Caucasian Americans donors

PURPOSE

To determine whether optic nerve head (ONH) astrocytes, a key cellular component of glaucomatous neuropathy, exhibit differential gene expression in primary cultures of astrocytes from normal African American (AA) donors compared to astrocytes from normal Caucasian American (CA) donors.

METHODS

We used oligonucleotide Affymetrix microarray (HG U133A & HG U133A 2.0 chips) to compare gene expression levels in cultured ONH astrocytes from twelve CA and twelve AA normal age matched donor eyes. Chips were normalized with Robust Microarray Analysis (RMA) in R using Bioconductor. Significant differential gene expression levels were detected using mixed effects modeling and Statistical Analysis of Microarray (SAM). Functional analysis and Gene Ontology were used to classify differentially expressed genes. Differential gene expression was validated by quantitative real time RT-PCR. Protein levels were detected by Western blots and ELISA. Cell adhesion and migration assays tested physiological responses. Glutathione (GSH) assay detected levels of intracellular GSH.

RESULTS

Multiple analyses selected 87 genes differentially expressed between normal AA and CA (P<0.01). The most relevant genes expressed in AA were categorized by function, including: signal transduction, response to stress, ECM genes, migration and cell adhesion.

CONCLUSIONS

These data show that normal astrocytes from AA and CA normal donors display distinct expression profiles that impact astrocyte functions in the ONH. Our data suggests that differences in gene expression in ONH astrocytes may be specific to the development and/or progression of glaucoma in AA.

Nidogens-Extracellular matrix linker molecules

Nidogens/entactins are a family of highly conserved, sulfated glycoproteins. Biochemical studies have implicated them as having a major structural role in the basement membrane. However despite being ubiquitous components of this specialized extracellular matrix and having a wide spectrum of binding partners, genetic analysis has shown that they are not required for the overall architecture of the basement membrane. Rather in development they play an important role in its stabilization especially in tissues undergoing rapid growth or turnover. Nidogen breakdown has been implicated as a key event in the basement membrane degradation occurring in mammary gland involution. A number of studies, most compellingly those in C. elegans, demonstrated that nidogens may have other nonstructural roles and be involved in axonal pathfinding and synaptic transmission.

Compositional differences between infant and adult human corneal basement membranes

PURPOSE

Adult human corneal epithelial basement membrane (EBM) and Descemet's membrane (DM) components exhibit heterogeneous distribution. The purpose of the study was to identify changes of these components during postnatal corneal development.

METHODS

Thirty healthy adult corneas and 10 corneas from 12-day- to 3-year-old children were studied by immunofluorescence with antibodies against BM components.

RESULTS

Type IV collagen composition of infant corneal central EBM over Bowman's layer changed from alpha1-alpha2 to alpha3-alpha4 chains after 3 years of life; in the adult, alpha1-alpha2 chains were retained only in the limbal BM. Laminin alpha2 and beta2 chains were present in the adult limbal BM where epithelial stem cells are located. By 3 years of age, beta2 chain appeared in the limbal BM. In all corneas, limbal BM contained laminin gamma3 chain. In the infant DM, type IV collagen alpha1-alpha6 chains, perlecan, nidogen-1, nidogen-2, and netrin-4 were found on both faces, but they remained only on the endothelial face of the adult DM. The stromal face of the infant but not the adult DM was positive for tenascin-C, fibrillin-1, SPARC, and laminin-332. Type VIII collagen shifted from the endothelial face of infant DM to its stromal face in the adult. Matrilin-4 largely disappeared after the age of 3 years.

CONCLUSIONS

The distribution of laminin gamma3 chain, nidogen-2, netrin-4, matrilin-2, and matrilin-4 is described in the cornea for the first time. The observed differences between adult and infant corneal BMs may relate to changes in their mechanical strength, corneal cell adhesion and differentiation in the process of postnatal corneal maturation.

