In vitro secretion of ecdysteroids by Y-organs of the crayfish,Procambarus clarkii

Characterization of Shed genes encoding ecdysone 20-monooxygenase (CYP314A1) in the Y-organ of the blackback land crab, Gecarcinus lateralis

Molting in decapod crustaceans is controlled by ecdysteroid hormones synthesized and secreted by the molting gland, or Y-organ (YO). Halloween genes encode cytochrome P450 enzymes in the ecdysteroid synthetic pathway. The current paradigm is that YOs secrete an inactive precursor (e.g., ecdysone or E), which is hydroxylated at the #20 carbon to form an active hormone (20-hydroxyecdysone or 20E) by a mitochonrial 20-monooxygenase (CYP314A1) in peripheral tissues. 20-Monooxygenase is encoded by Shed in decapods and Shade in insects. We used eastern spiny lobster Shed sequences to extract six orthologs in the G. lateralis YO transcriptome. Phylogenetic analysis of the deduced amino acid sequences from six decapod species organized the Sheds into seven classes (Sheds 1-7), resulting in the assignment of the G. lateralis Sheds to Gl-Shed1, 2, 4A, 4B, 5A, and 5B. The mRNA levels of the six Gl-Sheds in the YO of intermolt animals were comparable to those in nine other tissues that included hepatopancreas and muscle. qPCR was used to compare the effects of molt induction by multiple leg autotomy (MLA) and eyestalk ablation (ESA) on Gl-Shed mRNA levels in the YO. Molt stage had little effect on Gl-Shed1 and Gl-Shed5B expression in the YO of MLA animals. Gl-Shed5A was expressed at the highest mRNA levels in the YO and was significantly increased during early and mid premolt stages. By contrast, ESA ± SB431542 had no effect on Gl-Shed expression at 1, 3, 5, and 7 days post-ESA. SB431542, which inhibits Transforming Growth Factor-β/activin signaling and blocks YO commitment, decreased Gl-Shed2 and Gl-Shed4A mRNA levels at 14 days post-ESA. A targeted metabolomic analysis showed that YOs cultured in vitro secreted E and 20E to the medium. These data suggest that the YO expresses 20-monooygenases that can convert E to 20E, which may contribute to the increase in active hormone in the hemolymph during premolt.

Identification of ecdysteroid receptor-mediated signaling pathways in the hepatopancreas of the red swamp crayfish, Procambarus clarkii

The hepatopancreas of crustaceans plays an important role in lipid and carbohydrate metabolism, digestion of food, and biogenesis. In this study, the hepatopancreas transcriptome from the red crayfish Procambarus clarkii was characterized for the first time using high-throughput sequencing, producing approximately 41.4 million reads were obtained. After de novo assembly, 57,363 unigenes with an average length of 725bp were identified, Gene Ontology analysis categorized 22,580 as being involved in biological processes, among which metabolic process and cellular process groups were the most highly enriched. A total of 8034 unigenes were assigned to 223 metabolic pathways following mapping against the Kyoto encyclopedia of genes and genomes (KEGG) database. Ecdysteroid receptor (EcR)-mediated signaling pathways were investigated using digital gene expression (DGE) analysis following RNA interference targeting the EcR. A total of 529 differentially expressed genes (DEGs) were identified, including 322 downregulated and 207 upregulated unigenes. Of these, 445 (84.12%) were annotated successfully by alignment with known sequences, many of which were related to catalytic activity and binding functional categories. Using KEGG enrichment analysis, 183 DEGs were clustered into 78 pathways, and six significantly enriched pathways were predicted. The expression patterns of candidate genes identified by real-time PCR were consistent with the DGE results.

