1
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Bessonova Y, Raman B. Serotonergic amplification of odor-evoked neural responses maps onto flexible behavioral outcomes. eLife 2024; 12:RP91890. [PMID: 39078877 PMCID: PMC11288630 DOI: 10.7554/elife.91890] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 08/02/2024] Open
Abstract
Behavioral responses to many odorants are not fixed but are flexible, varying based on organismal needs. How such variations arise and the role of various neuromodulators in achieving flexible neural-to-behavioral mapping is not fully understood. In this study, we examined how serotonin modulates the neural and behavioral responses to odorants in locusts (Schistocerca americana). Our results indicated that serotonin can increase or decrease appetitive behavior in an odor-specific manner. On the other hand, in the antennal lobe, serotonergic modulation enhanced odor-evoked response strength but left the temporal features or the combinatorial response profiles unperturbed. This result suggests that serotonin allows for sensitive and robust recognition of odorants. Nevertheless, the uniform neural response amplification appeared to be at odds with the observed stimulus-specific behavioral modulation. We show that a simple linear model with neural ensembles segregated based on behavioral relevance is sufficient to explain the serotonin-mediated flexible mapping between neural and behavioral responses.
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Affiliation(s)
- Yelyzaveta Bessonova
- Department of Biomedical Engineering, Washington University in St. LouisSt. LouisUnited States
| | - Baranidharan Raman
- Department of Biomedical Engineering, Washington University in St. LouisSt. LouisUnited States
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2
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Lee M, Park SH, Joo KM, Kwon JY, Lee KH, Kang K. Drosophila HCN mediates gustatory homeostasis by preserving sensillar transepithelial potential in sweet environments. eLife 2024; 13:RP96602. [PMID: 39073076 PMCID: PMC11286260 DOI: 10.7554/elife.96602] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 07/30/2024] Open
Abstract
Establishing transepithelial ion disparities is crucial for sensory functions in animals. In insect sensory organs called sensilla, a transepithelial potential, known as the sensillum potential (SP), arises through active ion transport across accessory cells, sensitizing receptor neurons such as mechanoreceptors and chemoreceptors. Because multiple receptor neurons are often co-housed in a sensillum and share SP, niche-prevalent overstimulation of single sensory neurons can compromise neighboring receptors by depleting SP. However, how such potential depletion is prevented to maintain sensory homeostasis remains unknown. Here, we find that the Ih-encoded hyperpolarization-activated cyclic nucleotide-gated (HCN) channel bolsters the activity of bitter-sensing gustatory receptor neurons (bGRNs), albeit acting in sweet-sensing GRNs (sGRNs). For this task, HCN maintains SP despite prolonged sGRN stimulation induced by the diet mimicking their sweet feeding niche, such as overripe fruit. We present evidence that Ih-dependent demarcation of sGRN excitability is implemented to throttle SP consumption, which may have facilitated adaptation to a sweetness-dominated environment. Thus, HCN expressed in sGRNs serves as a key component of a simple yet versatile peripheral coding that regulates bitterness for optimal food intake in two contrasting ways: sweet-resilient preservation of bitter aversion and the previously reported sweet-dependent suppression of bitter taste.
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Affiliation(s)
- MinHyuk Lee
- Neurovascular Unit Research Group, Korea Brain Research InstituteDaeguRepublic of Korea
- Department of Anatomy and Cell Biology, Sungkyunkwan University School of Medicine, Samsung Biomedical Research Institute, Samsung Medical CenterSuwonRepublic of Korea
- Department of Biological Sciences, Sungkyunkwan UniversitySuwonRepublic of Korea
| | - Se Hoon Park
- Department of Brain Sciences, DGISTDaeguRepublic of Korea
| | - Kyeung Min Joo
- Department of Anatomy and Cell Biology, Sungkyunkwan University School of Medicine, Samsung Biomedical Research Institute, Samsung Medical CenterSuwonRepublic of Korea
| | - Jae Young Kwon
- Department of Biological Sciences, Sungkyunkwan UniversitySuwonRepublic of Korea
| | - Kyung-Hoon Lee
- Department of Anatomy and Cell Biology, Sungkyunkwan University School of Medicine, Samsung Biomedical Research Institute, Samsung Medical CenterSuwonRepublic of Korea
| | - KyeongJin Kang
- Neurovascular Unit Research Group, Korea Brain Research InstituteDaeguRepublic of Korea
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3
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Fulton KA, Zimmerman D, Samuel A, Vogt K, Datta SR. Common principles for odour coding across vertebrates and invertebrates. Nat Rev Neurosci 2024; 25:453-472. [PMID: 38806946 DOI: 10.1038/s41583-024-00822-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 04/30/2024] [Indexed: 05/30/2024]
Abstract
The olfactory system is an ideal and tractable system for exploring how the brain transforms sensory inputs into behaviour. The basic tasks of any olfactory system include odour detection, discrimination and categorization. The challenge for the olfactory system is to transform the high-dimensional space of olfactory stimuli into the much smaller space of perceived objects and valence that endows odours with meaning. Our current understanding of how neural circuits address this challenge has come primarily from observations of the mechanisms of the brain for processing other sensory modalities, such as vision and hearing, in which optimized deep hierarchical circuits are used to extract sensory features that vary along continuous physical dimensions. The olfactory system, by contrast, contends with an ill-defined, high-dimensional stimulus space and discrete stimuli using a circuit architecture that is shallow and parallelized. Here, we present recent observations in vertebrate and invertebrate systems that relate the statistical structure and state-dependent modulation of olfactory codes to mechanisms of perception and odour-guided behaviour.
