Changes in gelsolin expression during ascidian metamorphosis

Gelsolin is an actin regulatory protein that is expressed in a wide variety of tissues and is especially abundant in muscle and blood cells. The role of gelsolin during structural reorganization of the body, such as during me tamorphosis or regeneration, is poorly understood. We analyzed changes in g elsolin expression during ascidian embryogenesis and metamorphosis using nu cleic acid probes and a monoclonal antibody (AS23) specific for ascidian ge lsolin; our results indicated that gelsolin is maternally provided and that its de novo gene transcription is initiated during the neurula stage. In t he larva, gelsolin was detectable in specific types of nerve cells, i.e. th e adhesive papillae, motor neurons and epidermal sensory neurons. During me tamorphosis, the expression of gelsolin changes markedly: the expression is suppressed in nerve tissues after tail resorption but is induced in mesode rmal tissues. Gelsolin accumulated in mesenchyme cells until the onset of t ail resorption, and following tail resorption, these cells migrated to the tunic and differentiated into tunic cells with many fine processes. Migrati on of the mesenchyme cells into the tunic was completely inhibited by treat ment with cytochalasin B. Gelsolin was colocalized with actin in tunic cell s, suggesting that it is involved in the rearrangement of actin filaments d uring cell locomotion or morphogenesis.