A Role of Suppressor of Cytokine Signaling 2 in the Regulation of Ecdysteroid Signaling Pathway in Procambarus clarkii

A suppressor of cytokine signaling 2 (SOCS-2) homolog was identified from the red crayfish Procambarus clarkii. Phylogenic analysis showed that P. clarkii SOCS-2 (Pc-SOCS-2) was very similar to that of invertebrates. The sequence contains a central SH2 domain, a conserved SOCS box, and a variable N-terminal domain. Real-time polymerase chain reaction showed that Pc-SOCS-2 mRNA level was higher in muscle and heart than in the other tissues examined. A 40-kDa recombinant protein was successfully expressed and purified from Escherichia coli cells as confirmed by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and Western blotting. Pc-SOCS-2 was significantly downregulated in the hepatopancreas after 20-hydroxyecdysone injection. Knockdown of Pc-SOCS-2 gene by small interfering RNA transfection in the hepatopancreas increased the expression levels of 20-hydroxyecdysone-responsive genes at 48 hr. Taken together, these results suggest that Pc-SOCS-2 is a negative regulator of ecdysteroid signaling transduction.

Light and electron microscopic studies on the Y organ of the freshwater crab Travancoriana schirnerae

The fine structure of the premoult Y organ in the freshwater crab Travancoriana schirnerae revealed elliptical epithelial gland cells with large, eccentric, multinucleolated nuclei and ample cytoplasm. The cytoplasm showed numerous polymorphic mitochondria with tubular cristae, highly anastomosed tubules and vesicles of smooth endoplasmic reticulum (SER), rich free ribosomes, small amounts of cisternae of rough endoplasmic reticulum (RER), microtubules and was devoid of Golgi complexes. Mitochondria were of two types the more abundant micromitochondria with electron dense matrix and the less abundant macromitochondria with moderately dense matrix. The tubular SER was particularly concentrated towards the basal region of the cell, intermingled with mitochondria and dense patches of free ribosomes while the vesicular SER lie close to the lateral plasma membrane. Large vesicles with flocculent substances, a few electron dense granules and multivesicular bodies could also be noticed in the gland cell cytoplasm. Aggregations of microvesicles which appeared close to the lateral plasma membrane, in association with dilated SER cisternae and microtubules, possibly suggest the intercellular exchange of substances. The plasma membrane beneath the basal lamina was composed of invaginations and the apical surface possessed numerous microvilli which serve to increase the surface area for metabolic exchange. Towards the apical region, the lateral plasma membrane of adjacent cells was linked by tight junctions. The presence of extraordinarily abundant tubular SER, high proportion of mitochondria with tubular cristae and rich free ribosomes could well be elucidated in favour of steroid production by the gland cells.

Ecdysteroid metabolism in crustaceans

The molting gland, or Y-organ (YO), is the primary site for ecdysteroid synthesis in decapod crustaceans. Ecdysteroid biosynthesis is divided into two stages: (1) conversion of cholesterol to 5β-diketol and (2) conversion of 5β-diketol to secreted products. Stage 1 involves the conversion of cholesterol to 7-dehydrocholesterol (7DC) by 7,8-dehydrogenase, the "Black Box" reactions involving 3-oxo-Δ(4) intermediates, and the conversion of Δ(4)-diketol to 5β-diketol by 5β[H]-reductase. The stage 2 reactions generate four major products, depending on species: ecdysone, 3-dehydroecdysone (3DE), 25-deoxyecdysone (25dE), and 3-dehydro-25-deoxyecdysone (3D25dE). Peripheral tissues convert these compounds to the active hormones 20-hydroxyecdysone (20E) and ponasterone A (25-deoxy-20-hydroxyecdysone or 25d20E). The hydroxylations at C25, C22, C2, and C20 are catalyzed by cytochrome P-450 mono-oxygenases, which are encoded by the Halloween genes Phantom, Disembodied, Shadow, and Shade, respectively, in insects. Orthologs of these genes are present in the Daphnia genome and a cDNA encoding Phantom has been cloned from prawn. Inactivation involves conversion of ecdysteroids to polar metabolites and/or conjugates, which are eliminated in the urine and feces. The antennal gland is the major route for excretion of ecdysteroids synthesized by the YO. The hepatopancreas eliminates ingested ecdysteroids by forming apolar conjugates. The concentrations of ecdysteroids vary over the molt cycle and are determined by the combined effects biosynthesis, metabolism, and excretion.

