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Developmental myosins: expression patterns and functional significance.

Schiaffino S, Rossi AC, Smerdu V, Leinwand LA, Reggiani C - Skelet Muscle (2015)

Bottom Line: These myosins are re-expressed during muscle regeneration and provide a specific marker of regenerating fibers in the pathologic skeletal muscle.The biochemical and biophysical properties of developmental myosins have only partially been defined, and their functional significance is not yet clear.One possibility is that these myosins are specialized in contracting against low loads, and thus, they may be adapted to the prenatal environment, when fetal muscles contract against a very low load compared to postnatal muscles.

View Article: PubMed Central - PubMed

Affiliation: Venetian Institute of Molecular Medicine (VIMM), Via G. Orus 2, 35129 Padova, Italy.

ABSTRACT
Developing skeletal muscles express unique myosin isoforms, including embryonic and neonatal myosin heavy chains, coded by the myosin heavy chain 3 (MYH3) and MYH8 genes, respectively, and myosin light chain 1 embryonic/atrial, encoded by the myosin light chain 4 (MYL4) gene. These myosin isoforms are transiently expressed during embryonic and fetal development and disappear shortly after birth when adult fast and slow myosins become prevalent. However, developmental myosins persist throughout adult stages in specialized muscles, such as the extraocular and jaw-closing muscles, and in the intrafusal fibers of the muscle spindles. These myosins are re-expressed during muscle regeneration and provide a specific marker of regenerating fibers in the pathologic skeletal muscle. Mutations in MYH3 or MYH8 are responsible for distal arthrogryposis syndromes, characterized by congenital joint contractures and orofacial dysmorphisms, supporting the importance of muscle contractile activity and body movements in joint development and in shaping the form of the face during fetal development. The biochemical and biophysical properties of developmental myosins have only partially been defined, and their functional significance is not yet clear. One possibility is that these myosins are specialized in contracting against low loads, and thus, they may be adapted to the prenatal environment, when fetal muscles contract against a very low load compared to postnatal muscles.

No MeSH data available.


Related in: MedlinePlus

MyHC transcripts in developing human skeletal muscle. The transcripts were revealed by in situ hybridization using probes specific for the following MYH genes: MYH3 (Emb, a–d), MYH8 (Neo, e–h), MYH7 (Slow, i–l), MYH2 (2A, m–p), and MYH1 (2X, q–t). Muscles examined were quadriceps femoris from 9 and 19-week-old fetuses and vastus lateralis from 1-day- (P1) and 1-month-old (P30) newborns. Bar = 30 μm (from [48])
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Fig1: MyHC transcripts in developing human skeletal muscle. The transcripts were revealed by in situ hybridization using probes specific for the following MYH genes: MYH3 (Emb, a–d), MYH8 (Neo, e–h), MYH7 (Slow, i–l), MYH2 (2A, m–p), and MYH1 (2X, q–t). Muscles examined were quadriceps femoris from 9 and 19-week-old fetuses and vastus lateralis from 1-day- (P1) and 1-month-old (P30) newborns. Bar = 30 μm (from [48])

Mentions: The developmental pattern of myosin isoform expression in the human embryonic and fetal skeletal muscle has been comparatively less investigated. At week 8 of gestation, primary generation fibers with central nuclei are present in the human skeletal muscle, whereas secondary generation fibers are formed after week 10 and become the predominant fiber population by week 21 [42]. MyHC-emb, MyHC-slow, and MyHC-neo transcripts are detectable in the developing skeletal muscle at week 9 (Fig. 1). At the protein level, all primary myofibers express MyHC-emb and MyHC-slow [43, 44], with MyHC-emb being detectable before MyHC-slow in the initial myotubes [45]. The proportion of fibers staining for MyHC-slow decreases from 75 % at week 10 to 3 % at week 21 of gestation, due to the dramatic increase in secondary fibers that initially do not contain MyHC-slow [45]. Secondary generation fibers express only MyHC-emb at week 12, MyHC-neo protein being detected at later stages [45]. Quantitative RNA analysis indicates that MYH3 transcripts account for about 81 % of all MYH transcripts in the human fetal skeletal muscle at week 15 of gestation [46]. At week 16 to 17, a tertiary fiber population has been identified, initially composed of very small myofibers stained by an anti-myosin antibody reactive with adult fast but not with neonatal MyHC [44, 47]. In situ hybridization indicates that MyHC-2A transcripts are weakly expressed at week 19 and more strongly at birth, whereas MyHC-2X transcripts are barely present at birth and are clearly expressed at 30 days after birth (Fig. 1). After week 27, a proportion of secondary fibers starts to express MyHC-slow, and by week 30, about 50 % of all muscle fibers express MyHC-slow, like in adult muscle [45, 44]. In the developing human muscles, both developmental MyHC isoforms are downregulated toward the end of gestation, the corresponding MyHC transcripts are expressed at low levels at birth, and in a 1-month-old infant, MyHC-neo persists only in a few fibers [48] (Fig. 1). In conclusion, most human skeletal muscle fibers, probably more than 95 %, appear to derive from secondary and tertiary waves of myogenesis and their diversification into the fast type 2A or slow type 1 lineage occurs before birth, during the third trimester of gestation, whereas the differentiation of type 2X fibers takes place in the first week after birth.Fig. 1


Developmental myosins: expression patterns and functional significance.

