Human MYO18B, a Novel Unconventional Myosin Heavy Chain Expressed in Striated Muscles Moves into the Myonuclei upon Differentiation

• Published in: Journal of molecular biology 2003-02, Vol.326 (1), p.137-149
• Main Authors: Salamon, Michela, Millino, Caterina, Raffaello, Anna, Mongillo, Marco, Sandri, Claudia, Bean, Camilla, Negrisolo, Enrico, Pallavicini, Alberto, Valle, Giorgio, Zaccolo, Manuela, Schiaffino, Stefano, Lanfranchi, Gerolamo
• Format: Article
• Language: English
• Subjects: Animals; cardiac and skeletal muscle; Cell Differentiation; Cell Nucleus - metabolism; Cells, Cultured; Cytoplasm - metabolism; Fluorescent Antibody Technique; Gene Expression Profiling; Humans; In Vitro Techniques; Muscle Cells - cytology; Muscle Cells - metabolism; Muscle Fibers, Skeletal - cytology; Muscle Fibers, Skeletal - metabolism; Muscle, Skeletal - cytology; Muscle, Skeletal - metabolism; Myocytes, Cardiac - cytology; Myocytes, Cardiac - metabolism; myosin evolution; myosin heavy chain; Myosin Heavy Chains - chemistry; Myosin Heavy Chains - classification; Myosin Heavy Chains - genetics; Myosin Heavy Chains - metabolism; nuclear myosin; Phylogeny; Protein Transport; Rats; Rats, Wistar; Recombinant Proteins - genetics; Recombinant Proteins - metabolism; RNA, Messenger - genetics; RNA, Messenger - metabolism; unconventional myosin
• ISSN: 0022-2836; 1089-8638
• DOI: 10.1016/S0022-2836(02)01335-9

We have characterized a novel unconventional myosin heavy chain, named MYO18B, that appears to be expressed mainly in human cardiac and skeletal muscles and, at lower levels, in testis. MYO18B transcript is detected in all types of striated muscles but at much lower levels compared to class II sarcomeric myosins, and it is up regulated after in vitro differentiation of myoblasts into myotubes. Phylogenetic analysis shows that this myosin belongs to the recently identified class XVIII, however, unlike the other member of this class, it seems to be unique to Vertebrate since it contains two large amino acid domains of unknown function at the N and C-termini. Immunolocalization of MYO18B protein in skeletal muscle cells shows that this myosin heavy chain is located in the cytoplasm of undifferentiated myoblasts. After in vitro differentiation into myotubes, a fraction of this protein is accumulated in a subset of myonuclei. This nuclear localization was confirmed by immunofluorescence experiments on primary cardiomyocytes and adult muscle sections. In the cytoplasm MYO18B shows a punctate staining, both in cardiac and skeletal fibers. In some cases, cardiomyocytes show a partial sarcomeric pattern of MYO18B alternating that of α-actinin-2. In skeletal muscle the cytoplasmic MYO18B results much more evident in the fast type fibers.