Laminin, fibronectin, and collagen in synaptic and extrasynaptic portions of muscle fiber basement membrane.

Abstract

Light and electron microscope immunohistochemical methods were used to study the distribution of several proteins in rat skeletal muscle . The aims were to identify components of muscle fiber basement membrane and to compare the small fraction (0 .1%) of the basement membrane that extends through the synaptic cleft at the neuromuscular junction with the remaining, extrasynaptic portion . Synaptic basement membrane is functionally specialized and plays important roles in neuromuscular function and regeneration . Laminin, fibronectin, Collagen IV, Collagen V, and a collagenous protein (high-salt-soluble protein [HSP]) are all present in muscle fiber basement membrane . Laminin and Collagen IV are concentrated in basal lamina (the feltlike, inner layer of the basement membrane) and are shared by synaptic and extrasynaptic regions . Fibronectin, also present synaptically and extrasynaptically, is present in basal lamina and in the overlying reticular lamina . Collagen V and HSP are present throughout extrasynaptic basement membrane but are absent from synaptic sites; HSP is concentrated in the reticular lamina and on the outer surface of the basal lamina . These results, together with experiments reported previously (Sanes and Hall, 1979, /. Cell Biol. 83 :357-370), provide examples of three classes of components in muscle fiber basement membranesynaptic, extrasynaptic, and shared .Each muscle fiber in vertebrate skeletal muscles is ensheathed by a basement membrane . A small fraction of the basement membrane, -0.1% of the total, occupies the synaptic cleft between nerve and muscle at the neuromuscular junction. Recent experiments have demonstrated that this synaptic portion of the basement membrane is specialized and plays important roles in neuromuscular function and regeneration (1,2,5,19,28,36) . These results motivate molecular analysis of muscle-fiber basement membrane and comparison of its synaptic and extrasynaptic portions. In a previous study, we used immunohistochemical methods to show that several antigens are present in synaptic but not extrasynaptic basement membrane (35). Here, to extend this analysis to extrasynaptic areas, we asked two questions : (a) Are any proteins that have been purified and characterized from other sources present in rat muscle fiber basement membrane? And (b) are proteins which are present in extrasynaptic basement membrane also present at the synapse or are there antigens specific to extrasynaptic regions? We found that three proteins recently shown to be components of basement membranes in several tissues-laminin (9,13,25,32,37,46), collagen IV (4,33,38,45,51), and fibronectin (10,26,29,42,50)-are present in synaptic as well as extrasynaptic muscle fiber basement membrane . Two other proteins-collagen V (4,6,11,15,16,31,33) and a collagenous protein (HSP) isolated from skeletal muscle connective tissueare present in extrasynaptic basement membrane but are excluded from synaptic sites . MATERIALS AND METHODS AntibodiesLAMININ : Antibodies to laminin were provided by ...

Extracellular matrix organization in developing muscle: correlation with acetylcholine receptor aggregates.

“…The resolution of this form of immunocytochemistry is insufficient to determine rigorously whether staining was associated with the synaptic cleft or with other connective tissue adjacent to the neuromuscular junction. Fibronectin may, however, in addition to its location in reticular connective tissue, also be present in muscle basal lamina (39). In contrast to the above observations, neither antigen-39 nor antigen-35 appeared to extend into the synaptic cleft or show obvious accumulation in the synaptic region (data not shown).…”

“…Moreover, studies of regenerating nerve and muscle have suggested that elements of the synaptic basal lamina can induce both the differentiation of regenerating nerve terminals (40) and the accumulation of the acetylcholine receptor (AChR) l within the postsynaptic membrane (3,8). When immunohistochemical techniques were employed to compare synaptic and extrasynaptic basal lamina, some antigenic determinants were detected in both regions, some were detected only in extrasynaptic regions, and some appeared to be limited to synaptic basal lamina (39,41). Since most of the synaptic antigens have been defined only by serological criteria, their biochemical identities remain unknown.…”

Basal lamina development in chicken muscle spindles

“…Diversity was observed in intrafusal basal laminas in reference to time of appearance, proportional representation of compounds at various loci, and occurrence of different isoforms. These findings are consistent with previous reports (Sanes and Cheney, 198213;Engvall et al, 1990;Sanes et al, 1990;Brubacher et al, 1991;Glukhova et al, 1993;Vanden Heuvel and Abrahamson, 1993) on variations of basal lamina structure and composition in extrafusal muscle and other tissues.…”

Relationship of Collagen‐Tailed Acetylcholinesterase with Basal Lamina Components

“…We examined whether Electrophorus or bovine acetylcholinesterase would interact with collagens, fibronectin or laminin. These proteins were purified from a mouse tumor (Engelbreth-Holm-Swarm), which produces large amounts of basement membrane components, o r from human placenta [21]. The experiments were done in two ways: either using radioactive iodinated matrix proteins, with an excess of acetylcholinesterase (Tables 2 and 3), or following only the enzyme's activity in sucrose gradients, in the presence of an excess of cold proteins (Table 4).…”

“…Laminin and fibronectin have been demonstrated immunohistologically at the surface of Electrophorus electroplaques, with a distribution similar to that of acetylcholinesterase [20]. The same proteins together with type IV collagen are found also in the synaptic regions of rat skeletal muscle while type V collagen appears restricted to the extrasynaptic regions [21].…”