ACTIVE PROJECTS
LARVAL TASTE PERCEPTION:
Researchers: Ji-Eun Ahn PhD. , Shinsukek Fujii PhD.,
Alumni: Dushyant Mishra. PhD., Christopher Jagge PhD.
Insect development and growth is characterized by several distinct features, including very rapid embryonic development (24 hours in the case of Drosophila), almost total reorganization of the insect’s body plan during metamorphosis, and an exceptionally prolific growth phase during the larval life phase. This last feature is remarkable because during the four days of Drosophila larval development, the bodyweight is doubled almost twice each day. We have been investigating the role of taste perception in larvae and made some intriguing discoveries. In contrast to flies which use a combination of 8 different sugar receptor genes (sGrs), larvae use a single sugar taste receptor, Gr43a, which is not only expressed in taste organs, but also the gut and the brain. This receptor is narrowly tuned to fructose and sucrose (a disaccharide of glucose and fructose). Intriguingly, brain neurons expressing Gr43a allows larvae to sense even non-fructose containing sugar that they ingest, as such sugars are partially converted into fructose after ingestion (Mishra et al., 2013). We also discovered that Drosophila can sense RNA and ribonucleosides, which they need in relative large amounts to sustain the rapid growth phase during the larval stages (Mishra et al., 2018). Intriguingly this taste preference, which is mediated by the highly conserved Gr28a receptor, is conserved across many dipteran insects, including mosquitoes (Fujii et al., 2023).
Gr28a is a member of a highly conserved subfamily, members of which are broadly expressed in many other tissues and organs. In larvae, the other Gr28 proteins are encoded by five genes (Gr28b.a, Gr28b.b, Gr28b.c, Gr28b.d and Gr28b.e) which are expressed in largely different Gustatory Receptor Neurons (GRNs) than Gr28a. In fact, we recently found that despite their high conservation, the Gr28b receptors are sensing bitter compounds that larvae strongly avoid. (Ahn and Amrein, 2023).
Representative publications:
Mishra, D., Miyamoto, T., Rezenom, Y.H., Broussard, A., Yavuz, A., Slone, J., Russell D.H. and Amrein, H. (2013) The molecular basis of sugar sensing in Drosophila larvae Current Biology 23 (15), PMID: 23850280.
Mishra, D, Thorne, N., Miyamoto, C. Jagge C and Amrein, H. (2018). The taste of ribonucleosides: novel macronutrients essential for larval growth are sensed by Drosophila gustatory receptor proteins PLoS Biology 16 (8), e2005570. PMID: 30086130
Fuji, S., Ahn., J.-E., Jagge, Shetty, V., C., Janes C., Mohanty, A., Wright G., Slotman, S., Adelman Z.N., and Amrein H. (2023). RNA Taste is Conserved in Dipteran Insects. Journal of Nutrition 153 (5),1636-1645. PMID: 36907444
Ahn J.-E. and Amrein H. (2023). Opposite chemosensory functions of closely related taste
receptors of the Gr28 subfamily. eLife (in press).
NEUROPEPTIDES:
Researchers: Tetsuya Miyamoto, PhD., and Veronika Mojikova B.S and PhD. candidate
Neuropeptides (NPs) are ancient signaling molecules that have a wide range of different functions, regulate many physiological processes and can act at different time scales. NPs bind to specific receptors of the G protein coupled receptor family, often expressed in a specific tissue, activating a signaling event that affects its physiology. Many NPs have been shown to have conserved functions across different species, even between vertebrates and insects. Our interest in NP arose from the serendipitous discovery of Glucose – 6 – phosphatase (G6P) being expressed in diverse NP secreting neurons. G6P is a conserved enzyme involved in carbohydrate metabolism, and it is mainly known for its key role in hepatic gluconeogenesis in mammals. While a process almost identical to gluconeogenesis exists in insects, the very step that G6P occupies in the mammalian liver is carried out by the enzyme Trehalose Phosphate Synthase in Drosophila, since trehalose and not glucose is the main blood sugar in Drosophila and many other insects. Our recent work revealed that G6P has been appropriated for modulating the release of several NPs in the Drosophila neurosecretory system. A group of closely related NPs, the FMRFamides, are of special interest to us, because we discovered that they are G6P dependent signaling molecules that regulate and co-ordinate glycogen metabolism across a range of tissues, including several muscle groups and the fat body.
Representative publications:
Miyamoto, T, and Amrein, H. (2017). Gluconeogenesis, an ancient biochemical pathway with a twist. Fly 11 (1). PMID: 28121487
Miyamoto, T., and Amrein, H. (2019) Neural Gluconeogenesis regulates systemic glucose homeostasis in Drosophila melanogaster. Current Biology 29 (8), 1263-1272. PMID: 30930040
SUGAR PERCEPTION IN FLIES:
Researchers: Shinsuke Fujii, PhD.
Alumni: Natasha Thorne, PhD., Jesse Slone PhD., Christopher Jagge PhD., and Alejandra Gonzales PhD.