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Affiliation(s)
- Kara A Fulton
- Department of Neuroscience, Harvard Medical School, Boston, MA, USA
| | - David Zimmerman
- Department of Physics, Harvard University, Cambridge, MA, USA
| | - Aravi Samuel
- Department of Physics, Harvard University, Cambridge, MA, USA
| | - Katrin Vogt
- Department of Physics, Harvard University, Cambridge, MA, USA.
- Department of Biology, University of Konstanz, Konstanz, Germany.
- Centre for the Advanced Study of Collective Behaviour, University of Konstanz, Konstanz, Germany.
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4
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Puri P, Wu ST, Su CY, Aljadeff J. Peripheral preprocessing in Drosophila facilitates odor classification. Proc Natl Acad Sci U S A 2024; 121:e2316799121. [PMID: 38753511 PMCID: PMC11126917 DOI: 10.1073/pnas.2316799121] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2023] [Accepted: 04/16/2024] [Indexed: 05/18/2024] Open
Abstract
The mammalian brain implements sophisticated sensory processing algorithms along multilayered ("deep") neural networks. Strategies that insects use to meet similar computational demands, while relying on smaller nervous systems with shallow architectures, remain elusive. Using Drosophila as a model, we uncover the algorithmic role of odor preprocessing by a shallow network of compartmentalized olfactory receptor neurons. Each compartment operates as a ratiometric unit for specific odor-mixtures. This computation arises from a simple mechanism: electrical coupling between two differently sized neurons. We demonstrate that downstream synaptic connectivity is shaped to optimally leverage amplification of a hedonic value signal in the periphery. Furthermore, peripheral preprocessing is shown to markedly improve novel odor classification in a higher brain center. Together, our work highlights a far-reaching functional role of the sensory periphery for downstream processing. By elucidating the implementation of powerful computations by a shallow network, we provide insights into general principles of efficient sensory processing algorithms.
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Affiliation(s)
- Palka Puri
- Department of Physics, University of California, San Diego, La Jolla, CA92093
| | - Shiuan-Tze Wu
- Department of Neurobiology, University of California, San Diego, La Jolla, CA92093
| | - Chih-Ying Su
- Department of Neurobiology, University of California, San Diego, La Jolla, CA92093
| | - Johnatan Aljadeff
- Department of Neurobiology, University of California, San Diego, La Jolla, CA92093
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5
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Schuh E, Cassau S, Ismaieel AR, Stieber R, Krieger J, Hansson BS, Sachse S, Bisch-Knaden S. Females smell differently: characteristics and significance of the most common olfactory sensilla of female silkmoths. Proc Biol Sci 2024; 291:20232578. [PMID: 38228178 DOI: 10.1098/rspb.2023.2578] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2023] [Accepted: 12/13/2023] [Indexed: 01/18/2024] Open
Abstract
In the silkmoth Bombyx mori, the role of male sensilla trichodea in pheromone detection is well established. Here we study the corresponding female sensilla, which contain two olfactory sensory neurons (OSNs) and come in two lengths, each representing a single physiological type. Only OSNs in medium trichoids respond to the scent of mulberry, the silkworm's exclusive host plant, and are more sensitive in mated females, suggesting a role in oviposition. In long trichoids, one OSN is tuned to (+)-linalool and the other to benzaldehyde and isovaleric acid, both odours emitted by silkworm faeces. While the significance of (+)-linalool detection remains unclear, isovaleric acid repels mated females and may therefore play a role in avoiding crowded oviposition sites. When we examined the underlying molecular components of neurons in female trichoids, we found non-canonical co-expression of Ir8a, the co-receptor for acid responses, and ORco, the co-receptor of odorant receptors, in long trichoids, and the unexpected expression of a specific odorant receptor in both trichoid sensillum types. In addition to elucidating the function of female trichoids, our results suggest that some accepted organizational principles of the insect olfactory system may not apply to the predominant sensilla on the antenna of female B. mori.
