Localization of the gene (LAMA4) to chromosome 6q21 and isolation of a partial cDNA encoding a variant laminin A chain

Determining the Likelihood of Disease Pathogenicity Among Incidentally Identified Genetic Variants in Rare Dilated Cardiomyopathy-Associated Genes

Background As utilization of clinical exome sequencing (ES) has expanded, criteria for evaluating the diagnostic weight of incidentally identified variants are critical to guide clinicians and researchers. This is particularly important in genes associated with dilated cardiomyopathy (DCM), which can cause heart failure and sudden death. We sought to compare the frequency and distribution of incidentally identified variants in DCM-associated genes between a clinical referral cohort with those in control and known case cohorts to determine the likelihood of pathogenicity among those undergoing genetic testing for non-DCM indications. Methods and Results A total of 39 rare, non-TTN DCM-associated genes were identified and evaluated from a clinical ES testing referral cohort (n=14 005, Baylor Genetic Laboratories) and compared with a DCM case cohort (n=9442) as well as a control cohort of population variants (n=141 456) derived from the gnomAD database. Variant frequencies in each cohort were compared. Signal-to-noise ratios were calculated comparing the DCM and ES cohort with the gnomAD cohort. The likely pathogenic/pathogenic variant yield in the DCM cohort (8.2%) was significantly higher than in the ES cohort (1.9%). Based on signal-to-noise and correlation analysis, incidental variants found in FLNC, RBM20, MYH6, DSP, ABCC9, JPH2, and NEXN had the greatest chance of being DCM-associated. Conclusions The distribution of pathogenic variants between the ES cohort and the DCM case cohort was gene specific, and variants found in the ES cohort were similar to variants found in the control cohort. Incidentally identified variants in specific genes are more associated with DCM than others.

In silico identification of molecular mimics involved in the pathogenesis of Clostridium botulinum ATCC 3502 strain

Bacterial pathogens invade and disrupt the host defense system by means of protein sequences structurally similar at global and local level both. The sharing of homologous sequences between the host and the pathogenic bacteria mediates the infection and defines the concept of molecular mimicry. In this study, various computational approaches were employed to elucidate the pathogenicity of Clostridium botulinum ATCC 3502 at genome-wide level. Genome-wide study revealed that the pathogen mimics the host (Homo sapiens) and unraveled the complex pathogenic pathway of causing infection. The comparative 'omics' approaches helped in selective screening of 'molecular mimicry' candidates followed by the qualitative assessment of the virulence potential and functional enrichment. Overall, this study provides a deep insight into the emergence and surveillance of multidrug resistant C. botulinum ATCC 3502 caused infections. This is the very first report identifying C. botulinum ATCC 3502 proteome enriched similarities to the human host proteins and resulted in the identification of 20 potential mimicry candidates, which were further characterized qualitatively by sub-cellular organization prediction and functional annotation. This study will provide a variety of avenues for future studies related to infectious agents, host-pathogen interactions and the evolution of pathogenesis process.

Laminins 411 and 421 differentially promote tumor cell migration via α6β1 integrin and MCAM (CD146)

α4-laminins, such as laminins 411 and 421, are mesenchymal laminins expressed by blood and lymphatic vessels and some tumor cells. Laminin-411 promotes migration of leukocytes and endothelial cells, but the effect of this laminin and laminin-421 on tumor cells is poorly understood. In the present study, we demonstrate that laminin-411 and, to a greater extent, laminin-421 significantly promote migration of tumor cells originated from melanomas, gliomas and different carcinomas via α6β1 integrin. In solid-phase binding assays, both laminins similarly bound α6β1 integrin but only laminin-421, among several laminin isoforms, readily bound MCAM (CD146), a cell-surface adhesion molecule strongly associated with tumor progression. Accordingly, a function-blocking mAb to MCAM inhibited tumor cell migration on laminin-421 but not on laminins 411 or 521. In tumor tissues, melanoma cells co-expressed MCAM, laminin α4, β1, β2 and γ1 chains, and integrin α6 and β1 chains. The present data highlight the novel role of α4-laminins in tumor cell migration and identify laminin-421 as a primary ligand for MCAM and a putative mediator of tumor invasion and metastasis.

Three heterotrimeric laminins produced by human keratinocytes

Laminins are a family of glycoproteins composed of alpha,beta and gamma chains. Five alpha(alpha1-alpha5), three beta (beta1-beta3) and twogamma (gamma1 and gamma2) chains have been cloned fromhuman and their replaceable assembly into heterotrimers producesthe variety of laminins. Reverse transcription-polymerase chainreaction of mRNAs showed that human keratinocytes express thealpha3, alpha5, beta1, beta3, gamma1 andgamma2 genes at high level among the ten cloned lamininchains. Western blot and immunoprecipitation of the cell lysatewith antiserum directed against mouse laminin-1(alpha1beta1gamma1) detected two trimers with thecomposition of alphaxbeta1gamma1 (probablylaminin-10 with the composition of alpha5beta1gamma1and alphaybeta1gamma1. Meanwhile, antiserum directedagainst a synthetic peptide of human alpha3 detected onlyalpha3beta3gamma2 trimer (laminin-5). We thus show thatkeratinocytes produce three heterotrimeric laminins. We couldnot detect the assembly of alpha3 with beta1 and gamma1chains to form alpha3beta1gamma1 (laminin-6) in keratinocytes.