Junction restructuring and spermatogenesis: the biology, regulation, and implication in male contraceptive development

Spermatogenesis that occurs in the seminiferous epithelium of adult mammalian testes is associated with extensive junction restructuring at the Sertoli-Sertoli cell, Sertoli-germ cell, and Sertoli-basement membrane interface. While this morphological phenomenon is known and has been described in great details for decades, the biochemical and molecular changes as well as the mechanisms/signaling pathways that define changes at the cell-cell and cell-matrix interface remain largely unknown until recently. In this chapter, we summarize and discuss findings in the field regarding the coordinated efforts of the anchoring [e.g., adherens junction (AJ), such as basal ectoplasmic specialization (basal ES)] and tight junctions (TJs) that are present in the same microenvironment, such as at the blood-testis barrier (BTB), or at distinctly opposite ends of the Sertoli cell epithelium, such as between apical ectoplasmic specialization (apical ES) in the apical compartment, and the BTB adjacent to the basal compartment of the epithelium. These efforts, in turn, regulate and coordinate different cellular events that occur during the seminiferous epithelial cycle. For instance, the events of spermiation and of preleptotene spermatocyte migration across the BTB both take place concurrently at stage VIII of the epithelial cycle of spermatogenesis. Recent findings suggest that these events are coordinated by protein complexes found at the apical and basal ES and TJ, which are located at different ends of the Sertoli cell epithelium. Besides, we highlight important areas of research that can now be undertaken, and functional studies that can be designed to tackle different issues pertinent to junction restructuring during spermatogenesis.

Characterization of extracellular matrix components in the limbal epithelial stem cell compartment

A specialized microenvironment or niche, which regulates maintenance, self-renewal, activation, and proliferation of stem cells by external signals, is one of the key prerequisites for stem cell function. However, the parameters determining the limbal stem cell niche are not yet defined. In order to characterize the role of basement membrane (BM) and extracellular matrix components in the generation of a microenvironmental niche for limbal stem and progenitor cells, we extensively analyzed the topographical variations of the BM zone of human ocular surface epithelia using immunohistochemistry and a large panel of antibodies to most of the presently described intrinsic and associated BM components. Apart from BM components uniformly expressed throughout all ocular surface epithelia (e.g. type IV collagen alpha5 and alpha6 chains, collagen types VII, XV, XVII, and XVIII, laminin-111, laminin-332, laminin chains alpha3, beta3,and gamma2, fibronectin, matrilin-2 and -4, and perlecan), the BM of the limbal epithelium shared many similarities with that of the conjunctival epithelium, including positive labelling for type IV collagen alpha1 and alpha2 chains, laminin alpha5, beta2, and gamma1 chains, nidogen-1 and -2, and thrombospondin-4, whereas type IV collagen alpha3, type V collagen, fibrillin-1 and -2, thrombospondin-1, and endostatin were present in the corneal BM, but lacking or more weakly expressed in the limbal and conjunctival BMs. As compared to both the corneal and conjunctival BMs, the limbal BM showed a markedly increased immunoreactivity for laminin alpha1, alpha2, beta1 chains, and agrin, and a specific but patchy immunoreactivity for laminin gamma3 chain, BM40/SPARC, and tenascin-C, which co-localized with ABCG2/p63/K19-positive and K3/Cx43/desmoglein/integrin-alpha2-negative cell clusters comprising putative stem and early progenitor cells in the basal epithelium of the limbal palisades. Components that were particularly expressed in the corneal-limbal transition zone included type XVI collagen, fibulin-2, tenascin-C/R, vitronectin, bamacan, chondroitin sulfate, and versican, all of which co-localized with vimentin-positive cell clusters comprising putative late progenitor cells in the basal epithelium. This pronounced heterogeneity of the BM in the limbal area, both in the region of limbal palisades and the corneal-limbal transition zone, appears to be involved in providing unique microenvironments for corneal epithelial stem and late progenitor cells. Identification of specific niche parameters might not only help to understand limbal stem cell regulation, but also to improve their selective enrichment and in vitro expansion for therapeutic strategies.

