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Fiber polymorphism in skeletal muscles of the American lobster, Homarus americanus: continuum between slow-twitch (S1) and slow-tonic (S2) fibers.
J Exp Biol. 2004 Jul; 207(Pt 16):2755-67.JE

Abstract

In recent years, an increasing number of studies has reported the existence of single fibers expressing more than one myosin heavy chain (MHC) isoform at the level of fiber proteins and/or mRNA. These mixed phenotype fibers, often termed hybrid fibers, are currently being recognized as the predominant fiber type in many muscles, and the implications of these findings are currently a topic of great interest. In a recent study, we reported single fibers from the cutter claw closer muscle of lobsters that demonstrated a gradation between the slow-twitch (S1) and slow-tonic (S2) muscle phenotype. In the present study, we focused on S1 and S2 fibers from the superficial abdominal muscles of the lobster as a model to study the continuum among muscle fiber types. Complementary DNAs (cDNA) encoding an S2 isoform of myosin heavy chain (MHC) and an S2 isoform of tropomyosin (Tm) were isolated from the superficial abdominal flexor muscles of adult lobsters. These identified sequences were used to design PCR primers used in conjunction with RT-PCR and real-time PCR to measure expression levels of these genes in small muscle samples and single fibers. The relative expression of the corresponding S1 MHC and S1 Tm isoforms was measured in the same samples with PCR primers designed according to previously identified sequences. In addition, we measured the relative proportions of MHC, troponin (Tn) T and I protein isoforms present in the same samples to examine the correlation of these proteins with one another and with the MHC and Tm mRNAs. These analyses revealed significant correlations among the different myofibrillar proteins, with the S1 and S2 fibers being characterized by a whole assemblage of myofibrillar isoforms. However, they also showed that small muscle samples, and more importantly single fibers, existed as a continuum from one phenotype to another. Most fibers possessed mixtures of mRNA for MHC isoforms that were unexpected based on protein analysis. These findings illustrate that muscle fibers in general may possess a phenotype that is intermediate between the extremes of 'pure' fiber types, not only at the MHC level but also in terms of whole myofibrillar assemblages. This study supports and extends our recent observations of mixed phenotype fibers in lobster claw and leg muscles. The existence of single fiber polymorphism in an invertebrate species underscores the generality of the phenomenon in skeletal muscles and emphasizes the need for an understanding of the proximal causes and physiological consequences of these intermediate fiber types.

Authors+Show Affiliations

Department of Biology, Colorado State University, Fort Collins, CO 80523, USA. smedler@lamar.colostate.eduNo affiliation info availableNo affiliation info available

Pub Type(s)

Comparative Study
Journal Article
Research Support, U.S. Gov't, Non-P.H.S.
Research Support, U.S. Gov't, P.H.S.

Language

eng

PubMed ID

15235004

Citation

Medler, Scott, et al. "Fiber Polymorphism in Skeletal Muscles of the American Lobster, Homarus Americanus: Continuum Between Slow-twitch (S1) and Slow-tonic (S2) Fibers." The Journal of Experimental Biology, vol. 207, no. Pt 16, 2004, pp. 2755-67.
Medler S, Lilley T, Mykles DL. Fiber polymorphism in skeletal muscles of the American lobster, Homarus americanus: continuum between slow-twitch (S1) and slow-tonic (S2) fibers. J Exp Biol. 2004;207(Pt 16):2755-67.
Medler, S., Lilley, T., & Mykles, D. L. (2004). Fiber polymorphism in skeletal muscles of the American lobster, Homarus americanus: continuum between slow-twitch (S1) and slow-tonic (S2) fibers. The Journal of Experimental Biology, 207(Pt 16), 2755-67.
Medler S, Lilley T, Mykles DL. Fiber Polymorphism in Skeletal Muscles of the American Lobster, Homarus Americanus: Continuum Between Slow-twitch (S1) and Slow-tonic (S2) Fibers. J Exp Biol. 2004;207(Pt 16):2755-67. PubMed PMID: 15235004.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Fiber polymorphism in skeletal muscles of the American lobster, Homarus americanus: continuum between slow-twitch (S1) and slow-tonic (S2) fibers. AU - Medler,Scott, AU - Lilley,Travis, AU - Mykles,Donald L, PY - 2004/7/6/pubmed PY - 2004/10/6/medline PY - 2004/7/6/entrez SP - 2755 EP - 67 JF - The Journal of experimental biology JO - J Exp Biol VL - 207 IS - Pt 16 N2 - In recent years, an increasing number of studies has reported the existence of single fibers expressing more than one myosin heavy chain (MHC) isoform at the level of fiber proteins and/or mRNA. These mixed phenotype fibers, often termed hybrid fibers, are currently being recognized as the predominant fiber type in many muscles, and the implications of these findings are currently a topic of great interest. In a recent study, we reported single fibers from the cutter claw closer muscle of lobsters that demonstrated a gradation between the slow-twitch (S1) and slow-tonic (S2) muscle phenotype. In the present study, we focused on S1 and S2 fibers from the superficial abdominal muscles of the lobster as a model to study the continuum among muscle fiber types. Complementary DNAs (cDNA) encoding an S2 isoform of myosin heavy chain (MHC) and an S2 isoform of tropomyosin (Tm) were isolated from the superficial abdominal flexor muscles of adult lobsters. These identified sequences were used to design PCR primers used in conjunction with RT-PCR and real-time PCR to measure expression levels of these genes in small muscle samples and single fibers. The relative expression of the corresponding S1 MHC and S1 Tm isoforms was measured in the same samples with PCR primers designed according to previously identified sequences. In addition, we measured the relative proportions of MHC, troponin (Tn) T and I protein isoforms present in the same samples to examine the correlation of these proteins with one another and with the MHC and Tm mRNAs. These analyses revealed significant correlations among the different myofibrillar proteins, with the S1 and S2 fibers being characterized by a whole assemblage of myofibrillar isoforms. However, they also showed that small muscle samples, and more importantly single fibers, existed as a continuum from one phenotype to another. Most fibers possessed mixtures of mRNA for MHC isoforms that were unexpected based on protein analysis. These findings illustrate that muscle fibers in general may possess a phenotype that is intermediate between the extremes of 'pure' fiber types, not only at the MHC level but also in terms of whole myofibrillar assemblages. This study supports and extends our recent observations of mixed phenotype fibers in lobster claw and leg muscles. The existence of single fiber polymorphism in an invertebrate species underscores the generality of the phenomenon in skeletal muscles and emphasizes the need for an understanding of the proximal causes and physiological consequences of these intermediate fiber types. SN - 0022-0949 UR - https://www.unboundmedicine.com/medline/citation/15235004/Fiber_polymorphism_in_skeletal_muscles_of_the_American_lobster_Homarus_americanus:_continuum_between_slow_twitch__S1__and_slow_tonic__S2__fibers_ L2 - http://jeb.biologists.org/cgi/pmidlookup?view=long&pmid=15235004 DB - PRIME DP - Unbound Medicine ER -