Molt-inhibiting hormone from Chinese mitten crab (Eriocheir sinensis): Cloning, tissue expression and effects of recombinant peptide on ecdysteroid secretion of YOs

Molt-inhibiting hormone (MIH), a member of the crustacean hyperglycemic hormone (CHH) family, inhibits the synthesis of ecdysteroid in Y-organ (YO) and plays a significant role in the regulation of molting and growth of crustaceans. A complete cDNA sequence encoding MIH (Ers-MIH, GenBank Accession No.: DQ341280) was cloned from eyestalk of Chinese mitten crab (Eriocheir sinensis) by 5' and 3' RACEs and PCR cloning. The full-length cDNA consists of 1457 bp with a 330 bp open reading frame, encoding 110 amino acids, containing a 75 amino acid mature peptide. The deduced amino acid sequence contains a typical CHH domain. Transcripts of Ers-MIH mRNA were detected in eyestalk by Northern blotting. The production of purified recombinant Ers-MIH (rErs-MIH) expressed in Escherichia coli was 0.3g/L. The LC-ESI-MS analysis showed that two peptide fragments of the recombinant protein were identical to the deduced amino acid sequence of Ers-MIH. By in vitro assay on E. sinensis YOs, a cGMP mediated suppression of rErs-MIH on ecdysteroidogenesis could be observed. Accumulation of cGMP in YOs showed a concentration-dependent manner within 0.01-1 nmol/mL of rErs-MIH; ecdysteroid secretion was inhibited significantly at the range of 0.01-100 nmol/mL rErs-MIH; furthermore, a significant inhibition effect on ecdysteroid releasing was shown when cGMP analog (8-Br-cGMP) concentration rose up to 100 nmol/mL. This study would facilitate to investigate the roles of MIH in molt cycle regulation.

The effects of farnesoic acid and 20-hydroxyecdysone on vitellogenin gene expression in the lobster, Homarus americanus, and possible roles in the reproductive process

Reproduction in female lobster (Homarus americanus) is characterized by the maturation of the ovary, with a gradual increase in its size as a result of uptake of yolk protein precursor, vitellogenin (Vg) to the final product vitellin (Vn). Vn is formed by aggregation of several Vg subunits. In most decapods, the hepatopancreas is the major site of vitellogenin biosynthesis. The production of vitellogenin is controlled by endocrine factors. In this study, the effect of farnesoic acid (FA) and 20-hydroxyecdysone (20E) on production of vitellogenin by hepatopancreas (HaVg1) was investigated by in vitro organ explant HaVg1 gene expression was stimulated by FA or 20E in a dose-dependent manner. A 2-fold and 2.2-fold increase in HaVg1 gene expression was observed with 4.2 microM FA and 0.7 microM 20E, respectively. The stimulatory effect by either FA or 20E was observed principally during the first 90 min. Stimulation of HaVg1 gene expression by FA and 20E together is greater (3.3-fold increase) than that of either hormone alone. This stimulation was also observed within the first 90 min. To study the synergistic effect of these two hormones, FA and 20E were tested separately and together at low concentration (42.3 nM and 6.7 nM, respectively). Combined use of FA and 20E increased HaVg1 gene expression synergistically, but not additively. These findings should contribute to our understanding of lobster reproduction and provide insights into manipulation of lobster reproduction in aquaculture or under captive conditions.