Bridging structure with function: structural, regulatory, and developmental role of laminins

The basement membrane is a highly intricate and organized portion of the extracellular matrix that interfaces with a variety of cell types including epithelial, endothelial, muscle, nerve, and fat cells. The laminin family of glycoproteins is a major constituent of the basement membrane. The 16 known laminin isoforms are formed from combinations of alpha, beta, and gamma chains, with each chain containing specific domains capable of interacting with cellular receptors such as integrins and other extracellular ligands. In addition to its role in the assembly and architectural integrity of the basement membrane, laminins interact with cells to influence proliferation, differentiation, adhesion, and migration, processes activated in normal and pathologic states. In vitro these functions are regulated by the post-translational modifications of the individual laminin chains. In vivo laminin knockout mouse studies have been particularly instructive in defining the function of specific laminins in mammalian development and have also highlighted its role as a key component of the basement membrane. In this review, we will define how laminin structure complements function and explore its role in both normal and pathologic processes.

Laminin isoforms in development and disease

The members of the laminin family of heterotrimers are major constituents of all basement membranes, sheet-like extracellular structures, present in almost all organs. The laminins bind to cell surface receptors and thereby tightly connect the basement membrane to the adjacent cell layer. This provides for the specific basement membrane functions to stabilize cellular structures, to serve as effective physical barriers, and furthermore, to govern cell fate by inducing intracellular signalling cascades. Many different types of diseases involve basement membranes and laminins. Metastasizing solid tumors must pass through basement membranes to reach the vascular system, and various microbes and viruses enter the cells through direct interaction with laminins. Furthermore, whereas mutations in one specific laminin chain lead to a muscular disorder, mutations of other laminin chains cause skin blistering and kidney defects, respectively. This review summarizes recent progress concerning the molecular mechanisms of laminins in development and disease. The current knowledge may lead to clinical treatment of lamininopathies and may include stem-cell approaches as well as gene therapy.

Alpha11 beta1 integrin-dependent regulation of periodontal ligament function in the erupting mouse incisor

The fibroblast integrin alpha11beta1 is a key receptor for fibrillar collagens. To study the potential function of alpha11 in vivo, we generated a null allele of the alpha11 gene. Integrin alpha11(-/-) mice are viable and fertile but display dwarfism with increased mortality, most probably due to severely defective incisors. Mutant incisors are characterized by disorganized periodontal ligaments, whereas molar ligaments appear normal. The primary defect in the incisor ligament leads to halted tooth eruption. alpha11beta1-defective embryonic fibroblasts displayed severe defects in vitro, characterized by (i) greatly reduced cell adhesion and spreading on collagen I, (ii) reduced ability to retract collagen lattices, and (iii) reduced cell proliferation. Analysis of matrix metalloproteinase in vitro and in vivo revealed disturbed MMP13 and MMP14 synthesis in alpha11(-/-) cells. We show that alpha11beta1 is the major receptor for collagen I on mouse embryonic fibroblasts and suggest that alpha11beta1 integrin is specifically required on periodontal ligament fibroblasts for cell migration and collagen reorganization to help generate the forces needed for axial tooth movement. Our data show a unique role for alpha11beta1 integrin during tooth eruption.

Laminin isoforms and lung development: All isoforms are not equal

Laminins are a major component of basement membranes. Each laminin molecule is a heterotrimeric glycoprotein composed of one alpha, one beta, and one gamma chain. Fifteen laminin isoforms exist, assembled from various combinations of 5alpha, 3beta, and 3gamma chains. The embryonic lung has abundant laminin isoforms. Increasing evidence suggests that different laminin isoforms have unique functions in lung development. Studies of embryonic lung explants and organotypic co-cultures show that laminin alpha1 and laminin 111 are important for epithelial branching morphogenesis and that laminin alpha2 and laminin 211 have a role in smooth muscle cell differentiation. In vivo studies of laminin alpha5-deficient mice indicate that this laminin chain, found in laminins 511 and 521, is essential for normal lobar septation in early lung development and normal alveolization and distal epithelial cell differentiation and maturation in late lung development. However, not all of the laminin chains present in the developing lung appear to be necessary for normal lung development since laminin alpha4 null mice do not have obvious lung abnormalities and laminin gamma2 null mice have only minimal changes in lung development. The mechanisms responsible for the lung phenotypes in mice with laminin mutations are unknown, but it is clear that multiple laminin isoforms are crucial for lung development and that different laminin isoforms exhibit specific, non-overlapping functions.

