Expression of myosin heavy chain isoforms and myogenesis of intrafusal fibres in rat muscle spindles

Abstract

This review concerns the pattern of expression and regulation of myosin heavy chain (MHC) isoforms in intrafusal fibres of rat muscle spindles detected by immunocytochemistry. The three types of intrafusal fibres--nuclear bag1, nuclear bag2, and nuclear chain fibres--are unique in co-expressing several MHCs including special isoforms such as slow tonic and alpha cardiac-like MHC and isoforms typical of muscle development, such as embryonic and neonatal MHC. The distinct intrafusal fibre types appear sequentially during rat hind limb development, the nuclear bag2 precursors being first identifiable at 17-18 days in utero as the only primary myotubes expressing slow tonic MHC. Sensory innervation is required for the expression of "spindle-specific" MHC isoforms. Motor innervation contributes to the diversity in distribution of the different MHCs along the length of the nuclear bag fibres. It is suggested that unique populations of myoblasts are destined to become intrafusal fibres during development in the rat hind limb muscles and that the regional heterogeneity in MHC expression is related both to sensory and motor innervation and to the properties of the myoblast lineages. These distinct features make intrafusal fibres an attractive in situ model for investigating myogenesis, myofibrillogenesis, and the mechanisms regulating MHC expression.

Loss ofProx1in striated muscle causes slow to fast skeletal muscle fiber conversion and dilated cardiomyopathy

“…4A), which is ordinarily enriched in slow-twitch muscle (5,29). In contrast, levels of the fast-twitch MyHC genes Myh2 and Myh1 were significantly up-regulated, although Myh4-the fastest MyHC gene-expression remained equivalent between all genotypes (Fig.…”

Myopathy caused by HRAS germline mutations: implications for disturbed myogenic differentiation in the presence of constitutive HRas activation

“…There are indications that unique populations of myogenic cells are destined to become intrafusal fibres. 21 Muscle spindle formation is also dependent on trophic factors released by sensory Ia afferent neurons in a subpopulation of myotubules that receive sensory myoneural contacts and are followed by c innervation. The exact mechanisms of muscle spindle development are incompletely understood, but there is evidence that growth factors such as neurotrophin-3, 22 neuregulin-1, 23 24 and glial cellderived neurotrophic factor 25 are involved in the process.…”

Expression of nestin, desmin and vimentin in intact and regenerating muscle spindles of rat hind limb skeletal muscles

“…In rat hind limb skeletal muscles, intact muscle spindles contain usually four intrafusal myoWbers: one nuclear bag 1 , one nuclear bag 2 and two nuclear chain Wbers (Soukup 1976; for review see Zelená 1994;Soukup et al 1995). Myelinated sensory axons belonging to group Ia and II innervate muscle spindles by encircling the middle portion of both types of intrafusal Wbers.…”