SIFamide: Biological Overview | References
Gene name - SIFamide
Cytological map position - 60D5-60D5
Function - secreted neuropeptide
Symbol - SIFa
FlyBase ID: FBgn0053527
Genetic map position - chr2R:24,577,566-24,578,143
NCBI classification - neuropeptide
Cellular location - secreted
Animal behavior is, on the one hand, controlled by neuronal circuits that integrate external sensory stimuli and induce appropriate motor responses. On the other hand, stimulus-evoked or internally generated behavior can be influenced by motivational conditions, e.g., the metabolic state. Motivational states are determined by physiological parameters whose homeostatic imbalances are signaled to and processed within the brain, often mediated by modulatory peptides. This study investigate the regulation of appetitive and feeding behavior in the fruit fly, Drosophila melanogaster. Four neurons in the fly brain that release SIFamide were found to be integral elements of a complex neuropeptide network that regulates feeding. SIFamidergic cells integrate feeding stimulating (orexigenic) and feeding suppressant (anorexigenic) signals to appropriately sensitize sensory circuits, promote appetitive behavior, and enhance food intake. This study advances the cellular dissection of evolutionarily conserved signaling pathways that convert peripheral metabolic signals into feeding-related behavior (Martelli, 2017).
Animals have interlaced neuronal and endocrine systems to control feeding behavior by integrating internal information about metabolic needs and external stimuli signaling the availability and quality of nutrition. In mammals, various internal sensors monitor the metabolic state and convey endocrine and neuronal signals to peripheral organs and the brain, e.g., through the release of peptides, such as leptin, ghrelin, insulin, and peptide YY, or through the neuronal activity of the sensory vagus nerve afferents. The hypothalamus (HT) represents a main integrator of these signals and contains neuronal circuits regulating energy homeostasis. Antagonistically acting populations of neurons in the arcuate nucleus that express neuropeptide Y (NPY), agouti-related peptide (AgRP), peptides derived from the precursors pro-opiomelanocortin (POMC), or cocaine- and amphetamine-regulated transcript (CART), respectively, integrate these peripheral signals. Activating NPY/AgRP-releasing and orexin-releasing neurons, or injection of these peptides, enhances food intake, whereas activating POMC- and CART-expressing neurons or injection of these peptides decreases it. How exactly these peptides modulate neuronal circuits that control feeding-related behavior remains unclear (Martelli, 2017).
The brain of the fruit fly, Drosophila melanogaster, is much simpler in terms of cell numbers when compared to the mammalian brain. Its often individually identifiable neurons can be genetically targeted and manipulated or monitored using DNA-encoded Ca2+ sensors. Feeding-related behavior ranging from odor-guided foraging to food uptake has been exceedingly well described in Drosophila and other flies. Neural circuits controlling distinct aspects of feeding, e.g., the detection of gustatory and olfactory food stimuli, internal sensing of hemolymph sugar concentration, motor control of proboscis extension, food intake, and feeding-induced suppression of alternative behaviors like locomotion, have been characterized. Also in flies, peptidergic neurons modulate feeding behavior. The release of short neuropeptide F (sNPF) increases appetitive odor-guided behavior and food uptake. Conversely, drosulfakinin, a cholecystokinin homolog, allatostatin A (AstA), and myosin inhibitory peptide (MIP) reduce food intake. However, a function for the neuropeptide SIFamide in feeding-related behavior remains unclear. The SIFamide amino acid sequence is largely conserved across the arthropod lineage (Verleyen, 2004) and has been implicated in courtship behavior and sleep in Drosophila (Terhzaz, 2007, Park, 2014, Sellami, 2015), aggression in a freshwater prawn, as well as in various feeding-related physiological processes, e.g., the modulation of the stomatogastric ganglion in lobsters or the control of salivary glands in blood-sucking ticks. The SIFamide receptor (SIFaR) (Jørgensen, 2006) is a homolog of the vertebrate gonadotropin inhibitory hormone receptor (GnIHR), although their respective ligands, SIFamide and GnIH, are not sequence related. GnIHR regulates food intake and reproductive behavior in opposite directions, thereby promoting feeding behavior over alternative behavioral tasks in periods of metabolic needs. However, it remains unclear whether the functions of the SIFamide- and GnIH-signaling pathways, respectively, are conserved across phyla (Martelli, 2017).
This study used Drosophila to study the role of SIFamide in feeding behavior. Thermogenetic activation of SIFamidergic neurons was shown to enhance appetitive behavior evoked by gustatory and olfactory stimuli, as well as food intake. Second, it was shown that release of SIFamide sensitizes olfactory signaling in the antennal lobe (AL). Third, it was demonstrated that orexigenic as well as anorexigenic peptidergic neurons interact anatomically and functionally with SIFamidergic cells in the brain. These findings together identify SIFamide neurons as an interface between intrinsic metabolic signals and sensory neuronal circuits mediating appetitive behavior and food intake (Martelli, 2017).
