Desmin/vimentin intermediate filaments are dispensible for many aspects of myogenesis
An expression vector was prepared containing a cDNA coding for a truncated version of the intermediate filament protein desmin. The encoded truncated desmin protein lacks a portion of the highly conserved $\alpha$-helical rod region as well as the entire non-helical carboxy-terminal domain. When transiently expressed in primary fibroblasts, or in differentiating postmitotic myoblasts and multinucleated myotubes, the truncated protein induces the complete dismantling of the preexisting vimentin or desmin/vimentin IF networks, respectively. Instead, in both cell types vimentin and desmin are packaged into hybrid spheroid bodies scattered throughout the cytoplasm. Despite the complete lack of intact IFs, myoblasts and myotubes expressing truncated desmin synthesize myofibrillar proteins, fuse, assemble and laterally align normal striated myofibrils, and contract spontaneously in a manner indistinguishable from that of control myogenic cells. In older cultures the spheroid bodies shift from a longitudinal to a predominantly transverse orientation and loosely align along the I-Z-I-regions of striated myofibrils, analogous to the translocation of intact desmin/vimentin IFs in control muscle. The effects of the transiently expressed truncated protein are surprisingly widespread and long-lived. Over 95% of the myotubes in truncated desmin-transfected cultures display enormous numbers of desmin+/vimentin+ spheroid bodies and are totally devoid of IFs. Fourteen days after transfection, myotubes are still filled with immense numbers of small desmin+/vimentin+ spheroid bodies and show no signs of reconstituting normal IF networks. These results suggest the need for a critical reexamination of commonly held concepts regarding the functions of desmin IFs in early and late stages of myogenesis.
Anatomy & physiology|Biology
Schultheiss, Thomas M, "Desmin/vimentin intermediate filaments are dispensible for many aspects of myogenesis" (1991). Dissertations available from ProQuest. AAI9125752.