Tissue-Specific Patterns and Steady-State Concentrations of Ecdysteroid Receptor and Retinoid-X-Receptor mRNA during the Molt Cycle of the Fiddler Crab,Uca pugilator

Abstract

In the fiddler crab,Uca pugilator,we have investigated the temporal expression of receptors in various tissues using probes that encodeUcaecdysteroid receptor (UpEcR) and retinoid-X-receptor (UpRXR) gene homologs. During molt stages C4through D1–4,UpEcRandUpRXRtranscripts are expressed in regenerating limb buds, gills, eyestalks, hypodermis, hepatopancreas, muscle from nonregenerating walking legs, and the large cheliped. Some of these tissues have not previously been recognized as ecdysteroid-target tissues. Levels of ecdysteroids in the hemolymph fluctuate significantly during the molt cycle ofU. pugilator.The variation in steady-state concentrations ofUpEcRtranscripts in tissues from C4to D1–4implies molt cycle-related differences in the potential of these tissues to respond to changing titers of ecdysteroids in the hemolymph. In singly autotomized crabs, highest concentrations ofUpEcRtranscript in some tissues did not coincide with the highest levels of circulating ecdysteroids, suggesting thatUpEcRexpression in these tissues is not dependent on high ecdysteroid titers and may be induced by low or rising concentrations of ecdysteroids.UpEcRandUpRXRgenes were expressed simultaneously in tissues, supporting the possibility of heterodimerization for EcR and RXRin vivo.In some tissues, however, levels of transcripts differed, suggesting other possible receptor interactions. Moreover,UpEcRexpression in tissues from multiply autotomized crabs differed from the expression patterns in tissues from singly autotomized crabs.