Amino acid sequences and activities of multiple hyperglycemic hormones from the Kuruma prawn, Penaeus japonicus

Serotonergic regulation of crustacean hyperglycemic hormone secretion in the crayfish, Procambarus clarkii

These studies investigate if crustacean hyperglycemic hormone (CHH) is involved in 5-hydroxytryptamine (5-HT)-induced hyperglycemia. Eyestalk ganglia with intact X-organ-sinus gland complex were dissected from the crayfish Procambarus clarkii and incubated under various experimental conditions. Incubation media were then analyzed for the presence of released hyperglycemic factor using an in vivo bioassay. The results show that 5-HT enhanced release of hyperglycemic factor in a dose-dependent manner. This stimulatory effect of 5-HT was significantly decreased by adding ketanserin or methysergide (both 5-HT receptor antagonists) into incubation of eyestalk ganglia. Further, activity of the 5-HT-released hyperglycemic factor could be eliminated by adsorption of incubation media with anti-CHH serum but not by preimmune or anti-5-HT serum. These results confirm the hypothesis that 5-HT enhances release of CHH, which in turn elicits hyperglycemic responses. It is probable that 5-HT activates an excitation-secretion coupling mechanism by interacting with receptors located on the X-organ neurosecretory cells.

Involvement of crustacean hyperglycemic hormone in the control of gill ion transport in the crab Pachygrapsus marmoratus

Total extracts of sinus glands (SG) of the euryhaline grapsid crab Pachygrapsus marmoratus contain peptidic factor(s) that stimulate osmoregulatory processes in isolated and perfused posterior gills from crabs acclimated to dilute seawater. This study investigated the nature of the active factor(s). Separation of P. marmoratus SG peptides by reverse-phase HPLC, followed by a direct enzyme-linked immunosorbent assay using an anti-Carcinus maenas crustacean hyperglycemic hormone (CHH) antiserum, identified a major immunoreactive chromatographic peak. A glucose quantification bioassay demonstrated a strong and specific hyperglycemic activity following injection of the immunoreactive peak, therefore defined as the CHH of P. marmoratus. Isolated posterior gills were then perfused with HPLC fractions using a dose of 4 SG equivalents/assay. The CHH fraction consistently and significantly increased the transepithelial potential difference and Na(+) influx by about 50%. The effect was rapid and reversible. Another substance of unknown nature (eluted earlier than CHH in the HPLC gradient) caused a small increase in Na(+) influx (14%) but had no effect on the transepithelial potential difference. No other peptidic product from the SG had significant effect on the measured osmoregulatory parameters. These results indicate that CHH, in addition to its hyperglycemic activity, is also implicated in the control of branchial ionic transport. This neuropeptide may thus constitute a major factor involved in the control of osmoregulation in decapod crustaceans.

A hyperglycemic peptide hormone from the Caribbean shrimp Penaeus (litopenaeus) schmitti

From a crude extract of the sinus glands of the shrimp Penaeus (litopenaeus) schmitti a peptide with hyperglycemic activity in a homologous bioassay was isolated and characterized by a combination of automatic Edman degradation, enzymatic digestions, TLC of dansyl-amino acids, and mass spectrometry. Its M(r) is 8359.4 Da by MS, which coincides with the deduced sequence. Its N-terminus is free and its C-terminus is amidated. It has 6 Cys residues in conserved positions compared with other known CHHs. This is the first sinus gland hormone from an Atlantic Ocean shrimp characterized to date. It has a remarkable 90% sequence similarity to the Indo-Pacific shrimp P. (marsupenaeus) japonicus Pej-VII hyperglycemic hormone.

