Ecdysteroid binding sites in gastrolith forming tissue and stomach during the molting cycle of crayfish Procambarus clarkii

Reciprocal changes in calcification of the gastrolith and cuticle during the molt cycle of the red claw crayfish Cherax quadricarinatus

Mobilization of calcium during the molt cycle from the cuticle to transient calcium deposits is widely spread in crustaceans. The dynamics of calcium transport to transient calcium deposits called gastroliths and to the cuticle over the course of the molt cycle were studied in the crayfish Cherax quadricarinatus. In this species, calcium was deposited in the gastroliths during premolt and transported back to the cuticle during postmolt, shown by digital X-ray radiograph analysis. The predominant mineral in the crayfish is amorphous calcium carbonate embedded in an organic matrix composed mainly of chitin. Scanning electron micrographs of the cuticle during premolt showed that the endocuticle and parts of the exocuticle were the source of most of the labile calcium, while the epicuticle did not undergo degradation and remained mineralized throughout the molt cycle. The gastroliths are made of concentric layers of amorphous calcium carbonate intercalated between chitinous lamella. Measurements of pH and calcium levels during gastrolith deposition showed that calcium concentrations in the gastroliths, stomach, and muscle were about the same (10 to 11 mmol l(-1)). On the other hand, pH varied greatly, from 8.7+/-0.15 in the gastrolith cavity through 7.6+/-0.2 in muscle to 6.9+/-0.5 in the stomach.

Paradox of epithelial cell calcium homeostasis during vectorial transfer in crayfish kidney

The molting cycle of the freshwater crayfish, Procambarus clarkii, has been used as a model to study the cellular physiology and molecular biology of Ca "supply" proteins that effect transcellular vectorial Ca(2+) movement to achieve organismal Ca homeostasis. Specifically, periods of net Ca(2+) influx (postmolt) have been compared with periods of net Ca(2+) balance (intermolt). The broader goal is to understand the paradox facing epithelial cells of maintaining low cytosolic Ca(2+)in the face of mass Ca(2+)transit across epithelial cells. This mini-review compares mRNA and protein expression profiles for a series of proteins that are of strategic importance in effecting transcellular Ca(2+) flux in a selected epithelium, the antennal gland (kidney analog) specifically during apical to basolateral Ca(2+) conveyance. Target proteins were selected as representative of key "stages" in the transcellular transfer of Ca(2+): import (epithelial Ca(2+) channel, ECaC); storage (sarco/endoplasmic reticulum Ca(2+) ATPase, SERCA); buffering (sarcoplasmic Ca(2+) binding protein, SCP); and export (plasma membrane Ca(2+) ATPase, PMCA and Na(+)/Ca(2+) exchanger, NCX). The purpose of this review is to assess coordination of expression of these target proteins at times of high Ca(2+) demand (premolt and postmolt) compared to low Ca demand (intermolt) as a function of cellular location (apical vs. basolateral; endomembranes vs. plasma membranes) and relative abundance within different regions of the antennal gland. Understanding the spatiotemporal regulation of Ca(2+) handling proteins involved in transcellular transport is fundamental to investigating their endocrine regulation.

Non-genomic ecdysone effects and the invertebrate nuclear steroid hormone receptor EcR--new role for an "old" receptor?

The ecdysteroids (Ec), invertebrate steroid hormones, elicit genomic but also non-genomic effects. By analogy to vertebrates, non-genomic responses towards Ec may be mediated not only by distinct membrane-integrated but also by membrane-associated receptors like the classical nuclear ecdysteroid receptor (EcR) of arthropods. This is supported by a comparison of physiological properties between invertebrate and vertebrate steroid hormone systems and recent findings on the subcellular localization of EcR. The measured or predicted high degree of conformational flexibility of both Ec and the ligand binding domain (LBD) of EcR give rise to a conformational compatibility model: the compatibility between conformations of the cognate receptor's ligand binding domain and structures or conformations of the ligand would determine their interaction and eventually the initiation of genomic versus non-genomic pathways. This model could also explain why specific non-genomic effects are generally not observed with non-steroidal agonists of the bisacylhydrazine group.

Characterization and spatiotemporal expression of orchestin, a gene encoding an ecdysone-inducible protein from a crustacean organic matrix

We report the characterization of a new gene encoding an acidic protein named Orchestin. This protein is a component of the organic matrix of calcium storage structures (calcareous concretions) elaborated during the moulting cycles of the terrestrial crustacean Orchestia cavimana. The deduced molecular mass of Orchestin is estimated to be 12.4 kDa and the pI to be 4.4, whereas the native protein extracted from the calcium deposits migrates as a 23 kDa band on SDS/PAGE. This discrepancy is probably due to the richness of this protein in acidic amino acids (approx. 30%). The protein obtained by expressing the Orchestin cDNA in Escherichia coli presents an electrophoretic mobility of 25 kDa. Antibodies raised against the recombinant protein recognize the 23 kDa native protein exclusively among the organic-matrix components. Spatiotemporal analysis of the expression of the orchestin gene shows that it is expressed only in the storage organ cells when the concretions are elaborated during the premoult period and also, to a smaller extent, during the postmoult period. The translation products are expressed in accordance with the transcript expression during both the premoult and postmoult periods. Study of the hormonal stimulation of orchestin reveals that 20-hydroxyecdysone induces this gene as a secondary-response or late-response gene.