Mecanismos celulares e moleculares que controlam o desenvolvimento e o crescimento muscular
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Data
2007-07-01
Autores
Silva, Maeli Dal Pai [UNESP]
Carvalho, Robson Francisco [UNESP]
Título da Revista
ISSN da Revista
Título de Volume
Editor
Sociedade Brasileira de Zootecnia
Resumo
O músculo estriado esquelético é formado pela associação de fibras musculares com a matriz extracelular. Esse tecido possui alta plasticidade e o conhecimento das características morfológicas, da miogênese, e da dinâmica do crescimento é importante para o entendimento da morfofisiologia bem como para a seleção de animais visando a melhoria na produção de carne. A maioria dos músculos estriados originam-se de células precursoras do mesoderma a partir dos somitos do embrião e o controle da diferenciação ocorre pela ação de fatores indutores ou inibidores. Um grupo de fatores transcricionais, pertencentes à família MyoD tem um papel central na diferenciação muscular. Coletivamente chamados de Fatores de Regulação Miogênica (MRFs), são conhecidos quatro tipos: MyoD, myf-5, miogenina e MRF4. Esses fatores ligam-se à seqüências de DNA conhecidas como Ebox (CANNTG) na região promotora de vários genes músculo-específicos, levando à expressão dos mesmos. As células embrionárias com potencial para diferenciação em células musculares (células precursoras miogênicas) expressam MyoD e Myf-5 e são denominadas de mioblastos. Essas células proliferam, saem do ciclo celular, expressam miogenina e MRF4, que regulam a fusão e a diferenciação da fibra muscular. Uma população de mioblastos que se diferencia mais tardiamente, as células miossatélites, são responsáveis pelo crescimento muscular no período pós natal, que pode ocorrer por hiperplasia e hipertrofia das fibras. As células satélites quiescentes não expressam os MRFs, porém, sob a ação de estímulos como fatores de crescimento ou citocinas, ocorre a ativação desse tipo celular que prolifera e expressa os MRFs de maneira similar ao que ocorre com as células precursoras miogênicas durante a miogênese. Os mecanismos de crescimento muscular são regulados pela expressão temporal dos (MRFs), que controlam a expressão dos genes relacionados com o crescimento muscular.
Skeletal muscle consists predominantly of muscle fibers surrounded by a connective tissue layer. This tissue has a great plasticity, and the knowledge of the morphological characteristics, myogenesis, and growth dynamics is important to the understanding of its physiology and to the farm animal selection for meat production. Most skeletal muscles are derived from mesodermal precursor cells originated from the somites. During embryonic development, specification of mesodermal precursor cells to the myogenic lineage is regulated by positive and negative signals from surrounding tissues. Specification to the myogenic lineage requires the up-regulation of four muscle-specific transcriptional factors (MyoD, Myf5, myogenin, and MRF4), called myogenic regulatory factors (MRFs), which have a well-defined role in skeletal muscle development and differentiation. The MRFs belong to the basic helix-loop-helix (bHLH) super family of transcription factors, that forms heterodimers and bind to the E-box (CANNTG) DNA sequence motif found in the promoters of many muscle specific genes. Specification to the myogenic lineage requires the up-regulation of the MRFs MyoD and Myf5. Proliferative MyoD and/or Myf5 positive myogenic cells are termed myoblasts. Proliferating myoblasts withdraw from the cell cycle to become terminally differentiated myocytes that express the late MRFs, myogenin and MRF4. Specialized populations of myogenic stem cells, termed satellite cells, arise during the late stages of embryogenesis are highly active during the postnatal muscle growth, which may occur by muscle fiber hyperplasia or hypertrophy. Quiescent satellite cells do not express detectable levels of MRF; however, during muscle growth, in response to several growth factors, activated satellite cells proliferate and express the MRFs in a similar manner to muscle precursor cells during skeletal muscle development. Muscle growth mechanisms are controlled by the temporally expression of muscle growth related genes induced by the MRFs.
Skeletal muscle consists predominantly of muscle fibers surrounded by a connective tissue layer. This tissue has a great plasticity, and the knowledge of the morphological characteristics, myogenesis, and growth dynamics is important to the understanding of its physiology and to the farm animal selection for meat production. Most skeletal muscles are derived from mesodermal precursor cells originated from the somites. During embryonic development, specification of mesodermal precursor cells to the myogenic lineage is regulated by positive and negative signals from surrounding tissues. Specification to the myogenic lineage requires the up-regulation of four muscle-specific transcriptional factors (MyoD, Myf5, myogenin, and MRF4), called myogenic regulatory factors (MRFs), which have a well-defined role in skeletal muscle development and differentiation. The MRFs belong to the basic helix-loop-helix (bHLH) super family of transcription factors, that forms heterodimers and bind to the E-box (CANNTG) DNA sequence motif found in the promoters of many muscle specific genes. Specification to the myogenic lineage requires the up-regulation of the MRFs MyoD and Myf5. Proliferative MyoD and/or Myf5 positive myogenic cells are termed myoblasts. Proliferating myoblasts withdraw from the cell cycle to become terminally differentiated myocytes that express the late MRFs, myogenin and MRF4. Specialized populations of myogenic stem cells, termed satellite cells, arise during the late stages of embryogenesis are highly active during the postnatal muscle growth, which may occur by muscle fiber hyperplasia or hypertrophy. Quiescent satellite cells do not express detectable levels of MRF; however, during muscle growth, in response to several growth factors, activated satellite cells proliferate and express the MRFs in a similar manner to muscle precursor cells during skeletal muscle development. Muscle growth mechanisms are controlled by the temporally expression of muscle growth related genes induced by the MRFs.
Descrição
Palavras-chave
crescimento e desenvolvimento muscular, fatores reguladores miogênicos, músculo esquelético, muscle development and growth, myogenic regulatory factors, skeletal muscle
Como citar
Revista Brasileira de Zootecnia. Sociedade Brasileira de Zootecnia, v. 36, p. 21-31, 2007.