Recombinant domains of mouse nidogen-1 and their binding to basement membrane proteins and monoclonal antibodies

Structural extracellular matrix-mediated molecular signaling in wound repair and tissue regeneration

The extracellular matrix (ECM) is a complex, non-cellular network of molecules that offers structural support for cells and tissues. The ECM is composed of various structural components, including collagen, fibronectin, laminin, perlecan, nidogen, tenascin, and fibulin, which are capable of binding to each other and to cell-to-adhesion receptors, endowing the ECM with unique physical and biochemical properties that are essential for its function in maintaining health and managing disease. Over the past three decades, extensive research has shown that the core of the ECM can significantly impact cellular events at the molecular level. Structural modifications have also been strongly associated with tissue repair. Through interactions with cells, matrix proteins regulate critical processes such as cell proliferation and differentiation, migration, and apoptosis, essential for maintaining tissue homeostasis, formation, and regeneration. This review emphasizes the interlocking networks of ECM macromolecules and their primary roles in tissue regeneration and wound repair. Through studying ECM dynamics, researchers have discovered molecular signaling pathways that demonstrate how the ECM influences protein patterns and open up more possibilities for developing therapeutics that target the ECM to enhance wound repair and tissue regeneration.

C. elegans touch receptor neurons direct mechanosensory complex organization via repurposing conserved basal lamina proteins

The sense of touch is conferred by the conjoint function of somatosensory neurons and skin cells. These cells meet across a gap filled by a basal lamina, an ancient structure found in metazoans. Using Caenorhabditis elegans, we investigate the composition and ultrastructure of the extracellular matrix at the epidermis and touch receptor neuron (TRN) interface. We show that membrane-matrix complexes containing laminin, nidogen, and the MEC-4 mechano-electrical transduction channel reside at this interface and are central to proper touch sensation. Interestingly, the dimensions and spacing of these complexes correspond with the discontinuous beam-like extracellular matrix structures observed in serial-section transmission electron micrographs. These complexes fail to coalesce in touch-insensitive extracellular matrix mutants and in dissociated neurons. Loss of nidogen reduces the density of mechanoreceptor complexes and the amplitude of the touch-evoked currents they carry. Thus, neuron-epithelium cell interfaces are instrumental in mechanosensory complex assembly and function. Unlike the basal lamina ensheathing the pharynx and body wall muscle, nidogen recruitment to the puncta along TRNs is not dependent upon laminin binding. MEC-4, but not laminin or nidogen, is destabilized by point mutations in the C-terminal Kunitz domain of the extracellular matrix component, MEC-1. These findings imply that somatosensory neurons secrete proteins that actively repurpose the basal lamina to generate special-purpose mechanosensory complexes responsible for vibrotactile sensing.

Biophysical and structural studies of fibulin-2

Fibulin-2 is a multidomain, disulfide-rich, homodimeric protein which belongs to a broader extracellular matrix family. It plays an important role in the development of elastic fiber structures. Malfunction of fibulin due to mutation or poor expression can result in a variety of diseases including synpolydactyly, limb abnormalities, eye disorders leading to blindness, cardiovascular diseases and cancer. Traditionally, fibulins have either been produced in mammalian cell systems or were isolated from the extracellular matrix, a procedure that results in poor availability for structural and functional studies. Here, we produced seven fibulin-2 constructs covering 62% of the mature protein (749 out of 1195 residues) using a prokaryotic expression system. Biophysical studies confirm that the purified constructs are folded and that the presence of disulfide bonds within the constructs makes them extremely thermostable. In addition, we solved the first crystal structure for any fibulin isoform, a structure corresponding to the previously suggested three motifs related to anaphylatoxin. The structure reveals that the three anaphylatoxins moieties form a single-domain structure.

Vertebrate extracellular matrix protein hemicentin-1 interacts physically and genetically with basement membrane protein nidogen-2

Hemicentins are large proteins of the extracellular matrix that belong to the fibulin family and play pivotal roles during development and homeostasis of a variety of invertebrate and vertebrate tissues. However, bona fide interaction partners of hemicentins have not been described as yet. Here, applying surface plasmon resonance spectroscopy and co-immunoprecipitation, we identify the basement membrane protein nidogen-2 (NID2) as a binding partner of mouse and zebrafish hemicentin-1 (HMCN1), in line with the formerly described essential role of mouse HMCN1 in basement membrane integrity. We show that HMCN1 binds to the same protein domain of NID2 (G2) as formerly shown for laminins, but with an approximately 3.5-fold lower affinity and in a competitive manner. Furthermore, immunofluorescence and immunogold labeling revealed that HMCN1/Hmcn1 is localized close to basement membranes and in partial overlap with NID2/Nid2a in different tissues of mouse and zebrafish. Genetic knockout and antisense-mediated knockdown studies in zebrafish further show that loss of Nid2a leads to similar defects in fin fold morphogenesis as the loss of Laminin-α5 (Lama5) or Hmcn1. Finally, combined partial loss-of-function studies indicated that nid2a genetically interacts with both hmcn1 and lama5. Together, these findings suggest that despite their mutually exclusive physical binding, hemicentins, nidogens, and laminins tightly cooperate and support each other during formation, maintenance, and function of basement membranes to confer tissue linkage.

Nidogen: A matrix protein with potential roles in musculoskeletal tissue regeneration

Basement membrane proteins are known to guide cell structures, differentiation, and tissue repair. Although there is a wealth of knowledge on the functions of laminins, perlecan, and type IV collagen in maintaining tissue homeostasis, not much is known about nidogen. As a key molecule in the basement membrane, nidogen contributes to the formation of a delicate microenvironment that proves necessary for stem cell lineage-specific differentiation. In this review, the expression of nidogen is delineated at both cellular and tissue levels from embryonic to adult stages of development; the effect of nidogens is also summarized in the context of musculoskeletal development and regeneration, including but not limited to adipogenesis, angiogenesis, chondrogenesis, myogenesis, and neurogenesis. Furthermore, potential mechanisms underlying the role of nidogens in stem cell-based tissue regeneration are also discussed. This concise review is expected to facilitate our existing understanding and utilization of nidogen in tissue engineering and regeneration.

DSS-induced damage to basement membranes is repaired by matrix replacement and crosslinking

Basement membranes are an ancient form of animal extracellular matrix. As important structural and functional components of tissues, basement membranes are subject to environmental damage and must be repaired while maintaining functions. Little is known about how basement membranes get repaired. This paucity stems from a lack of suitable in vivo models for analyzing such repair. Here, we show that dextran sodium sulfate (DSS) directly damages the gut basement membrane when fed to adult Drosophila DSS becomes incorporated into the basement membrane, promoting its expansion while decreasing its stiffness, which causes morphological changes to the underlying muscles. Remarkably, two days after withdrawal of DSS, the basement membrane is repaired by all measures of analysis. We used this new damage model to determine that repair requires collagen crosslinking and replacement of damaged components. Genetic and biochemical evidence indicates that crosslinking is required to stabilize the newly incorporated repaired Collagen IV rather than to stabilize the damaged Collagen IV. These results suggest that basement membranes are surprisingly dynamic.

