A Novel Neuropeptide with Molt-inhibiting Activity from the Sinus Gland of the Crayfish, Procamharus clarkii

Localization and identification of crustacean hyperglycemic hormone producing neurosecretory cells in the eyestalk of blue swimmer crab, Portunus pelagicus

This study intensely focuses on to the localization and identification of crustacean hyperglycemic hormone (CHH) producing neurosecretory cells in the eyestalk of the blue swimmer crab Portunus pelagicus. Anti-Carcinus maenas-CHH was used to identify the location of CHH neurosecretory cells by immunohistochemistry. Ten pairs of eyestalks were collected from intact adult intermoult female crab and fixed in Bouin's fixative. Eyestalks were serially sectioned and stained with chrome-hematoxylin-phloxine stain. Histological studies show the presence of different types of neurosecretory cells namely A (multipolar), B (tripolar), C (bipolar), D (unipolar), E (oval), and F (spherical) in the medulla interna, externa, and terminalis regions based on their size, shape, and tinctorial properties. The neurohemal organ, sinus gland (SG) was observed laterally between medulla interna and terminalis regions. Immunohistochemical studies showed the presence of distinct CHH-like immunoreactivity in the optic ganglia. Divergent group of neurosecretory cells with varying degree of immunoreactivity with Anti-Carcinus maenas-CHH (low, moderate, and intense reactivity) were identified in medulla terminalis, medulla interna, medulla externa, and sinus gland. The present study maps the various types of neurosecretory cells in the optic ganglia and also shows the presence of CHH-like immunoreactivity in various regions of optic ganglia in P. pelagicus. The presence of these unique neurosecretory cell types with larger cell diameter in medulla terminalis, a region that bears the neurosecretory cell bodies, suggest high secretory activity.

Expression of crustacean (Callinectes sapidus) molt-inhibiting hormone in Escherichia coli: characterization of the recombinant peptide and assessment of its effects on cellular signaling pathways in Y-organs

A neuropeptide, molt-inhibiting hormone (MIH), negatively regulates the synthesis of ecdysteroid molting hormones by crustacean Y-organs. We report here the expression of blue crab (Callinectes sapidus) MIH in Escherichia coli. Bacteria were transformed with an expression plasmid containing a cDNA insert encoding MIH. After induction of protein synthesis, recombinant MIH (recMIH) was detected in the insoluble fraction of cell lysates. The insoluble recMIH was refolded and purified by reversed-phase high performance liquid chromatography (RP-HPLC). The refolded peptide was MIH-immunoreactive and comigrated with native MIH on RP-HPLC. Mass and CD spectral analyses showed the mass number and secondary structure of the recombinant peptide were as predicted for MIH. Bioassays showed recMIH dose-dependently suppresses ecdysteroid synthesis by Y-organs. The combined results suggest that recMIH is properly folded. In subsequent experiments, recMIH was used to assess cellular signaling pathways linked to MIH-mediated suppression of ecdysteroidogenesis. Incubation of Y-organs with recMIH produced an increase in intracellular cGMP content, but had no effect on intracellular cAMP. Further, a cGMP analog significantly suppressed ecdysteroid production, but neither cAMP analogs nor an activator of adenylyl cyclase had a detectable effect on ecdysteroidogenesis. The results are consistent with the hypothesis that MIH-induced suppression of ecdysteroidogenesis in Y-organs of C. sapidus is mediated by a cGMP second messenger. We anticipate recMIH will be a useful tool for additional studies of the cellular actions and physiological functions of MIH.

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.

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.

The eyestalk-androgenic gland-testis endocrine axis in the crayfish Cherax quadricarinatus

In decapod crustaceans, a number of neurohormones regulating a variety of physiological processes, including reproduction, are to be found in the X-organ-sinus gland complex of the eyestalk. Bilateral eyestalk ablation was thus performed in mature males of the Australian red claw crayfish Cherax quadricarinatus with the aim of studying the role of eyestalk-borne hormones on spermatogenic activity in the testis and on the androgenic gland (AG). The latter gland controls the differentiation and functioning of male sexual characteristics in crustaceans. Eyestalk ablation caused hypertrophy of the AG, as indicated by an increase in gland weight (3.9 +/- 0.44 mg vs < 0.1mg in intact males) and by overexpression of AG polypeptides. In the testes of eyestalk-ablated males, empty spermatogenic lobules were common, while lobules containing primary spermatocytes were infrequent. These findings were reflected in decreased amounts of DNA in these testes and a consequent increase in the relative weights of the sperm ducts. Since it was found that eyestalk ablation affected both the AG and the reproductive system, in vitro experiments were conducted to study the direct effects of the sinus gland on the AG and testes and of the AG on the testes. Sinus gland extracts inhibited by 30% the incorporation of radiolabeled amino acids into AG polypeptides and almost totally inhibited the secretion of radiolabeled AG polypeptides into the culture medium. However, sinus gland extracts had no significant effects on testicular tissue. On the other hand, AG extracts affected the in vitro phosphorylation of a testicular polypeptide (of 28 kDa), in a time- and dose-dependent manner, suggesting a direct effect of AG-borne hormones on the testes. The above findings, together with the evidence for direct inhibition by the sinus gland on the AG, suggest an endocrine axis-like relationship between the sinus gland, the AG, and the male reproductive system in decapod crustaceans.

Expression of crustacean (Callinectes sapidus) molt-inhibiting hormone in insect cells using recombinant baculovirus

Molt-inhibiting hormone (MIH) negatively regulates the synthesis of ecdysteroid molting hormones by crustacean Y-organs. We report here the expression of blue crab (Callinectes sapidus) MIH in insect cells using recombinant baculovirus. Insect Sf9 cells were transfected with recombinant baculovirus containing a DNA insert encoding the C. sapidus MIH prohormone (signal sequence plus mature hormone). The construct was designed to yield a mature, fully processed recombinant MIH (recMIH). Several baculovirus recombinants showing no contamination with wild-type viral DNA were subsequently analyzed for their ability to direct expression of recMIH. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of proteins from infected cells revealed time-dependent expression of two proteins of approximately the predicted size for the C. sapidus MIH prohormone and mature hormone. Western blot results (using antiserum against MIH of Carcinus maenas) indicated that the proteins were MIH-immunoreactive. N-Terminal amino acid sequence data and mass spectral analysis indicated the expressed proteins were of the correct sequence and molecular mass. Cell lysates containing the recombinant protein dose-dependently suppressed the synthesis of ecdysteroids by Y-organs in vitro. We anticipate the recombinant peptide will prove useful for studies of the structure and function of MIH.

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.

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.