Primary structures of a second hyperglycemic peptide and of two truncated forms in the spiny lobster, Jasus lalandii

We have isolated a 72-amino acid peptide from extracts of sinus glands of the South African rock lobster, Jasus lalandii, and identified it, functionally and immunologically, as a hyperglycemic hormone. This is the second peptide with hyperglycemic activity found in this palinurid species and, because it occurs in smaller quantities (approximately 3 pmol/sinus gland) than the previously identified hyperglycemic hormone [14], this minor isoform is designated Jala cHH-II. The complete elucidation of the primary structure of cHH-II, as determined by automated Edman degradation of the N-terminus enzymatic digests of the non-reduced peptide, chemical cleavage and mass spectrometry, is presented here. Jala cHH-II (molecular mass of 8357 Da) is more hydrophobic than Jala cHH-I (8380 Da). The two cHHs have a free N-terminus a blocked C-terminus; and share 90% sequence homology. We also present structural data of a further two peptides isolated from sinus gland extracts that were immunopositive to cHH antisera. These peptides, with masses of 7665 and 7612 Da, structurally represent C-terminally truncated forms of the major and the minor Jala cHH peptides, respectively, but do not have any hyperglycemic activity in vivo. We demonstrate that the prevalence of these truncated forms can be reduced by the addition of proteases to the homogenization buffer during preparation of the tissues.

Amino acid sequences of both isoforms of crustacean hyperglycemic hormone (CHH) and corresponding precursor-related peptide in Cancer pagurus

Both isoforms of the crustacean hyperglycemic hormone (CHH) and corresponding crustacean hyperglycemic hormone precursor-related peptide (CPRP) derived from HPLC-purified sinus gland extracts from the edible crab Cancer pagurus were fully characterised by microsequencing and mass spectrometry. The amino acid sequences of the CHH isoforms were almost identical except that the N-terminus of the minor isoform (CHH-I), was glutamine rather than pyroglutamate in the major isoform (CHH-II). Both CHH isoforms were of similar biological activity, as tested by in vivo hyperglycemia bioassays and in vitro repression of ecdysteroid synthesis. Comparison with other published CHH and CPRP sequences show that for crabs, these peptides form a distinct group, that the presence of CHH isoforms with free and blocked N-termini seems unique to crabs. It is argued that this phenomenon reflects a slow post-translational modification in sinus gland neurosecretory terminals. This study appears to complete the entire sinus gland inventory of functionally and structurally characterised CHH-related peptides in a crab.

Hyperglycaemic hormones inhibit protein and mRNA synthesis in in vitro-incubated ovarian fragments of the marine shrimp Penaeus semisulcatus

The present work shows for the first time that peptides belonging to the Crustacean hyperglycaemic hormone family (CHH-family hormones) from Penaeus japonicus affect protein and mRNA synthesis in in vitro-incubated ovarian explant fragments removed from vitellogenic females of Penaeus semisulcatus. Reduced levels of protein synthesis, determined by TCA-precipitable 35S-labeled proteins, were found in the presence of crude sinus gland extracts from both P. semisulcatus and P. japonicus. A similar inhibitory effect compared to controls was found with each of the seven CHH-family peptides. Non-CHH-family peptides did not reduce protein synthesis. Crude sinus gland extracts prepared from P. semisulcatus were at least 20-fold more effective than sinus gland extracts of P. japonicus. The inhibition level was directly related to the concentration of the peptide in the incubation media, but its degree varied among the different tested peptides. The profile of proteins synthesized during in vitro incubation was analyzed using polyacrylamide gel electrophoresis under denatured and reduced conditions (SDS-PAGE), followed by autoradiography. Synthesis of several proteins was reduced, including proteins with electrophoretic mobility similar to that of vitellin. Immunoprecipitation with antiserum prepared against native ovarian vitellin confirmed the inhibitory effect of CHH-family peptides on vitellin synthesis. The crude sinus gland extract and CHH-family peptides also inhibited RNA synthesis, as determined by [3H]uridine incorporation into mRNA of ovarian fragments. It is concluded that in addition to their role in carbohydrate metabolism, CHH-family peptides may also influence ovarian physiology in crustaceans.