NID1 variant associated with occipital cephaloceles in a family expressing a spectrum of phenotypes

Autosomal dominant Dandy-Walker malformation and occipital cephalocele (ADDWOC) is a rare, congenital, and incompletely penetrant malformation that is considered to be part of the Dandy-Walker spectrum of disorders. Affected individuals often present with an occipital cephalocele with a bony skull defect, but typically have normal neurological development. Here, we report on a three-generation family in which individuals have variable phenotypes that are consistent with the ADDWOC spectrum: arachnoid cysts in the proband and his maternal grandfather, an occipital cephalocele in the proband and his brother, and a small bony defect in the proband's mother. Whole exome sequencing identified a rare heterozygous variant in NID1 (NM_002508.2:c.1162C>T, (p.Gln388Ter)) in the proband, his brother, and his mother. Sanger sequencing confirmed the presence of this variant in the maternal grandfather. The identical c.1162C>T variant was previously identified in variably affected members of a three-generation family with ADDWOC. This case report provides further evidence that variants in NID1 may be clinically relevant for the development of a phenotype that is consistent with ADDWOC, and extends the phenotype of NID1-associated ADDWOC to include arachnoid cysts. Given that the Dandy-Walker malformation itself is not a pre-requisite to this spectrum of phenotypes, we also suggest a novel term for the NID1-associated disorder in order to give emphasis to this phenotypic variability: "Autosomal Dominant Posterior Fossa Anomalies with Occipital Cephaloceles."

Role of meprin metalloproteinases in cytokine processing and inflammation

Meprin metalloendopeptidases, comprising α and β isoforms, are widely expressed in mammalian cells and organs including kidney, intestines, lungs, skin, and bladder, and in a variety of immune cells and cancer cells. Meprins proteolytically process many inflammatory mediators, including cytokines, chemokines, and other bioactive proteins and peptides that control the function of immune cells. The knowledge of meprin-mediated processing of inflammatory mediators and other target substrates provides a pathophysiologic link for the involvement of meprins in the pathogenesis of many inflammatory disorders. Meprins are now known to play important roles in inflammatory diseases including acute kidney injury, sepsis, urinary tract infections, bladder inflammation, and inflammatory bowel disease. The proteolysis of epithelial and endothelial barriers including cell junctional proteins by meprins promotes leukocyte influx into areas of tissue damage to result in inflammation. Meprins degrade extracellular matrix proteins; this ability of meprins is implicated in the cell migration of leukocytes and the invasion of tumor cells that express meprins. Proteolytic processing and maturation of procollagens provides evidence that meprins are involved in collagen maturation and deposition in the fibrotic processes involved in the formation of keloids and hypertrophic scars and lung fibrosis. This review highlights recent progress in understanding the role of meprins in inflammatory disorders in both human and mouse models.

A scar-like lesion is apparent in basement membrane after wound repair in vivo

Basement membrane is a highly conserved sheet-like extracellular matrix in animals, underlying simple and complex epithelia, and wrapping around tissues like muscles and nerves. Like the tissues they support, basement membranes become damaged by environmental insults. Although it is clear that basement membranes are repaired after damage, virtually nothing is known about this process. For example, it is not known how repaired basement membranes compare to undamaged ones, whether basement membrane components are necessary for epithelial wound closure, or whether there is a hierarchy of assembly that repairing basement membranes follow, similar to the hierarchy of assembly of embryonic basement membranes. In this report, we address these questions using the basement membrane of the Drosophila larval epidermis as a model system. By analyzing the four main basement membrane proteins - laminin, collagen IV, perlecan, and nidogen - we find that although basement membranes are repaired within a day after mechanical damage in vivo, thickened and disorganized matrix scars are evident with all four protein components. The new matrix proteins that repair damaged basement membranes are provided by distant adipose and muscle tissues rather than by the local epithelium, the same distant tissues that provide matrix proteins for growth of unwounded epithelial basement membranes. To identify a hierarchy of repair, we tested the dependency of each of the basement membrane proteins on the others for incorporation after damage. For proper incorporation after damage, nidogen requires laminin, and perlecan requires collagen IV, but surprisingly collagen IV does not to depend on laminin. Thus, the rules of basement membrane repair are subtly different than those of de novo assembly.

Dissection of Nidogen function in Drosophila reveals tissue-specific mechanisms of basement membrane assembly

Basement membranes (BMs) are thin sheet-like specialized extracellular matrices found at the basal surface of epithelia and endothelial tissues. They have been conserved across evolution and are required for proper tissue growth, organization, differentiation and maintenance. The major constituents of BMs are two independent networks of Laminin and Type IV Collagen in addition to the proteoglycan Perlecan and the glycoprotein Nidogen/entactin (Ndg). The ability of Ndg to bind in vitro Collagen IV and Laminin, both with key functions during embryogenesis, anticipated an essential role for Ndg in morphogenesis linking the Laminin and Collagen IV networks. This was supported by results from cultured embryonic tissue experiments. However, the fact that elimination of Ndg in C. elegans and mice did not affect survival strongly questioned this proposed linking role. Here, we have isolated mutations in the only Ndg gene present in Drosophila. We find that while, similar to C.elegans and mice, Ndg is not essential for overall organogenesis or viability, it is required for appropriate fertility. We also find, alike in mice, tissue-specific requirements of Ndg for proper assembly and maintenance of certain BMs, namely those of the adipose tissue and flight muscles. In addition, we have performed a thorough functional analysis of the different Ndg domains in vivo. Our results support an essential requirement of the G3 domain for Ndg function and unravel a new key role for the Rod domain in regulating Ndg incorporation into BMs. Furthermore, uncoupling of the Laminin and Collagen IV networks is clearly observed in the larval adipose tissue in the absence of Ndg, indeed supporting a linking role. In light of our findings, we propose that BM assembly and/or maintenance is tissue-specific, which could explain the diverse requirements of a ubiquitous conserved BM component like Nidogen.

Basement membranes (BMs) are thin layers of specialized extracellular matrices present in every tissue of the human body. Its main constituents are two networks of laminin and Type IV Collagen linked by Nidogen (Ndg) and proteoglycans. They form an organized scaffold that regulates organ morphogenesis and function. Mutations affecting BM components are associated with organ dysfunction and several congenital diseases. Thus, a better comprehension of BM assembly and maintenance will not only help to learn more about organogenesis but also to a better understanding and, hopefully, treatment of these diseases. Here, we have used the fruit fly Drosophila to analyse the role of Ndg in BM formation in vivo. Elimination of Ndg in worms and mice does not affect survival, strongly questioning its proposed linking role, derived from in vitro experiments. Here, we show that in the fly, Ndg is dispensable for BM assembly and preservation in many tissues, but absolutely required in others. Furthermore, our functional study of the different Ndg domains challenges the significance of some interactions between BM components derived from in vitro experiments, while confirming others, and reveals a new key requirement for the Rod domain in Ndg function and incorporation into BMs.