Purification, kinetic characterization, and molecular cloning of a novel enzyme, ecdysteroid 22-kinase

This is the first report succeeding in the isolation and characterization of an enzyme and its gene involved in the phosphorylation of a steroid hormone. It has been demonstrated that ecdysteroid 22-phosphates in insect ovaries, which are physiologically inactive, serve as a "reservoir" that supplies active free ecdysteroids during early embryonic development and that their dephosphorylation is catalyzed by a specific enzyme, ecdysteroid-phosphate phosphatase (Yamada, R., and Sonobe, H. (2003), J. Biol. Chem. 278, 26365-26373). In this study, ecdysteroid 22-kinase (EcKinase) was purified from the cytosol of the silkworm Bombyx mori ovaries to about 1,800-fold homogeneity in six steps of column chromatography and biochemically characterized. Results obtained indicated that the reciprocal conversion of free ecdysteroids and ecdysteroid 22-phosphates by two enzymes, EcKinase and ecdysteroid-phosphate phosphatase, plays an important role in ecdysteroid economy of the ovary-egg system of B. mori. On the basis of the partial amino acid sequence obtained from purified EcKinase, the nucleotide sequence of the cDNA encoding EcKinase was determined. The full-length cDNA of EcKinase was composed of 1,850 bp with an open reading frame encoding a protein of 386 amino acid residues. The cloned cDNA was confirmed to encode the functional EcKinase using the transformant harboring the open reading frame of EcKinase. A data base search showed that EcKinase has an amino acid sequence characteristic of phosphotransferases, in that it harbors Brenner's motif and putative ATP binding sites, but there are no functional proteins that share high identity with the amino acid sequence of EcKinase.

Molt-inhibiting hormone-mediated regulation of ecdysteroid synthesis in Y-organs of the crayfish (Procambarus clarkii): involvement of cyclic GMP and cyclic nucleotide phosphodiesterase

Crustacean molt-inhibiting hormone (MIH), a polypeptide secreted by the X-organ/sinus gland complex of the eyestalks, regulates molting by inhibiting the synthesis of ecdysteroids by Y-organs. Previous results indicate the biosynthetic activity of Y-organs is likely controlled not only by the level of hemolymphatic MIH, but also by the responsiveness of Y-organs to MIH. The present studies were conducted to (a) identify the second messenger that mediates MIH-induced suppression of ecdysteroidogenesis, and (b) assess the possible involvement of cyclic nucleotide phosphodiesterase (PDE) in determining the responsiveness of Y-organs to MIH. Adding 8-bromo cAMP or 8-bromo cGMP to incubation medium significantly suppressed ecdysteroid production by Y-organs of the crayfish (Procambarus clarkii). Incubating Y-organs with MIH produced a significant increase in glandular cGMP, but MIH had no effect on glandular cAMP. The composite data indicate that MIH-induced suppression of ecdysteroidogenesis in Y-organs of P. clarkii is mediated by cGMP. Subsequently, Y-organs from various stages of the molt cycle were incubated with MIH, 3-isobutyl-1-methylxanthine (IBMX, an inhibitor of PDE), or both. Y-Organs from middle and late premolt stages were poorly responsive to MIH alone. Including IBMX in the incubation medium enhanced the responsiveness of the Y-organs to MIH at these stages. Moreover, glandular PDE activity in the Y-organs at these stages was significantly higher than other stages. The combined results suggest that molt cycle-associated changes in PDE activity affect the ability of MIH to stimulate cGMP accumulation and suppress ecdysteroidogenesis in Y-organs of P. clarkii.

Cloning and characterization of a molt-inhibiting hormone-like peptide from the prawn Marsupenaeus japonicus

Recently, it was demonstrated by PCR amplification that an additional molt-inhibiting hormone (MIH)-like peptide was present in the kuruma prawn Marsupenaeus japonicus. In this study, a cDNA encoding this peptide designated Pej-MIH-B was cloned. The Pej-MIH-B gene was expressed strongly in the nerve cord, and weakly in the eyestalk. It was possible to isolate Pej-MIH-B from the sinus glands in the eyestalks. The recombinant Pej-MIH-B expressed in Escherichia coli showed low molt-inhibiting activity, but did not exhibit hyperglycemic activity. These results suggest that Pej-MIH-B does not function as MIH or CHH intrinsically, but may have some unknown functions.

