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At least 19 recordsLinked to original sources
PubMed1999

Anchorage-dependent regulation of the mitogen-activated protein kinase cascade by growth factors is supported by a variety of integrin alpha chains.

Integrin cooperation with growth factor receptors to enable permissive signaling to the mitogen-activated protein (MAP) kinase pathway has important implications for cell proliferation, differentiation, and survival. Here we have sought to determine whether anchorage regulation of the MAP kinase pathway is specific to the alpha chain subunit of the integrins employed during adhesion. Human umbilical vein endothelial cells (HUVECs) anchored via endogenous alpha(2), alpha(3), or alpha(5) integrin subunits or NIH3T3 fibroblast cells lines anchored via ectopically expressed human integrin alpha(2) or alpha(5) subunits displayed comparable MAP kinase activation upon growth factor stimulation, regardless of the integrin alpha chain employed. In contrast, when either cell type was maintained in suspension, growth factor treatment inefficiently activated the MAP kinase pathway. The integrin-mediated enhancement of MAP kinase activation by growth factor correlated with the tyrosine phosphorylation of focal adhesion kinase but was independent of Shc. These data indicate that integrin modulation of the MAP kinase pathway is supported by a variety of integrin complexes and imply that other pathways may be required for the previously reported alpha chain-specific effects on cell cycle regulation and cell differentiation.

3T3 Cells↗
PubMed1997

Comparison of integrin alpha chain expression in benign and malignant salivary gland tumors.

OBJECTIVE: This study investigates the distribution of the alpha chain of the integrin family of extracellular matrix receptors in a series of adenomas and carcinomas of salivary gland origin to determine if the malignant phenotype is associated with modification of the expression of these receptors. STUDY DESIGN: Cryostat sections of 36 tumor specimens were stained by a standard streptavidin-biotin-peroxidase technique using primary monoclonal antibodies against alpha 1-6 and alpha v integrin chains. The immunohistochemical reaction was scored using a three-point scale and the results were analyzed using Fisher's exact test. RESULTS: In salivary adenomas, alpha 2, alpha 3, alpha 4, alpha 6, and alpha v chains were widely expressed in most of the cases studied. The alpha 1 subunit was prominently expressed by the epithelial cells of Warthin's tumor, whereas a minority of pleomorphic adenomas showed immunoreactivity for this antigen. We observed alpha 5 subunit expression only in the mesenchymal-like component of pleomorphic adenomas. In salivary carcinomas, integrin alpha chain expression was heterogeneous, varying greatly between different histotypes and within the same histotype. The distribution of the antigens was similar to that of adenomas, except for the alpha 6 chain, which localized not only at the interface between cell and matrix, but also at sites of cell-cell contact. When the immunohistochemical levels of integrin alpha chain expression were compared in adenomas and carcinomas, expression significantly decreased for the alpha 6 and alpha v chains (p = 0.0007; p = 0.002, respectively). CONCLUSIONS: Loss of alpha 6 and alpha v integrin subunits occurring in salivary gland carcinomas could modify the adhesive properties of malignant cells, contributing to the invasive potential of these tumors.

Adenocarcinoma↗
PubMed1992

H36-alpha 7 is a novel integrin alpha chain that is developmentally regulated during skeletal myogenesis.

