Limb Regeneration in the Fiddler Crab,Uca pugilator: Hormonal and Growth Factor Control

SYNOPSIS. This paper summarizes recent work on various aspects of hormonal control of regeneration in the crustacean, Uca pugilator. Hormonal control in this crab is effected by means of the crustactean steroid hormones, the ecdysteroids. New evidence is presented supporting a role for the retinoid hormones, all-trans retinoic acid and 9-cis retinoic acid, in the control of regeneration in these animals. The possible role of fibroblast growth factors in organization of the limb blastema is explored and the similarities between vertebrate and invertebrate control of regeneration are discussed. REGENERATION IN CRUSTACEANS The hard exoskeleton of crustaceans makes growth in these animals quite re- markable. In order to increase in size, these animals must periodically shed (called molt or ecdysis) their old exoskeleton, then ex- pand a new, soft, pliant exoskeleton that has been formed beneath the old one. The length of time from one molt to the next is called the intermolt cycle. The length of the cycle is variable and determined by time of year, nutritional status, and other factors in- cluding whether or not the animal is regen- erating a limb. Regeneration is a special type of growth