Neural cell adhesion molecule (N-CAM) is elevated in adult avian slow muscle fibers with multiple terminals.

Abstract

Many adult avian muscles contain two types of muscle fiber: those that receive innervation at single focal terminals and those with multiple terminals. The muscles of the syrinx, the vocal organ of birds, are such mixed muscles. To study this heterogeneity of fiber type and innervation, we combined immunocytochemistry to classify muscle fibers with techniques to visualize neuromuscular junctions. One monoclonal antibody, S58, directed against a slow class of myosin, labels only fibers that have multiple terminals. We also examined the distribution of immunoreactivity for neural cell adhesion molecule (N-CAM), which has been suggested to play a role in innervation of muscle and formation of neuromuscular junctions. S58-positive fibers have elevated N-CAM staining, indicating that multiple innervation of a fiber is correlated with the fiber's expression of high levels of N-CAM immunoreactivity. Most, and perhaps all, fibers that have multiple terminals also contain abundant N-CAM immunoreactivity. This suggests that N-CAM may play a role in the maintenance of multiterminal innervation in adult innervated muscle.While fast-twitch muscle fibers are innervated by a single axon at a single focal terminal, many muscle fibers have a distinct pattern of innervation with multiple small terminals (1). The classic comparison of differences in muscle innervation is between the posterior and anterior latissimus dorsi muscles (PLD and ALD) in the chicken (2, 3). The PLD is a fast-twitch muscle of the wing; the ALD is an adjacent postural muscle composed of slow tonic fibers, incapable of fast contractions but able to sustain contractions for much longer than PLD fibers (3). PLD fibers have predominantly "fast" isoforms of myosin and other protein, while ALD fibers contain "slow" isoforms (see ref. 4 for review; refs. 5 and 6). In addition to differences in physiology and biochemistry, these two muscles differ in their pattern of innervation (7). Muscle fibers in the adult PLD are innervated by single motoneurons at single focal end plates, one on each fiber. ALD fibers are innervated by multiple motoneurons and have multiple small terminals scattered along their lengths. The ALD and PLD are composed almost exclusively of multiterminal and single-terminal fibers, respectively. However, there are muscles, such as the biventer cervis, the "complexus" and the sartorius muscles of the chicken (3,4,8), and the extraocular and intrinsic ear muscles of mammals (reviewed in ref. 9) that include both multi-and single-terminal fibers.The present report focuses on the intrinsic muscles of the syrinx and combines techniques of immunocytochemistry to classify muscle fibers with techniques to visualize neuromuscular junctions. MATERIALS AND METHODSMaterials. All muscles were from male and female zebra finches in good health and full adult plumage.Supernatants containing mouse monoclonal antibodies MF30, ALD66, ALD19, ALD58, MF1, and MF20 were generously provided by D. Fischman and D. M. Bader (Cornell University School of Medicine). ...

Innervation of the syrinx of the zebra finch (Taeniopygia guttata)

“…In the present work and in agreement with Bleisch et al () and Wild and Suthers (unpublished observations in various songbird species), we did not find any evidence of muscle spindles in any of the syringeal muscles. Furthermore, Duc, Barakat‐Walter, and Droz () found calbindin immunopositive axons innervating spindles in chicken hindlimb muscles, whereas in the syringeal muscles, we did not find any calbindin immunoreactivity.…”

“…In coronal sections of the syrinx, these endplates looked like en plaque endplates previously described by Chinoy and George () and Grim et al (), which is consistent with the extremely fast contraction rates exhibited by the syringeal muscles (Elemans, Mead, Rome, & Goller, ). In dissociated fibers from zebra finch intrinsic syringeal muscles, Bleisch, Scharff, and Nottebohm () visualised the location of motor endplates using alpha bungarotoxin conjugated to fluorescein isothiocyanate, and found that most of the fibers exhibited a single motor endplate, but all muscles had a certain number of multiply innervated fibers. Therefore, it is possible that the zebra finch syrinx has a small proportion of en grappe endplates, which we could not identify in our material because of the steric constrains associated with sectioned tissue.…”

Evidence for myoblast-extrinsic regulation of slow myosin heavy chain expression during muscle fiber formation in embryonic development.

“…Slow tonic fibers retain multiple innervation and exhibit graded contractions, in contrast to the monoinnervation and all-or-nothing contractile response of both fast and slow twitch fibers in mammals (for review see Schmalbruch, 1985). Indeed, in zebra finch muscles, an antibody that recognizes the SM2 slow myosin of chicken reacts only with fibers that have multiple terminals (Bleisch et al, 1989). Thus, it may be that the expression of the slow isoform SM2 by early but not late chicken myoblasts represents additional fiber-type heterogeneity typical of avian but not mammalian muscle.…”

Skeletal myogenesis by human embryonic stem cells

“…These cells are located next to the muscle fiber and under the basal lamina [1]. Depending on their state, satellite cells may express Pax7, Myf5, NCAM, or M-cadherin [18,24,25]. Immunochemical analyses of muscle tissue 2-16 weeks after transplantation revealed the presence of many human-originated satellite cells existing adjacent to myofibers ( Figure 3D).…”

“…To determine the optimal dose of irradiation, 8-week-old NOD-SCID mice were treated with either 20 mg of cardiotoxin alone or in combination with different doses of irradiation (18,25,or 50 Gy). Myogenic cells (1×10 6 ) derived from hES cells were transplanted to TA muscles 24 h after irradiation.…”