Electron microscopic studies on the myotomes of larval lamprey, Lampetra japonica

Abstract

Myotomes of the caudal one-third of the body of 26-day-old larval lampreys, Lampetra japonica, were studied by electron microscopy. Each myotome consists of horizontally stacked muscle lamellae. The myotomes are covered laterally by a single layer of flattened cells called here "lateral cells", and the other aspect is covered by an external lamina. The myotomes are midsegmentally innervated. Each muscle lamella usually contains two single cortical layers of myofibrils along the dorsal and ventral sarcolemma with a nucleus and mitochondria interposed between two layers. Numerous peripheral couplings are observed with relatively less developed triads. There are no membrane specializations to connect adjacent muscle lamellae within a myotome. Intermyotomal junctions are, however, noted between tips of cytoplasmic processes of muscle lamellae of adjoining myotomes. They resemble tight or gap junctions. No myofibrils are present in these cytoplasmic processes. Myotendinous junctions, with "terminal couplings" (Nakao, '75), are seen under development at the myoseptal ends of muscle lamellae. Lateral cells contain only ordinary organelles and no special structures such as myofibrils are found in the cytoplasm. They are connected to each other and to muscle lamellae by primitive desmosomes. They generally have no external lamina investment.

The Australian lungfish (Neoceratodus forsteri) - fish or amphibian pattern of muscle development?

“…He believed that these cells participate in the development of dermal structures. A similar layer of cells, external to the embryonic myotome, has been found in B. lanceolatum (Maurer, 1906), L. tridentata larvae (Nakao, 1977), African clawed frog Xenopus laevis (Grimaldinet al, 2005) and European common frog (Rana temporaria) (Maurer, 1906). Recently, Devoto et al, (2006), have described morphologically and molecularly a layer of non-muscular cells on the external surface of the embryonic myotome, homologous to the amniote dermatomyotome, in fish.…”

“…In these species the myotome is built of wedge-shaped, flattened multinucleate lamellae, stacked on top of each other in a dorsoventral direction. Moreover, the multinuclear muscle lamellae in sturgeons and lungfish resemble, in their structure, the mononucleated muscle lamellae present in the larval and adult musculature of amphioxus (Branchiostoma lanceolatum) (Holand et al, 1995) and in the larval musculature of Pacific lamprey (Lampetra tridentata) (Nakao, 1977).…”

Muscle stem cells and model systems for their investigation

“…However, the recent identification of the external Pax7-expressing somitic layer in zebrafish (Hollway et al, 2007;Stellabotte et al, 2007;Hammond et al, 2007) and its role in muscle growth strongly suggests that this cell population may correspond to a dermomyotome. Importantly, a similar layer of cells external to the embryonic myotome has been previously detected in several other lower vertebrates such as the lamprey (Nakao, 1977), sturgeon (Devoto et al, 2006), and lungfish (Maurer, 1906). They have been found in diverse teleosts, including the sea bass (Veggetti et al, 1990), herring (Johnston, 1993), and gilthead sea bream (Ramirez-Zarzoza et al, 1995), as well as in the amphibians Xenopus laevis (Hamilton, 1969) and European common frog (Maurer, 1906).…”

Extraocular Muscles in the Lamprey, <i>Lampetra fluviatilis</i> L.

“…In the adult lamprey this organization was found only in cardiac muscle cells [Kilarski, 1964]. These features seem to be primitive, since a similar oganization has been described in the myotomal muscles in lam prey larvae [Nakao, 1977] and in locomotory muscles in Tunicata [Bone and Ryan, 1973;Toselli and Harbison, 1977], Such similarities can be, partially at least, a result of convergence, since some authors believe [Bone and Ryan, 1973] that the striated muscles in vertebrates have their evolutio nary origin in the striated muscles of ascidian larvae rather than of adults. As Bone and Ryan [1973] argued, the organization of muscle fibres in Tunicata and Acrania might result from a direct conduction of a stimulus from the sarcolemma to the cisternae of the sarcoplasmic reticulum without the involve ment of the T system tubules, which are absent in these animals.…”

“…Cyclostomata. Scarce studies on the morphology of myomere muscles in the Atlantic hagfish, Myxine glutinosa L. [Korneliussen and Nicolaysen, 1973] , as well as in larval [Nakao, 1977] and adult lampreys [Teravainen, 1971;Lie, 1974] indicate that these muscles consider ably differ from the skeletal muscles occur ring in other vertebrates. The extraocular muscles of the lamprey described in this study also show a number of specific fea tures.…”