Release of Ecdysteroid-Phosphates from Egg Yolk Granules and Their Dephosphorylation during Early Embryonic Development in Silkworm, Bombyx mori

Newly laid eggs of many insect species store maternal ecdysteroids as physiologically inactive phosphoric esters. In the silkworm Bombyx mori, we previously reported the presence of a specific enzyme, called ecdysteroid-phosphate phosphatase (EPPase), which catalyzes the dephosphorylation of ecdysteroid-phosphates to increase the amount of free ecdysteroids during early embryonic development. In this study, we demonstrated that (1) EPPase is found in the cytosol of yolk cells, (2) ecdysteroid-phosphates are localized in yolk granules, being bound to the yolk protein vitellin (Vn), and (3) Vn-bound ecdysteroid-phosphates are scarcely hydrolyzed by EPPase, although free ecdysteroid-phosphates are completely hydrolyzed by EPPase. Thus, we investigated the mechanism by which ecdysteroid-phosphates dissociate from the Vn-ecdysteroid-phosphate complex, and indicated that the acidification of yolk granules causes the dissociation of ecdysteroid-phosphates from the Vn-ecdysteroid-phosphate complex and thereby ecdysteroid-phosphates are released from yolk granules into the cytosol. Indeed, the presence of vacuolar-type proton-translocating ATPase in the membrane fraction of yolk granules was also verified by Western blot analysis. Our experiments revealed that Vn functions as a reservoir of maternal ovarian ecdysteroid-phosphates as well as a nutritional source during embryonic development. This is the first report showing the biochemical mechanism by which maternal Vn-bound ecdysteroid-phosphates function during early embryonic development.

Regulation of ecdysteroid secretion from the Y-organ by molt-inhibiting hormone in the American crayfish, Procambarus clarkii

In crustaceans, molt-inhibiting hormone (MIH) has been proposed to regulate molting by inhibiting the secretion of ecdysteroids from the Y-organ. Thus, MIH titer in the hemolymph should be inversely related to ecdysteroid titers during the molt cycle. However, it has not been demonstrated whether the MIH titer in the hemolymph changes during the molt cycle. The purpose of this study was to determine the changes in the MIH titers in the hemolymph during the molt cycle of the American crayfish, Procambarus clarkii, and to discuss the role of MIH in regulation of molting. As predicted by the hypothesis, the hemolymph MIH titer was high at the intermolt stage when the hemolymph ecdysteroid titer was low, and the MIH titer decreased to a basal level at the early premolt stage when the hemolymph ecdysteroid titer began to increase slightly. At the middle premolt stage when the hemolymph ecdysteroid titer increased, the MIH titer was restored to a level as high as that during the intermolt stage. This is in contradiction to the hypothesis. However, the Y-organs at this stage scarcely responded to MIH both in vitro and in vivo. The present findings suggest that ecdysteroid secretion from the Y-organ may be regulated not only by changes in the hemolymph MIH titer, but also by changes in the responsiveness of the Y-organ to MIH.

Purification, kinetic characterization, and molecular cloning of a novel enzyme ecdysteroid-phosphate phosphatase