Schiaffino S, Rossi AC, Smerdu V, Leinwand LA, Reggiani C - Skelet Muscle (2015)

MyHC transcripts in developing human skeletal muscle. The transcripts were revealed by in situ hybridization using probes specific for the following MYH genes: MYH3 (Emb, a–d), MYH8 (Neo, e–h), MYH7 (Slow, i–l), MYH2 (2A, m–p), and MYH1 (2X, q–t). Muscles examined were quadriceps femoris from 9 and 19-week-old fetuses and vastus lateralis from 1-day- (P1) and 1-month-old (P30) newborns. Bar = 30 μm (from [48])
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4502549&req=5

Fig1: MyHC transcripts in developing human skeletal muscle. The transcripts were revealed by in situ hybridization using probes specific for the following MYH genes: MYH3 (Emb, a–d), MYH8 (Neo, e–h), MYH7 (Slow, i–l), MYH2 (2A, m–p), and MYH1 (2X, q–t). Muscles examined were quadriceps femoris from 9 and 19-week-old fetuses and vastus lateralis from 1-day- (P1) and 1-month-old (P30) newborns. Bar = 30 μm (from [48])
Mentions: The developmental pattern of myosin isoform expression in the human embryonic and fetal skeletal muscle has been comparatively less investigated. At week 8 of gestation, primary generation fibers with central nuclei are present in the human skeletal muscle, whereas secondary generation fibers are formed after week 10 and become the predominant fiber population by week 21 [42]. MyHC-emb, MyHC-slow, and MyHC-neo transcripts are detectable in the developing skeletal muscle at week 9 (Fig. 1). At the protein level, all primary myofibers express MyHC-emb and MyHC-slow [43, 44], with MyHC-emb being detectable before MyHC-slow in the initial myotubes [45]. The proportion of fibers staining for MyHC-slow decreases from 75 % at week 10 to 3 % at week 21 of gestation, due to the dramatic increase in secondary fibers that initially do not contain MyHC-slow [45]. Secondary generation fibers express only MyHC-emb at week 12, MyHC-neo protein being detected at later stages [45]. Quantitative RNA analysis indicates that MYH3 transcripts account for about 81 % of all MYH transcripts in the human fetal skeletal muscle at week 15 of gestation [46]. At week 16 to 17, a tertiary fiber population has been identified, initially composed of very small myofibers stained by an anti-myosin antibody reactive with adult fast but not with neonatal MyHC [44, 47]. In situ hybridization indicates that MyHC-2A transcripts are weakly expressed at week 19 and more strongly at birth, whereas MyHC-2X transcripts are barely present at birth and are clearly expressed at 30 days after birth (Fig. 1). After week 27, a proportion of secondary fibers starts to express MyHC-slow, and by week 30, about 50 % of all muscle fibers express MyHC-slow, like in adult muscle [45, 44]. In the developing human muscles, both developmental MyHC isoforms are downregulated toward the end of gestation, the corresponding MyHC transcripts are expressed at low levels at birth, and in a 1-month-old infant, MyHC-neo persists only in a few fibers [48] (Fig. 1). In conclusion, most human skeletal muscle fibers, probably more than 95 %, appear to derive from secondary and tertiary waves of myogenesis and their diversification into the fast type 2A or slow type 1 lineage occurs before birth, during the third trimester of gestation, whereas the differentiation of type 2X fibers takes place in the first week after birth.Fig. 1

Bottom Line: These myosins are re-expressed during muscle regeneration and provide a specific marker of regenerating fibers in the pathologic skeletal muscle.The biochemical and biophysical properties of developmental myosins have only partially been defined, and their functional significance is not yet clear.One possibility is that these myosins are specialized in contracting against low loads, and thus, they may be adapted to the prenatal environment, when fetal muscles contract against a very low load compared to postnatal muscles.

View Article: PubMed Central - PubMed

Affiliation: Venetian Institute of Molecular Medicine (VIMM), Via G. Orus 2, 35129 Padova, Italy.

ABSTRACT
Developing skeletal muscles express unique myosin isoforms, including embryonic and neonatal myosin heavy chains, coded by the myosin heavy chain 3 (MYH3) and MYH8 genes, respectively, and myosin light chain 1 embryonic/atrial, encoded by the myosin light chain 4 (MYL4) gene. These myosin isoforms are transiently expressed during embryonic and fetal development and disappear shortly after birth when adult fast and slow myosins become prevalent. However, developmental myosins persist throughout adult stages in specialized muscles, such as the extraocular and jaw-closing muscles, and in the intrafusal fibers of the muscle spindles. These myosins are re-expressed during muscle regeneration and provide a specific marker of regenerating fibers in the pathologic skeletal muscle. Mutations in MYH3 or MYH8 are responsible for distal arthrogryposis syndromes, characterized by congenital joint contractures and orofacial dysmorphisms, supporting the importance of muscle contractile activity and body movements in joint development and in shaping the form of the face during fetal development. The biochemical and biophysical properties of developmental myosins have only partially been defined, and their functional significance is not yet clear. One possibility is that these myosins are specialized in contracting against low loads, and thus, they may be adapted to the prenatal environment, when fetal muscles contract against a very low load compared to postnatal muscles.

No MeSH data available.


Related in: MedlinePlus