Trophoblast-specific expression and function of the integrin alpha 7 subunit in the peri-implantation mouse embryo

For implantation and placentation to occur, mouse embryo trophoblast cells must penetrate the uterine stroma to make contact with maternal blood vessels. A major component of the uterine epithelial basement membrane and underlying stromal matrix with which they interact is the extracellular matrix protein laminin. We have identified integrin alpha 7 beta 1 as a major receptor for trophoblast-laminin interactions during implantation and yolk sac placenta formation. It is first expressed by trophectoderm cells of the late blastocyst and by all trophectoderm descendants in the early postimplantation embryo through E8.5, then disappears except in cells at the interface between the allantois and the ectoplacental plate. Integrin alpha 7 expression is a general characteristic of the early differentiation stages of rodent trophoblast, given that two different cultured trophoblast cell lines also express this integrin. Trophoblast cells interact with at least three different laminin isoforms (laminins 1, 2/4, and 10/11) in the blastocyst and in the uterus at the time of implantation. Outgrowth assays using function-blocking antibodies show that alpha 7 beta 1 is the major trophoblast receptor for laminin 1 and a functional receptor for laminins 2/4 and 10/11. When trophoblast cells are cultured on substrates of these three laminins, they attach and spread on all three, but show decreased proliferation on laminin 1. These results show that the alpha 7 beta 1 integrin is expressed by trophoblast cells and acts as receptor for several isoforms of laminin during implantation. These interactions are not only important for trophoblast adhesion and spreading but may also play a role in regulating trophectoderm proliferation and differentiation.

Hydra and Niccolo Paganini (1782-1840)--two peas in a pod? The molecular basis of extracellular matrix structure in the invertebrate, Hydra

The body wall of Hydra is organized as an epithelial bilayer with an intervening extracellular matrix (ECM). Molecular and biochemical analyses of Hydra ECM have established that it contains components similar to those seen in more complicated vertebrates such as human. In terms of biophysical parameters, Hydra ECM is highly flexible; a property that facilitates continuous movements along the organism's longitudinal and radial axis. A more rigid ECM, as in vertebrates, would not be compatible with this degree of movement. The flexible nature of Hydra ECM can now be explained in part by the unique structure of the organism's collagens. Interestingly, some aspects of the structural features of Hydra collagens mimic what is seen in Ehlers-Danlos syndrome, an inherited condition in humans that results in an abnormally flexible ECM that can be debilitating in extreme cases. This review will focus on structure-function relationships of the ECM of Hydra.

Differential expression of laminin alpha chains during proliferative and differentiation stages in a model for skin morphogenesis

The purpose of this study was to determine the mRNA and protein expression of laminin alpha chains at various stages of in vitro skin morphogenesis. Fibroblasts in mono-cultures express low levels of the mRNA of laminin alpha1,alpha2, alpha3 and alpha4 chains. When co-cultured with keratinocytes for 28 days, they expressed the mRNA for all these chains. Keratinocytes in monolayer expressed the laminin alpha3 chain mRNA and very low levels of the mRNA of the alpha1 and alpha2 chains, although, when recombined with fibroblasts they also expressed laminin alpha1and alpha2 mRNA, but not the laminin alpha4 mRNA. Immunocytochemistry of cells in co-culture showed that laminin alpha1, alpha3 and alpha5 chains were expressed in the epidermis, while the laminin alpha2, beta1, and gamma1 chains were noted in the dermis and at the epidermo-dermal interface. The laminin alpha1chain was first expressed during the proliferative stage (14-21 days) and the laminin alpha2 and alpha5 chains appeared later, during the differentiation stage (28-42 days). The above results suggest that epithelial-mesenchymal interactions are involved in the expression of laminin alpha chain mRNA during in vitro skin morphogenesis. In addition, there is distinct temporal and spatial expression of these chains during proliferative and differentiation stages, possibly reflecting different functions.

Laminins: structure and genetic regulation

The laminins form a large family of modular proteins found in basement membranes, but also elsewhere. They function as structural components and are essential for morphogenesis, but in addition interact with cell surface receptors such as integrins and alpha-dystroglycan. By virtue of their receptor interactions, they initiate intracellular signalling events that regulate cellular organization and differentiation. The many interactions of laminins are mediated by binding sites, often contributed by single domains, which may differ between different forms of laminin. In the present article, we describe how the diversity of laminins and the genetic regulation of the expression of different laminin forms lead to the formation of extracellular matrices with variable laminin composition and thereby different biological properties.

Form and function: the laminin family of heterotrimers

The laminins are a family of glycoproteins that provide an integral part of the structural scaffolding of basement membranes in almost every animal tissue. Each laminin is a heterotrimer assembled from alpha, beta, and gamma chain subunits, secreted and incorporated into cell-associated extracellular matrices. The laminins can self-assemble, bind to other matrix macromolecules, and have unique and shared cell interactions mediated by integrins, dystroglycan, and other receptors. Through these interactions, laminins critically contribute to cell differentiation, cell shape and movement, maintenance of tissue phenotypes, and promotion of tissue survival. Recent advances in the characterization of genetic disruptions in humans, mice, nematodes and flies have revealed developmental roles for the different laminin subunits in diverse cell types, affecting differentiation from blastocyst formation to the post-natal period. These genetic defects have challenged some of the previous concepts about basement membranes and have shed new light on the diversity and complexity of laminin functions as well as established the molecular basis of several human diseases.

