Unique features of myogenesis in Egyptian cobra (Naja haje) (Squamata: Serpentes: Elapidae)

Abstract

During early stages of myotomal myogenesis, the myotome of Egyptian cobra (Naja haje) is composed of homogenous populations of mononucleated primary myotubes. At later developmental phase, primary myotubes are accompanied by closely adhering mononucleated cells. Based on localization and morphology, we assume that mononucleated cells share features with satellite cells involved in muscle growth. An indirect morphological evidence of the fusion of mononucleated cells with myotubes is the presence of numerous vesicles in the subsarcolemmal region of myotubes adjacent to mononucleated cell. As differentiation proceeded, secondary muscle fibres appeared with considerably smaller diameter as compared to primary muscle fibre. Studies on N. haje myotomal myogenesis revealed some unique features of muscle differentiation. TEM analysis showed in the N. haje myotomes two classes of muscle fibres. The first class was characterized by typical for fast muscle fibres regular distribution of myofibrils which fill the whole volume of muscle fibre sarcoplasm. White muscle fibres in studied species were a prominent group of muscles in the myotome. The second class showed tightly paced myofibrils surrounding the centrally located nucleus accompanied by numerous vesicles of different diameter. The sarcoplasm of these cells was characterized by numerous lipid droplets. Based on morphological features, we believe that muscle capable of lipid storage belong to slow muscle fibres and the presence of lipid droplets in the sarcoplasm of these muscles during myogenesis might be a crucial adaptive mechanisms for subsequent hibernation in adults. This phenomenon was, for the first time, described in studies on N. haje myogenesis.

Does the grass snake (Natrix natrix) (Squamata: Serpentes: Natricinae) fit the amniotes-specific model of myogenesis?

“…The above-described features, confirmed by our immunocytochemical studies, are not characteristic for the typical muscle fibres that appear during myogenesis in other vertebrates. This observation is in agreement with the results obtained from a study of Naja haje myogenesis (Khannoon et al 2016 ) which indicated that the muscles capable of storing lipid droplets were slow muscles. According to these authors, lipid droplets are the most economical form of storing energy and are used during hibernation.…”

“…A few studies of the muscle differentiation in this highly divergent group of animals have been carried out on the sand lizard ( Lacerta agilis ), the Egyptian cobra ( Naja haje ), the Chinese soft-shelled turtle ( Pelodiscus sinensis ) and the American alligator ( Alligator mississippiensis ), which represent various modes of locomotion (Nagashima et al 2005 ; Rupik et al 2012 ; Kusumi et al 2013 ; Khannoon et al 2016 ). Because the subject of reptilian trunk muscle development still remains elusive, we decided to shed more light on this topic.…”

Structural and ultrastructural studies on the developing vomeronasal sensory epithelium in the grass snake Natrix natrix (Squamata: Colubroidea)

“…The heads of embryos were fixed in a 1:1 mixture of 2.5% glutaraldehyde and 2% paraformaldehyde in 0.1 mol L −1 phosphate buffer (pH 7.4) at 4°C for at least 24 h (Hermyt et al, 2020; Khannoon et al, 2016; Kowalska & Rupik, 2020; Lewandowski et al, 2017; Rupik et al, 2012; Swadźba & Rupik, 2010). After rinsing in phosphate buffer, the VNOs were isolated or only the posterior parts of the heads (without VNOs) were removed.…”

Unique Features of River Lamprey (Lampetra fluviatilis) Myogenesis

“…In amphibians, myoblasts fuse to form multinucleated myotubes (e.g., Triturus vulgaris , Rana lessonae ) or, bypassing fusion, directly differentiate into mononucleated myotubes (e.g., Xenopus laevis , Hymenochirus boettgeri , Bombina variegata ) [ 17 , 18 , 19 , 20 , 21 , 22 ]. Mononucleated myotubes were also observed during primary myogenesis in amniotes [ 5 , 23 , 24 , 25 , 26 ].…”