H36 is a 120,000-D membrane glycoprotein that is expressed during the differentiation of skeletal muscle. H36 cDNA clones were isolated from a lambda UniZapXR rat myotube cDNA library and sequenced. The deduced amino acid sequence demonstrates that H36 is a novel integrin alpha chain that shares extensive homology with other alpha integrins that includes: (a) the GFFKR sequence found in all alpha integrins; (b) a single membrane spanning region; (c) conservation of 18 of 22 cysteines; and (d) a protease cleavage site found in the non-I region integrin alpha chains. The cytoplasmic domain of H36 is unique and additional regions of nonhomology further indicate H36 is distinct from all other alpha chains. In keeping with current nomenclature we designate this alpha chain alpha 7. Northern blots demonstrate that expression of H36-alpha 7 mRNA is regulated both early in the development of the myogenic lineage and later, during terminal differentiation. Detection of H36-alpha 7 mRNA coincides with conversion of H36- myogenic precursor cells to H36+ cells. H36-alpha 7 mRNA is present in replicating myoblasts: expression increases upon terminal differentiation and is markedly reduced in developmentally defective myoblasts. In addition, H36-alpha 7 mRNA is not detected in C3H10T1/2 cells. It is in myotubes derived from myoblasts obtained by treatment of 10T1/2 cells with azacytidine or transfection with MRF4. Immunoblots and immunofluorescence demonstrate that the H36-alpha 7 chain is associated with integrin beta 1. Affinity chromatography demonstrates that H36-alpha 7 beta 1 selectively binds to laminin. The expression of H36-alpha 7 on secondary myoblasts during the development of the limb in vivo corresponds with the appearance of laminin in the limb, with the responsiveness of secondary myoblast proliferation to laminin, and with the onset of increased muscle mass, suggesting that H36-alpha 7 modulates this stage in limb development. We conclude that H36-alpha 7 is a novel alpha integrin laminin binding protein whose expression is developmentally regulated during skeletal myogenesis.

Amino Acid Sequence↗
PubMed1992

Differential expression of integrin alpha chains by renal epithelial cells.

We have investigated the expression of integrin chains by human renal epithelial cells during in vivo renal differentiation and in vitro cell culture on different extracellular matrices. Using the immunoperoxidase technique to visualize the binding of monoclonal antibodies to different integrin chains in fetal and adult kidneys, we found a change during development from alpha 1 beta 1, alpha 3 beta 1, and alpha 4 beta 1-positive blastemal cells to alpha 2 beta 1, alpha 3 beta 1, and alpha 6 beta 1-positive epithelial cells. The pattern of integrin expression correlates with the presence in the extracellular matrix of the appropriate ligands. In in vitro cell culture experiments, renal epithelium expressed alpha 3 and alpha 5 integrins on all extracellular matrices. Integrins alpha 2 and alpha 6 were found only in cells grown on a laminin-containing substratum. Fibronectin and alpha 5 integrin co-localized on the ventral surface of cells grown on a laminin substratum and at the periphery of cells on glass coverslips. These results suggest that there is a close relationship between integrin alpha chain usage and the presence of appropriate ligands in the extracellular matrix.

Antibodies, Monoclonal↗
PubMed1998

Differential effects of integrin alpha chain mutations on invasin and natural ligand interaction.

To determine if recognition of the Yersinia pseudotuberculosis invasin protein and natural substrates requires identical integrin residues, a region of the human alpha3 integrin chain predicted to be involved in substrate adhesion was targeted for mutation. One point mutation located in a region of the third N-terminal repeat of the alpha3 chain, alpha3-W220A, failed to promote adhesion to the natural alpha3 beta1 substrate epiligrin but maintained near wild type levels of adhesion to invasin. A second nearby mutation, alpha3-Y218A, which showed no detectable adhesion to epiligrin, was only partially attenuated for invasin binding as well as invasin-mediated bacterial uptake. A third substitution, alpha3-D154A, predicted to be in the second N-terminal repeat not known to be implicated in cell adhesion, was competent for invasin-promoted adhesion events and appeared to encode a receptor of increased activity, as it had a higher efficiency than wild type receptor for adhesion to epiligrin. Cell lines expressing this derivative were not recognized by a function blocking anti-alpha3 antibody, indicating that the second and third repeats of the alpha3 chain are either closely linked in space or the second repeat can modulate activity of the third. Differential effects on substrate adhesion do not appear to be associated with all integrin alpha chain mutations, as alpha4 chain mutations affecting the divalent cation binding domains depressed adhesion to invasin to a significant extent.

