Arthropod neuropeptides

G. Gade H. G. Marco, Structure, Function and Mode of Action of Selected Arthropod Neuropeptides. In Studies in Natural Product Chemistry (Bioactive Natural Products) Atta-ur-Ftahman, Ed. Elsevier Amsterdam, 2006 Vol. 33, pp 69-139. 

STRUCTURE, FUNCTION AND MODE OF ACTION OF SELECT ARTHROPOD NEUROPEPTIDES... 

A suite of methods has been successfully applied over the past few decades in the research on arthropod neuropeptides the relevant methods are mentioned only briefly here with some examples relating to crustacean neuropeptides the reader is referred to [10] for a more detailed description of the general methods employed in the isolation and characterization of insect neuropeptides. 

Unlike the situation in nematodes and arthropods, where hundreds of neuropeptides have been elucidated using biochemical, physiological and molecular techniques, flatworm neuropeptide discovery is still in its infancy. This is despite the characterization of the first flat-worm neuropeptide almost 15 years ago (Maule et al., 1991). Progress has been hindered by the inability to obtain large quantities of flatworm neuronal tissues and the absence, until recently, of a significant body of genomic and/or EST data for flatworms. Nevertheless, the available evidence does provide a snapshot of what appear to be the most abundant and widespread flatworm neuropeptides. 

The similarity of the crustacean blanching substance (Factor A) found in crustacean sinus glands and insect corpora cardiaca has been confirmed by the structural identification of a family of neuropeptides common to arthropods. The first identified member of this family is RPCH (red pigment concentrating hormone), an octapeptide (pGlu-Leu-Asn-Phe-Ser-Pro-Gly-Trp-amide) isolated from eyestalks of the shrimp Pandalus borealis (28). Shortly thereafter, a related peptide--designated as adipokinetic hormone (AKH)--was purified from locust... 

Like the AKH/RPCH peptides, insect PDFs and crustacean PDHs are now an established family of neuropeptides common to arthropods. Whereas the fimctions of AKHs are varied and well defined in insects, the function of PDFs in insects remains unknown. The immunocytochemical distribution of PDF in the cephalic nervous tissues of orthopteran insects points to a neuromodulatory role, with potential functions in circadian rhythms this would be an exciting area for further research. 

It is by no means surprising that structurally homologous neuropeptides have been identified in crustaceans and insects - they share, after all, a common ancestry. The functions of some of these neuropeptides have not been conserved in these arthropod groups and we discuss here a selection of neuropeptide families common to both. For each peptide family, we... 

Proctolin, H-Arg-Tyr-Leu-Pro-Thr-OH, a bioactive neuropeptide modulating in-terneuronal and neuromuscular synaptic transmissions in a wide variety of arthropods. It was discovered as an excitatory neurotransmitter from the intestinal musculature of insects. Extremely low concentrations (10 mol L ) cause violent contraction of the end of the gut. For the first isolation of proctolin, 125,000 cockroaches (Periplaneta americana) were required. Although proctolin was the first insect neuropeptide to be discovered, it is now regarded as the main neuromuscular trans-mitter/modulator in the gut of most insect species. In 2003, a G protein-coupled receptor for proctolin in Drosophila mdanogaster was identified and characterized [A. N. Star-ratt, B. E. Brown, Life Sci. 1975, 17, 1253 D. Konopihska, G. Rozihski, J. Peptide Sci. 1999, 5, 533 E. J. Johnson et al., Proc. Natl. Acad. Sci. USA 2003, 100, 6198]. 

The study of arthropods is of intense interest for basic research into comparative endocrinology. Active areas of research involve the evolutionary endocrinology of the MIH/CHH family of neuropeptides. Slight alterations in structure result in dramatic changes in function. These peptides evolved from a common ancestor to develop into an extremely multifunctional family of hormones. 

Webster SG (1998) Neuropeptides inhibiting growth and reproduction in crustaceans. In Coast GM, Webster SG (eds) Recent advances in arthropod endocrinology. Cambridge University Press, Cambridge, pp 33-52... 

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