Blood platelets contain and secrete laminin-8 (alpha4beta1gamma1) and adhere to laminin-8 via alpha6beta1 integrin

Laminins, a family of heterotrimeric proteins with cell adhesive/signaling properties, are characteristic components of basement membranes of vasculature and tissues. In the present study, permeabilized platelets were found to react with a monoclonal antibody to laminin gamma1 chain by immunofluorescence. In Western blot analysis of platelet lysates, several monoclonal antibodies to gamma1 and beta1 laminin chains recognized 220- to 230-kDa polypeptides, under reducing conditions, and a structure with much slower electrophoretic mobility under nonreducing conditions. Immunoaffinity purification on a laminin beta1 antibody-Sepharose column yielded polypeptides of 230, 220, 200, and 180 kDa from platelet lysates. In the purified material, mAbs to beta1 and gamma1 reacted with the two larger polypeptides, while affinity-purified rabbit antibodies to laminin alpha4 chain recognized the smallest polypeptide. Identity of the polypeptides was confirmed by microsequencing. One million platelets contained on average 1 ng of laminin (approximately 700 molecules per cell), of which 20-35% was secreted within minutes after stimulation with either thrombin or phorbol ester. Platelets adhered to plastic surfaces coated with the purified platelet laminin, and this process was largely inhibited by antibodies to beta1 and alpha6 integrin chains. We conclude that platelets contain and, following activation, secrete laminin-8 (alpha4beta1gamma1) and that the cells adhere to the protein by using alpha6beta1 integrin.

Distribution of ten laminin chains in dystrophic and regenerating muscles

Using immunohistochemical methods, we assessed the distribution of all 10 known laminin chains (alpha1-5, beta1-3, gamma1 and gamma2) in skeletal muscles from patients with Duchenne, congenital, limb girdle, or Emery-Dreifuss muscular dystrophies. The alpha2, beta1 and gamma1 chains were abundant in the basal lamina surrounding muscle fibers in normal controls; alpha1, alpha3-alpha5, beta3, and gamma2 were undetectable; and beta2 was present at a low level. Compared to controls, levels of the alpha5 chain were increased in muscles from many dystrophic patients; levels of beta1 were reduced and/or levels of beta2 were increased in a minority. However, these changes were neither specific for, nor consistent within, diagnostic categories. In contrast, levels of alpha4 were increased in muscles from all patients with alpha2 laminin (merosin)-deficient congenital muscular dystrophy. Loss of alpha2 laminin in congenital dystrophy is disease-specific but some other changes in laminin isoform expression in dystrophic muscles could be secondary consequences of myopathy, denervation, regeneration or immaturity. To distinguish among these possibilities, we compared the laminins of embryonic, denervated, regenerating, and mutant mouse muscles with those in normal adult muscle. Embryonic muscle basal lamina contained alpha4 and alpha5 along with alpha2, and regenerating muscle re-expressed alpha5 but not alpha4. Levels of alpha5 but not alpha4 were increased in dystrophin (mdx) mutants and in dystrophin/utrophin double mutants (mdx:utrn -/-), models for Duchenne dystrophy. In contrast, laminin alpha4 was upregulated more than alpha5 in muscles of laminin alpha2 mutant mice (dy/dy; a model for alpha2-deficient congenital dystrophy). Based on these results, we hypothesize that the expression of alpha5 in many dystrophies reflects the regenerative process, whereas the selective expression of alpha4 in alpha2-deficient muscle is a specific compensatory response to loss of alpha2.

Molecular cloning and tissue-specific expression of a novel murine laminin gamma3 chain

A novel laminin gamma3 chain was identified from the expressed sequence tag data base at the National Center for Biotechnology Information. A complete cDNAderived peptide sequence reveals a 1592-amino acid-long primary translation product, including a tentative 33-amino acid-long signal peptide. Comparison with the laminin gamma1 chain predicts that the two polypeptides have equal spatial dimensions. In addition, the well conserved domains VI and III(LE4) predict that gamma3 containing laminins are able to integrate to the laminin network and also via nidogen connect to other protein networks in the basement membranes. Combination of Northern analysis and in situ hybridization experiments indicate that expression of the gamma3 chain is highly tissue- and cell-specific, being significantly strong in capillaries and arterioles of kidney as well as in interstitial Leydig cells of testis.

Laminin-5 promotes adhesion and migration of epithelial cells: identification of a migration-related element in the gamma2 chain gene (LAMC2) with activity in transgenic mice

The effects of laminin-5 and its subunit gamma2 chain on cell adhesion and migration were studied, and a migration-related cis-acting element was identified in the gamma2 chain gene (LAMC2) using promoter-reporter gene constructs in transgenic mice. Intact laminin-5 molecules, but not recombinant gamma2 chain promoted cell adhesion of human keratinocytes and mouse squamous carcinoma cells, indicating that the gamma2 chain does not contain a cellular binding site. However, the gamma2 chain as such is probably involved in the process of cell locomotion, as antibodies against the short arm of the chain inhibited migration of carcinoma cells in an in vitro assay. Further evidence for the involvement of the gamma2 chain in cell migration was obtained by the identification of a cis-acting element in a promoter-lacZ reporter gene construct that was active in migratory epithelial cells of healing wounds in mice made transgenic by microinjection of the construct into fertilized oozytes. The migration active element was located in the sequence between -613 and +55. The same construct, and another one containing 5900 base pairs of the 5' flanking region, yielded very limited expression in cells of normal tissues. The limited expression was, however, only observed in epithelial cells of different tissues, i.e. cell types that normally express laminin-5 in vivo. The results show that the sequence between -613 and +55 contains elements that can drive expression during epithelial cell migration and that also partially confers more general epithelium expression. However, elements outside -5900 and +55 are needed for normal epithelium expression of the LAMC2 gene.

The laminins: role in intestinal morphogenesis and differentiation

Dynamic and reciprocal heterotypic cell interactions are crucial for intestinal morphogenesis and differentiation. This paper emphasizes the role of basement membrane molecules and in particular of laminins as potent mediators in this intercellular cross talk. Changes in the expression or localization of laminin isoforms or of integrins during development and cell migration strengthen the concept that heterogeneity in cell-matrix interactions could mediate distinct cell responses. A combination of genetic or biochemical approaches associated with in vitro models allows us to study the potential role of each laminin isoform in basement membrane assembly, cell migration, or cell differentiation.

