Molt-cycle correlated patterns of synthesis of integumentary proteins in the land crab Gecarcinus lateralis

Molt cycle related changes and effect of short term starvation on the biochemical constituents of the blue swimmer crab Portunus pelagicus

Synthesis and hardening of a new exoskeleton are essential to the arthropod molting process. The present study emphasizes the variations in the levels of hemolymph total free sugars, hepatopancreas glycogen and cuticular proteins during the molting stages of Portunus pelagicus. It also reports the effect of short-term starvation conditions on the biochemical constituents of the hemolymph. Intermolt crabs were subjected to 6 days of starvation and hemolymph samples were taken. Standard biochemical procedures were followed toward the quantification of total proteins, total free sugars and total lipids. The total free sugar level in the hemolymph of P. pelagicus was observed to increase during early premolt D0 (3.108 ± 0.032 g/ml) and a gradual decrease till late postmolt B stage (0.552 ± 0.124 g/ml), suggesting the need for total free sugars to provide energy for the apolysis process. Increase in the levels of hepatopancreas glycogen was observed from 1225 ± 0.04 μg/mg in early premolt D0 to 1700 ± 0.3 μg/mg in late premolt D2-3. This is in correlation with the decreased levels of free sugars during premolt stages, suggesting an increase in the storage of glycogen reserves in the hepatopancreas. Cuticular proteins increased during stage B (2.702 ± 0.093 g/ml) and stage C (3.065 ± 0.012 g/ml), indicating exoskeleton hardening and mineralization. Results of the starvation studies clearly showed a steady decline in the level of total free sugars till day 6 (0.099 ± 0.00 g/ml) when compared to the control (8.646 ± 0.08 g/ml). Gradual decrease of total lipids was also observed from the first day of the experiment (6.088 ± 2.44 g/ml) to the last day of the study (0.401 ± 0.20 g/ml) which was 85% lesser than the control (8.450 ± 0.49 g/ml)suggesting the efficient usage of total sugars to consolidate the loss of energy reserves during starvation. The knowledge of Molt-cycle events can be used as a tool for the evaluation of the developmental state providing a morphological reference system for physiological and biochemical studies related to crab aquaculture. Starvation studies enlightens that increasing carbohydrate levels in crab feed together with good protein content could alleviate the natural effects of starvation, improve farm productivity and reduce the deleterious impact of nitrogen pollution generated by rich-protein feeds used in crab farming.

Hepatopancreatic multi-transcript expression patterns in the crayfish Cherax quadricarinatus during the moult cycle

Alterations of hepatopancreatic multi-transcript expression patterns, related to induced moult cycle, were identified in male Cherax quadricarinatus through cDNA microarray hybridizations of hepatopancreatic transcript populations. Moult was induced by X-organ sinus gland extirpation or by repeated injections of 20-hydroxyecdysone. Manipulated males were sacrificed at premoult or early postmoult, and a reference population was sacrificed at intermoult. Differentially expressed genes among the four combinations of two induction methods and two moult stages were identified. Biologically interesting clusters revealing concurrently changing transcript expressions across treatments were selected, characterized by a general shift of expression throughout premoult and early postmoult vs. intermoult, or by different premoult vs. postmoult expressions. A number of genes were differentially expressed in 20-hydroxyecdysone-injected crayfish vs. X-organ sinus gland extirpated males.

Search for hepatopancreatic ecdysteroid-responsive genes during the crayfish molt cycle: from a single gene to multigenicity

