THE MODULATION AND SPATIAL-DISTRIBUTION OF AN ANTI-ALPHA-SM-1 REACTIVE ACTIN DURING PLANARIAN WOUND REPAIR

An anti-alpha SM-1 reactive actin, specifically recognized by the anti -alpha SM-1 antibody directed against the N-terminal region of alpha-s mooth muscle (alpha SM) actin of endothermic vertebrates (Skalli et al ., 1986), is expressed in specific cytoplasmic domains of planarian ep idermal cells (ECs). In non-injured epidermis, the anti-alpha SM-1 rea ctive actin is mainly localized in the basal portion of ECs. Using the anti-total actin antibody a positive reaction is also observed close to microvilli, apical microfilaments and along septate junctions. Woun d repair in planaria begins immediately after injury by the movement o f a monolayered epidermal sheet across the wound surface to form the f irst protective covering. Migrating ECs undergo marked phenotypic chan ges including disappearance of hemidesmosomes and the formation of sho rt microfilament bundles, stained by the anti-alpha SM-1 antibody, and terminating at cell-matrix contacts. During wound repair precursors o f epidermal cells (PECs), migrating from the parenchyma to recruit the wound epidermis, express the anti-alpha SM-1 reactive actin molecule associated with stress fiber-like structures. These structures, which are strongly labelled by the anti-alpha SM-1 antibody, undergo a spati al and temporal rearrangement during EC differentiation The modulation of anti-alpha SM-1 reactive actin during wound repair suggests its in volvement in EC migration and differentiation.