Biomarkers Discovery for Colorectal Cancer: A Review on Tumor Endothelial Markers as Perspective Candidates

Colorectal cancer (CRC) is the third most common cancer in the world. The early detection of CRC, during the promotion/progression stages, is an enormous challenge for a successful outcome and remains a fundamental problem in clinical approach. Despite the continuous advancement in diagnostic and therapeutic methods, there is a need for discovery of sensitive and specific, noninvasive biomarkers. Tumor endothelial markers (TEMs) are associated with tumor-specific angiogenesis and are potentially useful to discriminate between tumor and normal endothelium. The most promising TEMs for oncogenic signaling in CRC appeared to be the TEM1, TEM5, TEM7, and TEM8. Overexpression of TEMs especially TEM1, TEM7, and TEM8 in colorectal tumor tissue compared to healthy tissue suggests their role in tumor blood vessels formation. Thus TEMs appear to be perspective candidates for early detection, monitoring, and treatment of CRC patients. This review provides an update on recent data on tumor endothelial markers and their possible use as biomarkers for screening, diagnosis, and therapy of colorectal cancer patients.

Basement membrane protein nidogen-1 is a target of meprin β in cisplatin nephrotoxicity

Meprins are oligomeric metalloproteinases that are abundantly expressed in the brush-border membranes of renal proximal tubules. During acute kidney injury (AKI) induced by cisplatin or ischemia-reperfusion, membrane-bound meprins are shed and their localization is altered from the apical membranes toward the basolateral surface of the proximal tubules. Meprins are capable of cleaving basement membrane proteins in vitro, however, it is not known whether meprins are able to degrade extracellular matrix proteins under pathophysiological conditions in vivo. The present study demonstrates that a basement membrane protein, nidogen-1, is cleaved and excreted in the urine of mice subjected to cisplatin-induced nephrotoxicity, a model of AKI. Cleaved nidogen-1 was not detected in the urine of untreated mice, but during the progression of cisplatin nephrotoxicity, the excretion of cleaved nidogen-1 increased in a time-dependent manner. The meprin inhibitor actinonin markedly prevented urinary excretion of the cleaved nidogen-1. In addition, meprin β-deficient mice, but not meprin α-deficient mice, subjected to cisplatin nephrotoxicity significantly suppressed excretion of cleaved nidogen-1, further suggesting that meprin β is involved in the cleavage of nidogen-1. These studies provide strong evidence for a pathophysiological link between meprin β and urinary excretion of cleaved nidogen-1 during cisplatin-induced AKI.

Control of the basement membrane and cell migration by ADAMTS proteinases: Lessons from C. elegans genetics

The members of the ADAMTS (a disintegrin and metalloproteinase with thrombospondin motifs) family of secreted proteins, MIG-17 and GON-1, play essential roles in Caenorhabditis elegans gonadogenesis. The genetic and molecular analyses of these proteinases uncovered novel molecular interactions regulating the basement membrane (BM) during the migration of the gonadal leader cells. MIG-17, which is localized to the gonadal BM recruits or activates fibulin-1 and type IV collagen, which then recruits nidogen, thereby inducing the remodeling of the BM that is required for directional control of leader cell migration. GON-1 acts antagonistically with fibulin-1 to regulate the levels of type IV collagen accumulation in the gonadal BM, which facilitates active migration of the leader cells. The cooperative action of MIG-17 and GON-1 represents an excellent model for understanding the mechanisms of organogenesis mediated by ADAMTS proteinases.

Analysis of nidogen-1/laminin γ1 interaction by cross-linking, mass spectrometry, and computational modeling reveals multiple binding modes

We describe the detailed structural investigation of nidogen-1/laminin γ1 complexes using full-length nidogen-1 and a number of laminin γ1 variants. The interactions of nidogen-1 with laminin variants γ1 LEb2–4, γ1 LEb2–4 N836D, γ1 short arm, and γ1 short arm N836D were investigated by applying a combination of (photo-)chemical cross-linking, high-resolution mass spectrometry, and computational modeling. In addition, surface plasmon resonance and ELISA studies were used to determine kinetic constants of the nidogen-1/laminin γ1 interaction. Two complementary cross-linking strategies were pursued to analyze solution structures of laminin γ1 variants and nidogen-1. The majority of distance information was obtained with the homobifunctional amine-reactive cross-linker bis(sulfosuccinimidyl)glutarate. In a second approach, UV-induced cross-linking was performed after incorporation of the diazirine-containing unnatural amino acids photo-leucine and photo-methionine into laminin γ1 LEb2–4, laminin γ1 short arm, and nidogen-1. Our results indicate that Asn-836 within laminin γ1 LEb3 domain is not essential for complex formation. Cross-links between laminin γ1 short arm and nidogen-1 were found in all protein regions, evidencing several additional contact regions apart from the known interaction site. Computational modeling based on the cross-linking constraints indicates the existence of a conformational ensemble of both the individual proteins and the nidogen-1/laminin γ1 complex. This finding implies different modes of interaction resulting in several distinct protein-protein interfaces.

Proteolytic activity of prostate-specific antigen (PSA) towards protein substrates and effect of peptides stimulating PSA activity

Prostate-specific antigen (PSA or kallikrein-related peptidase-3, KLK3) exerts chymotrypsin-like proteolytic activity. The main biological function of PSA is the liquefaction of the clot formed after ejaculation by cleavage of semenogelins I and II in seminal fluid. PSA also cleaves several other substrates, which may explain its putative functions in prostate cancer and its antiangiogenic activity. We compared the proteolytic efficiency of PSA towards several protein and peptide substrates and studied the effect of peptides stimulating the activity of PSA with these substrates. An endothelial cell tube formation model was used to analyze the effect of PSA-degraded protein fragments on angiogenesis. We showed that PSA degrades semenogelins I and II much more efficiently than other previously identified protein substrates, e.g., fibronectin, galectin-3 and IGFBP-3. We identified nidogen-1 as a new substrate for PSA. Peptides B2 and C4 that stimulate the activity of PSA towards small peptide substrates also enhanced the proteolytic activity of PSA towards protein substrates. Nidogen-1, galectin-3 or their fragments produced by PSA did not have any effect on endothelial cell tube formation. Although PSA cleaves several other protein substrates, in addition to semenogelins, the physiological importance of this activity remains speculative. The PSA levels in prostate are very high, but several other highly active proteases, such as hK2 and trypsin, are also expressed in the prostate and may cleave protein substrates that are weakly cleaved by PSA.

