No 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.

Desmin is a muscle-specific intermediate filament protein which forms a network connecting the sarcomere, T tubules, sarcolemma, nuclear membrane, mitochondria and other organelles. Mutations in the gene coding for desmin (DES) cause skeletal myopathies often combined with cardiomyopathy, or isolated cardiomyopathies. The molecular pathomechanisms of the disease remain ambiguous. Here, we describe and comprehensively characterize two DES mutations found in Polish patients with a clinical diagnosis of desminopathy. The study group comprised 16 individuals representing three families. Two mutations were identified: a novel missense mutation (Q348P) and a small deletion of nine nucleotides (A357_E359del), previously described by us in the Polish population. A common ancestry of all the families bearing the A357_E359del mutation was confirmed. Both mutations were predicted to be pathogenic using a bioinformatics approach, including molecular dynamics simulations which helped to rationalize abnormal behavior at molecular level. To test the impact of the mutations on DES expression and the intracellular distribution of desmin muscle biopsies were investigated. Elevated desmin levels as well as its atypical localization in muscle fibers were observed. Additional staining for M-cadherin, α-actinin, and myosin heavy chains confirmed severe disruption of myofibrill organization. The abnormalities were more prominent in the Q348P muscle, where both small atrophic fibers as well large fibers with centrally localized nuclei were observed. We propose that the mutations affect desmin structure and cause its aberrant folding and subsequent aggregation, triggering disruption of myofibrils organization.

Cancer is a complex disease caused in part by predisposing germline gene polymorphisms. Knowledge of carcinogenesis in companion mammals (dog and cat) and some livestock species (pig and horse) is quite advanced. The prevalence of certain cancers varies by breed in these species, suggesting the presence of predisposing genetic variants in susceptible breeds. This review summarizes the present understanding of germline gene polymorphisms, including BRCA1, BRCA2, MC1R, KIT, NRAS and RAD51, associated with predisposition to melanoma, mammary cancer, osteosarcoma and histiocytic sarcoma in dogs, cats, pigs and horses. The predisposing variants in these species are discussed in the context of human germline gene polymorphisms associated with the same types of cancer.