Comparison of myosins from the masseter muscle of adult rat, mouse and guinea-pig. Persistence of neonatal-type isoforms in the murine muscle

Abstract

Adult rat, mouse, and guinea-pig masseter muscles display distinct myosin electrophoretic patterns. The rat muscle contains four main forms which by reference to the myosins of the IIB tensor fasciae latae, of the IIA mylohyoid, and of the red and white portions of the sternomastoid muscles, correspond respectively to the intermediate-type and to the three fast-type isoforms. The mouse masseter muscle contains only three main myosins, the intermediate-type and two fast-type isoforms. The guinea-pig muscle also displays only three bands, whose assignment is, however, less straightforward than in the murine species; their electrophoretic mobilities are not strictly the same as those of their homologous forms in rat and mouse. Comparison with the myosins of the tensor fasciae latae and of the sternomastoid muscles of guinea-pig allows their identification as intermediate and fast-type myosins.In addition to these typical adult-type forms, adult murine masseter muscles are observed to contain between zero and 30% of neonatal-type myosins. The comparison of the developmental transitions of myosins in the rat masseter with those in the skeletal muscles of the same animal indicates a delay in the appearance of the adult as well as in the disappearance of the neonatal-type myosins in the masseter muscle.Both the variability in myosin types with the animal species and the atypical presence of neonatal forms in the murine adults suggest that myosin expression in the masseter muscle is subjected to unusual regulations.A number of available observations tend to imply that fast-twitch muscles undergo similar transitions from neonatal to adult myosin in the first weeks following birth and that the same muscles from various mammals contain the same types of skeletal myosins in the adult state. Although these statements will probably need adjustments when more results are described, they seem to be true on the whole for the trunk and limb muscles. They may, however, not extend to other types of skeletal muscles with different innervation and distinct embryologic origin. These include the muscles of mastication, for instance the masseter muscle, which is of branchiomeric origin and is innervated by cranial nerves [l].Histochemical studies have indeed pointed out the striking differences in the properties of this muscle depending on the species [2]. The masseter of beef, which masticates slowly, has only slow-type I fibers, while the corresponding muscle of rat and mouse, which eat rapidly, presents type I and type IIA fibers. The masseter of guinea-pig displays only type IIA fibers, that of rabbit a mixture of I, IIA and IIB fibers, and those of predators such as cat and dog have type I1 M fibers. This variability from one mammal to another is uncommon and represents an interesting example of muscle adaptation to specific functional requirements.

Myosin heavy chain isoforms in postnatal muscle development of mice

“…Finally in the masseter which is used for rapid chewing only at 2-3 weeks after birth, the embryonic isoform was detected until 14 days after birth and the neonatal isoform persisted for at least 3 month in the adult mouse. Several studies (d 'Albis et al, 1986;Widmer et al, 2002) have also described the presence of the neonatal MyHC isoform in mouse masseter but the function of this isoform in the adult masseter has not yet been clarified. Neuromuscular activity plays a key role in the establishment of specific muscle fiber phenotypes during development and in the maintenance of their phenotypic properties (Rubinstein and Kelly, 1978;Pette and Vrbova, 1985).…”

Contractile differentiation of foetal cattle muscles: intermuscular variability

“…In pig ST muscle, Lefaucheur et al [13] [16] and human [1] muscles, whereas in pig muscle, secondary fibres are highly organised around primary ones [13]. 4 [6] observed a new population of small-diameter fibres which could be distinguished from primary and secondary myotubes by their specific staining with an adult fast MHC antibody. This third generation of cells was already suggested in sheep [36] and in pigs [13,15], but during the first weeks after birth.…”

Muscle fibre ontogenesis in farm animal species

“…Two developmental MHC are expressed at specific stages during development: embryonic MHC "MHC emb" and foetal MHC "MHC foet" also called neonatal MHC "MHC neo". These developmental MHC usually disappear in adult muscles, except in particular muscles such as the extraocular muscle [98], masseter [17] and intrafusal fibres [51]. In avian species, at least seven fast MHC genes have been identified (see [4] for a review) which cannot be unambiguously assigned to the different subtypes of fast fibres.…”