Secreted modular calcium-binding protein-1 localization during mouse embryogenesis

BM-40 is an extracellular matrix-associated protein and is characterized by an extracellular calcium-binding domain as well as a follistatin-like domain. Secreted modular calcium-binding protein-1 (SMOC-1) is a new member of the BM-40 family. It consists of two thyroglobulin-like domains, a follistatin-like domain and a new domain without known homologues and is expressed ubiquitously in many adult murine tissues. Immunofluorescence studies, as well as immunogold electron microscopy, have confirmed the localization of SMOC-1 in or around basement membranes of adult murine skin, blood vessels, brain, kidney, skeletal muscle, and the zona pellucida surrounding the oocyte. In the present work, light microscopic immunohistochemistry has revealed that SMOC-1 is localized in the early mouse embryo day 7 throughout the entire endodermal basement membrane zone of the embryo proper. SMOC-1 mRNA is synthesized, even in early stages of mouse development, by mesenchymal as well as epithelial cells deriving from all three germ layers. In embryonic stage day 12, and fetal stages day 14, 16, and 18, the protein is present in the basement membrane zones of brain, blood vessels, skin, skeletal muscle, lung, heart, liver, pancreas, intestine, and kidney. This broad and organ-specific distribution suggests multifunctional roles of SMOC-1 during mouse embryogenesis.

Laminin alpha 3 forms a complex with beta3 and gamma3 chains that serves as the ligand for alpha 6beta1-integrin at the apical ectoplasmic specialization in adult rat testes

Apical ectoplasmic specialization (ES) is a testis-specific hybrid cell/cell actin-based adherens junction and cell/matrix focal contact anchoring junction type restricted to the interface between Sertoli cells and developing spermatids. Recent studies have shown that laminin gamma3, restricted to elongating spermatids, is a putative binding partner of alpha 6beta 1-integrin localized in Sertoli cells at the apical ES. However, the identity of the alpha and beta chains, which constitute a functional laminin ligand with the gamma3 chain at the apical ES, is not known. Using reverse transcription-PCR and immunoblotting to survey all laminin chains in cells of the seminiferous epithelium, it was noted that alpha 2, alpha 3, beta1, beta2, beta3, and gamma3 chains were found in germ cells, whereas alpha 1, alpha 2, alpha 4, alpha 5, beta1, beta2, gamma1, gamma2, and gamma3 chains were found in Sertoli cells, implying that alpha 3 and beta3 are the plausible laminin chains restricted to germ cells that may be the bona fide partners of gamma3. To verify this postulate, recombinant proteins based on domain G of alpha 3 and domain I of beta3 and gamma3 chains were produced and used to obtain the corresponding specific polyclonal antibodies. Additional studies have demonstrated that the laminin alpha 3, beta3, and gamma3 chains indeed are restricted to germ cells at the apical ES, co-localizing with each other and with beta1-integrin. Furthermore, co-immunoprecipitation studies have confirmed the interactions among laminin alpha 3, beta3, and gamma3, as well as beta1-integrin. When the functional laminin ligand at the apical ES was disrupted via blocking antibodies, such as using anti-laminin alpha 3 or gamma3 IgG, this treatment perturbed adhesion between Sertoli and germ cells (mostly spermatids), leading to germ cell loss from the epithelium. More important, a transient disruption of the blood-testis barrier was also detected.

Slit coordinates cardiac morphogenesis in Drosophila

Slit is a secreted guidance cue that conveys repellent or attractive signals from target and guidepost cells. In Drosophila, responsive cells express one or more of three Robo receptors. The cardial cells of the developing heart express both Slit and Robo2. This is the first report of coincident expression of a Robo and its ligand. In slit mutants, cardial cell alignment, polarization and uniform migration are disrupted. The heart phenotype of robo2 mutants is similar, with fewer migration defects. In the guidance of neuronal growth cones in Drosophila, there is a phenotypic interaction between slit and robo heterozygotes, and also with genes required for Robo signaling. In contrast, in the heart, slit has little or no phenotypic interaction with Robo-related genes, including Robo2, Nck2, and Disabled. However, there is a strong phenotypic interaction with Integrin genes and their ligands, including Laminin and Collagen, and intracellular messengers, including Talin and ILK. This indicates that Slit participates in adhesion or adhesion signaling during heart development.

