An invertebrate smooth muscle with striated muscle myosin filaments

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 112; no. 42; pp. E5660 - E5668
• Main Authors: Sulbarán, Guidenn, Alamo, Lorenzo, Pinto, Antonio, Márquez, Gustavo, Méndez, Franklin, Padrón, Raúl, Craig, Roger
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 20.10.2015; National Acad Sciences
• Series: PNAS Plus
• Subjects: Amino Acid Sequence; Animals; Arthropoda; Biological Sciences; Human subjects; Hybrids; Invertebrata; Microscopy, Electron; Molecular Sequence Data; Muscle, Smooth - metabolism; Muscle, Smooth - ultrastructure; Muscles; Muscular system; Myosins - chemistry; Myosins - metabolism; Parasites; Phylogeny; PNAS Plus; Proteins; Schistosoma mansoni; Schistosoma mansoni - metabolism; Sequence Homology, Amino Acid; Tissues; Schistosoma mansoni; muscle contraction; thick filament; muscle structure; schistosome
• ISSN: 0027-8424; 1091-6490; 1091-6490
• DOI: 10.1073/pnas.1513439112

Muscle tissues are classically divided into two major types, depending on the presence or absence of striations. In striated muscles, the actin filaments are anchored at Z-lines and the myosin and actin filaments are in register, whereas in smooth muscles, the actin filaments are attached to dense bodies and the myosin and actin filaments are out of register. The structure of the filaments in smooth muscles is also different from that in striated muscles. Here we have studied the structure of myosin filaments from the smooth muscles of the human parasiteSchistosoma mansoni. We find, surprisingly, that they are indistinguishable from those in an arthropod striated muscle. This structural similarity is supported by sequence comparison between the schistosome myosin II heavy chain and known striated muscle myosins. In contrast, the actin filaments of schistosomes are similar to those of smooth muscles, lacking troponin-dependent regulation. We conclude that schistosome muscles are hybrids, containing striated muscle-like myosin filaments and smooth muscle-like actin filaments in a smooth muscle architecture. This surprising finding has broad significance for understanding how muscles are built and how they evolved, and challenges the paradigm that smooth and striated muscles always have distinctly different components.