Editorial        275        Cell Adhesion and Myogenesis. Editorial
                                    Mindy George-Weinstein and Eric Cochran     [Full text pdf 76.6 Kb]
 

Articles         277        The Neural Cell Adhesion Molecule and Heart Development: What is NCAM doing in the heart?
                                    Michiko Watanabe     [Full text pdf 564 Kb]
 

                      293        A Conserved Developmental Role of Adhesion Molecules in  Cardiac and Skeletal Myogenesis
                                    Kersti K. Linask     [Full text pdf 403 Kb]
 

                      303        Unexpected Effects of Wnt-1 on the Differentiation and Adhesion of Myogenic Cells
                                    Mindy George-Weinstein, Jeffrey Dare, Jacquelyn Gerhart,Anthony M.C. Brown, Ann Redfield,
                                    Heather Brown, Karen A. Knudsen     [Full text pdf 483 Kb]

                      315        Intercellular Adhesion in Developing and Adult Skeletal Muscle: Analysis of M-cadherin
                                    Dieter Link, Dirk Winnekendonk, Ulrike Kaufmann, Janos Palinas, Claudia Heuser,
                                    Matthias Kammann and Anna Starzinski-Powitz     [Full text pdf 465 Kb]
 
    
                      325        A Novel Periodic Localization for alpha 1 Integrin in Skeletal Muscle
                                    Camille DiLullo, A. Sue Menko, Nancy J. Philp, Patrisia Mattioli, Patrick Gilhool,
                                    Christine McGinley and David Boettiger     [Full text pdf 657 Kb]
 
 
 
 

Cell Adhesion and Myogenesis

The dictionary offers several synonyms for adhesion including unwavering attachment, fidelity, devotion, of being sticky and holding fast. These terms are easily applied to an epithelium consisting of a sheet of tightly packed cells that serves as a barrier to unrestricted diffusion. All cells of an organism must adhere to other cells or to molecules of the extracellular matrix. Without such adhesions, the integrity of tissues and organs is lost and survival is compromised. The classic example of cell adhesion gone awry is the process of metastasis during which a transformed cell loosens its attachments with its neighbors and begins to migrate to distant sites.
The development of cardiac and skeletal muscle, as well as the maintenance and functioning of adult muscle, are dependent on the interactions of cell adhesion molecules. Adhesion proteins are found in both types of muscle during all stages of their development. These include the integrins, cadherins and a member of the immunoglobulin superfamily NCAM. Cadherins and NCAM function in cell-cell adhesions whereas the integrins mediate both the adhesion of cells to each other and to the extracellular matrix. Besides their obvious roles in maintaining the organization of cardiac and skeletal muscle tissues, engagement of adhesion molecules with their ligands on adjacent cells or within the extracellular matrix results in the transmission of signals intracellularly. Adhesion related signaling events regulate cell motility, proliferation, gene expression, myoblast fusion and contractile function.
The cadherins, NCAM and integrins are developmentally regulated in response to external and internal signals. The progression of myogenic cells towards differentiation and maturation is accompanied by alterations in the class of adhesion protein that is expressed by the cell, isoforms within a class, post-translational modifications and/or their amount and distribution on the cell surface. Post-translational modifications can be particularly important in regulating the strength of cell adhesion. For example, as myoblasts migrate from the somite to their appropriate locations throughout the embryo, N-cadherin mediated adhesions must be repressed to avoid premature differentiation, and integrins must bind to the extracellular matrix, but not too tightly that they become stuck in place.
The following papers review the structure and function of adhesion molecules in developing and adult cardiac and skeletal muscle. During the formation of the heart, NCAM appears to function in regulating epithelial to mesenchymal transitions, aligning myocytes, gap junction communication and innervation (Watanabe). N-cadherin may be important for defining boundaries and coordinating differentiation within a compartment of cells (Linask).
N-cadherin plays a similar role in the earliest stages in the development of skeletal muscle precursors as epiblast cells undergo gastrulation and during the formation of the somite, the source of most of the skeletal muscle of the body (George-Weinstein et al.; Linask). Although a small number of cells from the somite, the presomitic segmental plate mesoderm and epiblast can spontaneously undergo skeletal myogenesis in vitro, most require interactions with other cells via N-cadherin in order to differentiate. Epiblast cells cultured in the presence of the Wnt­1 protein fail to switch from E- to N-cadherin and the expression of sarcomeric myosin is inhibited (George-Weinstein et al.).
Another member of this family of adhesion molecules, M-cadherin, is expressed somewhat later than N-cadherin in skeletal muscle precursors (Link et al.). M-cadherin appears to function after the initiation of differentiation, during the alignment of myoblasts in preparation for fusion. M-cadherin also may mediate the adhesion of mononucleated myocytes on myofibers within the embryo and in adult muscle (Link et al.).
A third class of adhesion molecules, the integrins, play multiple roles during myogenesis (DiLullo et al.). Different alpha and beta subunits of the integrin heterodimer are expressed during various stages of skeletal muscle development. The particular alpha/beta combination dictates which molecule within the extracellular matrix or on the surface of an adjacent cell the integrin will bind, thereby generating tremendous functional versatility. Integrins regulate the replication, migration, differentiation and fusion of skeletal myoblasts and mediate adhesion within the neuromuscular and myotendinous junctions. In addition, integrins appear to be important for maintaining the structural integrity of muscle during contraction. The alpha/beta 1 integrin is present as a doublet within the I band, colocalizing with Ca²⁺ ATPase of the sarcoplasmic reticulum (DiLullo et al.). Thus, integrins may not only serve as a transmembrane link of the cytoskeleton to the extracellular matrix, but also may anchor the sarcoplasmic reticulum or T-tubule membrane systems to myofibrils.
A great deal of information has been obtained regarding the expression of different classes of adhesion proteins during all stages of myogenesis. Recombinant gene technology and antibody perturbation studies have yielded insights into the functions of various adhesion molecules in both cardiac and skeletal muscle cells. It is becoming increasingly clear that these proteins are not only cellular glue, but they transmit signals intracellularly to affect cytoplasmic and nuclear events. Although some of the downstream targets of these signaling systems have been determined, many remain a mystery, especially those genes that are sensitive to adhesive interactions. Another phenomenon that requires further analysis is the mechanisms by which different classes of adhesion molecules influence each others’ activities. Cross-talk between proteins engaged in cell-cell and cell-extracellular matrix adhesion occurs in transformed cells (Leppa et al., 1998. J. Cell Sci. 109, 1393-1403; Miyanki et al., 1998. Oncogene 11, 2547-2552) and myoblasts (Huttenlocher et al., 1998. J. Cell Biol. 141, 515-526). The molecular linkages between adhesion systems and the result of such communication on gene expression in myogenic cells is one of the most exciting areas for discovery in the field of muscle biology.

