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

Rossi AC, Mammucari C, Argentini C, Reggiani C, Schiaffino S - J. Physiol. (Lond.) (2009)

Bottom Line: 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.

View Article: PubMed Central - PubMed

Affiliation: Department of Biomedical Sciences, University of Padova, Padova, Italy.

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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Serial sections of developing rat EO muscles stained for embryonic MYH (left panels), MYH15 (middle panels) or MYH14 (right panels)Note that MYH15 is undetectable in fetal muscles (E20), is barely visible in the orbital layer at postnatal day 7 (P7) and is clearly expressed at P14. In contrast, MYH14 is expressed in all fibres in fetal EO muscles and disappears in most fibres except the slow-tonic fibres during early postnatal stages. Scale bar, 100 μm.
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fig05: Serial sections of developing rat EO muscles stained for embryonic MYH (left panels), MYH15 (middle panels) or MYH14 (right panels)Note that MYH15 is undetectable in fetal muscles (E20), is barely visible in the orbital layer at postnatal day 7 (P7) and is clearly expressed at P14. In contrast, MYH14 is expressed in all fibres in fetal EO muscles and disappears in most fibres except the slow-tonic fibres during early postnatal stages. Scale bar, 100 μm.

Mentions: During development, the pattern of expression of MYH15 is completely different from that of MYH14. MYH15 is not detected by PCR in skeletal muscle or heart from E12 mouse embryos (Fig. S6A), nor by immunofluorescence in fetal and neonatal hindlimb muscles (not shown). MYH15 is also not found in fetal and neonatal EO muscles, being first detected at postnatal day 7 (P7) and at higher levels at P14 (Fig. 5). Since its first appearance at P7, MYH15 is exclusively present in the peripheral region of EO muscles, corresponding to the developing orbital layer (Fig. 5). In contrast, MYH14 transcripts are detected by PCR at low levels in skeletal muscle and heart from E12 mouse embryos (Fig. S6A). In fetal and neonatal rat muscles, MYH14 protein is detected by immunofluorescence in the rare fibres, also stained by anti-ALD and S46 antibodies, destined to become the bag 2 fibres of muscle spindles (Fig. S6B). MYH14 protein is expressed at high levels in all rat EO muscle fibres since E16 (Fig. S6C) but disappears from most fibres, except the slow-tonic fibres, during the first two weeks after birth (Fig. 5).


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

Rossi AC, Mammucari C, Argentini C, Reggiani C, Schiaffino S - J. Physiol. (Lond.) (2009)

Serial sections of developing rat EO muscles stained for embryonic MYH (left panels), MYH15 (middle panels) or MYH14 (right panels)Note that MYH15 is undetectable in fetal muscles (E20), is barely visible in the orbital layer at postnatal day 7 (P7) and is clearly expressed at P14. In contrast, MYH14 is expressed in all fibres in fetal EO muscles and disappears in most fibres except the slow-tonic fibres during early postnatal stages. Scale bar, 100 μm.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2821527&req=5

fig05: Serial sections of developing rat EO muscles stained for embryonic MYH (left panels), MYH15 (middle panels) or MYH14 (right panels)Note that MYH15 is undetectable in fetal muscles (E20), is barely visible in the orbital layer at postnatal day 7 (P7) and is clearly expressed at P14. In contrast, MYH14 is expressed in all fibres in fetal EO muscles and disappears in most fibres except the slow-tonic fibres during early postnatal stages. Scale bar, 100 μm.
Mentions: During development, the pattern of expression of MYH15 is completely different from that of MYH14. MYH15 is not detected by PCR in skeletal muscle or heart from E12 mouse embryos (Fig. S6A), nor by immunofluorescence in fetal and neonatal hindlimb muscles (not shown). MYH15 is also not found in fetal and neonatal EO muscles, being first detected at postnatal day 7 (P7) and at higher levels at P14 (Fig. 5). Since its first appearance at P7, MYH15 is exclusively present in the peripheral region of EO muscles, corresponding to the developing orbital layer (Fig. 5). In contrast, MYH14 transcripts are detected by PCR at low levels in skeletal muscle and heart from E12 mouse embryos (Fig. S6A). In fetal and neonatal rat muscles, MYH14 protein is detected by immunofluorescence in the rare fibres, also stained by anti-ALD and S46 antibodies, destined to become the bag 2 fibres of muscle spindles (Fig. S6B). MYH14 protein is expressed at high levels in all rat EO muscle fibres since E16 (Fig. S6C) but disappears from most fibres, except the slow-tonic fibres, during the first two weeks after birth (Fig. 5).

Bottom Line: 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.

View Article: PubMed Central - PubMed

Affiliation: Department of Biomedical Sciences, University of Padova, Padova, Italy.

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.

Show MeSH
Related in: MedlinePlus