J. Anim Sci. 2008. 86:E205-E206. doi:10.2527/jas.2007-0439
© 2008 American Society of Animal Science
Growth and development symposium: Transcriptional factors and cell mechanisms for regulation of growth and development with application to animal agriculture
H. Chester-Jones* and
S. G. Velleman
,1
* Department of Animal Science, University of Minnesota Southern Research and Outreach Center, Waseca 56093; and
Department of Animal Sciences, Ohio Agricultural Research and Development Center, The Ohio State University, Wooster 44691
The symposium "Transcriptional factors and cell mechanisms for regulation of growth and development with application to animal agriculture" was held at the 2007 joint annual meeting of the American Dairy Association, Poultry Science Association, Asociación Mexicana de Producción Animal, and American Animal Science Association in San Antonio, TX, on July 11, 2007. The topic of this symposium was selected to cover new and emerging areas in animal growth, with a focus on cellular mechanisms regulating skeletal muscle development. The approach used in the selection of the papers to be presented was to begin from the basic cellular mechanisms involved in the development of muscle and to proceed to the applied aspects of muscle growth. Frequently, the basic science of the muscle cell is viewed to be independent of the applied issues affecting muscle growth and, ultimately, meat quality. The objective of this symposium was to demonstrate the relationship between the cellular aspects regulating cell growth and how the cell affects applied areas important to the animal industries.
Zipora Yablonka-Reuveni presented the first paper on "Defining the transcriptional signature of skeletal muscle stem cells" (Yablonka-Reuveni et al., 2008
). The presentation focused on how the myofiber is maintained. Particular focus was given to the paired box factors, myogenic regulatory factors, and sex-determining region Y (sry)-box gene (Sox) families of transcription factors that regulate the formation of muscle and how the expression of each of these families dictates whether the muscle cell is in a state of quiescence, proliferation, or differentiation. The role of satellite cells in the growth of muscle was also discussed and how these cells are regulated by transcription factors. Satellite cells are myogenic precursor cells located between the plasma membrane and basement membrane of skeletal muscle fibers. These cells are largely responsible for postnatal muscle growth by donating their nuclei to existing muscle fibers increasing the amount of protein synthesis which will lead to muscle fiber hypertrophy. With age, the number of satellite cells declines from a juvenile animal having approximately 30% of their muscle nuclei from satellite cells to only 1 to 5% in the adult. Because satellite cells are critical to the growth and maintenance of muscle mass, a critical question to resolve is how the molecular signature of satellite cells changes with age and the impact of these cellular events on muscle growth.
Tara G. McDaneld proceeded to discuss the new emerging area of microRNAs (miR) and the role they play in muscle development (Smith et al., 2007). The miR are small molecules in the range of 18 to 26 nucleotides that, to date, represent approximately 1 to 5% of the known genes. They influence the expression of genes and regulate gene expression. This regulation of gene expression is particularly important to the development of tissues and organs. Research attention directed to the miR in agriculturally important animals has been limited to date. However, in cattle the miR have been shown to affect proliferation, differentiation, and hypertrophy of muscle cells. The different miR molecules can act at specific stages of muscle development. Although an understanding of miR is in the early stages, it is clear that they can significantly impact phenotype.
The cellular response to growth factors plays an important role in either stimulating or inhibiting proliferation and differentiation in muscle. The importance of growth factor signaling is well illustrated by the double muscling condition in cattle resulting from an absence of myostatin expression, which is a potent inhibitor of muscle cell proliferation and differentiation. William R. Dayton presented a talk on "Cellular and molecular regulation of muscle growth and development in meat animals" (Dayton and White, 2008). Dayton’s presentation focused on the effects of IGF and IGFBP in regulating skeletal muscle growth in cattle. Insulin-like growth factor stimulates skeletal muscle proliferation and differentiation, stimulates protein synthesis, and decreases protein degradation. The IGFBP contain 6 members that can function in an IGF-dependent or -independent fashion to affect muscle proliferation, differentiation, and apoptosis. New data indicates that IGFBP-3 and -5 may play a role in regulating the inhibitory actions on muscle growth by myostatin and transforming growth factor beta.
How cellular mechanisms affect muscling and meat quality was addressed by Brad J. Johnson in the final talk, "Application of cellular mechanisms to growth and development of food producing animals" (Chung and Johnson, 2008). Johnson discussed the use of anabolic steroid implants to promote muscle growth in beef cattle. The steroid implants likely increase protein deposition through the stimulation of satellite cells. The anabolic steroids also attenuate the transdifferentiation of primitive mesenchymal cells to adipocytes. Thus, the anabolic steroids affect both growth-mediated and adipogenic pathways affecting marbling and ultimately meat quality.
The speakers in the symposium presented the emerging areas of transcriptional regulatory factors, miR, growth factor regulation, and the effect of anabolic steroids. The relationship of each of these areas to muscle growth was delineated as well as the impact on meat quality. It is our hope that this symposium illustrated the integral relationship between issues affecting meat quality and the basic biology affecting the muscle cell, this being especially relevant to our current understanding of the mechanistic intricacies involved in using cell biology to identify new complex pathways to enhance our ability to refine application to meat animals.
1 Corresponding author: velleman.1{at}osu.edu
Received for publication July 19, 2007.
Accepted for publication July 29, 2007.
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 LITERATURE CITED
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Chung, K. Y., and B. J. Johnson. 2008. Application of cellular mechanisms to growth and development of food producing animals. J. Anim. Sci. 86(E. Suppl):E226–E235.[Abstract/Free Full Text]
Dayton, W. R., and M. E. White. 2008. Cellular and molecular regulation of muscle growth and development in meat animals. J. Anim. Sci. 86(E. Suppl.):E217–E225.[Abstract/Free Full Text]
Smith, T. P. L., T. G. McDaneld, M. E. Doumit, L. K. Matukumalli, T. Sonstegard, L. L. Coutinho, and R. Wiedmann. 2007. The role of microRNAs in muscle development. J. Anim. Sci. 85(Suppl. 1):637. (Abstr.)
Yablonka-Reuveni, Z., K. Day, A. Vine, and G. Shefer. 2008. Defining the transcriptional signature of skeletal muscle stem cells. J.Anim. Sci. 86(E. Suppl.):E207–E216.
