The role of titin and nebulin in myofibril assembly in cultured embryonic chick muscle cells

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Kurpakus, Michelle
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Ted W. Huiatt
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Biochemistry, Biophysics and Molecular Biology

The Department of Biochemistry, Biophysics, and Molecular Biology was founded to give students an understanding of life principles through the understanding of chemical and physical principles. Among these principles are frontiers of biotechnology such as metabolic networking, the structure of hormones and proteins, genomics, and the like.

The Department of Biochemistry and Biophysics was founded in 1959, and was administered by the College of Sciences and Humanities (later, College of Liberal Arts & Sciences). In 1979 it became co-administered by the Department of Agriculture (later, College of Agriculture and Life Sciences). In 1998 its name changed to the Department of Biochemistry, Biophysics, and Molecular Biology.

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  • Department of Biochemistry and Biophysics (1959–1998)

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The purpose of this study was to examine the role of the two high molecular weight proteins, titin and nebulin, in skeletal muscle myofibrillogenesis. A monoclonal antibody against chicken breast titin was produced, and used in conjunction with polyclonal antibodies against chicken breast titin and nebulin, and monoclonal antibodies to actin and muscle-specific myosin in a series of double-label immunofluorescence studies to examine the organization of these proteins in cultured skeletal muscle cells derived from 12 day chick embryos. Postmitotic, mononucleated myoblasts synthesized titin, myosin, actin, and nebulin. Initial myofibril assembly events involved the coalescence of titin and myosin in a continuous pattern along actin containing structures morphologically similar to stress fibers. Titin and myosin organization into the skeletal muscle myofibril appeared to be coupled, as adult-like titin banding patterns were not observed in the absence of myosin organization into A bands. Titin and actin organization, in contrast, did not appear to be linked. Organization of titin into adult-like double bands along nascent myofibrils consistently preceded that of actin. Neither nebulin and myosin nor nebulin and titin assembly appeared to be linked, since the appearance of nebulin banding was seen after the formation of titin and myosin bands along nascent myofibrils. Nebulin organization occurred either at the same time or after the assembly of actin into I bands. A possible correlation between the formation of adult-like nebulin double bands and the appearance of phase-dense Z lines was noted, however. Labeling experiments were repeated with cultures exposed to the mutagenic alkylating agent ethyl methanesulfonate (EMS). The results of labeling experiments of EMS cells confirmed those found in the normal culture system. In conclusion, it appears that titin does not play a scaffolding or template role for subsequent thick filament alignment into A bands. The possibility of a template role for thin filament alignment into I bands can not be excluded, however, because titin organization precedes actin. The relationship between nebulin organization and the appearance of Z lines suggests that nebulin may be involved in Z line assembly or may regulate the insertion of thin filaments into Z lines.

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Fri Jan 01 00:00:00 UTC 1988