The Drosophila gene fruitless expresses male and female specific transcription factors which are responsible for the generation of male specific neuronal circuitry for courtship behavior. Mutations in this gene may lead to bisexual behavior in males. Bisexual behavior in males also occurs in the absence of the neuropeptide SIFamide. SIFamide neurons do not express fruitless. However, when fruitless neurons are made to express RNAi specific for the SIFamide receptor, male flies engage in bisexual behavior, showing that SIFamide acts on fruitless neurons. If neurons expressing a SIFaR-gal4 transgene are killed by the apoptotic protein Reaper or when these neurons express SIFamide receptor RNAi, males also show male-male courtship behavior. This transgene was used to localize neurons that express the SIFamide receptor. Such neurons are ubiquitously present in the central nervous, and two neurons were also found in the uterus that project into the central nervous system (Sellami, 2015).
SIFamide receptor (SIFR) is a Drosophila G protein-coupled receptor for the neuropeptide SIFamide (SIFa). Although the sequence and spatial expression of SIFa are evolutionarily conserved among insect species, the physiological function of SIFa/SIFR signaling remains elusive. This study provides genetic evidence that SIFa and SIFR promote sleep in Drosophila. Either genetic ablation of SIFa-expressing neurons in the pars intercerebralis (PI) or pan-neuronal depletion of SIFa expression shortened baseline sleep and reduced sleep-bout length, suggesting that it caused sleep fragmentation. Consistently, RNA interference-mediated knockdown of SIFR expression caused short sleep phenotypes as observed in SIFa-ablated or depleted flies. Using a panel of neuron-specific Gal4 drivers, SIFR effects were further mapped to subsets of PI neurons. Taken together, these results reveal a novel physiological role of the neuropeptide SIFa/SIFR pathway to regulate sleep through sleep-promoting neural circuits in the PI of adult fly brains (Park 2014).
This study provides new evidence that the neuropeptide SIFa and its G protein-coupled receptor SIFR are novel mediators for promoting sleep in Drosophila. Either genetic ablation of SIFa-expressing neurons or depletion of SIFa expression shortened baseline sleep and caused sleep fragmentation by decreasing sleep-bout length. Consistent with these observations, a recent study independently revealed a possible sleep promoting role of SIFa-expressing neurons in DD conditions (Shang, 2013). Using neuron-specific SIFR depletion, this study further mapped the sleep-promoting SIFR function to Dilp2-negative, SIFR-positive PI neurons (Park 2014).
The PI in adult fly brain is homologous to the mammalian hypothalamus, the control center for neurotransmitter regulation. Several therapeutic targets for human sleep disorders are concentrated in the hypothalamus. For instance, dopaminergic neurons blocked by amphetamine-like drugs induce wake-promoting signals to cure narcolepsy. Benzodiazepine compounds increase gamma-aminobutryic acid (GABA)ergic neuronal transmission to enhance sleep-promoting signals to treat insomnia. Octopamine, which is similar to mammalian norepinephrine, has been identified as a wake-promoting molecule in Drosophila. When octopamine biosynthesis is compromised, flies exhibit enhanced sleep. On the other hand, octopamine promotes wakefulness in flies, particularly at night. Moreover, octopamine and OAMB, an octopamine receptor, act in Dilp2-expressing PI neurons to promote wakefulness through the cyclic AMP (cAMP) pathway. This is in contrast with the current finding that Dilp2-negative PI neurons are important for SIFR-dependent sleep promotion. Therefore, this study has defined a novel PI circuit that promotes sleep via the SIFa-SIFR signaling pathway (Park 2014).
Additional genes have been identified as sleep regulators in the PI region of adult fly brain, including members of the rhomboid family, which are integral membrane proteases and star, a transmembrane cargo receptor. They process epidermal growth factor receptor (EGFR)- activating ligands, such as spitz, gurken, and keren, so that extracellular signal-regulated kinase (ERK) is activated by phosphorylation. When EGFR is activated, flies exhibit excessive sleep. Interestingly, depletion of rhomboid, one of the processors for the ligand of the EGF receptor in c767-Gal4 expressing PI neurons shortened sleep. Given that SIFR and rhomboid promote sleep in the same PI neurons, it might be possible that SIFR and rhomboid function together to regulate sleep through the EGFR-ERK signaling pathway. Not much is known about the SIFR in terms of its downstream effectors and how it exerts its physiological effects. In general, GPCR activates the protein kinase A (PKA)-cAMP pathway via Gs or Ca2+ through a Gq regulator. It was recently shown that lethality in flies with SIFR knock-down is rescued by the overexpression of dSTIM, one of the key regulators of store-operated Ca2+ entry (Agrawal, 2013). Furthermore, the nuclear factor of activated T cells (NFAT), a Ca2+-activated transcription factor, is regulated by SIFR in a Schneider 2 (S2) cell-based dsRNA screening (Gwack et al., 2006), suggesting that sleep regulation by SIFR might involve Ca2+ signaling. Future studies will address which signaling pathways SIFR affects to regulate neuronal activity and sleep behavior (Park, 2014).
