title: F-actin serves as a template for cytokeratin organization in cell free extracts.
abstract: The microtubule, F-actin, and intermediate filament systems are often studied as isolated systems, yet the three display mutual interdependence in living cells. To overcome limitations inherent in analysis of polymer-polymer interactions in intact cells, associations between these systems were assessed in Xenopus egg extracts. In both fixed and unfixed extract preparations, cytokeratin associated with F-actin cables that spontaneously assembled in the extracts. Time-course experiments revealed that at early time points cytokeratin cables were invariably associated with F-actin cables, while at later time points they could be found without associated F-actin. In extract samples where F-actin assembly was prevented, cytokeratin formed unorganized aggregates rather than cables. Dynamic imaging revealed transport of cytokeratin by moving F-actin as well as examples of cytokeratin release from F-actin. Experimental alteration of F-actin network organization by addition of alpha-actinin resulted in a corresponding change in the organization of the cytokeratin network. Finally, pharmacological disruption of the F-actin network in intact, activated eggs disrupted the normal pattern of cytokeratin assembly. These results provide direct evidence for an association between F-actin and cytokeratin in vitro and in vivo, and indicate that this interaction is necessary for proper cytokeratin assembly after transition into the first mitotic interphase of Xenopus.
authors.affiliation: Department of Zoology, University of Wisconsin, Madison, Madison, WI 53706, USA.
authors.forename: Kari L
authors.initials: KL
authors.lastname: Weber
authors.forename: William M
authors.initials: WM
authors.lastname: Bement
mesh_terms: D000199:Actins / Q000378:metabolism*; D000818:Animals; D002457:Cell Extracts / Q000737:chemistry*; D002474:Cell-Free System; D005260:Female; D007382:Intermediate Filaments / Q000737:chemistry / Q000648:ultrastructure*; D007633:Keratins / Q000032:analysis* / Q000378:metabolism; D008868:Microtubule Proteins / Q000737:chemistry; D008870:Microtubules / Q000737:chemistry / Q000378:metabolism; D009865:Oocytes / Q000378:metabolism; D014981:Xenopus
chemical_list: D000199:Actins; D002457:Cell Extracts; D008868:Microtubule Proteins; D007633:Keratins