Cleavage of nidogen-1 by cathepsin S impairs its binding to basement membrane partners

Cathepsin S (catS), which is expressed in normal human keratinocytes and localized close to the dermal-epidermal junction (DEJ) degrades some of major basement membrane (BM) constituents. Among them, catS readily hydrolyzed in a time and dose dependent manner human nidogen-1 (nid-1) and nidogen-2, which are key proteins in the BM structure. CatS preferentially cleaved nid-1 at both acid and neutral pH. Hydrolysis of nid-1 was hampered in murine ctss^−/− spleen lysates pretreated with inhibitors of other classes of proteases. Nid-1 was cleaved within its G2 and G3 globular domains that are both involved in interactions with other BM components. Binding assays with soluble and immobilized ligands indicated that catS altered the formation of complexes between nid-1 and other BM components. Assuming that the cleavage of nid-1 impairs its ability to crosslink with BM partners and perturbs the viscoelastic properties of BM matrix, these data indicate that catS may participate in BM proteolysis, in addition to already identified proteases.

Schwann cell myelination requires integration of laminin activities

Laminins promote early stages of peripheral nerve myelination by assembling basement membranes (BMs) on Schwann cell surfaces, leading to activation of β1 integrins and other receptors. The BM composition, structural bonds and ligands needed to mediate this process, however, are not well understood. Mice hypomorphic for laminin γ1-subunit expression that assembled endoneurial BMs with reduced component density exhibited an axonal sorting defect with amyelination but normal Schwann cell proliferation, the latter unlike the null. To identify the basis for this, and to dissect participating laminin interactions, LAMC1 gene-inactivated dorsal root ganglia were treated with recombinant laminin-211 and -111 lacking different architecture-forming and receptor-binding activities, to induce myelination. Myelin-wrapping of axons by Schwann cells was found to require higher laminin concentrations than either proliferation or axonal ensheathment. Laminins that were unable to polymerize through deletions that removed critical N-terminal (LN) domains, or that lacked cell-adhesive globular (LG) domains, caused reduced BMs and almost no myelination. Laminins engineered to bind weakly to α6β1 and/or α7β1 integrins through their LG domains, even though they could effectively assemble BMs, decreased myelination. Proliferation depended upon both integrin binding to LG domains and polymerization. Collectively these findings reveal that laminins integrate scaffold-forming and cell-adhesion activities to assemble an endoneurial BM, with myelination and proliferation requiring additional α6β1/α7β1-laminin LG domain interactions, and that a high BM ligand/structural density is needed for efficient myelination.

Different domains in nidogen-1 and nidogen-2 drive basement membrane formation in skin organotypic cocultures

Nidogen-1 and nidogen-2 are homologous proteins found in all basement membranes (BMs). They show comparable binding activities in vitro and partially redundant functions in vivo. Previously, we showed that in skin organotypic cocultures, BM formation was prevented in the absence of nidogens and that either nidogen was able to rescue this failure. We now dissected the two nidogens to identify the domains required for BM deposition. For that purpose, HaCaT cells were grown on collagen matrices containing nidogen-deficient, murine fibroblasts. After addition of nidogen-1 or nidogen-2 protein fragments comprising different binding domains, BM deposition was analyzed by immunofluorescence and electron microscopy. We could demonstrate that the rod-G3 domain of nidogen-2 was sufficient to achieve deposition of BM components at the epidermal-collagen interface. In contrast, for nidogen-1, both the G2 and G3 domains were required. Immunoblot analysis confirmed that all BM components were present in comparable amounts under all culture conditions. This finding demonstrates that nidogens, although homologous proteins, exert their effect on BM assembly through different binding domains, which may in turn result in alterations of BM structure and functions, thus providing an explanation for the phenotypical differences observed between nidogen-1 and -2 deficient mice.

Role of MUC4-NIDO domain in the MUC4-mediated metastasis of pancreatic cancer cells

MUC4 is a large transmembrane type I glycoprotein that is overexpressed in pancreatic cancer (PC) and has been shown to be associated with its progression and metastasis. However, the exact cellular and molecular mechanism(s) through which MUC4 promotes metastasis of PC cells has been sparsely studied. Here we showed that the NIDO domain of MUC4, which is similar to the G1-domain present in the nidogen or entactin (an extracellular matrix protein), contributes to the protein-protein interaction property of MUC4. By this interaction, MUC4 promotes breaching of basement membrane integrity, and spreading of cancer cells. These observations are corroborated with the data from our study using an engineered MUC4 protein without the NIDO domain, which was ectopically expressed in the MiaPaCa PC cells, lacking endogenous MUC4 and nidogen protein. The in vitro studies demonstrated an enhanced invasiveness of MiaPaCa cells expressing MUC4 (MiaPaCa-MUC4) compared to vector-transfected cells (MiaPaCa-Vec; p=0.003) or cells expressing MUC4 without the NIDO domain (MiaPaCa-MUC4-NIDO^Δ; p=0.03). However, the absence of NIDO-domain has no significant role on cell growth and motility (p=0.93). In the in-vivo studies, all the mice orthotopically implanted with MiPaCa-MUC4 cells developed metastasis to the liver as compared to MiaPaCa-Vec or the MiaPaCa-MUC4-NIDO^Δ group, hence, supporting our in vitro observations. Additionally, a reduced binding (p=0.0004) of MiaPaCa-MUC4-NIDO^Δ cells to the fibulin-2 coated plates compared to MiaPaCa-MUC4 cells indicated a possible interaction between the MUC4-NIDO domain and fibulin-2, a nidogen-interacting protein. Furthermore, in PC tissue samples, MUC4 colocalized with the fibulin-2 present in the basement membrane. Altogether, our findings demonstrate that the MUC4-NIDO domain significantly contributes to the MUC4-mediated metastasis of PC cells. This may be partly due to the interaction between the MUC4-NIDO domain and fibulin-2.

Molecular organization of the basement membrane zone

The dermal-epidermal basement membrane is a complex assembly of proteins that provide adhesion and regulate many important processes such as development, wound healing, and cancer progression. This contribution focuses on the structure and function of individual components of the basement membrane, how they assemble together, and how they participate in human tissues and diseases, with an emphasis on skin involvement. Understanding the composition and structure of the basement membrane provides insight into the pathophysiology of inherited blistering disorders, such as epidermolysis bullosa, and acquired bullous diseases, such as the pemphigoid group of autoimmune diseases and epidermolysis bullosa acquisita.

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.

