| Despite the wealth of in vitro evidence, the mechanisms underlying intermediate filament (IF) assembly, disassembly, and maintenance in vivo, have been poorly understood. IF networks in cells appear to consist of several structural forms that include non-filamentous, precursor particles, short IF or squiggles, and long IF. The major focus of the work described in this dissertation is the synthesis, assembly and function of the IF precursor particle as well as the dynamics of fully polymerized IF in vivo. The results show that the motility and targeting of IF mRNA containing particles (mRNPs), their translational control, and the assembly of an IF cytoskeletal system are linked together in a process we have termed 'dynamic co-translation'. This evidence is supported in part by a combination of RNA fluorescence in situ hybridization (FISH) and the simultaneous imaging of both mRNA and its protein product, in vivo. Quantitative analyses of IF mRNPs demonstrate the presence of multiple copies of mRNA in each mRNP. This observation may reflect a mechanism responsible for the coordinated synthesis of coiled-coil IF dimers, the building blocks of IF. These results not only provide novel insights into the dynamic properties and assembly of IF networks in vivo but also pertains to general cell biology as it shows, for the first time, the dynamics between an mRNA and its product in live cells.; IF play numerous roles in major cellular processes that include cell motility, the determination and maintenance of cell shape, cell signaling, and are major determinants of the mechanical properties of cells. Combined with their cell type and differentiation specific expression, it is clear that they play an important role in tailoring the cytoplasmic environment and architecture for each cell type. Increasing our knowledge of the assembly and maintenance of IF networks in vivo will be crucial for understanding the cytoskeletons' roles in cell physiological processes. |