Lung development in laminin gamma2 deficiency: abnormal tracheal hemidesmosomes with normal branching morphogenesis and epithelial differentiation

Background

Laminin γ2 (Lamc2), one of the polypeptides in laminin-332 (laminin-5), is prominent in the basement membrane of alveolar walls and airways of developing and adult lung. Laminins are important for lung morphogenesis and based on its localization, a function for laminin γ2 in lung development has been hypothesized. Targeted deletion of the laminin γ2 gene in mice results in skin blistering and neonatal death at 3–5 days after birth due to failure to thrive.

Methods

Examination of lung development in Lamc2-/- mice through 1–2 days postnatal was accomplished by morphometric analysis, lung bud culture, electron microscopy, immunohistochemical and immunofluorescence staining.

Results

Compared to littermate controls, Lamc2-/- lungs were similar in morphology during embryonic life. At post-natal day 1–2, distal saccules were mildly dilated by chord length measurements. Epithelial differentiation as evaluated by immunohistochemical staining for markers of ciliated cells, Clara cells, alveolar type I cells and alveolar type II cells did not reveal a difference between Lamc2-/- and littermate control lungs. Likewise, vascular development, smooth muscle cell differentiation, and elastic fiber formation looked similar, as did airway basement membrane ultrastructure. Branching morphogenesis by lung bud culture was similar in Lamc2-/- and littermate control lungs. Since laminin-332 is important for hemidesmosome formation, we examined the structure of tracheal hemidesmosomes by transmission electron microscopy. Compared to littermate controls, Lamc2-/- tracheal hemidesmosomes were less organized and lacked the increased electron density associated with the basement membrane abutting the hemidesmosome.

Conclusion

These findings indicate that laminin γ2 and laminin-332, despite their prominence in the lung, have a minimal role in lung development through the saccular stage.

Survey of the year 2005 commercial optical biosensor literature

We identified 1113 articles (103 reviews, 1010 primary research articles) published in 2005 that describe experiments performed using commercially available optical biosensors. While this number of publications is impressive, we find that the quality of the biosensor work in these articles is often pretty poor. It is a little disappointing that there appears to be only a small set of researchers who know how to properly perform, analyze, and present biosensor data. To help focus the field, we spotlight work published by 10 research groups that exemplify the quality of data one should expect to see from a biosensor experiment. Also, in an effort to raise awareness of the common problems in the biosensor field, we provide side-by-side examples of good and bad data sets from the 2005 literature.

Laminin {alpha}1 chain corrects male infertility caused by absence of laminin {alpha}2 chain

Laminins are important for basement membrane structure and function. The laminin alpha2 chain is a major component of muscle basement membranes, and mutations in the laminin alpha2 gene lead to congenital muscular dystrophy in humans and mice. Although the laminin alpha2 chain is prominently expressed in testicular basement membranes, its role in testis has remained unclear. Here, we show that laminin alpha1, alpha2, beta1, beta2, gamma 1, and gamma 3 chains are the major laminin chains in basement membranes of seminiferous tubules. In laminin alpha2 chain-deficient dy(3 K)/dy(3 ASK) mice, lack of laminin alpha2 chain led to concurrent reduction of laminin gamma 3 chain and abnormal testicular basement membranes. Seminiferous tubules of laminin alpha2 chain-deficient dy(3 K)/dy(3 K) mice displayed a defect in the timing of lumen formation, resulting in production of fewer spermatides. We also demonstrate that overexpression of laminin alpha1 chain in testis of dy(3 K)/dy(3 K) mice compensated for laminin alpha2 chain deficiency and significantly reversed the appearance of the histopathological features. We thus provide genetic data that laminin alpha chains are essential for normal testicular function in vivo.

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.