Nerve invasion distance is dependent on laminin gamma2 in tumors of pancreatic cancer

The distance of nerve invasion is an important prognostic factor in pancreatic cancer. The extracellular matrix (ECM) of nerve, mainly composed of laminin, collagen IV and anchoring fibrils, might affect nerve invasion. However, this relationship has not been demonstrated. Our study aimed at discovering the promoting factor of nerve invasion within the tumoral ECM. An animal model was established to evaluate the distance of nerve invasion in murine sciatic nerves by intraneural injection of 6 human pancreatic cancer cell lines. mRNA expression of laminins and anchoring fibrils was compared to the distance of nerve invasion for each cancer cell line. A target molecule provided the strong association between mRNA expression and the distance of nerve invasion. To evaluate the role of a target molecule in nerve invasion, protein expression and function were examined using an animal model and surgical cases. Cancer cells with high laminin gamma2 mRNA and protein expression in their basement membranes were associated with long nerve invasion. Knockdown of laminin gamma2 in cancer cells significantly shortened nerve invasion in the animal model. In 75 patients with pancreatic cancer, a large distance of nerve invasion was associated with high expression levels of laminin gamma2 mRNA and basement membranous deposition of laminin gamma2 protein. Our results indicate that laminin gamma2 plays an important role in nerve invasion. The measurement of the nerve invasion distance in our mouse nerve invasion model is useful for evaluating the molecular mechanisms of nerve invasion.

Basement membranes in development and disease

Basement membranes (BMs) are specializations of the extracellular matrix that act as key mediators of development and disease. Their sheet like protein matrices typically serve to separate epithelial or endothelial cell layers from underlying mesenchymal tissues, providing both a biophysical support to overlying tissue as well as a hub to promote and regulate cell-cell and cell-protein interactions. In the latter context, the BM is increasingly being recognized as a mediator of growth factor interactions during development. In this review, we discuss recent findings regarding the structure of the BM and its roles in mediating the normal development of the embryo, and we examine congenital diseases affecting the BM which impact embryonic development and health in later life.

Scaffold-forming and Adhesive Contributions of Synthetic Laminin-binding Proteins to Basement Membrane Assembly

Laminins that possess three short arms contribute to basement membrane assembly by anchoring to cell surfaces, polymerizing, and binding to nidogen and collagen IV. Although laminins containing the alpha4 and alpha5 subunits are expressed in alpha2-deficient congenital muscular dystrophy, they may be ineffective substitutes because they bind weakly to cell surfaces and/or because they lack the third arm needed for polymerization. We asked whether linker proteins engineered to bind to deficient laminins that provide such missing activities would promote basement membrane assembly in a Schwann cell model. A chimeric fusion protein (alphaLNNd) that adds a short arm terminus to laminin through the nidogen binding locus was generated and compared with the dystrophy-ameliorating protein miniagrin (mAgrin) that binds to the laminin coiled-coil dystroglycan and sulfatides. alphaLNNd was found to mediate laminin binding to collagen IV, to bind to galactosyl sulfatide, and to selectively convert alpha-short arm deletion-mutant laminins LmDeltaalphaLN and LmDeltaalphaLN-L4b into polymerizing laminins. This protein enabled polymerization-deficient laminin but not an adhesion-deficient laminin lacking LG domains (LmDeltaLG) to assemble an extracellular matrix on Schwann cell surfaces. mAgrin, on the other hand, enabled LmDeltaLG to form an extracellular matrix on cell surfaces without increasing accumulation of non-polymerizing laminins. These gain-of-function studies reveal distinct polymerization and anchorage contributions to basement membrane assembly in which the three different LN domains mediate the former, and the LG domains provide primary anchorage with secondary contributions from the alphaLN domain. These findings may be relevant for an understanding of the pathogenesis and treatment of laminin deficiency states.

MIG-17/ADAMTS controls cell migration by recruiting nidogen to the basement membrane in C. elegans

Mutations in the a disintegrin and metalloprotease with thrombospondin motifs (ADAMTS) family of secreted proteases cause diseases linked to ECM abnormalities. However, the mechanisms by which these enzymes modulate the ECM during development are mostly unexplored. The Caenorhabditis elegans MIG-17/ADAMTS protein is secreted from body wall muscle cells and localizes to the basement membrane (BM) of the developing gonad where it controls directional migration of gonadal leader cells. Here we show that specific amino acid changes in the ECM proteins fibulin-1C (FBL-1C) and type IV collagen (LET-2) result in bypass of the requirement for MIG-17 activity in gonadal leader cell migration in a nidogen (NID-1)-dependent and -independent manner, respectively. The MIG-17, FBL-1C and LET-2 activities are required for proper accumulation of NID-1 at the gonadal BM. However, mutant FBL-1C or LET-2 in the absence of MIG-17 promotes NID-1 localization. Furthermore, overexpression of NID-1 in mig-17 mutants substantially rescues leader cell migration defects. These results suggest that functional interactions among BM molecules are important for MIG-17 control of gonadal leader cell migration. We propose that FBL-1C and LET-2 act downstream of MIG-17-dependent proteolysis to recruit NID-1 and that LET-2 also activates a NID-1-independent pathway, thereby inducing the remodeling of the BM required for directional control of leader cell migration.

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.

Early postnatal pulmonary failure and primary hypothyroidism in mice with combined TPST-1 and TPST-2 deficiency

Protein-tyrosine sulfation is a post-translational modification of an unknown number of secreted and membrane proteins mediated by two known Golgi tyrosylprotein sulfotransferases (TPST-1 and TPST-2). Tpst double knockouts were generated to investigate the importance of tyrosine sulfation in vivo. Double knockouts were born alive at the expected frequency, were normal in size, and their tissues do not synthesize sulfotyrosine. However, most pups die in the early postnatal period with signs of cardiopulmonary insufficiency. A combination of clinical, magnetic resonance imaging, and histological data indicated that lungs of Tpst double knockouts fail to expand at birth resulting in acute pulmonary hypertension, right-to-left shunting, and death by asphyxia in the early postnatal period. Some double knockouts survive the postnatal period, but fail to thrive and display delayed growth that is due in part to hypothyroidism. In addition, we find that Tpst2-/- mice have primary hypothyroidism, but that Tpst1-/- mice are euthyroid. This suggests that a protein(s) required for thyroid hormone production is sulfated and cannot be sulfated in the absence of TPST-2. Thus, Tpst1 and Tpst2 are the only Tpst genes in mice, tyrosine sulfation is required for normal pulmonary function at birth, and TPST-2 is required for normal thyroid gland function.