SIFamide is the short name and also the C terminus of the Drosophila neuropeptide AYRKPPFNGSIFamide. SIFamide has been isolated or predicted from various insects and crustaceans, and appears to be extremely well conserved among these arthropods. However, the function of this neuropeptide is still enigmatic. This study has identified the Drosophila gene (CG10823) coding for the SIFamide receptor. When expressed in Chinese hamster ovary cells, the receptor is only activated by Drosophila SIFamide (EC(50), 2x10-8M) and not by a library of 32 other insect neuropeptides and eight biogenic amines. Database searches revealed SIFamide receptor orthologues in the genomes from the malaria mosquito Anopheles gambiae, the silkworm Bombyx mori, the red flour beetle Tribolium castaneum, and the honey bee Apis mellifera. An alignment of the five insect SIFamide or SIFamide-like receptors showed, again, an impressive sequence conservation (67-77% amino acid sequence identities between the seven-transmembrane areas; 82-87% sequence similarities). The identification of well-conserved SIFamide receptor orthologues in all other insects with a sequenced genome, suggests that the SIFamide/receptor couple must have an essential function in arthropods. This paper is the first report on the identification of a SIFamide receptor (Jorgensen, 2006).
The expression of Drosophila neuropeptide AYRKPPFNGSIFamide (SIFamide) was shown by both immunohistology and in situ hybridization to be restricted to only four neurons of the pars intercerebralis. The role of SIFamide in adult courtship behavior in both sexes was studied using two different approaches to perturb the function of SIFamide; targeted cell ablation and RNA interference (RNAi). Elimination of SIFamide by either of these methods results in promiscuous flies; males perform vigorous and indiscriminant courtship directed at either sex, while females appear sexually hyper-receptive. These results demonstrate that SIFamide is responsible for these behavioral effects and that the four SIFamidergic neurons and arborizations play an important function in the neuronal circuitry controlling Drosophila sexual behavior (Terhzaz, 2007).
Neb-LFamide or AYRKPPFNGSLFamide was originally purified from the grey flesh fly Neobellieria bullata as a myotropic neuropeptide. The occurrence of this peptide and its isoforms was studied in the central nervous system of different insect species by means of whole mount fluorescence immunohistochemistry, mass spectrometry, and data mining. Both sequence and immunoreactive distribution pattern are very conserved in the studied insects. In all species and stages two pairs of immunoreactive cells were coundted in the pars intercerebralis. These cells projected axons throughout the ventral nerve cord. In the adult CNSs they formed a large number of immunoreactive varicosities as well. Mass spectrometry and data mining revealed that SIFamide exists in two isoforms: [G1]-SIFamide and [A1]-SIFamide. In addition, the SIFamide joining peptide is relatively well conserved throughout arthropod species. The conserved presence of two cysteine residues, separated by six amino acid residues, allows the formation of disulphide bridges (Verleyen, 2004).
Search PubMed for articles about Drosophila
Agrawal, T., Sadaf, S. and Hasan, G. (2013). A genetic RNAi screen for IP(3)/Ca(2)(+) coupled GPCRs in Drosophila identifies the PdfR as a regulator of insect flight. PLoS Genet 9(10): e1003849. PubMed ID: 24098151
Jorgensen, L. M., Hauser, F., Cazzamali, G., Williamson, M. and Grimmelikhuijzen, C. J. (2006). Molecular identification of the first SIFamide receptor. Biochem Biophys Res Commun 340(2): 696-701. PubMed ID: 16378592
Martelli, C., Pech, U., Kobbenbring, S., Pauls, D., Bahl, B., Sommer, M. V., Pooryasin, A., Barth, J., Arias, C. W. P., Vassiliou, C., Luna, A. J. F., Poppinga, H., Richter, F. G., Wegener, C., Fiala, A. and Riemensperger, T. (2017). SIFamide translates hunger signals into appetitive and feeding behavior in Drosophila. Cell Rep 20(2): 464-478. PubMed ID: 28700946
Park, S., Sonn, J. Y., Oh, Y., Lim, C. and Choe, J. (2014). SIFamide and SIFamide receptor defines a novel neuropeptide signaling to promote sleep in Drosophila. Mol Cells 37(4): 295-301. PubMed ID: 24658384
Sellami, A. and Veenstra, J. A. (2015). SIFamide acts on fruitless neurons to modulate sexual behavior in Drosophila melanogaster. Peptides 74: 50-56. PubMed ID: 26469541
Shang, Y., Donelson, N. C., Vecsey, C. G., Guo, F., Rosbash, M. and Griffith, L. C. (2013). Short neuropeptide F is a sleep-promoting inhibitory modulator. Neuron 80(1): 171-183. PubMed ID: 24094110
Terhzaz, S., Rosay, P., Goodwin, S. F. and Veenstra, J. A. (2007). The neuropeptide SIFamide modulates sexual behavior in Drosophila. Biochem Biophys Res Commun 352(2): 305-310. PubMed ID: 17126293
Verleyen, P., Huybrechts, J., Baggerman, G., Van Lommel, A., De Loof, A. and Schoofs, L. (2004). SIFamide is a highly conserved neuropeptide: a comparative study in different insect species. Biochem Biophys Res Commun 320(2): 334-341. PubMed ID: 15219831
date revised: 5 November 2017
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