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Affiliation(s)
- Elisa Schuh
- Department of Evolutionary Neuroethology, Max Planck Institute for Chemical Ecology, Hans-Knoell-Straße 8, 07745 Jena, Germany
- Research Group Olfactory Coding, Max Planck Institute for Chemical Ecology, Hans-Knoell-Straße 8, 07745 Jena, Germany
| | - Sina Cassau
- Institute of Biology/Zoology, Department of Animal Physiology, Martin Luther University Halle-Wittenberg, Hoher Weg 8, 06120 Halle (Saale), Germany
| | - Ahmed R Ismaieel
- Department of Evolutionary Neuroethology, Max Planck Institute for Chemical Ecology, Hans-Knoell-Straße 8, 07745 Jena, Germany
- Entomology Department, Faculty of Science, Ain Shams University, Abbassia, Cairo 11566, Egypt
| | - Regina Stieber
- Department of Evolutionary Neuroethology, Max Planck Institute for Chemical Ecology, Hans-Knoell-Straße 8, 07745 Jena, Germany
| | - Jürgen Krieger
- Institute of Biology/Zoology, Department of Animal Physiology, Martin Luther University Halle-Wittenberg, Hoher Weg 8, 06120 Halle (Saale), Germany
| | - Bill S Hansson
- Department of Evolutionary Neuroethology, Max Planck Institute for Chemical Ecology, Hans-Knoell-Straße 8, 07745 Jena, Germany
| | - Silke Sachse
- Research Group Olfactory Coding, Max Planck Institute for Chemical Ecology, Hans-Knoell-Straße 8, 07745 Jena, Germany
| | - Sonja Bisch-Knaden
- Department of Evolutionary Neuroethology, Max Planck Institute for Chemical Ecology, Hans-Knoell-Straße 8, 07745 Jena, Germany
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6
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Bandyopadhyay P, Sachse S. Mixing things up! - how odor blends are processed in Drosophila. CURRENT OPINION IN INSECT SCIENCE 2023; 59:101099. [PMID: 37562651 DOI: 10.1016/j.cois.2023.101099] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/26/2023] [Revised: 07/26/2023] [Accepted: 08/02/2023] [Indexed: 08/12/2023]
Abstract
Insects have to navigate a complex and rich olfactory environment consisting of mixtures of odors at varying ratios. However, we understand little of how the olfactory system represents these complex blends. This review aims to highlight some of the recent results of studying this mixture code, in the Drosophila melanogaster olfactory system, as well as gives a short background to one of the most challenging questions in olfaction - how are mixtures encoded in the brain?
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Affiliation(s)
- Pramit Bandyopadhyay
- Research Group Olfactory Coding, Max Planck Institute for Chemical Ecology, Hans-Knoell-Str. 8, 07745 Jena, Germany
| | - Silke Sachse
- Research Group Olfactory Coding, Max Planck Institute for Chemical Ecology, Hans-Knoell-Str. 8, 07745 Jena, Germany.
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7
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Chandak R, Raman B. Neural manifolds for odor-driven innate and acquired appetitive preferences. Nat Commun 2023; 14:4719. [PMID: 37543628 PMCID: PMC10404252 DOI: 10.1038/s41467-023-40443-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2021] [Accepted: 07/27/2023] [Indexed: 08/07/2023] Open
Abstract
Sensory stimuli evoke spiking neural responses that innately or after learning drive suitable behavioral outputs. How are these spiking activities intrinsically patterned to encode for innate preferences, and could the neural response organization impose constraints on learning? We examined this issue in the locust olfactory system. Using a diverse odor panel, we found that ensemble activities both during ('ON response') and after stimulus presentations ('OFF response') could be linearly mapped onto overall appetitive preference indices. Although diverse, ON and OFF response patterns generated by innately appetitive odorants (higher palp-opening responses) were still limited to a low-dimensional subspace (a 'neural manifold'). Similarly, innately non-appetitive odorants evoked responses that were separable yet confined to another neural manifold. Notably, only odorants that evoked neural response excursions in the appetitive manifold could be associated with gustatory reward. In sum, these results provide insights into how encoding for innate preferences can also impact associative learning.