Role of Laminin Terminal Globular Domains in Basement Membrane Assembly

Laminins contribute to basement membrane assembly through interactions of their N- and C-terminal globular domains. To further analyze this process, recombinant laminin-111 heterotrimers with deletions and point mutations were generated by recombinant expression and evaluated for their ability to self-assemble, interact with nidogen-1 and type IV collagen, and form extracellular matrices on cultured Schwann cells by immunofluorescence and electron microscopy. Wild-type laminin and laminin without LG domains polymerized in contrast to laminins with deleted alpha1-, beta1-, or gamma1-LN domains or with duplicated beta1- or alpha1-LN domains. Laminins with a full complement of LN and LG domains accumulated on cell surfaces substantially above those lacking either LN or LG domains and formed a lamina densa. Accumulation of type IV collagen onto the cell surface was found to require laminin with separate contributions arising from the presence of laminin LN domains, nidogen-1, and the nidogen-binding site in laminin. Collectively, the data support the hypothesis that basement membrane assembly depends on laminin self-assembly through formation of alpha-, beta-, and gamma-LN domain complexes and LG-mediated cell surface anchorage. Furthermore, type IV collagen recruitment into the laminin extracellular matrices appears to be mediated through a nidogen bridge with a lesser contribution arising from a direct interaction with laminin.

Involvement of specific laminins and nidogens in the active remodeling of the basal lamina of labial salivary glands from patients with Sjögren's syndrome

OBJECTIVE

To investigate remodeling of the basal lamina of labial salivary glands (LSGs) from patients with Sjögren's syndrome (SS) by analyzing the expression of specific components that participate in its assembly and attachment to acinar and ductal cells.

METHODS

Two groups of SS patients with similar levels of remnant glandular tissue but with low and high levels of interacinar fibrosis, respectively, were studied. The expression of laminin alpha1, alpha4, and gamma2 chains and nidogens was examined at the messenger RNA (mRNA) and protein levels. Nidogens 1 and 2 were also studied in situ by immunohistochemistry.

RESULTS

Increases in the amount of mRNA and protein for both the processed and unprocessed laminin gamma2-chain were more pronounced in patients with low interacinar fibrosis. Increases in the protein levels of laminin alpha1 and alpha4 chains were observed in patients with low interacinar fibrosis, but not in those with high interacinar fibrosis. Nidogen mRNA and protein levels were similar in SS patients and controls. Interestingly, high levels of nidogen degradation were observed in patients with low interacinar fibrosis. Nidogens were readily detected by immunofluorescence in the basal lamina of the capillaries and stroma in SS patients, but were less apparent in the basal lamina of the acini and ducts.

CONCLUSION

These results suggest that the basal lamina of LSGs from patients with SS is undergoing active remodeling, such that alterations are less evident in patients who have advanced morphologic signs of the disease (high interacinar fibrosis). Nidogen proteolysis might account for the disorganization of the basal lamina that is typically observed in LSGs from SS patients, assuming that cleavage impairs their ability to crosslink type IV collagen and laminin networks.

Collagen XXVIII, a novel von Willebrand factor A domain-containing protein with many imperfections in the collagenous domain

Here we describe a novel collagen belonging to the class of von Willebrand factor A (VWA) domain-containing proteins. This novel protein was identified by screening the EST data base and was subsequently recombinantly expressed and characterized as an authentic tissue component. The COL28A1 gene on human chromosome 7p21.3 and on mouse chromosome 6A1 encodes a novel protein that structurally resembles the beaded filament-forming collagens. The collagenous domain contains several very short interruptions arranged in a repeat pattern. As shown for other novel minor collagens, the expression of collagen XXVIII protein in mouse is very restricted. In addition to small amounts in skin and calvaria, the major signals were in dorsal root ganglia and peripheral nerves. By immunoelectron microscopy, collagen XXVIII was detected in the sciatic nerve, at the basement membrane of certain Schwann cells surrounding the nerve fibers. Even though the protein is present in the adult sciatic nerve, collagen XXVIII mRNA was only detected in sciatic nerve of newborn mice, indicating that the protein persists for an extended period after synthesis.

Basal lamina disorganisation of the acini and ducts of labial salivary glands from patients with Sjogren's syndrome: association with mononuclear cell infiltration

OBJECTIVE

To study the expression of laminin and type IV collagen as biomarkers of the organisation of the basal lamina of acini and ducts in labial salivary glands from patients with Sjögren's syndrome, and to relate this organisation to inflammatory cell invasion of acini and ducts.

METHODS

Immunohistochemistry for laminin and type IV collagen was undertaken on sections of labial salivary glands from 30 patients with Sjögren's syndrome, 10 control subjects, and 24 controls with chronic sialoadenitis. Immunohistochemistry reaction, alterations to cell morphology, and the presence of inflammatory cells in acini and ducts were evaluated and scored using a semiquantitative method.

RESULTS

Changes in the expression of laminin and type IV collagen in the basal lamina of acini and ducts of labial salivary glands from patients with Sjögren's syndrome were more pronounced than in labial salivary glands from control groups. A remarkable characteristic was the disorganisation of the basal lamina in the labial salivary glands in Sjögren's syndrome. The pattern of immunoreactivity of the basal lamina of other structures (for example, blood vessels) did not change. In Sjögren's syndrome, invasion of cytotoxic T lymphocytes was only observed in acini and ducts which had a disorganised basal lamina.

CONCLUSIONS

The high state of disorganisation of the basal lamina of acini and ducts could allow invasion of cytotoxic T lymphocytes in Sjögren's syndrome, contributing to cell death and ductal hyperplasia.

Laminin-6 assembles into multimolecular fibrillar complexes with perlecan and participates in mechanical-signal transduction via a dystroglycan-dependent, integrin-independent mechanism

Mechanical ventilation is a valuable treatment regimen for respiratory failure. However, mechanical ventilation (especially with high tidal volumes) is implicated in the initiation and/or exacerbation of lung injury. Hence, it is important to understand how the cells that line the inner surface of the lung [alveolar epithelial cells (AECs)] sense cyclic stretching. Here, we tested the hypothesis that matrix molecules, via their interaction with surface receptors, transduce mechanical signals in AECs. We first determined that rat AECs secrete an extracellular matrix (ECM) rich in anastamosing fibers composed of the alpha3 laminin subunit, complexed with beta1 and gamma1 laminin subunits (i.e. laminin-6), and perlecan by a combination of immunofluorescence microscopy and immunoblotting analyses. The fibrous network exhibits isotropic expansion when exposed to cyclic stretching (30 cycles per minute, 10% strain). Moreover, this same stretching regimen activates mitogen-activated-protein kinase (MAPK) in AECs. Stretch-induced MAPK activation is not inhibited in AECs treated with antagonists to alpha3 or beta1 integrin. However, MAPK activation is significantly reduced in cells treated with function-inhibiting antibodies against the alpha3 laminin subunit and dystroglycan, and when dystroglycan is knocked down in AECs using short hairpin RNA. In summary, our results support a novel mechanism by which laminin-6, via interaction with dystroglycan, transduces a mechanical signal initiated by stretching that subsequently activates the MAPK pathway in rat AECs. These results are the first to indicate a function for laminin-6. They also provide novel insight into the role of the pericellular environment in dictating the response of epithelial cells to mechanical stimulation and have broad implications for the pathophysiology of lung injury.