Adhesins, Bacterial↗
PubMed1997

Integrin alpha chain cytoplasmic tails regulate "antibody-redirected" cell adhesion, independently of ligand binding.

Here we describe a novel "antibody-redirected cell adhesion" (ARCA) assay. This assay measures heterotypic cell-cell adhesion, resulting from antibody bridging between Fc gamma receptors type II (CD32) on leukocytes, and clustered integrins on adherent cell monolayers. This ARCA activity, facilitated by integrins alpha3 beta1 or alpha4 beta1, required an intact cytoskeleton, but did not involve typical integrin ligand binding sites or divalent cations. Furthermore, deletion of the alpha4 cytoplasmic tail almost completely abrogated integrin ARCA activity, suggesting an alteration of integrin recruitment into adhesive sites. If two or more tail residues were present after the conserved GFFKR motif, then ARCA activity was largely restored. Although alpha4 tail deletion caused loss of ARCA activity, it had no effect on the binding of VCAM-1 to intact alpha4-transfected K562 cells. In conclusion, the integrin alpha chain tail can positively regulate integrin-dependent cell adhesion by a receptor recruitment/clustering mechanism independent of conventional integrin ligand-binding considerations.

Actin Cytoskeleton↗
PubMed1995

Up-regulation of a novel integrin alpha-chain (alpha mt) on human fetal myotubes.

Integrin expression and distribution was studied in cloned human fetal G6 myoblasts and myotubes. Immunoprecipitation of beta 1 integrins from surface iodinated and metabolically labeled G6 cells typically showed a five-fold induction of a beta 1 integrin associated protein upon differentiation. Under non-reducing conditions this beta 1 associated protein migrated as 145 kD. No such beta 1 associated protein was observed in the myogenic L8 rat cell line, before or after differentiation. The beta 1 integrin associated cell surface protein present in G6 myotubes remained associated with the beta 1 subunit in the presence of 1% Triton X-100 and 0.5 M NaCl. Like integrin alpha-chains, the protein dissociated from the beta 1 integrin subunit at low pH. Immunoprecipitation of G6 myotubes further indicated the presence of alpha 1, alpha 3, alpha 5, and alpha v integrins, and small amounts of alpha 4 and alpha 6 integrins. Immunodepletion with integrin alpha-chain antibodies to alpha 1, alpha 3, alpha 4, alpha 5, alpha 6, and alpha v integrin chains could not deplete the beta 1 integrin associated protein, indicating that it did not interact with any of these known integrin heterodimers. Upon treatment with reducing agents, the beta 1 integrin associated protein migrated in SDS-PAGE as a 155 kD protein. The decreased mobility in SDS-PAGE upon reduction is a feature shared with alpha 1, alpha 2, and alpha 9 integrin alpha-chains. Antibodies to alpha 1 immunoprecipitated an integrin heterodimer distinct from the 155 kD protein.(ABSTRACT TRUNCATED AT 250 WORDS)

Cell Differentiation↗
PubMed1995

The alpha 4 integrin chain is a ligand for alpha 4 beta 7 and alpha 4 beta 1.

