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Cell Differentiation, Protein Synthesis Rate and Protein Accumulation in Muscle Cell Cultures Isolated from Embryos of Layer and Broiler Chickens¹

Michigan State University, East Lansing 48824

⁴ To whom all correspondence should be addressed: Dept. of Biol. Sci., University of Alabama, Hunstville 35899.

Abstract

Muscle cell cultures were prepared from the leg muscle of 12-d layer and broiler chicken embryos. Cultures were then compared over a 10-d period for their capacity to differentiate into multinucleated myotubes and to synthesize and accumulate protein. Differentiation was qualitatively similar in the two cell types as evidenced by myoblast fusion that occurred rapidly during the first 2 d and remained essentially constant between d 3 and 10. However, several quantitative differences were observed. Even though the number of myotubes per culture was comparable between layers and broilers throughout development, layer muscle cultures usually exhibited a higher percentage fusion and more myonuclei per culture than broiler muscle cultures. Additionally, the nuclear density (i.e., the number of nuclei per myotube segment) was approximately 25% greater in layer cultures than in broilers between d 2 and 10 in culture. The rate of incorporation of ³H-leucine into total protein during pulse labeling experiments was comparable in muscle cultures of layers and broilers; however, broiler muscle cells accumulated approximately 40% more total protein per nucleus between d 6 and 10. Myosin heavy chain synthesis rate was higher in layer than in broiler muscle cultures, but broiler muscle cultures accumulated approximately 30% more myosin heavy chain than layers between d 6 and 10. The half-life of myosin heavy chain was 45 h in layer muscle cultures and 103 h in broiler muscle cultures. Thus, the capacity of broiler cells to accumulate more muscle protein was primarily due to a drastically slower protein breakdown rate.

¹ Michigan Agr. Exp. Sta. Article No. 9939. This work was supported by grants from the Muscular Dystrophy Association, the Upjohn Company, NIH Grant #AM28461, and Michigan Agr. Exp. Sta. Project Nos. 1241 and 1265.

² Dept. of Food Sci. and Human Nutr.

³ Dept. of Anim. Sci.