• Open Access

Two novel/ancient myosins in mammalian skeletal muscles: MYH14/7b and MYH15 are expressed in extraocular muscles and muscle spindles

Authors

  • Alberto C. Rossi,

    1. Department of Biomedical Sciences, University of Padova, Padova, Italy
    2. Venetian Institute of Molecular Medicine (VIMM), Padova, Italy
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  • Cristina Mammucari,

    1. Department of Biomedical Sciences, University of Padova, Padova, Italy
    2. Venetian Institute of Molecular Medicine (VIMM), Padova, Italy
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  • Carla Argentini,

    1. Department of Biomedical Sciences, University of Padova, Padova, Italy
    2. Venetian Institute of Molecular Medicine (VIMM), Padova, Italy
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  • Carlo Reggiani,

    1. Department of Anatomy and Physiology, University of Padova, Padova, Italy
    2. Institute of Neuroscience of the Consiglio Nazionale delle Ricerche, Padova, Italy
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  • Stefano Schiaffino

    1. Department of Biomedical Sciences, University of Padova, Padova, Italy
    2. Venetian Institute of Molecular Medicine (VIMM), Padova, Italy
    3. Institute of Neuroscience of the Consiglio Nazionale delle Ricerche, Padova, Italy
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Corresponding author S. Schiaffino: Venetian Institute of Molecular Medicine, via G. Orus 2, 35129 Padova, Italy. Email: stefano.schiaffino@unipd.it

Abstract

The mammalian genome contains three ancient sarcomeric myosin heavy chain (MYH) genes, MYH14/7b, MYH15 and MYH16, in addition to the two well characterized clusters of skeletal and cardiac MYHs. MYH16 is expressed in jaw muscles of carnivores; however the expression pattern of MYH14 and MYH15 is not known. MYH14 and MYH15 orthologues are present in frogs and birds, coding for chicken slow myosin 2 and ventricular MYH, respectively, whereas only MYH14 orthologues have been detected in fish. In all species the MYH14 gene contains a microRNA, miR-499. Here we report that in rat and mouse, MYH14 and miR-499 transcripts are detected in heart, slow muscles and extraocular (EO) muscles, whereas MYH15 transcripts are detected exclusively in EO muscles. However, MYH14 protein is detected only in a minor fibre population in EO muscles, corresponding to slow-tonic fibres, and in bag fibres of muscle spindles. MYH15 protein is present in most fibres of the orbital layer of EO muscles and in the extracapsular region of bag fibres. During development, MYH14 is expressed at low levels in skeletal muscles, heart and all EO muscle fibres but disappears from most fibres, except the slow-tonic fibres, after birth. In contrast, MYH15 is absent in embryonic and fetal muscles and is first detected after birth in the orbital layer of EO muscles. The identification of the expression pattern of MYH14 and MYH15 brings to completion the inventory of the MYH isoforms involved in sarcomeric architecture of skeletal muscles and provides an unambiguous molecular basis to study the contractile properties of slow-tonic fibres in mammals.

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