The heterodimeric alpha 4 integrins alpha 4 beta 7 lymphocyte Peyer's patch adhesion molecule ([LPAM]-1) and alpha 4 beta 1 (very late antigen-4) are cell surface adhesion molecules involved in lymphocyte trafficking and lymphocyte-cell and matrix interactions. Known cellular ligands include vascular cell adhesion molecule (VCAM)-1, which binds to alpha 4 beta 1 and alpha 4 beta 7, and the mucosal addressin cell adhesion molecule (MAdCAM)-1, which binds to alpha 4 beta 7. Here we show that the alpha 4 chain of these integrins can itself serve as a ligand. The alpha 4 chain, immunoaffinity purified and immobilized on glass slides, binds thymocytes and T lymphocytes. Binding exhibits divalent cation requirements and temperature sensitivity which are characteristic of integrin-mediated interactions, and is specifically inhibited by anti-alpha 4 integrin antibodies, which exert their effect at the cell surface. Cells expressing exclusively alpha 4 beta 7 (TK-1) or alpha 4 beta 1 (L1-2) both bound avidly, whereas alpha 4-negative cells did not. A soluble 34-kD alpha 4 chain fragment retained binding activity, and it inhibited lymphocyte adhesion to alpha 4 ligands. It has been shown that alpha 4 integrin binding to fibronectin involves an leucine-aspartic acid-valine (LDV) motif in the HepII/IIICS region of fibronectin (CS-1 peptide), and homologous sequences are important in binding to VCAM-1 and MAdCAM-1. Three conserved LDV motifs occur in the extracellular sequence of alpha 4. A synthetic LDV-containing alpha 4-derived oligopeptide supports alpha 4-integrin-dependent lymphocyte adhesion and blocks binding to the 34-kD alpha 4 chain fragment. Our results suggest that alpha 4 beta 7 and alpha 4 beta 1 integrins may be able to bind to the alpha 4 subunit on adjacent cells, providing a novel mechanism for alpha 4 integrin-mediated and activation-regulated lymphocyte interactions during immune responses.

Amino Acid Sequence↗
PubMed1999

cDNA cloning and chromosomal localization of human alpha(11) integrin. A collagen-binding, I domain-containing, beta(1)-associated integrin alpha-chain present in muscle tissues.

We previously identified a novel integrin alpha-chain in human fetal muscle cells (Gullberg, D., Velling, T., Sjöberg, G., and Sejersen, T. (1995) Dev. Dyn. 204, 57-65). We have now isolated the full-length cDNA for this integrin subunit, alpha(11). The open reading frame of the cDNA encodes a precursor of 1188 amino acids. The predicted mature protein of 1166 amino acids contains seven conserved FG-GAP repeats, an I domain with a metal ion-dependent adhesion site motif, a short transmembrane region, and a unique cytoplasmic domain of 24 amino acids containing the sequence GFFRS. alpha(11), like other I domain integrins, lacks a dibasic cleavage site for generation of a heavy chain and a light chain, and it contains three potential divalent cation binding sites in repeats 5-7. The presence of 22 inserted amino acids in the extracellular stalk portion (amino acids 804-826) distinguishes the alpha(11) integrin sequence from other integrin alpha-chains. Amino acid sequence comparisons reveal the highest identity of 42% with the alpha(10) integrin chain. Immunoprecipitation with antibodies to alpha(11) integrin captures a 145-kDa protein distinctly larger than the 140-kDa alpha(2) integrin chain when analyzed by SDS-polyacrylamide gel electrophoresis under nonreducing conditions. Fluorescence in situ hybridization maps the integrin alpha(11) gene to chromosome 15q23, in the vicinity of an identified locus for Bardet-Biedl syndrome. Based on Northern blotting, integrin alpha(11) mRNA levels are high in the adult human uterus and in the heart and intermediate in skeletal muscle and some other tissues tested. During in vitro myogenic differentiation, alpha(11) mRNA and protein are up-regulated. Studies of ligand binding properties show that alpha(11)beta(1) binds collagen type I-Sepharose, and cultured muscle cells localize alpha(11)beta(1) into focal contacts on collagen type I. Future studies will reveal the importance of alpha(11)beta(1) for muscle development and integrity in adult muscle and other tissues.

Adult↗
PubMed1995

Direct binding of F actin to the cytoplasmic domain of the alpha 2 integrin chain in vitro.

