Assembly and Maintenance of Myofibrils in Striated Muscle

Abstract

In this chapter, we present the current knowledge on de novo assembly, growth, and dynamics of striated myofibrils, the functional architectural elements developed in skeletal and cardiac muscle. The data were obtained in studies of myofibrils formed in cultures of mouse skeletal and quail myotubes, in the somites of living zebrafish embryos, and in mouse neonatal and quail embryonic cardiac cells. The comparative view obtained revealed that the assembly of striated myofibrils is a three-step process progressing from premyofibrils to nascent myofibrils to mature myofibrils. This process is specified by the addition of new structural proteins, the arrangement of myofibrillar components like actin and myosin filaments with their companions into so-called sarcomeres, and in their precise alignment. Accompanying the formation of mature myofibrils is a decrease in the dynamic behavior of the assembling proteins. Proteins are most dynamic in the premyofibrils during the early phase and least dynamic in mature myofibrils in the final stage of myofibrillogenesis. This is probably due to increased interactions between proteins during the maturation process. The dynamic properties of myofibrillar proteins provide a mechanism for the exchange of older proteins or a change in isoforms to take place without disassembling the structural integrity needed for myofibril function. An important aspect of myofibril assembly is the role of actin-nucleating proteins in the formation, maintenance, and sarcomeric arrangement of the myofibrillar actin filaments. This is a very active field of research. We also report on several actin mutations that result in human muscle diseases.

Cardiac leiomodin2 binds to the sides of actin filaments and regulates the ATPase activity of myosin

“…In muscle cells actin dynamics is regulated by a large repertoire of ABPs [1, 2]. An essential member of this family in muscle cells is tropomyosin that decorates the side of actin filaments [48, 49].…”

“…The power of muscle contraction depends on the proper interactions of sarcomeric actin-based thin and myosin-based thick filaments [1, 2]. Actin filament remodeling is important for striated muscle function.…”

Qualitative and quantitative evaluation of TPM transcripts and proteins in developing striated chicken muscles indicate TPM4α is the major sarcomeric cardiac tropomyosin from early embryonic life to adulthood

“…We were the first to publish the complete nucleotide sequence of chicken TPM3α (Dube et al 2018). TPM3α transcripts are expressed in embryonic heart and skeletal muscle but are barely detectable in adult animals (Dube et al 2017). TPM4α, the sarcomeric isoform of the TPM4 gene, was reported to be expressed in cardiac but not in skeletal muscles (Forry-Schaudies et al 1990; Fleenor et al 1992).…”

“…RNA was isolated from specific tissues, from 3–5 embryos, which were frozen in liquid nitrogen. The details have been described elsewhere (Zajdel et al, 2003; Dube et al 2017). Tissues from adult leghorn chickens were procured from a local farm (Cobblestone Valley Farm, Preble, NY13141); also tissues from 15-day post hatch leghorn chickens were obtained from another local farm (Treasures of Joy Farm, Nedrow, NY 13120).…”

“…Tissues from adult leghorn chickens were procured from a local farm (Cobblestone Valley Farm, Preble, NY13141); also tissues from 15-day post hatch leghorn chickens were obtained from another local farm (Treasures of Joy Farm, Nedrow, NY 13120). RNA was isolated from tissues as described before (Zajdel et al, 2003; Dube et al 2017). The RIN (RNA Integrity Number) of RNA samples of heart and skeletal muscles are between 8.90 to 9.2, suggesting the RNA we used were of good quality.…”