Limb regeneration in the fiddler crab, Uca pugilator: Histological, physiological and molecular considerations

This paper summarizes our recent work on the histological, physiological an d molecular aspects of limb regeneration in the fiddler crab Uca pugilator and new information is presented on mitotic activity in the blastema during the first days of blastemal organization. We also report for the first tim e the localization of vertebrate growth factor immunoreactivitty (FGF 2 and FGF 4) in the regenerating blastema, In the first part of this paper we re view recent histological findings concerning the physical events that accom pany autotomy of limbs and propose a new function for the autotomy membrane -the tethering of the regenerating pedal nerve to the walls of the coxa. In the second part of the paper we review our recent findings on the identifi cation and characterization of the Uca ecdysteroid receptor (UpEcR, and its potential dimer partner, the retinoid-X-receptor, UpRXR), Using Uca-specif ic antibody probes raised in our lab, we have been able to identify specifi c cells in the early blastemal that express receptor proteins. The regenera ting limb of the fiddler crab is responsive to both steroids and retinoids and mRNA for steroid and retinoid receptors are expressed in the regenerati ng limb buds during all stages of regeneration, The DNA and deduced amino a cid sequences of the ecdysteroid receptor is very similar to the sequences of insect EcRs, while the retinoid receptor is similar to insect protein (u ltraspiracle) in the DNA-binding domain, but closer to vertebrate RXRs in t he ligand binding domain.