TITIN EXPRESSION AS AN EARLY INDICATION OF HEART AND SKELETAL-MUSCLE DIFFERENTIATION IN-VITRO - DEVELOPMENTAL REORGANIZATION IN RELATION TOCYTOSKELETAL CONSTITUENTS

Established myogenic cell lines of different species and tissue origin have been used to study expression and organisation of muscle-specifi c proteins during differentiation. Furthermore, primary cultures of ra t myocard cells were used to examine these same processes during dedif ferentiation. In particular, we were interested in the general mechani sm that underlies the changes in the supramolecular organisation of ti tin during in vitro myogenesis. It became obvious that in the differen tiating muscle cell cultures the redistribution of desmin, actin and m yosin in a typical, differentiation state dependent fashion, always sh owed a certain delay when compared to titin. The sequence of changes i n the assembly of cytoskeletal and sarcomeric structures observed duri ng differentiation of the cell lines was reversed during the process o f dedifferentiation in cultured rat myocard cells. These results all i ndicate that titin is an early marker of myogenic differentiation, bot h in vivo and in vitro, and that the typical reorganisation of this gi ant molecule is independent of species or muscle cell type.