Muscle regeneration in holothurians.

The muscle system of holothurians includes visceral (coelomic epithelium) and somatic (longitudinal muscle bands, retractors of aquapharyngeal complex) musculature. Visceral musculature regeneration is achieved by the transformation of myoepithelial cells via their dedifferentiation, migration, proliferation, and redifferentiation. During somatic muscle regeneration the new muscle bundles are formed due to dedifferentiation, migration, and immersion of the coelomic epithelial cells into the connective tissue. While submerging, the epithelial cells transform into myocytes and begin to produce myofibrils in their cytoplasm. Concomitantly, a basal lamina is formed around the group of myogenic cells, separating them from the surrounding extracellular matrix. The myohistogenesis is accompanied by a conspicuous DNA-synthetic activity. Proliferation is insignificant and seems to be of no essential importance for muscle regeneration. The synthesis of DNA followed by no cytokinesis results in an increase in the amount of DNA of myocyte nuclei. Copyright 2001 Wiley-Liss, Inc.