The transmembrane integrins have been shown to interact with the cytoskeleton via noncovalent binding between cytoplasmic domains (CDs) of integrin beta chains and various actin binding proteins within the focal adhesion complex. Direct or indirect integrin alpha chain CD binding to the actin cytoskeleton has not been reported. We show here that actin, as an abundant constituent of focal adhesion complex proteins isolated from fibroblasts, binds strongly and specifically to alpha 2 CD, but not to alpha 1 CD peptide. Similar specific binding to alpha 2 CD peptide was seen for highly purified F actin, free of putative actin-binding proteins. The bound complex of actin and peptide was visualized directly by coprecipitation, and actin binding was abrogated by removal of a five amino acid sequence from the alpha 2 CD peptide. Our findings may explain the earlier observation that, while integrins alpha 2 beta 1 and alpha 1 beta 1 both bind to collagen, only alpha 2 beta 1 can mediate contraction of extracellular collagen matrices.

Actins↗
PubMed1993

Functionally distinct roles for glycosylation of alpha and beta integrin chains in cell-matrix interactions.

Laminin interaction with gp120/140, a B16-F10 laminin-binding protein immunologically related to alpha 6 beta 1 integrin, has been shown to be dependent on oligosaccharides from both ligand and receptor. Lectin analysis of gp120/140 led to the conclusion that this integrin is a sialoglycoprotein bearing mainly complex antennary structures. By means of exoglycosidase treatment, it was possible to identify alpha-galactosyl residues on the integrin alpha chain as the laminin-binding determinants. These residues are involved in cell adhesion to laminin. On the other hand, beta-chain complex antennary structures, whose synthesis could be inhibited by swainsonine, were associated with cell spreading rather than cell adhesion. Thus, it was possible to modulate integrin-mediated cell adhesion and spreading through changes in the glycosylation state of integrin alpha and beta chains.

Animals↗
PubMed1996

Expression of the beta 7 integrin by human endothelial cells.

Integrin adhesion receptors mediate fundamental intercellular interactions of many cell types as well as cellular interactions with specific extracellular matrix molecules. To date, the beta 7 integrin has been shown to be expressed by leukocyte subsets and to mediate interactions of these cells with extracellular matrix molecules as well as with endothelial and epithelial cells. The data presented here indicate that human endothelial cells also express the beta 7 integrin both in vitro and in situ. Analysis of cDNA indicated that endothelial beta 7 was identical to that expressed by leukocytes. Cell surface expression of beta 7 was increased by exposure of the endothelium to the pro-inflammatory cytokines, tumor necrosis factor-alpha and interleukin-1 beta. In leukocytes, beta 7 complexes with alpha 4 or alpha E integrin chains. Endothelial cells also expressed a number of alpha-integrin chains, including alpha 4, but not alpha E. The expression and utilization of beta 7, presumably complexed with alpha 4, by endothelial cells may be instrumental in the maintenance of the function or phenotype of endothelial cells.

Antigens, CD↗
PubMed1991

Distribution of beta 1, alpha 1, alpha 2 and alpha 3 integrin chains in basal cell carcinomas.

The integrins are alpha beta heterodimeric transmembrane proteins mediating cell-substratum as well as cell-cell interactions. Changes in their expression and/or function seem to occur in a number of malignant epithelial neoplasms and may in part explain their abnormal patterns of growth and differentiation. Using monoclonal antibodies to the beta 1 (DH12), alpha 1 (TS2/7), alpha 2 (B1.515), and alpha 3 (E1.56) integrin chains, the alpha 1 beta 1 (VLA-1), alpha 2 beta 1 (VLA-2), and alpha 3 beta 1 (VLA-3) integrin receptors were studied on cryostat sections of 22 basal cell carcinomas (BCCs) and adjacent normal tissues by a standard peroxidase-antiperoxidase technique. In non-neoplastic skin, VLA-2 and VLA-3 were found in the basal layer, eccrine glands, and cells of the outer root sheath in which VLA-1 was detected. In BCCs, there was a considerably higher expression of VLA-2 and VLA-3 compared with epidermal basal cells but similar to that seen in hair bulb and outer root sheath. In two cases of nodular BCC showing evidence of regression, both VLA-2 and VLA-3 were completely negative, in contrast to non-regressing foci which were strongly positive. The high level of expression of two adhesion molecules (VLA-2 and VLA-3) involved in cell-substratum as well as cell-cell interactions may account for the more indolent pattern of growth characteristic of BCC and perhaps reflect its high degree of differentiation towards the hair follicle.

