Proctolin was the first peptide to be isolated and sequenced from an insect, the cockroach Periplaneta americana (Starratt and Brown, 1975). It is a myostimulatory pentapeptide with the sequence RYLPT conserved among arthropods. Even though the peptide was the first to be discovered, the precursor gene, which contains a single copy of proctolin, was only identified almost 30 years later in Drosophila (Taylor et al., 2004). The first proctolin receptor was cloned in Drosophila in 2003 (Johnson et al., 2003).
Proctolin is produced by certain motor neurons and also by small sets of interneurons in the CNS of a range of insect species (see for example Anderson et al., 1988; Clark et al., 2006a; Veenstra et al., 1985; Taylor et al., 2004). Both in locusts and Drosophila some proctolinergic neurons also innervate the corpora cardiaca (Clark et al., 2006b, Taylor et al., 2004). In the cockroach motor neurons, proctolin acts together with co-released glutamate at the neuromuscular junction (Adams and O’Shea, 1983).
Although proctolin was first discovered by its ability to stimulate muscle contractions in the hindgut, several other muscle types, including reproductive, skeletal and heart muscle, have been identified as targets (Adams and O’Shea, 1983; Orchard et al. 1989; Ormerod et al., 2016; Taylor et al. 2004). In locusts proctolin also appears to trigger release of adipokinetic hormone and biosynthesis of juvenile hormone (Clark et al., 2006b). In Drosophila larvae crawling behavior is modulated by proctolin, especially at higher temperatures (Ormerod et al., 2016).
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Johnson EC, Garczynski SF, Park D, Crim JW, Nässel DR, Taghert PH. 2003.
Identification and characterization of a G protein-coupled receptor for the neuropeptide proctolin in Drosophila melanogaster. Proc Natl Acad Sci U S A 100(10):6198-6203.
Ormerod KG, LePine OK, Bhutta MS, Jung J, Tattersall GJ, Mercier AJ. 2016. Characterizing the physiological and behavioral roles of proctolin in Drosophila melanogaster. J Neurophysiol 115(1):568-580.
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