A fibulin-1 homolog interacts with an ADAM protease that controls cell migration in C. elegans

ADAM (a disintegrin and metalloprotease) family proteins play important roles in animal development and pathogenesis. In C. elegans, a secreted ADAM protein, MIG-17, acts from outside the gonad to control the migration of gonadal distal tip cells (DTCs) that promote gonad morphogenesis. Here, we report that dominant mutations in the fbl-1 gene encoding fibulin-1 spliced isoforms, which are calcium binding extracellular matrix proteins, bypass the requirement for MIG-17 activity in directing DTC migration. Specific amino acid substitutions in the third EGF-like motif of one of the two isoforms, FBL-1C, which corresponds to mammalian fibulin-1C, suppress mig-17 mutations. FBL-1C is synthesized in the gut cells and localizes strongly to the gonadal basement membrane in a MIG-17-dependent manner. Localization of mutant FBL-1C is weaker than that of the wild-type protein and is insensitive to MIG-17 activity, suggesting that it gains a novel function that compensates for its reduced molecular density. We propose that proteolysis by MIG-17 recruits FBL-1C to the gonadal basement membrane, where it is required for the guidance of DTCs, and that mutant FBL-1C acts in a manner that mimics the downstream events of MIG-17-mediated proteolysis.

Identification of a binding partner for the endothelial cell surface proteins TEM7 and TEM7R

Tumor endothelial marker 7 (TEM7) was recently identified as an mRNA transcript overexpressed in the blood vessels of human solid tumors. Here, we identify several new variants of TEM7, derived by alternative splicing, that are predicted to be intracellular (TEM7-I), secreted (TEM7-S), or on the cell surface membrane (TEM7-M) of tumor endothelium. Using new antibodies against the TEM7 protein, we confirmed the predicted expression of TEM7 on the cell surface and demonstrated that TEM7-M protein, like its mRNA, is overexpressed on the endothelium of various tumor types. We then used an affinity purification strategy to search for TEM7-binding proteins and identified cortactin as a protein capable of binding to the extracellular region of both TEM7 and its closest homologue, TEM7-related (TEM7R), which is also expressed in tumor endothelium. The binding domain of cortactin was mapped to a unique nine-amino acid region in its plexin-like domain. These studies establish the overexpression of TEM7 protein in tumor endothelium and provide new opportunities for the delivery of therapeutic and imaging agents to the vessels of solid tumors.

Abnormal gene expression profiles in human ovaries from polycystic ovary syndrome patients

Polycystic ovary syndrome (PCOS) represents the most common cause of anovulatory infertility and affects 5-10% of women of reproductive age. The etiology of PCOS is still unknown. The current study is the first to describe consistent differences in gene expression profiles in human ovaries comparing PCOS patients vs. healthy normoovulatory individuals. The microarray analysis of PCOS vs. normal ovaries identifies dysregulated expression of genes encoding components of several biological pathways or systems such as Wnt signaling, extracellular matrix components, and immunological factors. Resulting data may provide novel clues for ovarian dysfunction in PCOS. Intriguingly, the gene expression profiles of ovaries from (long-term) androgen-treated female-to-male transsexuals (TSX) show considerable overlap with PCOS. This observation provides supportive evidence that androgens play a key role in the pathogenesis of PCOS. Presented data may contribute to a better understanding of dysregulated pathways in PCOS, which might ultimately reveal novel leads for therapeutic intervention.

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.

Identification and characterization of AMACO, a new member of the von Willebrand factor A-like domain protein superfamily with a regulated expression in the kidney

The genes coding for human and mouse AMACO, an extracellular matrix protein containing VWA-like domains related to those in MAtrilins and COllagens, were detected in databases, the cDNAs were cloned, and the primary structures were deduced from the nucleotide sequences. The genes consist of 14 exons and have a similar exon/intron organization. The protein consists of a signal peptide sequence, an N-terminal VWA domain connected to two additional, tandem VWA domains by a cysteine-rich sequence and an epidermal growth factor (EGF)-like domain. The C terminus is made up of another EGF-like domain followed by a unique sequence present in mouse, but absent in human. The predicted molecular weight of the proteins is 79,485 in human and 83,024 in mouse. Full-length AMACO was expressed in 293-EBNA cells, purified by use of an affinity tag and subjected to biochemical characterization. Both monomers and aggregates of AMACO were recovered, as shown by electron microscopy and SDS-PAGE. AMACO was found in the media of a variety of established cell lines of both fibroblast and epithelial origin. In the matrix formed by 293-EBNA cells overexpressing the protein, AMACO was deposited in patchy structures that were often cell-associated. Affinity-purified antibodies detect expression in cartilage and expression associated with certain basement membranes. In the kidney of adult mice, a second promoter located in intron 4 is active. If the resulting transcript is translated it could not yield a secreted protein because of the lack of a signal peptide sequence. The developmental switch from an AMACO mRNA, expressed by the newborn kidney, to the truncated transcript found in the adult kidney indicates an unusual regulation of AMACO expression.

Fibulins: a versatile family of extracellular matrix proteins

Fibulins are a newly recognized family of extracellular matrix proteins. The five known members of the family share an elongated structure and many calcium-binding sites, owing to the presence of tandem arrays of epidermal growth factor-like domains. They have overlapping binding sites for several basement-membrane proteins, tropoelastin, fibrillin, fibronectin and proteoglycans, and they participate in diverse supramolecular structures. New insights into their biological roles are now emerging from studies of transgenic mice and of some inherited human diseases.

Survey of the year 2001 commercial optical biosensor literature

We have assembled references of 700 articles published in 2001 that describe work performed using commercially available optical biosensors. To illustrate the technology's diversity, the citation list is divided into reviews, methods and specific applications, as well as instrument type. We noted marked improvements in the utilization of biosensors and the presentation of kinetic data over previous years. These advances reflect a maturing of the technology, which has become a standard method for characterizing biomolecular interactions.

Evidence of nidogen-2 compensation for nidogen-1 deficiency in transgenic mice

Previous studies have shown that inhibition of nidogen-laminin binding interferes with basement membrane stabilization in various mouse organ cultures while no overt phenotype has been observed following inactivation of the nidogen-1 gene in mice. We have now used recombinant mouse nidogen-1 and nidogen-2 in order to evaluate a possible compensation between the two isoforms in the knock-out mice. Essentially, a comparable in vitro binding of nidogens-1 and -2 to the same laminin gamma1 chain structure and to several other basement membrane proteins has been revealed. Quantitative radioimmuno-assays have demonstrated high concentrations of nidogen-1 exceeding those of laminin gamma1 and nidogen-2 by factors of 5 and 20-50, respectively, in tissue extracts of wild-type mice. A three- to sevenfold increase in nidogen-2 was observed in heart and muscle of mice with nidogen-1 deficiency and confirmed by a similar increase in the intensity of immunogold staining of these tissues. However, a few of the tissues from mice with the gene knock-out still contained some nidogen-1-like immunoreactivity (1% of wild-type). Furthermore, both nidogen isoforms showed a similar distribution in various organs during embryonic development which, however, as shown previously, changed in some adult tissues. The data support the nidogen-2 compensation hypothesis to explain the limited phenotype observed following elimination of the nidogen-1 gene.

