Satellite cells. Muscle fiber growth. Muscle: factors affecting pre- and post-natal growth. Longitudinal: Radial ( girth):

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1 Satellite cells Muscle: factors affecting pre- and post-natal growth Animal Science 123 Animal Growth & Development R. D. Sainz Lecture 11 Unfused myoblasts adjacent to the sarcolemma Fuse with existing fibers as needed to provide nuclei Can be cultured from adult muscle in vitro, where they follow a myogenic program The number of muscle fibers is set prior to birth (around the end of the second trimester; Remember this? Future satellite cells Therefore, post-natal muscle growth involves increases in length and girth of existing muscle fibers. From: Swatland, HJ Structure and Function of Meat Animals. Prentice-Hall, Inc., Englewood Cliffs, NJ. Muscle fiber growth Longitudinal: addition of sarcomeres in series Radial ( girth): addition of myofibrils addition of nuclei - from satellite cells Fig. 9. Shows the incorporation of radioactive adenosine into the newly formed actin (sarcomeres) in the end regions of young and adult muscle indicating that this is the region of longitudinal growth in vertebrate striated muscle. From: Goldspink, G Growth of muscle. In: Goldspink, DF (Ed.) Development and Specialization of Skeletal Muscle. Cambridge University Press, Cambridge. 1

2 Effects of body size on weight (kg) and fiber diameters (µm)( Species Mice Sheep Pigs Cattle Body wt Birth Fiber diameter Body wt Maturity Fiber diameter Hormonal control of muscle development and growth IGF-I, IGF-II proliferation differentiation Basic FGF, TGF-β proliferation differentiation GH no direct effects? Increase in muscle "cell number" and "cell size" in sheep Effects of TGF-β on muscle gene expression Age, d 3 Protein 1.8 DNA Time after transfer, h Myogenin -TGF + TGF JunB -TGF + TGF Type I collagen -TGF + TGF From: Johns, JT and Bergen, WG Growth in sheep. Pre-and post-weaning hormone changes and muscle and liver development. Journal of Animal Science 43: From: Reeds, PJ Future trends in growth biology research. Journal of Animal Science 69 (Suppl. 3): Sex Males have more muscle (7 vs. 64% of carcass wt) and less fat (11 vs. 16%) than females BUT: Distribution of carcass muscle, fat and bone in cattle (% of carcass wt) Tissue Muscle Fat Bone Forequarter F M Hindquarter F M Genetics Species and breeds vary in muscularity Muscle distribution relatively constant among cattle breeds Exceptions exist, e.g. athletes, double-muscled cattle, callipyge sheep SO: The advantage (for meat yield) is in the lowervalue forequarter, i.e., neck & shoulders. 2

3 Muscle distribution Bulls Steers Effects of the double-muscled mutation on muscle cellularity Muscle group Body weight, kg Hereford Holstein Hereford Holstein % of total muscle Muscle wt, g Normal 1,78 Double-muscled 1,534 Proximal hind leg Around backbone Proximal front leg Hind quarter Front quarter Expensive muscles Total protein, g Total DNA, g From: Berg, RT and Butterfield, RM New Concepts of Cattle Growth. From: Ashmore, R. personal communication. From: Lawrence, TLJ and Fowler, VR Growth of Farm Animals. CAB International, New York. 3

4 From: Goldspink, G Growth of muscle. In: Goldspink, DF (Ed.) Development and Specialization of Skeletal Muscle. Cambridge University Press, Cambridge. Concentrations of DNA, RNA and protein in longissimus muscles from normal and callipyge lambs DNA, µg/g RNA, µg/g Protein, mg/g Protein:RNA RNA:DNA Normal 2, Callipyge 2, Pooled S.D P From: Sainz et al., From: Goldspink, G Growth of muscle. In: Goldspink, DF (Ed.) Development and Specialization of Skeletal Muscle. Cambridge University Press, Cambridge. Exercise & activity pattern SO fibers are recruited first and most frequently FG and FOG fibers are recruited when large or sudden forces are required, or when SO fibers are fatigued Heavy lifting: largest fiber hypertrophy apparent increase in fiber number (splitting) Type of exercise vs. changes in fiber types From: Goldspink, DF Physiological factors influencing protein turnover and muscle growth. In: Goldspink, DF (Ed.) Development and Specialization of Skeletal Muscle. Cambridge University Press, Cambridge. 4

5 Source: Hill et al., 24. Animal Physiology, Sinauer Associates, Sunderland, MA. Source: Hill et al., 24. Animal Physiology, Sinauer Associates, Sunderland, MA. Animal experiments Human experiments From: Goldspink, G Growth of muscle. In: Goldspink, DF (Ed.) Development and Specialization of Skeletal Muscle. Cambridge University Press, Cambridge. Source: Hill et al., 24. Animal Physiology, Sinauer Associates, Sunderland, MA. 5