From eggs of the silkworm Bombyx mori, we isolated a novel enzyme that is involved in the conversion of physiologically inactive conjugated ecdysteroids, such as ecdysone 22-phosphate and 20-hydroxyecdysone 22-phosphate, to active free ecdysteroids. This enzyme, called ecdysteroid-phosphate phosphatase (EPPase), was located in the cytosol fraction and differed from nonspecific lysosomal acid phosphatases in various enzymic properties. EPPase was purified about 3,000-fold to homogeneity by seven steps of column chromatography. The cDNA clone encoding EPPase was isolated by reverse transcription polymerase chain reaction using degenerate primers on the basis of the partial amino acid sequence obtained from purified EPPase and by subsequent 3'- and 5'-rapid amplification of cDNA ends. The full-length cDNA of EPPase was found to be composed of 1620 bp with an open reading frame encoding a protein of 331 amino acid residues. A data base search showed that there was no functional protein with the amino acid sequence identical to that of EPPase. Northern blot analysis revealed that EPPase mRNA was expressed predominantly during gastrulation and organogenesis in nondiapause eggs but was not detected in diapause eggs whose development was arrested at the late gastrula stage. In nondiapause eggs, the developmental changes in the expression pattern of EPPase mRNA corresponded closely to changes in the enzyme activity and in the amounts of free ecdysteroids in eggs.

The molt-inhibiting hormone in the American crayfish Procambarus clarkii: its chemical synthesis and biological activity

The molt-inhibiting hormone of the American crayfish Procambarus clarkii (Prc-MIH), a 75-residue polypeptide containing three disulfide bridges, was synthesized by chemical ligation of two peptides, i.e., synthetic Prc-MIH(1-39) and Prc-MIH(40-75)-NH(2), and by subsequent folding to form the native disulfide-containing peptide molecule. The synthetic peptide was comparable to the natural Prc-MIH in inhibiting ecdysteroid secretion by in vitro bioassay and shared features with the natural Prc-MIH in some biochemical analyses. These results indicate that the chemical ligation method can be used for the synthesis of Prc-MIH. Furthermore, it was demonstrated that synthetic Prc-MIH has hyperglycemic activity, although the activity was weaker than that of the authentic crustacean hyperglycemic hormone in the American crayfish. To examine the structural requirement of the Prc-MIH for eliciting biological activity, an antibody raised against the C-terminal region (residues 55-75) and two synthetic peptides, i.e., a core region (residues 1-54) containing three disulfide bridges and the C-terminal region, were utilized. It is suggested that Prc-MIH exerts its activities through coordination between the core region and the C-terminal region.

Ecdysteroid hormones and metabolites of the stone crab, Menippe mercenaria

The Y-organs of the xanthid crab Menippe mercenaria secrete the ecdysteroids, 3-dehydroecdysone (3DE) and lesser amounts of 3-dehydro (or 2-dehydro)-25-deoxyecdysone (3D25dE) in vitro. These ecdysteroids were identified by elution-time comparisons with authentic standards, mass spectrography, and, for 3D25dE, infrared spectrometry. Tissues were incubated 18 hr with [(3)H]3DE. Activities representing 3beta-reductase and 20-hydroxylase generally were present, evidenced by finding in the tissue/medium extract labeled ecdysone (E) and 20-hydroxyecdysone (20E). Labeled 3-dehydro-20-hydroxyecdysone (3D20E) also appeared to be present. Tissue blanks and hemolymph were devoid of activity. Muscle was low, hypodermis was intermediate, and hindgut and gonads were high in activity of the enzymes. Consistent with the presence of these enzymes in peripheral tissues, ecdysteroid products identified in the hemolymph were 20E, 3D20E, and 25-deoxy-20-hydroxyecdysone (25d20E; ponasterone A). Structures of 20E and 3D20E were confirmed by co-elution with authentic standards in high-performance liquid chromatography (HPLC), co-elution of derivatives in gas chromatography, and mass spectroscopy. Ponasterone A (identified by HPLC co-elution with the standard), like 20E is present in the hemolymph in prominent amounts. These data indicate that Menippe, among crustaceans thus far studied, secretes a unique combination of ecdysteroid hormones, namely, a 3- (or 2-) oxo compound and a 25-deoxy compound. This represents a different kind of branch point from 5beta-diketol in ecdysteroid biosynthesis, in which the intermediate, 5beta-ketodiol is bypassed. A result is the joint appearance in the circulation of the hormones, 20E and ponasterone A, which in other species are singly prominent.