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Affiliation(s)
- Rishabh Chandak
- Department of Biomedical Engineering, Washington University in St. Louis, St. Louis, MO, 63130, USA
| | - Baranidharan Raman
- Department of Biomedical Engineering, Washington University in St. Louis, St. Louis, MO, 63130, USA.
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8
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Puri P, Wu ST, Su CY, Aljadeff J. Shallow networks run deep: Peripheral preprocessing facilitates odor classification. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.07.23.550211. [PMID: 37546820 PMCID: PMC10401955 DOI: 10.1101/2023.07.23.550211] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 08/08/2023]
Abstract
The mammalian brain implements sophisticated sensory processing algorithms along multilayered ('deep') neural-networks. Strategies that insects use to meet similar computational demands, while relying on smaller nervous systems with shallow architectures, remain elusive. Using Drosophila as a model, we uncover the algorithmic role of odor preprocessing by a shallow network of compartmentalized olfactory receptor neurons. Each compartment operates as a ratiometric unit for specific odor-mixtures. This computation arises from a simple mechanism: electrical coupling between two differently-sized neurons. We demonstrate that downstream synaptic connectivity is shaped to optimally leverage amplification of a hedonic value signal in the periphery. Furthermore, peripheral preprocessing is shown to markedly improve novel odor classification in a higher brain center. Together, our work highlights a far-reaching functional role of the sensory periphery for downstream processing. By elucidating the implementation of powerful computations by a shallow network, we provide insights into general principles of efficient sensory processing algorithms.
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Affiliation(s)
- Palka Puri
- Department of Physics, University of California San Diego, La Jolla, CA, 92093, USA
| | - Shiuan-Tze Wu
- Department of Neurobiology, University of California San Diego, La Jolla, CA, 92093, USA
| | - Chih-Ying Su
- Department of Neurobiology, University of California San Diego, La Jolla, CA, 92093, USA
| | - Johnatan Aljadeff
- Department of Neurobiology, University of California San Diego, La Jolla, CA, 92093, USA
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9
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Álvarez-Ocaña R, Shahandeh MP, Ray V, Auer TO, Gompel N, Benton R. Odor-regulated oviposition behavior in an ecological specialist. Nat Commun 2023; 14:3041. [PMID: 37236992 DOI: 10.1038/s41467-023-38722-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2022] [Accepted: 05/10/2023] [Indexed: 05/28/2023] Open
Abstract
Colonization of a novel ecological niche can require, or be driven by, evolution of an animal's behaviors promoting their reproductive success. We investigated the evolution and sensory basis of oviposition in Drosophila sechellia, a close relative of Drosophila melanogaster that exhibits extreme specialism for Morinda citrifolia noni fruit. D. sechellia produces fewer eggs than other drosophilids and lays these almost exclusively on noni substrates. We show that visual, textural and social cues do not explain this species-specific preference. By contrast, we find that loss of olfactory input in D. sechellia, but not D. melanogaster, essentially abolishes egg-laying, suggesting that olfaction gates gustatory-driven noni preference. Noni odors are detected by redundant olfactory pathways, but we discover a role for hexanoic acid and the cognate Ionotropic receptor 75b (Ir75b) in odor-evoked oviposition. Through receptor exchange in D. melanogaster, we provide evidence for a causal contribution of odor-tuning changes in Ir75b to the evolution of D. sechellia's oviposition behavior.
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Affiliation(s)
- Raquel Álvarez-Ocaña
- Center for Integrative Genomics, Faculty of Biology and Medicine, University of Lausanne, CH-1015, Lausanne, Switzerland
| | - Michael P Shahandeh
- Center for Integrative Genomics, Faculty of Biology and Medicine, University of Lausanne, CH-1015, Lausanne, Switzerland
| | - Vijayaditya Ray
- Evolutionary Ecology, Ludwig-Maximilians Universität München, Fakultät für Biologie, Biozentrum, Grosshaderner Strasse 2, 82152, Planegg-Martinsried, Germany
| | - Thomas O Auer
- Center for Integrative Genomics, Faculty of Biology and Medicine, University of Lausanne, CH-1015, Lausanne, Switzerland
| | - Nicolas Gompel
- Evolutionary Ecology, Ludwig-Maximilians Universität München, Fakultät für Biologie, Biozentrum, Grosshaderner Strasse 2, 82152, Planegg-Martinsried, Germany
| | - Richard Benton
- Center for Integrative Genomics, Faculty of Biology and Medicine, University of Lausanne, CH-1015, Lausanne, Switzerland.
