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Intracellular Motility of Intermediate Filaments

Leube RE, Moch M, Windoffer R

The establishment and continuous cell type–specific adaptation of cytoplasmic intermediate filament (IF) networks are linked to various types of IF motility. Motor protein–driven active transport, linkage to other cellular structures, diffusion of small soluble subunits, and intrinsic network elasticity all contribute to the motile behavior of IFs. These processes are subject to regulation by multiple signaling pathways. IF motility is thereby connected to and involved in many basic cellular processes guarding the maintenance of cell and tissue integrity. Disturbances of IF motility are linked to diseases that are characterized by cytoplasmic aggregates containing IF proteins together with other cellular components.

Keratin filaments nucleate close to the cortical interdesmosomal network in murine blastocysts. The overview at left shows an animated maximum intensity projection of the fluorescence recorded in the trophectoderm of a late murine Krt8-YFP knock-in blastocyst (see also corresponding Fig. 1c). The time-lapse fluorescence images at right were recorded at the cell border of two trophectoderm cells of the same blastocyst every 62.5 s (see also corresponding Fig. 1d). The top reveals the appearance of growing keratin particles from the interdesmosomal subcortical keratin system. These motile and highly flexible particles fuse and enlarge before merging with the cytoplasmic KF network (arrowheads delineate a few selected examples; contrast was enhanced per frame to compensate for bleaching). The lower plane shows the same region at enhanced contrast settings to unravel further details in the selected focal planes.


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The 3D animation of a z-stack recording depicts the fluorescence of keratin and desmosome reporters in a confluent HaCaT cell culture. The images (maximum intensity projection) were obtained from mixed HaCaT cell cultures containing cells producing HK5-EYFP (clone B10) delineating KFs and Dsc2-mCerulean delineating desmosomes (for details see legend to corresponding Fig. 2b). The animation first shows rotating views of the keratin-desmosome fluorescence, then rotating views of the desmosome fluorescence by itself, and then top-to-bottom views of single focal planes of double keratin-desmosome fluorescence.


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Intracellular Motility of Intermediate Filaments