Characterization of EcR and RXR gene homologs and receptor expression during the molt cycle in the crab, Uca pugilator

Crustaceans have the remarkable ability to regenerate limbs. Unlike insects , crustaceans also continue to increase in body size with age, and new limb regeneration must occur in concert with the growth and reproductive activi ties of the adult. In the fiddler crab, Uca pugilator, regeneration consist s of the formation of a blastema (limb primordium) from cells migrating int o the site of the wound. Over a time course related to the physiology and g rowth cycle of the animal, these cells proliferate and differentiate into a n intact miniature limb, which will then increase in size and emerge as a f unctional appendage with the nest molting of the body exoskeleton In arthro pods, changes in gene expression mediating both growth (e.g., cuticular mol ting) and differentiation (e.g., insect metamorphosis) are regulated by ecd ysteroids. We hypothesize that ecdysteroids and their receptors are also in volved in the regulation of limb regeneration in crabs. To investigate this hypothesis, clones representing the crustacean ecdysteroid receptor have b een isolated and are providing the basis for the development of nucleic aci d and immunological probes to identify, at the tissue level, the pattern of receptor expression relative to changes in hormone titer during all stages of regeneration. In support of this hypothesis, we have detected the expre ssion of the nuclear receptor genes encoding the ecdysteroid receptor at th e earliest stages of blastemal development. We hare also shown that recepto r transcript synthesis can be influenced by external factors (retinoid expo sure) which disrupt Uca blastemal differentiation. These studies allow us t o identify and characterize putative ecdysteroid target tissues. They begin to address the goal of defining how a common signal (e.g, circulating horm ones) can influence a variety of discrete developmental programs.