Expression of a recombinant molt-inhibiting hormone of the kuruma prawn Penaeus japonicus in Escherichia coli

The crustacean molt-inhibiting hormone (MIH) suppresses ecdysteroid synthesis by the Y-organ. The MIH of the kuruma prawn Penaeus japonicus has recently been isolated and its cDNA cloned. In this study, we expressed the MIH in Escherichia coli to obtain a large quantity of this hormone with biological activity. The MIH cDNA was processed and ligated into an expression plasmid. E. coli was transformed with this plasmid, and then the recombinant MIH (r-MIH) was expressed. The r-MIH was put through the refolding reaction and was purified by reverse-phase HPLC. N-terminal amino acid sequence and time-of-flight mass spectral analyses supported the idea that the r-MIH had the entire sequence. By in vitro bioassay using the Y-organ of the crayfish, the r-MIH was found to be comparable to natural MIH in inhibiting ecdysteroid synthesis.

2-Deoxyecdysone is a circulating ecdysteroid in the beetle Zophobas atratus

A qualitative analysis of ecdysteroids has been performed during the post-embryonic development of the tenebrionid beetle, Zophobas atratus, by high performance liquid chromatography (HPLC) combined with enzyme immunoassay (EIA) using two different antibodies. Three HPLC peaks were found to be immunoreactive, in hemolymph extracts of both sexes. Moreover, these peaks had ecdysteroid-like UV spectra, determined using a photodiode array detector. The use of two different HPLC systems (reverse and normal phases), in combination with two different EIA antibodies, allowed us to identify 20-hydroxyecdysone (20E) and ecdysone (E), as the two main ecdysteroids, but also suggested the presence of 2-deoxyecdysone (2dE) as the third hemolymph component. Secretion of putative 2dE, together with E (but not 20E) was also demonstrated in vitro from incubations of prothoracic glands and of tegumental explants. In these experiments, either in vivo or in vitro, 3-dehydroecdysone was never observed. Our observations thus strongly suggest that 2dE is a circulating ecdysteroid in Z. atratus and may function as a prohormone during the development of some insects.

Involvement of a 3beta-hydroxysteroid dehydrogenase activity in ecdysteroid biosynthesis

Ecdysteroid biosynthesis was analyzed in vitro using dissociated Y-organ cells from the shore crab Carcinus maenas. 3-Dehydroecdysone (3DE) was detected as a minor secretory product, in addition to the formerly identified end-products 25-deoxyecdysone and ecdysone (E). In conversion studies, 3DE was formed from tritiated 5beta-ketodiol (2,22,25-trideoxyecdysone), 2,22-deoxyecdysone and 2-deoxyecdysone but not from E. Further experiments were performed in order to understand the interconversions between 3-oxo and 3beta-OH compounds in the crab Y-organ. The enzyme involved in 3beta-dehydrogenation was not ecdysone oxidase, a soluble enzyme found in peripheral tissues of many arthropods but it presented strong similarities with 3beta-hydroxysteroid dehydrogenase enzymes from vertebrates: it was membrane-bound and NAD+-dependent. Moreover, a NADH-dependent 3beta-reduction of several 3-oxo-ecdysteroids was obtained using the same microsomal fraction (100,000 x g pellet) of Y-organs, indicating that the reaction might be reversible. As this activity was specific of molting glands, we hypothesize that there is at least one 3beta-hydroxysteroid dehydrogenase enzyme involved in the biosynthetic pathway of ecdysteroids.