Sickle Cell Adhesion to Laminin: Potential Role for the 5 Chain

Sickle red blood cell (RBC) adhesion to the endothelium and to exposed, underlying subendothelial proteins is believed to contribute to vascular occlusion in sickle cell disease. Laminin, a major component of the subendothelium, supports significant adhesion of sickle, but not normal RBCs. The purpose of this study was to define the adhesive region for sickle RBCs within a human laminin preparation using a flow adhesion assay designed to mimic physiologic flow through postcapillary venules. Because sickle RBCs did not adhere to the common laminin contaminants entactin or collagen type IV, neither of these proteins are likely to contribute to the observed adhesion to laminin. Known adhesive regions of laminin neither supported nor inhibited sickle RBC adhesion to laminin, suggesting a mechanism of adhesion previously uncharacterized in other laminin adhesion studies. Moreover, sickle RBCs did not adhere to mouse EHS laminin or to human laminin-2 (merosin), eliminating the 1, 2, β1, and γ1 chains as mediators of sickle cell adhesion. The monoclonal antibody 4C7, which binds at or near the G-domain of the laminin 5 chain, significantly inhibited sickle RBC adhesion. These results suggest that an adhesive region for sickle RBCs is contained within the laminin 5 chain.

© 1998 by The American Society of Hematology.

Sickle Cell Adhesion to Laminin: Potential Role for the 5 Chain

Sickle red blood cell (RBC) adhesion to the endothelium and to exposed, underlying subendothelial proteins is believed to contribute to vascular occlusion in sickle cell disease. Laminin, a major component of the subendothelium, supports significant adhesion of sickle, but not normal RBCs. The purpose of this study was to define the adhesive region for sickle RBCs within a human laminin preparation using a flow adhesion assay designed to mimic physiologic flow through postcapillary venules. Because sickle RBCs did not adhere to the common laminin contaminants entactin or collagen type IV, neither of these proteins are likely to contribute to the observed adhesion to laminin. Known adhesive regions of laminin neither supported nor inhibited sickle RBC adhesion to laminin, suggesting a mechanism of adhesion previously uncharacterized in other laminin adhesion studies. Moreover, sickle RBCs did not adhere to mouse EHS laminin or to human laminin-2 (merosin), eliminating the 1, 2, β1, and γ1 chains as mediators of sickle cell adhesion. The monoclonal antibody 4C7, which binds at or near the G-domain of the laminin 5 chain, significantly inhibited sickle RBC adhesion. These results suggest that an adhesive region for sickle RBCs is contained within the laminin 5 chain.

© 1998 by The American Society of Hematology.

Integrin alpha3beta1-mediated interaction with laminin-5 stimulates adhesion, migration and invasion of malignant glioma cells

Gliomas, characterized by their progressively invasive phenotype, express integrin alpha3beta1 as a major receptor for the extracellular matrix both in vivo and in vitro. Since the integrin alpha3beta1 has been shown to be a specific receptor for laminin-5 (alpha3beta3gamma2), we examined the effects of purified human laminin-5 on adhesion, migration and invasion of human glioma cells. Among different types of laminin variants and other matrix proteins including fibronectin and vitronectin, laminin-5 was most potent in promoting adhesion and migration of different kinds of glioma cells. Laminin-5-mediated adhesion and migration were specifically inhibited by monoclonal antibodies against integrin alpha3 and beta1 chains, confirming the role of integrin alpha3beta1 as the major laminin-5 receptor. Invasion of the reconstituted basement membrane (i.e., Matrigel) by glioma cells was also selectively stimulated by laminin-5. Out results show that laminin-5 is the major extracellular stimulant for glioma cell adhesion, migration and invasion. The immunohistochemical distribution of laminin gamma2 chain, a laminin subunit unique to laminin-5, showed that it was expressed in the tumor parenchyma of human glioma tissues. Expression of laminin alpha3, beta3 and gamma2 chains in glioma tissues and in glioma cell lines was also demonstrated at the messenger RNA level by reverse transcription polymerase chain reaction. Our results, taken together, show that laminin-5 may be involved in the invasive phenotype of malignant gliomas both in vitro and in vivo.

FISH mapping of seven cDNA sequences in the pig

Fluorescence in situ hybridization (FISH) technique was applied to localize seven clones derived from a porcine (SSC) intestinal directionally cloned cDNA library. The size of the clones ranged from 1.1 to 1.3 kb. Three of the clones corresponded to histidyl-tRNA synthetase (HARS), immunoglobulin alpha (IGA) and lysozyme (LYZ) and mapped to SSC2q28-q29, 7q2.6 and 5p11 respectively. The available human-pig comparative painting data and sequence homology comparisons assisted in a tentative identification of the other three clones as glutathione-S-transferase (GST), glutathione-S-transferase mu (GSTM1) and immunoglobulin lambda gene cluster (IGL@). These clones mapped to SSC14q21, 5q2.4 and 14q22-q23 respectively. The remaining clone representing an EST mapped to 1p24-p25. These localizations contribute to the transcript map in pig and are significant as comparative markers. Difficulties associated with the mapping of small sequences using FISH are discussed.

