The ultrastructure of normal myogenesis in the limb of the mouse

Abstract

The ultrastructure of myogenesis in the mouse hind limb has been studied from day 12 to birth. Mononucleated cells with myofilaments are small and infrequent during myogenesis and never line myotubes. Only mononucleated cells without myofilaments cover the myotubes are involved in mass fusion. These mononucleated cells are pleomorphic and undifferentiated during early myogenesis. They have a heterochromatic nucleus and many accumulate mitochondria and lengthen during days 16-18. After day 18 they are normally elongate with a heterochromatic nucleus and packed with free ribosomes. The multinucleated cell development may be divided into four stages. 1. Immature myotube (days 14-15). Their fibrils are small, out of register and some poorly defined. Many myofilaments are not in rigid hexagonal alignment. The sarcoplasmic reticulum is simple and randomly oriented and triads are absent. Large clumps of glycogen occur between euchromatic nuclei which are in chain formation. 2. Mature myotube (days 16-18). Small groups of fibrils show alignment. Glycogen granules and sarcoplasmic reticulum become numerous between fibrils. Triads are sparse and mitochondria cluster in subsarcolemmal regions and between nuclei. 3. Young myofibers are present by day 19. More fibrils are aligned and compact. The filaments are in a rigid hexagonal array, the glycogen is dispersed and nuclei are peripherally located and moderately heterochromatic. Triads are frequent but often obliquely oriented and mitochondria are elongate and numerous between fibrils. 4. Mature myofibers occur postnatally (2 weeks).

Activation of paternally expressed genes and perinatal death caused by deletion of theGtl2gene

“…3D). These findings are consistent with reported ultrastructural studies of myotubes at gestational day 14-15 in mice (Platzer, 1978). These data suggest a delay in muscle maturation beyond the myotube stage in embryos with maternal deletion of the Gtl2 gene.…”

“…2D, inset). Central nucleation and central clearing are characteristics of immature muscle fibers called myotubes (Platzer, 1978;Stromer et al, 1974) or can be found postnatally in a severe congenital myopathy called X-linked myotubular myopathy (Pierson et al, 2005). Indeed, H&E skeletal muscle staining from wild-type 15.5 dpc embryos showed that virtually all myotubes contain either centrally localized nuclei or areas of central clearing (Fig.…”

Ultrastructural Analysis of Skeletal Muscle Development in the Fetal Pig

“…However, a few cells possessed the characteristics of immature myotubes, i.e., filamentous material was present but unor ganized, as sarcomeres were unidentifiable. The appearance of unorganized filaments before the appearance of striated fibrils in immature myotubes confirms previous inve stigations of myogenesis in other species , 1965;Fischman, 1972;Platzer, 1978], The developmental relation between primary and secondary myofibers was previously investigated in fetal pig muscle by Swatland [1973], We also noted the same relative shift from a first-formed population of primary fibers to exclusively the secondary form or mature fiber morpho logy. In addition, the immature fibers that developed in close association with a pri mary fiber were frequently observed with pseudopodial processes projecting into inva ginations of the sarcolemma of the primary fibers ( fig.…”

“…An ultrastructural analysis of the general scheme of development of fetal skeletal muscle has been conducted in the rat [Kelly and Zacks, 1969;Ontell, 1977], mouse [Platzer, 1978], chick [Allen and Pepe, 1965;Przybylski and Blumberg, 1966;Fischman, 1972;Shimadaet al, 1967], in man [Tomanek and Colling-Saltin, 1977;Ga mble et al, 1978] and other vertebrate spe cies. However, there has been no report on the ultrastructure of normal myogenesis in the skeletal muscle of the pig.…”

Ultrastructural analysis of the smooth‐to‐striated transition zone in the developing mouse esophagus: Emphasis on apoptosis of smooth and origin and differentiation of striated muscle cells

“…Using the same sampling principle at ultrastructural level, we could work out in the present study a detailed analysis of the striated myogenesis from skeletal muscle progenitor cells to mature striated muscle fibers in the P4 esophagus. Striated myogenesis in esophagus ultrastructurally in broad outline was very similar to skeletal muscle (Kelly and Zacks, 1969;Platzer, 1978;Ontell and Kozeka, 1984;Ontell et al, 1988), but we found remarkable differences in detail.…”