Amino acid sequence of a peptide with molt-inhibiting activity from the kuruma prawn Penaeus japonicus

Six major peptides (Pej-SGP-I-VI) that belong to the CHH family have been isolated from the sinus gland extracts of the kuruma prawn Penaeus japonicus. By in vitro assay using the Y-organ of the crayfish Procambarus clarkii, Pej-SGP-IV was found to be active in inhibiting ecdysteroid synthesis. We determined the complete amino acid sequence. Pej-SGP-IV consists of 77 amino acid residues, with both free aimno- and carboxyl-termini. The sequence of Pej-SGP-IV shows considerable similarity to that of MIH of the shore crab Carcinus maenas and less similarity to Pej-SGP-III, whose sequence has been previously determined.

Formation of ecdysteroids by Y-organs of the crab, Menippe mercenaria. II. Incorporation of cholesterol into 7-dehydrocholesterol and secretion products in vitro

The conversion in vitro of cholesterol (Ch) to nonpolar metabolites and ecdysteroids was studied in Y-organs of the xanthid crab, Menippe mercenaria. In one set of experiments, Y-organs were prelabeled in vivo by injecting crabs with 100 microCi of [3H]Ch, and halved glands were then incubated for 24 and 48 hr in the presence of unlabeled Ch. In another set, unlabeled Y-organs were incubated in standard medium containing 10 microCi/ml of [3H]Ch. Both polar and nonpolar metabolites were surveyed by HPLC. The early metabolite, 7-dehydrocholesterol (7-dhCh), was the only labeled derivative of Ch detectable in Y-organ tissue after incubation; preincubation amounts of 7-dhCh were higher in glands from de-eyestalked crabs vs glands from intact crabs, and labeling was an order of magnitude higher in glands incubated with labeled Ch vs those prelabeled in vivo. Specific activity calculations indicate highly efficient conversion of 7-dhCh to ecdysteroid secretions. Analyses of the incubation media revealed two polar secretory products, synthesized from Ch in vitro. These coeluted with the authentic standards, 3-dehydroecdysone and 25-deoxyecdysone. Secretion of 3-dehydroecdysone always exceeded that of 25-deoxyecdysone (ratio range, 1.9 to 14.4), in both de-eyestalked and intact crabs.

Formation of ecdysteroids by Y-organs of the crab, Menippe mercenaria. I. Biosynthesis of 7-dehydrocholesterol in vivo

Y-organs of the xanthid crab, Menippe mercenaria, secrete ecdysteroid hormones in vitro, apparently both 3-dehydroecdysone and 25-deoxyecdysone. Studies were initiated on the biosynthetic path(s), in which cholesterol is converted to these ecdysteroids. Crabs were injected with [3H]cholesterol. Y-organs and hemolymph were removed 12 hr later and extracted directly and the extracts were analyzed by HPLC. Both polar and nonpolar sterols were surveyed. The only metabolite of cholesterol detectable in Y-organs was 7-dehydrocholesterol (identified by mass spectrometry). The total amount of 7-dehydrocholesterol and the amount that was labeled were generally greater than for cholesterol and were higher in Y-organs from de-eyestalked crabs than in those from intact crabs. Subcellular fractionation of the Y-organs showed that over 70% of total radioactivity was in cholesterol and 7-dehydrocholesterol of mitochondria and microsomes, distributed about equally between the two organellar fractions. In hemolymph, the only nonpolar sterols present were cholesterol and 7-dehydrocholesterol; the concentration ratio was 20:1. However, 7-dehydrocholesterol was not significantly labeled. Analyses of polar compounds revealed two prominent, uv-absorbing ecdysteroids which coeluted with the authentic standards, 3-dehydro-20-hydroxyecdysone and 25-deoxy-20-hydroxyecdysone (ponasterone A). The radioactivity profile showed, in addition, a third prominent peak that corresponded in retention time with 3-dehydroecdysone. These results indicate that the Y-organs in vivo form 7-dehydrocholesterol from cholesterol and convert the latter to secretion products without accumulation of other intermediates. At least two ecdysteroids are secreted and appear to be converted peripherally in this crab to their respective 20-hydroxy derivatives.