The expression of the vitellogenin gene of the red-claw crayfish Cherax quadricarinatus (CqVg) was previously demonstrated in male crayfish during an endocrinologically induced molt cycle. The hypothesis that this expression is under the direct control of ecdysteroids was tested in this study both in vivo and in vitro. Unlike vitellogenin of insects, CqVg was not found to be ecdysteroid-responsive. Thus, a multigenic approach was employed for the identification of other hepatopancreatic ecdysteroid-responsive genes by a cDNA microarray. For the purposes of this study, a multi-parametric molt-staging technique, based on X-ray detection of gastrolith growth, was developed. To identify ecdysteroid-responsive genes during premolt, the molt cycle was induced by two manipulations, 20-hydroxyecdysone administration and X-organ–sinus gland complex removal; both resulted in significant elevation of ecdysteroids. Two clusters of affected genes (129 and 122 genes, respectively) were revealed by the microarray. It is suggested that only genes belonging to similarly responsive (up- or downregulated) gene clusters in both manipulations (102 genes) could be considered putative ecdysteroid-responsive genes. Some of these ecdysteroid-responsive genes showed homology to genes controlling chitin metabolism, proteases and other cellular activities, while 56.8% were unknown. The majority of the genes were downregulated, presumably by an energetic shift of the hepatopancreas prior to ecdysis. The effect of 20-hydroxyecdysone on representative genes from this group was confirmed in vitro using a hepatopancreas tissue culture. This approach for ecdysteroid-responsive gene identification could also be implemented in other tissues for the elucidation of ecdysteroid-specific signaling pathways during the crustacean molt cycle.

Immunocytochemical localization of actin and tubulin in the integument of land crab (Gecarcinus lateralis) and lobster (Homarus americanus)

The crustacean integument consists of the exoskeleton and underlying epithelium and associated tissues. The epithelium, which is composed of a single layer of cells, is responsible for the cyclical breakdown and synthesis of the exoskeleton associated with molting (ecdysis). During premolt (proecdysis) the epithelial cells lengthen and secrete the two outermost layers (epicuticle and exocuticle) of the new exoskeleton while partially degrading the two innermost layers (endocuticle and membranous layer) of the overlying old exoskeleton. This increased cellular activity is associated with increased protein synthesis and a change in cell shape from cuboidal to columnar. The cytoskeleton, composed of microfilaments (actin) and microtubules (tubulin), plays important roles in the intracellular organization and motility of eukaryotic cells. Immunoblot analysis shows that the land crab exoskeleton contains actin, tubulin, and actin-related proteins (Varadaraj et al. 1996. Gene 171:177-184). In the present study, immunocytochemistry of land crab and lobster integument showed that both proteins were localized in various cell types, including epithelia, connective tissue, tendinal cells, and blood vessels. Muscle immunostained for actin and myosin, but not for tubulin. The membranous layer of land crab (the other layers of the exoskeleton were not examined) and membranous layer and endocuticle of lobster also reacted specifically with anti-beta-actin and anti-alpha-tubulin monoclonal antibodies, but not with an anti-myosin heavy chain antibody. During proecdysis immunolabeling of the membranous layer decreased probably due to protein degradation. The staining intensity for actin and tubulin in the proecdysial epithelium was similar to that in the intermolt (anecdysial) epithelium, suggesting that there was a net accumulation of both proteins proportional to the increase in cellular volume. These results support the previous biochemical analyses and, more specifically, localize actin and tubulin in exoskeletal structures, suggesting that they may serve both intracellular and extracellular functions in crustaceans. J. Exp. Zool. 286:329-342, 2000.

Ultrastructural Effects of a Non-Steroidal Ecdysone Agonist, RH-5992, on the Sixth Instar Larva of the Spruce Budworm, Choristoneura fumiferana

Force feeding of RH-5992 (Tebufenozide), a non-steroidal ecdysone agonist to newly moulted sixth instar larvae of the spruce budworm, Choristoneura fumiferana, (Lepidoptera: Tortricidae) initiates a precocious, incomplete moult. Within 6h post treatment (pt) the larva stops feeding and remains quiescent. Around 12hpt, the head capsule slips partially revealing an untanned new head capsule that appears wrinkled and poorly formed. By 24hrpt, the head capsule slippage is pronounced and there is a mid-dorsal split of the old cuticle in the thoracic region but there is no ecdysis. The larva remains moribund in this state and ultimately dies of starvation and desiccation. The temporal sequence of the external and internal changes of the integument were studied using both scanning and transmission electron microscopy. Within 3hpt, there is hypertrophy of the Golgi complex indicating synthetic activity and soon after, large, putative ecdysial droplets are seen. Within 24h, a new cuticle that lacks the endocuticular lamellae is formed. The formation of the various cuticular components, the degradation of the old cuticle and changes in the organelles of the epidermal cells of the mesothoracic tergite are described. The difference between the natural moult and the one induced by RH-5992 are explained on the basis of molecular events that take place during the moulting cycle. The persistence of this ecdysone agonist in the tissues permits the expression of all the genes that are up-regulated by the presence of the natural hormone but those that are turned on in the absence of the hormone are not expressed.

