Differential Processing of Neuropeptides InfluencesDrosophilaHeart Rate

Abstract

Peptides that play critical physiological roles are often encoded in precursors that contain several structurally-related gene products. Differential processing of a precursor by cell-specific processing enzymes can yield multiple messengers with diverse distributions and activities. We have reported the isolation of SDNFMRFamide, DPKQDFMRFamide, and TPAEDFMRFamide from adult Drosophila melanogaster. The peptides are encoded in the FMRFamide gene and have a common C-terminal FMRFamide but different N-terminal extensions. In order to investigate the processing of the FMRFamide polypeptide protein precursor, we generated antisera to distinguish among the structurally-related neuropeptides. Utilizing a triple-label immunofluorescent protocol, we mapped the distribution of the peptides. Each peptide has a unique, non-overlapping cellular expression pattern in neural tissue suggesting that the precursor is differentially processed. In order to identify a biological activity of the peptides, we established an in vivo heart rate assay. SDNFMRFamide decreases heart rate but DPKQDFMRFamide and TPAEDFMRFamide do not, indicating that the N-terminal residues are critical for this activity. SDNFMRFamide immunoreactivity is present in the aorta, implying that SDNFMRFamide acts locally to affect heart rate; DPKQDFMRFamide and TPAEDFMRFamide antisera do not stain cardiac tissue. Our data support the conclusion that Drosophila contains cell-specific proteolytic enzymes to differentially process a polypeptide protein precursor resulting in unique expression patterns of structurally-related, yet functionally distinct neuropeptides.

Molecular cloning and functional expression of the first insect FMRFamide receptor

“…The Drosophila FMRFamides have been reported to activate larval neuromuscular junctions and to inhibit heartbeat (3,38,40,41). At the larval neuromuscular junctions, all FMRFamides acted similarly (except for FMRFamide-7, which was inactive), suggesting that these peptides were functionally redundant (3,40).…”

“…At the larval neuromuscular junctions, all FMRFamides acted similarly (except for FMRFamide-7, which was inactive), suggesting that these peptides were functionally redundant (3,40). At the heart, however, only FMRFamide-4 was active, whereas FMRFamide-2 and -3 were without effects (38,41). A comparison of these peptide effects with the characteristics of our FMRFamide receptor (Fig.…”

CCAP and FMRFamide-like peptides accelerate the contraction rate of the antennal accessory pulsatile organs (auxiliary hearts) of mosquitoes

“…However, the cardioacceleratory properties of FLPs are not universal. Depending on the N-terminal sequence of the peptide, and the insect being tested, some FLPs are cardioacceletatory (Cuthbert and Evans, 1989;Robb and Evans, 1990;Duve et al, 1993;Duttlinger et al, 2003), some are cardiodeceleratory (Cuthbert and Evans, 1989;Robb and Evans, 1990;Nichols et al, 1999;Lee et al, 2012), some have complex effects that are dependent on the presence of other molecules (Nichols, 2006), and yet others have no effect on heart physiology (Duve et al, 1993;Nichols et al, 1999;Nichols, 2006). In the present study, we confirm the cardioacceleratory activity of SALDKNFMRFamide and FMRFamide, and for the first time show in a holometabolous insect that FLPs accelerate the antennal APOs.…”

Roles of the Sarcoplasmic/Endoplasmic Reticulum Ca2+-ATPase, Plasma Membrane Ca2+-ATPase and Na+/Ca2+ Exchanger in Regulation of Heart Rate in Larval Drosophila~!2010-03-10~!2010-08-13~!2010-08-27~!

“…The HR varies throughout larval stages depending on whole animal activity (feeding and crawling) and the HR tends to slow down during pupation [15,28]. The larval heart is very susceptible to biogenic amines and peptides which could vary in the hemolymph depending on food source or intrinsic state of the animal [22,24,25,29,30].…”

“…Likewise, since the adult heart is modulated by neuronal inputs, this complicates addressing the function of the intrinsic cardiac pacemaker and ionic regulation in the intact heart [17,21]. The heart is known to be myogenic in the larval stage and can readily be removed or left in situ while being bathed by a defined physiological saline to limit compounding variables such as hormones or neural modulation [2,[22][23][24][25]. The myogenic nature of the larval heart is comparable to the mammalian heart in that there are pacemakers that drive the rest of the heart to pump fluid in a direction to be effective in bathing organs, despite the fact that Drosophila has an "open" circulatory system.…”