Basal Cell Carcinoma↗
PubMed1999

Crystal structure of the alpha1beta1 integrin I-domain: insights into integrin I-domain function.

The alpha1beta1 integrin is a major cell surface receptor for collagen. Ligand binding is mediated, in part, through a 200 amino acid inserted 'I'-domain contained in the extracellular part of the integrin alpha chain. Integrin I-domains contain a divalent cation binding (MIDAS) site and require cations to interact with integrin ligands. We have determined the crystal structure of recombinant I-domain from the rat alpha1beta1 integrin at 2.2 A resolution in the absence of divalent cations. The alpha1 I-domain adopts the dinucleotide binding fold that is characteristic of all I-domain structures that have been solved to date and has a structure very similar to that of the closely related alpha2beta1 I-domain which also mediates collagen binding. A unique feature of the alpha1 I-domain crystal structure is that the MIDAS site is occupied by an arginine side chain from another I-domain molecule in the crystal, in place of a metal ion. This interaction supports a proposed model for ligand-induced displacement of metal ions. Circular dichroism spectra determined in the presence of Ca2+, Mg2+ and Mn2+ indicate that no changes in the structure of the I-domain occur upon metal ion binding in solution. Metal ion binding induces small changes in UV absorption spectra, indicating a change in the polarity of the MIDAS site environment.

Animals↗
PubMed1996

Absence of integrin alpha 6 leads to epidermolysis bullosa and neonatal death in mice.

Cell-extracellular matrix interactions have important roles in many biological processes, including embryonic development, growth control and differentiation. Integrins are the principal receptors for extracellular matrix. They are composed of non-covalently associated alpha and beta chains. Integrin alpha 6 can associate with either beta 1 or beta 4 (refs 2,3). Both integrin complexes are receptors for laminins, major components of basement membranes. The distribution of alpha 6 (refs 4-10) as well as studies using function-blocking antibodies have suggested an essential role for this laminin receptor during embryogenesis, in processes such as endoderm migration or kidney tubule formation9. Here we report that, surprisingly, mice lacking the alpha 6 integrin chain develop to birth. However, they die at birth with severe blistering of the skin and other epithelia, a phenotype reminiscent of the human disorder epidermolysis bullosa. Hemidesmosomes are absent in mutant tissue. This absence is likely to result from the lack of alpha 6/beta 4, the only integrin in hemidesmosomes of stratified squamous and transitional epithelia. Mutations in the genes encoding integrin beta 4 and chains of laminin-5 have been implicated in junctional epidermolysis bullosa. Our study provides evidence that some forms of epidermolysis bullosa may originate from defects of the alpha 6 gene.

Animals↗
PubMed1995

Localization of the alpha 7 integrin gene (ITGA7) on human chromosome 12q13: clustering of integrin and Hox genes implies parallel evolution of these gene families.

