Antisense oligodeoxynucleotide-mediated alterations in slow troponin C gene expression during myogenesis

Abstract

The expression of genes for contractile proteins during terminal differentiation in myogenesis is coordinately regulated. It remains unclear how the transcriptional and translational machinery in the cell is fine tuned to achieve the proper stoichiometric representation of each polypeptide complement of the multicomponent myofilament. To help elucidate the complex regulatory mechanisms that govern myogenesis, the expression of the slow troponin C (s/c TnC) gene in cell culture as a model system has been studied. The effect on myogenesis, of specifically blocking the expression of the s/cTnC gene with an antisense phosphorothioate (PS) oligodeoxynucleotide (ODN) complexed with the DOSPER liposome (Boehringer Mannheim) was observed. A 4 day treatment period with 1 $\mu$M of the antisense ODN in 1 ml differentiation medium resulted in approximately a 80% and 50% decrease in the s/cTnC polypeptide synthesis and mRNA levels. However, a corresponding reduction of the steady state level of this polypeptide was not observed. There was also no appreciable alteration in the pattern of myogenesis by ODN treatment as judged by the synthesis of other muscle specific proteins. Furthermore, the antisense effect was found to be transient as the cells recovered to synthesize normal levels of s/c TnC polypeptide upon withdrawal of the antisense ODN from the culture medium. The results presented in this thesis suggests $\rm C\sb2C\sb{12}$ myotubes possesses an internal compensatory mechanism(s) that attempts to overcome the block on the expression of the s/cTnC gene to maintain the desired stoichiometry in the formation of a functional contractile apparatus.