Binding of mouse nidogen-2 to basement membrane components and cells and its expression in embryonic and adult tissues suggest complementary functions of the two nidogens

Nidogen-1 binds several basement membrane components by well-defined, domain-specific interactions. Organ culture and gene targeting approaches suggest that a high-affinity nidogen-binding site of the laminin gamma1 chain (gamma1III4) is important for kidney development and for nerve guidance. Other proteins may also bind gamma1III4, although human nidogen-2 binds poorly to the mouse laminin gamma1 chain. We therefore characterized recombinant mouse nidogen-2 and its binding to basement membrane proteins and cells. Mouse nidogen-1 and -2 interacted at comparable levels with collagen IV, perlecan, and fibulin-2 and, most notably, also with laminin-1 fragments P1 and gamma1III3-5, which both contain the gamma1III4 module. In embryos, nidogen-2 mRNA was produced by mesenchyme at sites of epithelial-mesenchymal interactions, but the protein was deposited on epithelial basement membranes, as previously shown for nidogen-1. Hence, binding of both nidogens to the epithelial laminin gamma1 chain is dependent on epithelial-mesenchymal interactions. Epidermal growth factor stimulated expression of both nidogens in embryonic submandibular glands. Both nidogens were found in all studied embryonic and adult basement membranes. Nidogen-2 was more adhesive than nidogen-1 for some cell lines and was mainly mediated by alpha3beta1 and alpha6beta1 integrins as shown by antibody inhibition. These findings revealed extensive coregulation of nidogen-1 and -2 expression and much more complementary functions of the two nidogens than previously recognized.

Gene structure and functional analysis of the mouse nidogen-2 gene: nidogen-2 is not essential for basement membrane formation in mice

Nidogens are highly conserved proteins in vertebrates and invertebrates and are found in almost all basement membranes. According to the classical hypothesis of basement membrane organization, nidogens connect the laminin and collagen IV networks, so stabilizing the basement membrane, and integrate other proteins. In mammals two nidogen proteins, nidogen-1 and nidogen-2, have been discovered. Nidogen-2 is typically enriched in endothelial basement membranes, whereas nidogen-1 shows broader localization in most basement membranes. Surprisingly, analysis of nidogen-1 gene knockout mice presented evidence that nidogen-1 is not essential for basement membrane formation and may be compensated for by nidogen-2. In order to assess the structure and in vivo function of the nidogen-2 gene in mice, we cloned the gene and determined its structure and chromosomal location. Next we analyzed mice carrying an insertional mutation in the nidogen-2 gene that was generated by the secretory gene trap approach. Our molecular and biochemical characterization identified the mutation as a phenotypic null allele. Nidogen-2-deficient mice show no overt abnormalities and are fertile, and basement membranes appear normal by ultrastructural analysis and immunostaining. Nidogen-2 deficiency does not lead to hemorrhages in mice as one may have expected. Our results show that nidogen-2 is not essential for basement membrane formation or maintenance.

The role of the posterior ciliary body in the biosynthesis of vitreous humour

Recently, several groups have published new information regarding the origins and structure of the vitreous humour, and the inner limiting lamina (ILL) of the retina. This short article provides an overview of this new information. It is proposed that vitreous proteins are derived from several different cell types with the posterior half of the non-pigmented ciliary epithelium being prominent in the expression of several connective tissue macromolecules. In addition, some basement membrane macromolecules are also expressed by the ciliary body and may subsequently be assembled on the surface of the Müller cells to form the ILL. New data suggest that the posterior half of the non-pigmented ciliary epithelium has substantial secretory activity and is likely to play a pivotal role in eye development.

Specific ablation of the nidogen-binding site in the laminin γ1 chain interferes with kidney and lung development

Basement membrane assembly is of crucial importance in the development and function of tissues and during embryogenesis. Nidogen 1 was thought to be central in the assembly processes, connecting the networks formed by collagen type IV and laminins, however, targeted inactivation of nidogen 1 resulted in no obvious phenotype. We have now selectively deleted the sequence coding for the 56 amino acid nidogen-binding site, γ1III4, within the Lamc1 gene by gene targeting. Here, we show that mice homozygous for the deletion die immediately after birth, showing renal agenesis and impaired lung development. These developmental defects were attributed to locally restricted ruptures in the basement membrane of the elongating Wolffian duct and of alveolar sacculi. These data demonstrate that an interaction between two basement membrane proteins is required for early kidney morphogenesis in vivo.

Latent transforming growth factor beta-binding protein-3 and fibulin-1C interact with the extracellular domain of the heparin-binding EGF-like growth factor precursor

BACKGROUND

The membrane-bound cell-surface precursor and soluble forms of heparin-binding epidermal growth factor-like growth factor (HB-EGF) contribute to many cellular developmental processes. The widespread occurrence of HB-EGF in cell and tissue types has led to observations of its role in such cellular and tissue events as tumor formation, cell migration, extracellular matrix formation, wound healing, and cell adherence. Several studies have reported the involvement of such extracellular matrix proteins as latent transforming growth factor beta-binding protein, TGF-beta, and fibulin-1 in some of these processes. To determine whether HB-EGF interacts with extracellular matrix proteins we used the extracellular domain of proHB-EGF in a yeast two-hybrid system to screen a monkey kidney cDNA library. cDNA clones containing nucleotide sequences encoding domains of two proteins were obtained and their derived amino acid sequences were evaluated.

RESULTS

From approximately equal to 3 x 10(6) screened monkey cDNA clones, cDNA clones were recovered that contained nucleotide sequences encoding domains of the monkey latent transforming growth factor-beta binding protein-3 (MkLTBP-3) and fibulin-1C protein. The amino acid sequence derived from the MkLTBP-3 gene shared 98.6% identity with human LTBP-3 and 86.7% identity with mouse LTBP-3 amino acid sequences. The amino acid sequence derived from the monkey fibulin-1C gene shared 97.2% identity with human fibulin-1C. Yeast two-hybrid screens indicate that LTBP-3 and fibulin-1C interact with proHB-EGF through their calcium-binding EGF-like modules.

CONCLUSIONS

The interactions of the extracellular domain of proHB-EGF with LTBP-3 and fibulin-1C suggest novel functions for HB-EGF between cell and tissue surfaces.