Expression of the alpha 7 integrin gene (ITGA7) is developmentally regulated during the formation of skeletal muscle. Increased levels of expression and production of isoforms containing different cytoplasmic and extracellular domains accompany myogenesis. To determine whether a single or multiple alpha 7 genes underlie the structural diversity in this alpha chain that accompanies development, we have examined the rat and human genomes by Southern blotting and in situ hybridization. Our results demonstrate that there is only one alpha 7 gene in both the rat and the human genomes. In the human, ITGA7 is present on chromosome 12q13. Phylogenetic analysis of the integrin alpha chain sequences suggests that the early integrin genes evolved in two pathways to form the I-integrins and the non-I-integrins. The I-integrin alpha chains contain an additional sequence of approximately 180 amino acids and arose as a result of an early insertion into the non-I-gene. The I-chain subfamily further evolved by duplications within the same chromosome. The non-I-integrin alpha chain genes are localized in clusters on chromosomes 2, 12, and 17, and this closely coincides with the localization of the human homeobox gene clusters. Non-I-integrin alpha chain genes appear to have evolved in parallel and in proximity to the Hox clusters. Thus, the Hox genes that underlie the design of body structure and the Integrin genes that underlie informed cell-cell and cell-matrix interactions appear to have evolved in parallel and coordinate fashions.

Amino Acid Sequence↗
PubMed1996

Lack of integrin alpha-chain endoproteolytic cleavage in furin-deficient human colon adenocarcinoma cells LoVo.

In the present report the biosynthesis of the integrin alpha-chains endowed with constitutive endoproteolytic cleavage was evaluated in LoVo cells where furin, a subtilisin-like convertase involved in post-translational endoproteolytic processing, is not functional. It was found that cell-surface alpha 3, alpha 6 and alpha v subunits were not processed endoproteolytically into heavy and light chains as they were in HT29-D4 cells, a furin-competent cell line. Complete removal of N-linked oligosaccharides and pulse-chase experiments confirmed that the cleavage of the alpha 6 integrin subunit occurring 45 min after translation in HT29 cells did not take place in LoVo cells. Apart from cleavage deficiency, alpha 6 subunit glycosylation, association with beta 4 subunits and targeting to the plasma membrane seemed comparable in LoVo and HT29 cells. The pro-alpha 6 and the pro-alpha 3 subunits immunopurified from LoVo cells were highly sensitive to endoproteolysis by recombinant furin. Furin cleavage was calcium dependent and resulted in the conversion of the 140 kDa pro-alpha 6 into a 120 kDa heavy chain. These results suggest strongly that furin is involved in the endoproteolytic processing of cleavable integrin alpha subunits.

ADP Ribose Transferases↗
PubMed1996

Distinct alpha 7A beta 1 and alpha 7B beta 1 integrin expression patterns during mouse development: alpha 7A is restricted to skeletal muscle but alpha 7B is expressed in striated muscle, vasculature, and nervous system.

The laminin binding alpha 7 beta 1 integrin has been described as a major integrin in skeletal muscle. The RNA coding for the cytoplasmic domain of alpha 7 integrin undergoes alternative splicing to generate two major forms, denoted alpha 7A and alpha 7B. In the current paper, we have examined the developmental expression patterns of the alpha 7A and alpha 7B splice variants in the mouse. The alpha 7 integrin expression is compared to that of the nonintegrin laminin receptor dystroglycan and to that of laminin-alpha 1 and laminin-alpha 2 chains. Alpha 7A integrin was found by in situ hybridization to be specific to skeletal muscle. Antibodies specific for alpha 7B integrin and in situ hybridization revealed the presence of alpha 7 mRNA and alpha 7B protein in the E10 myotome and later in primary and secondary myotubes. In the heart, alpha 7B integrin was not detectable in the endocardium or myocardium during embryonic and fetal heart development. Northern blot analysis and immunohistochemistry revealed a postnatal induction of alpha 7B in the myocardium. In addition to striated muscle, alpha 7B integrin was localized to previously unreported nonmuscle locations such as a subset of vascular endothelia and restricted sites in the nervous system. Comparison of the alpha 7 integrin expression pattern with that of different laminin isoforms and dystroglycan revealed a coordinated temporal expression of dystroglycan, alpha 7 integrin, and laminin-alpha 2, but not laminin-alpha 1, in the forming skeletal muscle. We conclude that the alpha 7A and alpha 7B integrin variants are expressed in a developmentally regulated, tissue-specific pattern suggesting different functions for the two splice forms.

Animals↗