Expression and potential role of the extracellular matrix in hepatic ontogenesis: a review

Studies from a number of laboratories have provided information on the temporal and spatial expression of a variety of extracellular matrix (ECM) components in the developing liver and insight into their potential roles in hepatogenesis. Collagen type IV and laminin are present in the basement membranes of the capsular mesothelium, vascular structures of the portal and hepatic vein branches, and the ductular elements of the developing liver. The mesothelial, vascular, and ductular epithelial cells synthesize laminin and type IV collagen. In contrast, fibronectin and type I collagen are restricted to the adjacent or surrounding interstitium of those ductal and vascular elements, but are not within the basement membrane proper. The hepatic perisinusoidal space (Space of Disse) of the fetal rat develops a delicate extracellular matrix by 12.5 days of gestation, which is characterized by banded collagen fibrils and bundles associated with filamentous and flocculent material. Fibronectin, laminin, and collagen types I, III, and IV are present in the developing perisinusoidal space by this early gestational date, with laminin being the most prevalent component detected. The laminin chains localized to that region in the fetal/neonatal period are alpha 2, beta 1, beta 2, and gamma 1, whereas the alpha 1 chain of laminin is absent from the developing Space of Disse. Similar data have been reported on the laminin phenotype in the perisinusoidal space during hepatic regeneration. Electron microscopy immunohistochemistry studies have demonstrated that the sinusoidal lining cells and hepatocytes synthesize these ECM proteins during hepatogenesis. By 6 to 8 weeks of postnatal life, laminin is not detectable in the perisinusoidal space. Both the transient expression of laminin and the similarity of the laminin chain phenotype expressed in the perisinusoidal space in the developing and regenerating liver suggests a role for this protein in the organization of the hepatic lobule in those forms of hepatic morphogenesis.

The human alpha3b is a 'full-sized' laminin chain variant with a more widespread tissue expression than the truncated alpha3a

We report the molecular cloning of the human laminin alpha3b chain variant and its mRNA expression pattern in adult human tissues when compared to the alpha3a variant. The mRNA encoding for the alpha3b variant is about 11 kb and the predicted translation product carries the complete set of domains typical for a 'full-sized' laminin alpha chain. Apart from the similar domain structure of alpha3b also the sequence of alpha3 resulted more closely related to the alpha5 than to the alpha4 chain. Quantitative analysis of the RNA expression in a broad panel of adult human tissues indicated that the alpha3b variant is more widely distributed than the alpha3a shorter variant.

Primary structure, developmental expression, and immunolocalization of the murine laminin alpha4 chain

The complete primary structure of the mouse laminin alpha4 chain was derived from cDNA clones. The translation product contains a 24-residue signal peptide preceding the mature alpha4 chain of 1,792 residues. Northern analysis on whole mouse embryos revealed that the expression was weak at day 7, but it later increased and peaked at day 15. In adult tissues the strongest expression was observed in lung and cardiac and skeletal muscles. Weak expression was also seen in other adult tissues such as brain, spleen, liver, kidney, and testis. By in situ hybridization of fetal and newborn tissues, expression of the laminin alpha4 chain was mainly localized to mesenchymal cells. Strong expression was seen in the villi and submucosa of the developing intestine, the mesenchymal stroma surrounding the branching lung epithelia, and the external root sheath of vibrissae follicles, as well as in cardiac and skeletal muscle fibers. In the developing kidney, intense but transient expression was associated with the differentiation of epithelial kidney tubules from the nephrogenic mesenchyme. Immunohistologic staining with affinity-purified IgG localized the laminin alpha4 chain primarily to lung septa, heart, and skeletal muscle, capillaries, and perineurium.

The structural organisation of LAMA4, the gene encoding laminin alpha4

We have determined the complete structural arrangement of LAMA4, the gene encoding the laminin alpha4 chain. Using both yeast artificial chromosome clones and total human genomic DNA and primers derived from the cDNA sequence, regions of the gene were amplified and sequenced to determine the splice donor and acceptor sites. The introns were sized by agarose gel electrophoresis of the PCR products. The gene consisted of 39 exons spanning 122 kb. All of the splice sites conformed to the GT/AG rule, except intron 7 which possessed a GC dinucleotide at the donor splice site. The intron/exon ratio was large at 17.8:1, mainly due to large introns at the 5' end of the gene. Regions at both the 5' and 3' end of the gene were subcloned from the yeast artificial chromosomes to enable untranscribed DNA to be sequenced. The gene represents the second of the laminin A gene family to be characterised and its structural organisation is similar to the equivalent regions of the LAMA2 gene.

Murine laminin alpha3A and alpha3B isoform chains are generated by usage of two promoters and alternative splicing

We already identified two distinct laminin alpha3A and alpha3B chain isoforms which differ in their amino-terminal ends and display different tissue-specific expression patterns. In this study we have investigated whether these two different isoforms are products of the same laminin alpha3 (lama3) gene and transcribed from one or two separate promoters. Genomic clones were isolated that encompass the sequences upstream to the 5' ends of both the alpha3A and the alpha3B cDNAs. Sequence analysis of the region upstream to the alpha3A open reading frame revealed the presence of a TATA box and potential binding sites for responsive elements. By primer extension analysis, the transcription start site of the alpha3B mRNA isoform was defined. The sequences upstream to the alpha3B mRNA transcription start site do not contain a TATA box near the transcription initiation sites, but AP-1, AP-2, and Sp1 consensus binding site sequences were identified. The genomic regions located immediately upstream of the alpha3A and alpha3B transcription start sites were shown to possess promoter activities in transfection experiments. In the promoter regions, response elements for the acute phase reactant signal and NF-interleukin 6 were found, and their possible relevance in the context of inflammation and wound healing is discussed. Our results demonstrate that the lama3 gene produces the two polypeptides by alternative splicing and contains two promoters, which regulate the production of the two isoforms alpha3A and alpha3B.

