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Still Heart Encodes a Structural HMT, SMYD1b, with Chaperone-Like Function during Fast Muscle Sarcomere Assembly.

Prill K, Windsor Reid P, Wohlgemuth SL, Pilgrim DB - PLoS ONE (2015)

Bottom Line: The cognate gene for the mutant was shown to be smyd1b and the still heart mutation results in an early nonsense codon.SMYD1 mutants show a lack of heart looping and chamber definition due to a lack of expression of heart morphogenesis factors gata4, gata5 and hand2.On a cellular level, fast muscle fibers in homozygous mutants do not form mature sarcomeres due to the lack of fast muscle myosin incorporation by SMYD1b when sarcomeres are first being assembled (19hpf), supporting SMYD1b as an assembly protein during sarcomere formation.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada.

ABSTRACT
The vertebrate sarcomere is a complex and highly organized contractile structure whose assembly and function requires the coordination of hundreds of proteins. Proteins require proper folding and incorporation into the sarcomere by assembly factors, and they must also be maintained and replaced due to the constant physical stress of muscle contraction. Zebrafish mutants affecting muscle assembly and maintenance have proven to be an ideal tool for identification and analysis of factors necessary for these processes. The still heart mutant was identified due to motility defects and a nonfunctional heart. The cognate gene for the mutant was shown to be smyd1b and the still heart mutation results in an early nonsense codon. SMYD1 mutants show a lack of heart looping and chamber definition due to a lack of expression of heart morphogenesis factors gata4, gata5 and hand2. On a cellular level, fast muscle fibers in homozygous mutants do not form mature sarcomeres due to the lack of fast muscle myosin incorporation by SMYD1b when sarcomeres are first being assembled (19hpf), supporting SMYD1b as an assembly protein during sarcomere formation.

No MeSH data available.


Related in: MedlinePlus

Myosin expression is unaffected by the absence of SMYD1b.At 24hpf, fast myosin (myhc4) expression in wild type (A) and still heart embryos (B) is similar within the trunk muscle. Slow myosin (smyhc1) expression in wild type (C) and still heart embryos (D) is also similar at 24hpf. Quantitative PCR on wild type and sth mutants for fast and slow myosin expression shows myosin expression is normal when compared to wild type embryos at 24hpf (E). (qPCR: n = 3, 30 embryos each time/phenotype. Error bars are standard deviation.).
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pone.0142528.g002: Myosin expression is unaffected by the absence of SMYD1b.At 24hpf, fast myosin (myhc4) expression in wild type (A) and still heart embryos (B) is similar within the trunk muscle. Slow myosin (smyhc1) expression in wild type (C) and still heart embryos (D) is also similar at 24hpf. Quantitative PCR on wild type and sth mutants for fast and slow myosin expression shows myosin expression is normal when compared to wild type embryos at 24hpf (E). (qPCR: n = 3, 30 embryos each time/phenotype. Error bars are standard deviation.).

Mentions: The predicted protein structure of SMYD1b contains SET domains that have been associated with histone methyltransferase function [22, 23], however more recent work has shown that SMYD1b binds myosin and localizes to the M-line of sarcomeres after myocyte differentiation [20]. To determine whether SMYD1b is playing a role in muscle development as a HMT, responsible for myosin expression, or a myosin chaperone that is required for assembly and maintenance of the sarcomere, we examined myosin expression and incorporation into the sarcomere. Still heart mutants do not swim away after being touched, a normal evasion response to predators that is seen in their wild type siblings. The lack of an avoid response suggests that the sth mutation is affecting fast skeletal muscle fibers that are used for rapid swimming in response to an acute stimulus. We analyzed the expression levels of fast and slow-twitch myosin mRNA in sth mutants and wild type siblings and found that there were no significant differences in myosin expression between homozygous mutants and sibs (Fig 2A–2E).


Still Heart Encodes a Structural HMT, SMYD1b, with Chaperone-Like Function during Fast Muscle Sarcomere Assembly.

Prill K, Windsor Reid P, Wohlgemuth SL, Pilgrim DB - PLoS ONE (2015)

Myosin expression is unaffected by the absence of SMYD1b.At 24hpf, fast myosin (myhc4) expression in wild type (A) and still heart embryos (B) is similar within the trunk muscle. Slow myosin (smyhc1) expression in wild type (C) and still heart embryos (D) is also similar at 24hpf. Quantitative PCR on wild type and sth mutants for fast and slow myosin expression shows myosin expression is normal when compared to wild type embryos at 24hpf (E). (qPCR: n = 3, 30 embryos each time/phenotype. Error bars are standard deviation.).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4636364&req=5

pone.0142528.g002: Myosin expression is unaffected by the absence of SMYD1b.At 24hpf, fast myosin (myhc4) expression in wild type (A) and still heart embryos (B) is similar within the trunk muscle. Slow myosin (smyhc1) expression in wild type (C) and still heart embryos (D) is also similar at 24hpf. Quantitative PCR on wild type and sth mutants for fast and slow myosin expression shows myosin expression is normal when compared to wild type embryos at 24hpf (E). (qPCR: n = 3, 30 embryos each time/phenotype. Error bars are standard deviation.).
Mentions: The predicted protein structure of SMYD1b contains SET domains that have been associated with histone methyltransferase function [22, 23], however more recent work has shown that SMYD1b binds myosin and localizes to the M-line of sarcomeres after myocyte differentiation [20]. To determine whether SMYD1b is playing a role in muscle development as a HMT, responsible for myosin expression, or a myosin chaperone that is required for assembly and maintenance of the sarcomere, we examined myosin expression and incorporation into the sarcomere. Still heart mutants do not swim away after being touched, a normal evasion response to predators that is seen in their wild type siblings. The lack of an avoid response suggests that the sth mutation is affecting fast skeletal muscle fibers that are used for rapid swimming in response to an acute stimulus. We analyzed the expression levels of fast and slow-twitch myosin mRNA in sth mutants and wild type siblings and found that there were no significant differences in myosin expression between homozygous mutants and sibs (Fig 2A–2E).

Bottom Line: The cognate gene for the mutant was shown to be smyd1b and the still heart mutation results in an early nonsense codon.SMYD1 mutants show a lack of heart looping and chamber definition due to a lack of expression of heart morphogenesis factors gata4, gata5 and hand2.On a cellular level, fast muscle fibers in homozygous mutants do not form mature sarcomeres due to the lack of fast muscle myosin incorporation by SMYD1b when sarcomeres are first being assembled (19hpf), supporting SMYD1b as an assembly protein during sarcomere formation.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada.

ABSTRACT
The vertebrate sarcomere is a complex and highly organized contractile structure whose assembly and function requires the coordination of hundreds of proteins. Proteins require proper folding and incorporation into the sarcomere by assembly factors, and they must also be maintained and replaced due to the constant physical stress of muscle contraction. Zebrafish mutants affecting muscle assembly and maintenance have proven to be an ideal tool for identification and analysis of factors necessary for these processes. The still heart mutant was identified due to motility defects and a nonfunctional heart. The cognate gene for the mutant was shown to be smyd1b and the still heart mutation results in an early nonsense codon. SMYD1 mutants show a lack of heart looping and chamber definition due to a lack of expression of heart morphogenesis factors gata4, gata5 and hand2. On a cellular level, fast muscle fibers in homozygous mutants do not form mature sarcomeres due to the lack of fast muscle myosin incorporation by SMYD1b when sarcomeres are first being assembled (19hpf), supporting SMYD1b as an assembly protein during sarcomere formation.

No MeSH data available.


Related in: MedlinePlus