Remodeling processes during anterior regeneration of Owenia fusiformis (Polychaeta, Annelidae): a morphological and immunocytochemical survey

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Abstract
Morphological and immunocytochemical studies were used to determine the correlations among cytoskeleton, junction complex, and basement membrane reorganization during anterior regeneration in Owenia fusiformis. Electron microscopical observations showed that, at the point of amputation, in conjunction with the disorganization of the extracellular matrix, alterations in the adhesive junctions caused dramatic changes in the distribution of intermediary filaments. Fluorescence microscopy investigations with fluorescein – phalloidin and antibodies to actin and Owenia tropomyosin visualized a basal actin network in epidermal cells, which was reorganized during regeneration. Two or three days after amputation, this cortical mat was not observed in blastema where the basal membrane was lacking. It was still incompletely reassembled after 4 or 5 days, i.e., when the thin reforming basal membrane, which stained with anti type IV collagen antibody, did not yet display collagen fibrils. In the epidermis of 6- to 7-day-old regenerates, the basal membrane, intercellular junctions, and actin and intermediary filament cytoskeletons exhibited nearly normal structural features. Use of antibody to Owenia paramyosin showed that the reorganization of the muscles during regeneration was concomitant with actin cytoskeletal reconstruction, as appeared after antitropomyosin labeling. Immunofluorescence findings were checked and (or) specified by immunogold staining.