The laminin alpha chains: expression, developmental transitions, and chromosomal locations of alpha1-5, identification of heterotrimeric laminins 8-11, and cloning of a novel alpha3 isoform

Laminin trimers composed of alpha, beta, and gamma chains are major components of basal laminae (BLs) throughout the body. To date, three alpha chains (alpha1-3) have been shown to assemble into at least seven heterotrimers (called laminins 1-7). Genes encoding two additional alpha chains (alpha4 and alpha5) have been cloned, but little is known about their expression, and their protein products have not been identified. Here we generated antisera to recombinant alpha4 and alpha5 and used them to identify authentic proteins in tissue extracts. Immunoprecipitation and immunoblotting showed that alpha4 and alpha5 assemble into four novel laminin heterotrimers (laminins 8-11: alpha4beta1gamma1, alpha4beta2gamma1, alpha5beta1gamma1, and alpha5beta2gamma1, respectively). Using a panel of nucleotide and antibody probes, we surveyed the expression of alpha1-5 in murine tissues. All five chains were expressed in both embryos and adults, but each was distributed in a distinct pattern at both RNA and protein levels. Overall, alpha4 and alpha5 exhibited the broadest patterns of expression, while expression of alpha1 was the most restricted. Immunohistochemical analysis of kidney, lung, and heart showed that the alpha chains were confined to extracellular matrix and, with few exceptions, to BLs. All developing and adult BLs examined contained at least one alpha chain, all alpha chains were present in multiple BLs, and some BLs contained two or three alpha chains. Detailed analysis of developing kidney revealed that some individual BLs, including those of the tubule and glomerulus, changed in laminin chain composition as they matured, expressing up to three different alpha chains and two different beta chains in an elaborate and dynamic progression. Interspecific backcross mapping of the five alpha chain genes revealed that they are distributed on four mouse chromosomes. Finally, we identified a novel full-length alpha3 isoform encoded by the Lama3 gene, which was previously believed to encode only truncated chains. Together, these results reveal remarkable diversity in BL composition and complexity in BL development.

Distribution of the ten known laminin chains in the pathways and targets of developing sensory axons

Laminins are heterotrimers of alpha, beta, and gamma chains. At present, five alpha, three beta, and two gamma chains have been described. The best characterized laminin (laminin 1 = alpha 1, beta 1, gamma 1) promotes neurite outgrowth from virtually all classes of developing neurons, implying that laminins may serve as axon guidance molecules in vivo. Moreover, different laminin trimers exert distinct effects on subsets of laminin-1-responsive cells, suggesting that isoform diversity may underlie some axonal choices in vivo. As a first step toward evaluating these hypotheses, we have documented the expression patterns of all 10-known laminin chains in the peripheral nervous system and spinal cord of the murine embryo. The alpha 2, alpha 4, beta 1, and gamma 1 chains are expressed in peripheral axonal pathways by embryonic day (E) 11.5, when sensory and motor axonal outgrowth is underway. Thus, laminins (but not laminin 1) may promote peripheral axonal outgrowth. By E 13.5, laminin chains are differentially expressed in the limb-bud, with prominent expression of alpha 2 and alpha 4 in muscle and of alpha 3 and alpha 5 in skin. This pattern raises the possibility that laminin isoform diversity contributes to the ability of cutaneous and muscle sensory axons to distinguish their targets. Later in development, some chains (e.g., alpha 2, alpha 4, and beta 1) are downregulated in peripheral nerve while others (e.g., gamma 1), continue to be expressed by Schwann cells into adulthood. In contrast to peripheral nerves and ganglia, laminin chains are expressed at low levels, if at all, in the developing spinal cord gray matter.

The complete cDNA coding sequence and tissue-specific expression of the mouse laminin alpha 4 chain

The full-length cDNA coding sequence is presented for the mouse laminin alpha 4 chain. Comparison of the encoded amino acid sequence with human laminin alpha 4 shows 88.3% identity. Northern blot analysis shows that mouse laminin alpha 4 is strongly expressed in heart, lung and skeletal muscle, with only limited expression in brain, spleen, liver, kidney and testes.

Structure of the human laminin alpha2-chain gene (LAMA2), which is affected in congenital muscular dystrophy

We have determined the structure and complete exon size pattern of the human laminin alpha2-chain gene (LAMA2), which has been shown to be affected in congenital muscular dystrophy (Helbling-Leclerc, A., Zhang, X., Topaloglu, H., Cruaud, C., Tesson, F., Weissenbach, J., Tomé, F. M. S., Schwartz, K., Fardeau, M., Tryggvason, K., and Guicheney, P. (1995) Nat. Genet. 11, 216-218). The gene is over 260, 000 base pairs and contains 64 exons. The sequence of all exon-intron borders was determined. Two of the exons, i.e. exons 43 and 52, are extremely small in size, 6 and 12 base pairs, respectively. Comparison of the exon pattern of the human LAMA2 gene with that of the Drosophila LAMA gene revealed that only 2 of 63 intron locations in the 5'-end of the human gene match the intron locations in the Drosophila gene, which contains 14 introns.

