Proctolin

Biological activities of crustacean cardioactive peptide (CCAP; PFCNAFTGCa) and leucomyosuppressin (Lem-MS; pQDVDHVFLRFa) were studied in heterologous bioassays in the larvae and adults of Tenebrio molitor. CCAP exerted a reversible and dose-dependent cardio-stimulatory effect on the semi-isolated heart of the experimental beetles at a concentration of >10(-7) M and induced an effect similar to the endogenic cardio-stimulatory peptide, proctolin. Injections of CCAP (10(-9)-10(-3) M) into 4-day-old adult reproductive females increased the concentration of soluble proteins in hemolymph in comparison to the saline injected controls. Electrophoretic analyses indicated significant increase in the level of two proteins 130 and 170 kDa, and a partial increase of the level of 67-kDa protein. The studies indicated that CCAP increased also free hemolymph sugar concentration in young larvae and adults of the mealworm beetle. The cardio-inhibitory peptide Lem-MS exerted the opposite effect: at concentration 10(-7)-10(-6) M, it significantly decreased the heartbeat frequency. The induced changes were dose-dependent and reversible, but at higher concentrations (>10(-5) M) the stimulatory effect disappeared.

Despite being used as models in the field of ecotoxicology, including use in studies of endocrine disruption, little is known about the hormonal systems of amphipods, particularly their peptidergic signaling systems. Here, transcriptome shotgun assembly (TSA) sequences were used to predict the structures of the first neuropeptides from members of this crustacean order. Using a well-established workflow, BLAST searches of the extant amphipod TSA data were conducted for putative peptide-encoding transcripts. The pre/preprohormones deduced from the identified TSA sequences were then used to predict the mature structures of amphipod neuropeptides. In total, 43 putative peptide-encoding transcripts were identified from three amphipods, Echinogammarus veneris, Hyalella azteca and Melita plumulosa. Collectively, 139 distinct mature peptides (110 from E. veneris alone) were predicted from these TSA sequences. The identified peptides included members of the adipokinetic hormone/red pigment concentrating hormone, allatostatin A, allatostatin B, allatostatin C, bursicon α, bursicon β, crustacean hyperglycemic hormone, diuretic hormone 31, FLRFamide, molt-inhibiting hormone, myosuppressin, neuroparsin, neuropeptide F, orcokinin, pigment dispersing hormone (PDH), proctolin, RYamide, SIFamide, sulfakinin and tachykinin-related peptide families.

The occurrence of allatostatins in retrocerebral complexes and antennal pulsatile organs of the American cockroach, Periplaneta americana, was investigated. Previously, molecular cloning of the P. americana allatostatin gene had predicted 14 peptides of this family [Ding et al., Comparison of the allatostatin neuropeptide precursors in the distantly related cockroaches Periplaneta americana and Diploptera punctata. Eur J Biochem 1997;234:737-746], however, only two forms had been identified by peptide isolation procedures [Weaver et al., Identification of two allatostatins from the CNS of the cockroach Periplaneta americana: novel members of a family of neuropeptide inhibitors of insect juvenile hormone biosynthesis. Comp Biochem Physiol 1994;107(C):119-127]. Using an extract of only 200 corpora cardiaca/corpora allata, we have found that at least 11 allatostatins occur in the retrocerebral complex. These peptides were already separated from other substances of the crude extract in the first HPLC step with heptafluorobutyric acid as organic modifier, and subsequently identified by MALDI-TOF mass spectrometry. Moreover, we have demonstrated the occurrence of nearly all allatostatins, including the cleavage product of Pea-AST-2 (LPVYNFGL-NH2), in antennal pulsatile organs of males and females.