Mindy George-Weinstein and Erie Cochran
Department of Anatomy
Philadelphia College of Osteopathic Medicine
4170 City Avenue
Philadelphia, PA 19131, USA

The Neural Cell Adhesion Molecule and Heart Development: What is NCAM Doing in the Heart?

Michiko Watanabe

Division of Pediatric Cardiology, Departments of Pediatrics and Genetics, Rainbow Babies and Childrens Hospital, Case Western Reserve University School of Medicine, Cleveland

The neural cell adhesion molecule (NCAM) may be as important in the heart as it is in the nervous system. NCAM is a cell surface glycoprotein which manifests great diversity in polypeptide isoform and glycosylation throughout cardiogenesis as well as neurogenesis. It is expressed on cardiac myocytes in the myocardium and on epicardial and endocardial cells as well as on the components that innervate the heart. The patterns of its expression suggest that it could be modulating a number of events including cardiomyocyte interactions from initial epithelialization and tubular heart stages, interactions of the developing His-Pukinje fiber myocytes, endocardial mesenchymal transformation, and neural crest cell migration into the heart. Approaches that can be pursued to support these hypotheses include taking advantage of transgenic mouse lines and utilizing the information available about NCAM function from studies of the nervous system and skeletal muscle. The challenge still remains to determine why a neural adhesion molecule such as NCAM would be needed in such abundance and with such a widespread expression in the developing, adult, and diseased heart.

Key words: cardiogenesis, cardiomyocytes, polysialic acid, cell-cell interactions, N-CAM.
Basic Appl. Myol. 8 (4): 277-291, 1998

A Conserved Developmental Role of Adhesion Molecules in Cardiac and Skeletal Myogenesis

Kersti K. Linask

Department of Cell Biology, University of Medicine and Dentistry of New Jersey, Stratford

Cell adhesion molecules are associated with the commitment of precardiac cells to the myocardial lineage. They are also important in the formation of the somitic structure, and subsequently, skeletal muscle development in the myotome. Specifically, the N-cadherin/ß-catenin complex appears to have an important role in the events leading to myogenesis in both types of muscle. The immunostaining patterns of N-cadherin/ß-catenin in the above regions are dynamic and developmentally regulated. They are associated with the early stages of commitment and differentiation of the myogenic populations. The known roles of fibronectin, NCAM and N-cadherin are reviewed in both cardiac and skeletal myogenesis. It appears that cell adhesion-mediated events have been evolutionarily conserved and underlie important mechanisms leading to myogenic compartments and early stages of myofibrillogenesis in the invertebrate and vertebrate embryos.
Key words: N-cadherin, fibronectin, N-CAM, heart, skeletal, muscle, myogenesis.
Basic Appl. Myol. 8 (4): 293-302, 1998

Unexpected Effects of Wnt-1 on the Differentiation and Adhesion of Myogenic Cells