Regulation of the beta 2 subunit chain of laminin in developing rabbit fetal lung tissue

Laminins are a family of basement membrane-associated heterotrimeric proteins that are important in mediating the growth, migration, and differentiation of a variety of cell types. The beta 2 subunit chain is a component of several laminin isoforms, e.g., laminin-3, laminin-4, laminin-7, and possibly other, as yet uncharacterized laminin isoforms. Utilizing monoclonal antibodies directed against the beta 2 subunit chain of laminin, we detected this protein in fetal, neonatal, and adult lung tissues. The relative amount of laminin beta 2 subunit chain in fetal lung tissue increased as gestation proceeded, reaching its peak around the time of alveolar type II cell differentiation in the rabbit. The laminin beta 2 subunit chain was localized in early gestational age rabbit fetal lung tissue primarily in basement membranes of prealveolar ducts, airways, and smooth muscle cells of airways and arterial blood vessels. A rabbit laminin beta 2 cDNA was generated using RT-PCR and utilized as a probe in northern blot analysis to characterize the levels of laminin beta 2 mRNA in developing rabbit lung tissue. Similar to the pattern of laminin beta 2 protein induction observed in fetal lung tissue, laminin beta 2 mRNA levels were maximal late in gestation. Utilizing a laminin beta 2 chain cRNA probe and in situ hybridization, we detected laminin beta 2 mRNA in the epithelial cells of prealveolar ducts, the alveolar wall, and airways, as well as in connective tissue cells, and the smooth muscle cells of airways and blood vessels in fetal and adult lung tissues. In addition, using an in vitro explant model, we determined that alveolar type II cells are capable of synthesizing laminin beta 2 subunit mRNA and depositing this laminin subunit chain in the basement membrane beneath type II cells. The results of this study are suggestive that the laminin beta 2 chain may be involved in alveolar epithelial cell differentiation.

The complete cDNA sequence of laminin alpha 4 and its relationship to the other human laminin alpha chains

We previously localised the gene (LAMA4) encoding a novel laminin alpha 4 chain to chromosome 6q21. In this study, we describe the complete coding sequence and compare the protein with the other three known human laminin alpha chains. Although closely linked to LAMA2, the LAMA4 product most closely resembles laminin alpha 3, a constituent of laminin 5. Like laminin alpha 3A, the alpha 4 chain is a truncated version of the alpha 1 and alpha 2 chains, with a much reduced short arm. While the alpha 4 molecule is most similar to alpha 3, it shares some features of the C-terminal domains G4 and G5 in common with alpha 2. Unlike the LAMA3 gene, LAMA4 appears to encode only a single transcript, as determined by 5' rapid amplification of cDNA ends. The cDNA sequence encodes 1816 amino acids, which include a 24-residue signal peptide. The gene is expressed in skin, placenta, heart, lung, skeletal muscle, and pancreas. We have also shown that the mRNA can be readily reverse transcribed and amplified from cultured dermal fibroblasts.

Structural organization of the human and mouse laminin beta2 chain genes, and alternative splicing at the 5' end of the human transcript

We have determined the structural organization of the human and mouse genes that encode the laminin beta2 chain (s-laminin), an essential component of the basement membranes of the neuromuscular synapse and the kidney glomerulus. The human and mouse genes have a nearly identical exon-intron organization and are the smallest laminin chain genes characterized to date, due to the unusually small size of their introns. The laminin beta2 chain genes of both species consist of 33 exons that span </=12 kilobase pairs of genomic DNA. The exon-intron pattern of the laminin beta2 chain gene is also highly similar to that of the human genes encoding the homologous laminin beta1 and beta3 chains. The putative promoter regions of the human and mouse laminin beta2 chain genes have features characteristic of the promoters of genes that have a limited tissue expression. Considerable conservation of the intron sequences of the mouse and human genes was observed. The first intron of the human gene, located 1 base pair upstream of the translation start codon, contains a non-consensus 5' splice site. This intron was shown to be inefficiently spliced in humans, suggesting that post-transcriptional mechanisms may be involved in the regulation of laminin beta2 chain gene expression.

Differential neural crest cell attachment and migration on avian laminin isoforms

A number of laminin isoforms have recently been identified and proposed to exert different functions during embryonic development. In the present study, we describe the purification and partial characterization of several isoforms isolated from chick heart and gizzard, and provide data on the molecular mechanisms underlying the interaction of avian neural crest cells with these molecules in vitro. Laminins extracted from heart and gizzard tissues were separated by gel filtration and purified to homogeneity by sequential lectin and immunoaffinity chromatography by utilizing monoclonal antibodies directed against the avian alpha 2, beta 2 and gamma 1 laminin chains. The sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) banding pattern of the polypeptide complexes obtained and immunoblotting with polyclonal antisera allowed the identification of Laminin-2 (alpha 2 beta 1 gamma 1), Laminin-4 (alpha 2 beta 2 gamma 1), and laminins comprising the beta 1, beta 2 and gamma 1 chains associated with a shorter alpha chain which, in SDS-PAGE, co-migrate with the beta/gamma complex in the 200 kDa region. These latter laminins, which are here arbitrarily denoted Laminin-alpha x (heart tissue) and Laminin-G (gizzard tissue), are somewhat distinct in their apparent molecular weight, are differentially associated with nidogen, and appear as "T"-shaped particles similar to Laminin-6 and Laminin-7 when analyzed by transmission electron microscopy following rotary shadowing. In contrast, the avian Laminin-2 and Laminin-4 isoforms exhibit the characteristic cruciform shape described previously for their mammalian counterparts. Isolated neural crest cells differentially attached and migrated on these laminin isoforms, showing a clear preference for Laminin-G. Similarly to the EHS Laminin-1, neural crest cells recognized all avian isoforms through their alpha 1 beta 1 integrin, shown previously to be the primary laminin-binding receptor on these cells. Neural crest cell interaction with the avian laminins was dependent upon maintenance of the secondary and tertiary structure of the molecules, as shown by the marked reduction in cell attachment and migration upon disruption of the alpha-helical coiled-coil structure of their constituent chains. The results demonstrate that different laminin isoforms may be differentially involved in the regulation of neural crest cell migration and suggest that this regulation operates through interaction of the cells with a structurally conserved cell binding site recognized by the alpha 1 beta 1 integrin.