Actin-encoding cDNAs and gene expression during the intermolt cycle of the Bermuda land crab Gecarcinus lateralis

Two actin-encoding cDNAs (act1 and act2) from Gecarcinus lateralis have been sequenced or partially sequenced and the corresponding proteins deduced. The act1 cDNA has a complete ORF; the act2 cDNA lacks most of the 5' end of the coding region. The nucleotide (nt) sequences of both clones are very similar to act sequences of many organisms, the most closely related being from another arthropod, the silkmoth Bombyx mori. The proteins Act1 and Act2 are more similar to vertebrate cytoplasmic actin isoforms (beta-actins) than to vertebrate muscle actins (alpha-actins); they are also more similar to animal actins than to those of fungi or plants. Codon usage is strongly biased toward C or G in the third position. The deduced number of amino acid (aa) residues and calculated Mr for Act1 are 376 aa and 41.94 kDa, respectively. The deduced aa sequence of Act1 is very similar to those of muscle actins of B. mori and Drosophila melanogaster. Southern blots indicated seven to eleven act genes in the crab genome. Northern blots probed with a segment from the 3' UTR of act1 showed a single band of approx. 1.6 kb in poly(A)+ mRNAs from epidermis, limb bud or claw muscle and in total RNAs from ovary and gill, and two bands of approx. 1.6 and 1.8 kb in total RNA from midgut gland. Western blots of one-dimensional gels of proteins from the four layers of the exoskeleton, epidermis, limb buds and claw muscle were probed with a monoclonal Ab against chicken gizzard actin; tissue- and stage-specific changes in actin content were observed. The presence of several isoforms, and differences in their number and occurrence at various stages of the intermolt cycle, were detected on Western blots of two-dimensional gels.

Amino acid sequence determination of a protein purified from the shell of the shrimp, Pandalus borealis

One of the urea-extractable proteins in the shell of the shrimp Pandalus borealis has been purified, and the complete amino acid sequence has been determined by the combined use of mass spectrometry and Edman degradation of the intact protein as well as of enzymatically derived peptides. Characteristic features of the sequence are discussed and compared to sequences from insect cuticular proteins and other structural proteins.

Cuticular proteins from the shrimp, Pandalus borealis

1. The percentages of mineral salts, chitin, and urea-extractable and non-extractable proteins were determined in pieces of cuticle from selected body regions of the shrimp, Pandalus borealis. 2. Two-dimensional gel-electrophoresis of the urea-extractable proteins shows that a large number of different proteins are present. Identical protein patterns are obtained from the various cuticular regions. 3. A fractionation scheme is presented, which is suitable for obtaining the major proteins in quantities sufficient for further characterization. The amino acid compositions are reported for several of the proteins.

A monoclonal antibody against an adult-specific cuticular protein of Tenebrio molitor (Insecta, Coleoptera)

To study the sequential expression of the epidermal program in the mealworm Tenebrio molitor, monoclonal antibodies were prepared against the water-soluble proteins from preecdysial adult cuticle. Among the 16 clones obtained, one of them (named K2F6) recognized a 20-kDa antigen, found only in adult extracts but not in the larval or pupal ones, as revealed by immunoblot analysis. Our results strongly suggest an epidermal origin for this protein. The monoclonal antibody K2F6 fails to react with water-soluble proteins from fat body and hemolymph taken during the deposition of the 20-kDa antigen. Electron microscopic immunogold localization of this antigen showed that it is secreted, just after epicuticle deposition, in the 30 first-deposited preecdysial lamellae of sternal and elytral cuticles only. The sclerotizing process, which modifies the physicochemical properties of these cuticles, does not prevent the immunoreaction. When the expression of the adult program was inhibited by application of a juvenile hormone analog (ZR 515), the water-soluble proteins from different pupal-adult intermediates were never recognized by the monoclonal antibody K2F6 using immunoblot analysis. These results support the conclusion that this 20-kDa antigen is a protein specific for the sclerotized cuticle of the adult stage.