Differences in the histogenesis of EDL and diaphragm in rat

Abstract

We have examined the histogenesis of the diaphragm and extensor digitorum muscle in rat embryos, with the aim of defining differences in developmental patterns that can be related to the functional requirements of these muscles during and after development.Patterns of interactions between myotubes and other cells, and frequency of gap junctions are quite different in the two muscles. In diaphragm, primary myotubes (at day 16 in utero) are closely associated with each other, forming parallel sheets or palisades and communicating by gap junctions. Secondary myotubes have formed by day 18, but are immature, and the frequency of gap junctions is lower. The arrangement in palisades is maintained even after fibers are separated from each other by their individual basal lamina. In EDL primary fibers at day 16 have fewer gap junctions, and the peak in communication occurs after the appearance of secondary myotubes (day 18 and 21). Secondary myotubes are more mature than in diaphragm at day 18. 0 1992 Wiley-Liss, Inc.

Polysialylated NCAM expression during motor axon outgrowth and myogenesis in the fetal rat

“…This profile shows PSA-NCAM immunolabelling on the surface of myotubes along the dorsoventral aspect of the diaphragm, transversely to the myotubes. The arrangement of primary myotubes from cross-sections of diaphragms taken from animals during age E15 was similar to that described by Yiping et al (1992), being tightly apposed and arranged in rows (palisades). The majority of the myotubes expressed PSA-NCAM.…”

“…8C). This corresponded with the onset of the majority of secondary myogenesis (Harris et al, 1989;Yiping et al, 1992). As during primary myogenesis, PSA-NCAM expression first appeared within the middle of myotubes, around the point of innervation, and progressed mediolaterally and dorsoventrally as secondary myogenesis proceeded into E18 (Fig.…”

“…8B). Down-regulation occurred in central muscle regions where primary myogenesis was essentially complete and primary myotubes had separated (Harris, 1981;Harris et al, 1989;Yiping et al, 1992). PSA-NCAM labelling had become limited to regions of most recent innervation (the more distal regions of sternal and dorsal muscle zones) and more recent myoblast addition (the more lateral extents of myotubes).…”

Dystrophy and myogenesis inmdx diaphragm muscle

“…20,21,39,61 Regenerating mdx limb muscles show extensive myoblast proliferation and fusion 43,67 in relation to endogenous expression of fibroblast growth factor (FGF) by myogenic cells, [2][3][4]6,19,23,47 although proliferation and new myotube formation are also present in the diaphragm. 7,23 So while the diaphragm muscle has a complex architecture, embryology, and innervation distinct from limb muscles, 24,25,28,37,38,66 an explanation for the differences between limb and diaphragm muscle responses to dystrophy has not emerged. …”

Neuronal involvement in muscular atrophy

“…These gap junctions are likely to coordinate gene expression and metabolic responses among differentiating myoblasts (Kalderon et al, 1977 ; Dennis et al, 1981 ; Constantin and Cronier, 2000 ; Araya et al, 2003 , 2004 ; von Maltzahn et al, 2004 ; Belluardo et al, 2005 ). In the terminal stage of myogenesis there is down regulation of Cx expression (Armstrong et al, 1983 ; Proulx et al, 1997 ; Constantin and Cronier, 2000 ), and the progressive decline of electrical coupling between myofibers (Dennis et al, 1981 ; Ling et al, 1992 ). Connexins are absent in normal skeletal muscle fibers but they have been detected in myofibers of adult muscles undergoing regeneration after injury (Araya et al, 2004 ; von Maltzahn et al, 2004 ; Belluardo et al, 2005 ) and in the sarcolemma of muscle fibers at 7 days post-denervation or 56 days after SCI (Cea et al, 2013 ).…”