Laminins, tenascin and type VII collagen in colorectal mucosa

The distribution of different laminin polypeptides, type VII collagen and tenascin has been studied in adult and foetal colorectal mucosa by using the indirect immunofluorescence technique. Immunoreactivity for laminin alpha 1 chain was located to basement membranes of epithelia, muscularis mucosae, and blood vessels, respectively in different segments of adult colon and rectum. Laminin beta 1 and gamma 1 chains were additionally expressed in lamina propria. Laminin alpha 2 chain was also found in lamina propria around the pericryptal fibroblasts. Immunoreactivity for laminin beta 2 chain was restricted to basement membranes in the muscularis mucosae and arteries. Laminin alpha 3 and beta 3 chains, suggestive for laminin-5, were confined especially to surface epithelial basement membranes. Immunoreactivity for type VII collagen was confined to basement membrane of surface epithelium in a punctate manner, while that for tenascin was seen slightly more broadly in the basement membrane zone and also in the muscular layer. The distribution of laminin chains in 16-week-foetal colon mostly resembled that of corresponding adult tissue, although immunoreactivities for laminin alpha 2 and beta 2 chains were lacking. Type VII collagen and the high molecular weight isoform of tenascin were also absent from the foetal colon. The results show that the basement membrane of the surface epithelium of colon and rectum express the components of epithelial adhesion complex, laminin-5 (alpha 3-beta 3-gamma 2) and type VII collagen, resembling in this respect small intestine and stomach while laminin-2 (alpha 2-beta 1-gamma 1) appears to be associated with pericryptal fibroblasts, and laminin-1 (alpha 1-beta 1-gamma 1) widely in most basement membranes.

Laminins: a family of diverse multifunctional molecules of basement membranes

Laminins represent a growing family of disulfide-linked heterotrimers constituted by the association of three genetically different polypeptides, the alpha, beta, and gamma chains. Laminins are endowed with structural and biological functions. They play a direct critical role in the control of cellular behavior by providing cells with specific information through interactions with cell surface receptors. Because of their structural properties, they represent crucial building blocks for tissue assembly, architecture, and stability. The expression of laminin chain variants is spatio-temporally regulated, which suggests that laminin isoforms might have different functions responsible for the biological and morphological polymorphism of basement membranes. The different cells present in the skin express several laminin chains, which lead to the deposition of various laminin isoforms, whose mechanical and biological functions are likely to be adapted to the properties of the dermo-epidermal junction. Recently, defective laminin isoforms have been shown to be associated with several inborn and acquired diseases, illustrating a major structural function for laminins in skin integrity.

Molecular cloning of a novel laminin chain, alpha 5, and widespread expression in adult mouse tissues

We have identified a fifth member of the alpha subfamily of vertebrate laminin chains. Sequence analysis revealed a close relationship of alpha 5 to the only known Drosophila alpha chain, suggesting that the ancestral alpha gene was more similar to alpha 5 than to alpha 1-4. Analysis of RNA expression showed that alpha 5 is widely expressed in adult tissues, with highest levels in lung, heart, and kidney. Our results suggest that alpha 5 may be a major laminin chain of adult basal laminae.

Cataloging altered gene expression in young and senescent cells using enhanced differential display

Recently, a novel PCR-based technique, differential display (DD), has facilitated the study of differentially expressed genes at the mRNA level. We report here an improved version of DD, which we call Enhanced Differential Display (EDD). We have modified the technique to enhance reproducibility and to facilitate sequencing and cloning. Using EDD, we have generated and verified a catalog of genes that are differentially expressed between young and senescent human diploid fibroblasts (HDF). From 168 genetags that were identified initially, 84 could be sequenced directly from PCR amplified bands. These sequences represent 27 known genes and 37 novel genes. By Northern blot analysis we have confirmed the differential expression of a total of 23 genes (12 known, 11 novel), while 19 (seven known, 12 novel) did not show differential expression. Several of the known genes were previously observed by others to be differentially expressed between young and senescent fibroblasts, thereby validating the technique.

Primary structure and expression of a novel human laminin alpha 4 chain

The complete primary structure of a novel human laminin alpha 4 chain was derived from cDNA clones. The translation product contains a 24-residue signal peptide preceding the mature alpha 4 chain of 1792 residues. The domain structure is similar to that of the recently described alpha 3 chain [Ryan, Tizard, Van Devanter and Carter (1994) J. Biol. Chem. 269, 22779-22787]. Northern analysis of RNA from human fetal and adult tissues revealed developmental regulation of expression. In adult, strong expression was observed in heart as well as lung, ovary, small and large intestines, placenta and liver, whereas weak or no expression was detected in skeletal muscle, kidney, pancreas, testis, prostate or brain. In contrast, fetal lung and kidney revealed high expression. In situ hybridization analysis of human fetal and newborn tissues showed expression of the laminin in alpha 4 chain in certain mesenchymal cells in tissues such as smooth muscle and dermis.

Cloning of the beta 3 chain gene (LAMB3) of human laminin 5, a candidate gene in junctional epidermolysis bullosa

Laminin 5 consists of three polypeptides, alpha 3, beta 3, and gamma 2, encoded by the genes LAMA3, LAMB3, and LAMC2, respectively. In this study, we have elucidated the exon-intron organization of the human LAMB3 gene. Characterization of five overlapping lambda phage DNA clones revealed that the gene was approximately 29 kb in size. Subsequent sequence data revealed that the gene consisted of 23 exons that varied from 64 to 379 bp in size, accounting for the full-length cDNA with an open reading frame of 3516 bp encoding 1172 amino acids. Comparison of the LAMB3 gene structure with the previously characterized LAMB1 gene revealed that LAMB3 was considerably more compact. Knowledge of the exon-intron organization of the LAMB3 gene will facilitate elucidation of mutations in patients with the junctional forms of epidermolysis bullosa, some of which have been associated with mutations in the laminin 5 genes.