Mindy George-Weinstein, Jeffrey Dare, Jacquelyn Gerhart, Anthony M.C. Brown⁽¹⁾, Ann Redfield⁽²⁾, Heather Brown⁽²⁾ and Karen A. Knudsen⁽²⁾

Department of Anatomy, Philadelphia College of Osteopathic Medicine, Philadelphia, (1) Strang Cancer Research Laboratory, The Rockefeller University, New York, Department of Cell Biology and Anatomy, Cornell University Medical College, New York and (2) Lankenau Medical Research Center, Wynnewood

Wnt proteins are critical for the development of a wide range of organisms. Wnt-1 is expressed by the neural tube and promotes skeletal myogenesis in cultures of intact somites. In other cell types, Wnt-1 enhances cell-cell adhesion mediated by cadherin/catenin complexes. The effect of Wnt-1 on myogenesis was examined in cultures of dissociated epiblast, segmental plate and somite tissues. Wnt-1 was provided by Rat-2 cells expressing Wnt-1 cDNA. Wnt-1 did not promote myogenesis in prestreak epiblast cultures. In primitive streak stage epiblast cultures, Wnt-1 inhibited myogenesis and the shift from E- to N-cadherin. Both the control and Wnt-1 expressing Rat-2 cells inhibited differentiation of somite and segmental plate cells; however, the inhibition was less for somite cells cultured with Wnt-1. The Rat-2 cells have myogenic potential in that they express desmin, M-cadherin, NCAM, MyoD and MEF-2, but they do not differentiate. They respond to Wnt-1 with an increase in b -catenin, a decrease in cell-cell adhesion and a downregulation of NCAM. The effects of Wnt-1 on adhesion and differentiation depend on intrinsic cell properties that vary with the stage of development.

Key words: Wnt-1, cadherin, NCAM, skeletal myogenesis.
Basic Appl. Myol. 8 (4): 303-314, 1998

Intercellular Adhesion in Developing and Adult Skeletal Muscle: Analysis of M-Cadherin

Dieter Link⁽¹⁾, Dirk Winnekendonk⁽¹⁾, Ulrike Kaufmann⁽¹⁾, Janos Palinkas, Claudia Heuser, Matthias Kammann and Anna Starzinski-Powitz⁽¹⁾

(1) Institut der Anthropologie und Humangenetik fuer Biologen, Johann-Wolfgang-Goethe-Universitaet Frankfurt, Frankfurt/Main, Germany

M-cadherin is a member of the family of calcium-dependent intercellular adhesion molecules, the cadherins. These are involved in the establishment of intercellular junctions and are associated with morphogenetic events. This article focusses on M-cadherin during skeletal muscle development emphasizing its pattern of expression, its interaction with catenins and cytoskeletal elements, and functional aspects. So far, expression and functional studies imply that M-cadherin plays a role during fusion of myoblasts to myotubes. Based on data from different groups, it is discussed whether M-cadherin is a marker for the complete satellite cell pool in vivo which would be helpful for studies of both, physiological and pathophysiological situations of skeletal muscle in development and in the adult. Finally, we describe the genomic structure of the murine M-cadherin gene which is the basis for further functional and regulatory studies in vivo.

Key words: M-cadherin, expression pattern, cytoskeleton, gene structure.
Basic Appl. Myol. 8 (4): 315-323, 1998

A Novel Periodic Localization for ?? Integrin in Skeletal Muscle

Camille DiLullo, A. Sue Menko⁽¹⁾, Nancy J. Philp⁽²⁾, Patrisia Mattioli, Patrick Gilhool, Christine McGinley and David Boettiger⁽³⁾

Philadelphia College of Osteopathic Medicine, Philadelphia, PA, (1) Thomas Jefferson University, Philadelphia, PA, (2) Pennsylvania College of Optometry, Philadelphia, PA and (3) University of Pennsylvania, Philadelphia, PA, USA

lntegrins influence myogenic mechanisms. A number of integrin subunits have already been demonstrated to have specific roles in various aspects of the developmental process. Data is presented that demonstrates a novel localization for al integrin in avian skeletal myofibers. Cultured chick pectoralis muscle was immunofluorescently labeled with antibodies to al integrin and several muscle specific proteins. al integrin was detected in postmitotic, mononucleated, elongated myocytes with a punctate distribution along the myofiber. As early as 3 days in culture, al integrin reorganized from a punctate pattern to one with a sarcomeric periodicity. The periodic al integrin band, which appeared as a single band in contracted muscle, was observed as a doublet band when the muscle was relaxed with one half of each doublet band localized on either side of the Z line. The identical periodic localization for a₁ integrin was found on intact myofibers from chick embryonic day 17 hind limb and cardiac muscle as well as on murine C2C12 myotubes. The temporal regulation of the punctate to periodic distribution indicates a possible role for this integrin subunit in the assembly of the myofiber early in myogenesis.

Key words: al integrin, myogenesis, skeletal muscle, development, avian.
Basic Appl. Myol. 8 (4): 325-340, 1998