Based on evolutionary arguments, we proposed that the Drosophila genome contains at least 8 sugar Gr genes (sGr) genes that encode receptors for various sugars: Gr5a, Gr61a and Gr64a, Gr64b, Gr64c, Gr64d, Gr64f and Gr64e. One of the central questions in sweet taste is how these receptors function (alone or as complexes) to detect a number of nutritionally relevant sugars present in fruits and other natural food sources (yeast etc), such as fructose, sucrose, trehalose, glucose, maltose, melezytose, glycogen etc., and how such sweet sensory information is encoded in the brain, i.e. whether the fly brain can discriminate between chemically different sugars (and other sweet compounds). We have undertaken a detailed expression analysis to examine the expression of individual sGr genes in the two main taste organs (labial palps and legs). Since in situ hybridization is not a reliable method for this purpose (due to low expression levels), we have employed homologous recombination and have made a number of gene knock-ins, whereby the coding sequence of specific sGr genes was replaced by the GAL4 coding sequence to assure accurate expression of GAL4-dependnet UAS-GFP reporters. Expression analyses of these eight genes indicate that they are only partially co-expressed. For example, Gr5a and Gr64f are expressed in each sugar GRNs of all 31 taste sensilla in the labial palp. In contrast, Gr61a is expressed in only about 15 GRNs, while Gr64a is only expressed in 1 to 2 GRNs in the tarsi and not all in GRNs of the labial palps. Likewise, sugar cells from different taste sensilla in the fore tarsi express different combinations of these Gr genes. Thus, individual sugar GRNs must have distinct sugar responses, based on the sGr genes they express.
We have conducted a reverse genetics approach to provide direct evidence that the sGr genes indeed encode sugar receptors, and we found that lack of the six clustered Gr64 genes (a-f) lead to loss of sensing virtually all sugars, with the exception of fructose. Moreover, lacking either Gr5a or Gr64a-f fail to detect trehalose, suggesting that sugar receptors function as multimeric complexes consisting of two or more GR subunits. In order to determine the composition of sugar receptors stimulated by specific sugars, we have generated a strain in which all eight sGr genes are deleted (Delta-sGr). Using the Gal4/UAS expression system, we are performing behavioral assays in Delta-sGrflies that express pair-wise combinations of sGr genes. These behavioral experiments are complemented using a cellular imaging assay, whereby activation of individual taste neurons is monitored after application of various sugar compounds.
Representative publications:
Slone, J., Daniels, J. and Amrein. H. (2007): Sugar Receptors in Drosophila. Current Biology 17, 1809-1816. PMID: 17919910
Miyamoto T., Chen, Y., Slone J. and Amrein, H. (2013) Identification of a Drosophila Glucose Receptor Using Ca 2+ Imaging of Single Chemosensory Neurons. PLoS ONE 8 (2), e56304. PMID: 23418550.
Yavuz, A., Jagge, C. and Amrein, H. (2014). A genetic tool kit for cellular and behavioral analyses of insect sugar receptor. Fly 8 (4), 189-196. PMID: 25984594.
Fujii, S., Yavuz, A., Slone, J., Jagge. C., Song, X., and Amrein, H. (2015). Drosophila Sugar Receptors in Sweet Perception, Olfaction and Internal Nutrient Sensing. Current Biology 25 (5), 621-627. PMID: 25702577
COMPLETED PROJECTS
INTERNAL NUTRIENT SENSING:
Researcher: Tetsuya Miyamoto, PhD.
Representative publications:
Miyamoto, T., Slone J., Song, X. and Amrein, H. (2012) A fructose receptor functions as a nutrient sensor in the Drosophila brain. Cell 151 (5), 1113-1125: PMID: 23178127
Miyamoto T, and Amrein, H. (2014) Diverse roles for Gr43a in taste perception and nutrient
sensing in Drosophila melanogaster. Fly 8 (1), 19-25, PMID: 24406333.
FAT AND SOUR TASTE:
Researchers: Ji-Eun Ahn PhD.
Alumni: Yan Chen PhD.
Representative publications:
Chen, Y., and Amrein, H (2017). Ionotropic Receptors mediate Drosophila oviposition preference through sour Gustatory Receptor Neurons. Current Biology 27 (18), 2741-2750. PMID: 28889974.
Ahn, J.E., Chen, Y., and Amrein, H. (2017). Molecular Basis of fatty acid taste in Drosophila. E-life 6: e301115 DOI: 10.7554/eLife.30115 PMID: 29231818.
Chen, Y. and Amrein, H. (2014) Enhancing Perception of Contaminated Food through Acid- mediated Modulation of Taste Neuron Responses. Current Biology 24 (17), 1969-1977. PMID:
25131671.
PHEROMONE RECEPTORS:
Researchers: Tetsuya Miyamoto, PhD.
Alumni: Steven Bray, PhD.
Collaborator: David Anderson, Ph.D., California Institute of Technology
Representative publications:
Bray, S. and Amrein, H. (2003). A Putative Drosophila Pheromone Receptor Expressed in Male- specific Taste Neurons is Required for Efficient Courtship. Neuron 39: 1019-1029. PMID: 12971900
Miyamoto, T., and Amrein H. (2008): Courtship Suppression by a Drosophila pheromone
receptor. Nature Neuroscience 11 (8), 874-876. PMID: 18641642
Wang, L., Han, X., Mehren, J., Billeter, J.C., Miyamoto, T., Amrein, H., Levine, J.D. and Anderson, D.J. (2011) Hierarchical chemosensory regulation of male-male social interactions in Drosophila. Nature Neuroscience 14 (6), 757-762. PMID: 21516101
CIRCADIAN MATING BEHAVIOR:
Researcher: Shinsuke Fujii, PhD.
Collaborator: Patrick Emery, PhD.
Representative publications:
Fujii, S, Emery, P. and Amrein, H. (2017). SIK3-HDAC4 signaling regulates Drosophila male sex drive rhythm via modulating the DN1 clock neurons. PNAS 114 (32), E6669-E6677. PMID: 28743754.
Fujii, S. and Amrein, H. (2010) Ventral lateral and DN1 clock neurons mediate distinct properties of male sex drive rhythm in Drosophila. PNAS 107 (21), 10590-105959. PMID: 20498055
Fujii, S. Toyoma, A., and Amrein H. (2008): male-specific and circadian regulated fatty acid omega-hydroxylase, SXE1, is necessary for efficient male mating in Drosophila melanogaster. Genetics 180, 179-190. PMID: 18716335
The Amrein Laboratory at Texas A&M University 