Ultrastructure of autotomy-induced atrophy of muscles in the crab Carcinus maenas

Abstract

In Carcinus maenas and other decapod crustaceans, limb autotomy results in pronounced atrophy of coxal and thoracic muscles located proximal to the fracture plane. These muscles were not denervated or otherwise injured by autotomy. The atrophic changes are reversed after the subsequent molt, when a regenerated limb becomes functional. In this study, we examined the ultrastructure of the coxal head of the anterior levator (ALc) muscle from the fifth pereiopod of intermolt crabs (control ALc) and from crabs bearing a limb bud (autotomized and contralateral ALc). Control muscles exhibit small regions of myofilament erosion that may be the result of normal turnover of structural elements. Characteristic features of autotomy-induced atrophy are (i) decrease in fiber area, (ii) increase in interfibrillar space, (iii) extensive myofilament erosion, (iv) loss of organelles, (v) disruption of sarcomere organization, and (vi) degeneration of neural and vascular tissues. Similar changes occur to a lesser degree in the contralateral ALc, where they may be characteristic of muscle in the premolt condition. We propose that the atrophic changes in muscles proximal to a limb bud are superimposed on generalized premolt catabolism of muscle protein, the rate of which is elevated in crabs regenerating limbs.