Involvement of unconventional myosin VI in myoblast function and myotube formation

Abstract

The important role of unconventional myosin VI (MVI) in skeletal and cardiac muscle has been recently postulated (Karolczak et al. in Histochem Cell Biol 139:873–885, 2013). Here, we addressed for the first time a role for this unique myosin motor in myogenic cells as well as during their differentiation into myotubes. During myoblast differentiation, the isoform expression pattern of MVI and its subcellular localization underwent changes. In undifferentiated myoblasts, MVI-stained puncti were seen throughout the cytoplasm and were in close proximity to actin filaments, Golgi apparatus, vinculin-, and talin-rich focal adhesion as well as endoplasmic reticulum. Colocalization of MVI with endoplasmic reticulum was enhanced during myotube formation, and differentiation-dependent association was also seen in sarcoplasmic reticulum of neonatal rat cardiomyocytes (NRCs). Moreover, we observed enrichment of MVI in myotube regions containing acetylcholine receptor-rich clusters, suggesting its involvement in the organization of the muscle postsynaptic machinery. Overexpression of the H246R MVI mutant (associated with hypertrophic cardiomyopathy) in myoblasts and NRCs caused the formation of abnormally large intracellular vesicles. MVI knockdown caused changes in myoblast morphology and inhibition of their migration. On the subcellular level, MVI-depleted myoblasts exhibited aberrations in the organization of actin cytoskeleton and adhesive structures as well as in integrity of Golgi apparatus and endoplasmic reticulum. Also, MVI depletion or overexpression of H246R mutant caused the formation of significantly wider or aberrant myotubes, respectively, indicative of involvement of MVI in myoblast differentiation. The presented results suggest an important role for MVI in myogenic cells and possibly in myoblast differentiation.

Myosins as fundamental components during tumorigenesis: diverse and indispensable

“…GOLPH2 is a type-II Golgi membrane protein and serves as a serum marker for various cancers, including hepatocellular carcinomas [161] and prostate cancer [26]. Myosin VI localizes in the Golgi membranes as a peripheral membrane protein and is implicated in the normal material transportation and maintenance of the Golgi's structure and functions [162–163]. In the fibroblasts of Snell's waltzer mice, the absence of myosin VI causes a reduced size of the Golgi and a limited level of protein secretion [49].…”

Expression and localization of myosin VI in developing mouse spermatids

“…These isoforms are differentially expressed in different tissues/cell types and are associated with specific subcellular compartments and functions. MVI has been implicated in several processes through functional studies in flies, worms, and mammals, including clathrin-mediated endocytosis, Golgi organization and secretion, basolateral targeting and sorting, cell adhesion and epithelial integrity, cell migration, actin dynamics, cytokinesis, transcription (see review by Buss and Kendrick-Jones 2008 ), and myogenesis (Karolczak et al 2013 , 2015 ). In these seemingly different cellular processes, MVI may function as a cargo transporter or as a protein anchor involved in actin organization/dynamics in specialized cells.…”

Identification of novel MYO18A interaction partners required for myoblast adhesion and muscle integrity

“…Unconventional myosins do not form the structure of myofibrils, however, they have been shown to play important roles in the regulation of a wide range of cellular functions, including cell migration, intracellular trafficking, adhesion and cytokinesis10, although their implication in muscle cell function remains elusive. At present, there is only a limited number of studies reporting their involvement in myofiber organization and myoblast differentiation1112, making this broad field quite open for further exploration.…”