Abstract
We have reinvestigated the possible presence or absence of the pentapeptide proctolin in Rhodnius prolixus and report here the cloning of the proctolin cDNA. The transcript is expressed in the central nervous system (CNS) and some peripheral tissues. The proctolin prepropeptide encodes a single copy of proctolin along with a possible proctolin-precursor-associated peptide. We have biochemically identified proctolin in CNS extracts and shown its distribution using proctolin-like immunoreactivity. Immunostained processes are found on the salivary glands, female and male reproductive tissues, and heart and associated alary muscles. Proctolin-like immunoreactive bipolar neurons are found on the lateral margins of the common oviduct and bursa. Proctolin is biologically active on R. prolixus tissues, stimulating increases in contraction of anterior midgut and hindgut muscles, and increasing heartbeat frequency. Contrary to the previous suggestion that proctolin is absent from R. prolixus, proctolin is indeed present and biologically active in this medically important bug.
Highlights
Proctolin was the first insect neuropeptide to be sequenced and synthesized (Starratt and Brown, 1975) and is found in a variety of arthropods
When the Rhopr-proctolin prepropeptide sequence was compared to other insects, A. pisum, T. castaneum and D. melanogaster, and the www.frontiersin.org crustaceans, L. vannamei, and D. pulex, it was found that the most conserved region included the proctolin sequence and sequences immediately following it (Figure 2)
The pentapeptide proctolin has some interesting features. It is present in some species of arthropods where it has been identified by mass spectrometry (MS), and may be unique to arthropods since there is no convincing evidence for its presence in other invertebrates or vertebrates
Summary
Proctolin was the first insect neuropeptide to be sequenced and synthesized (Starratt and Brown, 1975) and is found in a variety of arthropods (see Orchard et al, 1989; Nässel, 2002; Lange and Orchard, 2006). Proctolin appears to be unique to arthropods, and there is no convincing evidence for its presence in any other invertebrate or vertebrate It is present in interneurons, and in motoneurons that project to skeletal and visceral muscle where it stimulates or potentiates muscle contraction (see Lange and Orchard, 2006; Nässel and Winther, 2010). A recent study on neuropeptide precursor genes in Rhodnius prolixus failed to identify a proctolin gene, and it was suggested that R. prolixus lacks proctolin (Ons et al, 2011) This is an interesting and puzzling observation since earlier chemical assays and bioassays provided evidence for proctolin in R. prolixus. Proctolin is present in another hemipteran, A. pisum (Huybrechts et al, 2010)
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