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10
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Verschut TA, Ng R, Doubovetzky NP, Le Calvez G, Sneep JL, Minnaard AJ, Su CY, Carlsson MA, Wertheim B, Billeter JC. Aggregation pheromones have a non-linear effect on oviposition behavior in Drosophila melanogaster. Nat Commun 2023; 14:1544. [PMID: 36941252 PMCID: PMC10027874 DOI: 10.1038/s41467-023-37046-2] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2022] [Accepted: 02/28/2023] [Indexed: 03/23/2023] Open
Abstract
Female fruit flies (Drosophila melanogaster) oviposit at communal sites where the larvae may cooperate or compete for resources depending on group size. This offers a model system to determine how females assess quantitative social information. We show that the concentration of pheromones found on a substrate increases linearly with the number of adult flies that have visited that site. Females prefer oviposition sites with pheromone concentrations corresponding to an intermediate number of previous visitors, whereas sites with low or high concentrations are unattractive. This dose-dependent decision is based on a blend of 11-cis-Vaccenyl Acetate (cVA) indicating the number of previous visitors and heptanal (a novel pheromone deriving from the oxidation of 7-Tricosene), which acts as a dose-independent co-factor. This response is mediated by detection of cVA by odorant receptor neurons Or67d and Or65a, and at least five different odorant receptor neurons for heptanal. Our results identify a mechanism allowing individuals to transform a linear increase of pheromones into a non-linear behavioral response.
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Affiliation(s)
- Thomas A Verschut
- Groningen Institute for Evolutionary Life Sciences, University of Groningen, Nijenborgh 7, 9747 AG, Groningen, The Netherlands
- Department of Zoology, Stockholm University, 106 91, Stockholm, Sweden
| | - Renny Ng
- Neurobiology Section, Division of Biological Sciences, University of California, San Diego, La Jolla, CA, 92093, USA
| | - Nicolas P Doubovetzky
- Groningen Institute for Evolutionary Life Sciences, University of Groningen, Nijenborgh 7, 9747 AG, Groningen, The Netherlands
| | - Guillaume Le Calvez
- Stratingh Institute for Chemistry, University of Groningen, Nijenborgh 7, 9747 AG, Groningen, The Netherlands
| | - Jan L Sneep
- Stratingh Institute for Chemistry, University of Groningen, Nijenborgh 7, 9747 AG, Groningen, The Netherlands
| | - Adriaan J Minnaard
- Stratingh Institute for Chemistry, University of Groningen, Nijenborgh 7, 9747 AG, Groningen, The Netherlands
| | - Chih-Ying Su
- Neurobiology Section, Division of Biological Sciences, University of California, San Diego, La Jolla, CA, 92093, USA
| | - Mikael A Carlsson
- Department of Zoology, Stockholm University, 106 91, Stockholm, Sweden
| | - Bregje Wertheim
- Groningen Institute for Evolutionary Life Sciences, University of Groningen, Nijenborgh 7, 9747 AG, Groningen, The Netherlands
| | - Jean-Christophe Billeter
- Groningen Institute for Evolutionary Life Sciences, University of Groningen, Nijenborgh 7, 9747 AG, Groningen, The Netherlands.
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11
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Keesey IW. Sensory neuroecology and multimodal evolution across the genus Drosophila. Front Ecol Evol 2022. [DOI: 10.3389/fevo.2022.932344] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
The neural basis and genetic mechanisms for sensory evolution are increasingly being explored in depth across many closely related members of the Drosophila genus. This has, in part, been achieved due to the immense efforts toward adapting gene-editing technologies for additional, non-model species. Studies targeting both peripheral sensory variations, as well as interspecies divergence in coding or neural connectivity, have generated numerous, tangible examples of how and where the evolution of sensory-driven animal behavior has occurred. Here, we review and discuss studies that each aim to identify the neurobiological and genetic components of sensory system evolution to provide a comparative overview of the types of functional variations observed across both perceptual input and behavioral output. In addition, we examined the roles neuroecology and neuroevolution play in speciation events, such as courtship and intraspecies communication, as well as those aspects related to behavioral divergence in host navigation or egg-laying preferences. Through the investigation of comparative, large-scale trends and correlations across diverse, yet closely related species within this highly ecologically variable genus of flies, we can begin to describe the underlying pressures, mechanisms, and constraints that have guided sensory and nervous system evolution within the natural environments of these organisms.
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12
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Copy number changes in co-expressed odorant receptor genes enable selection for sensory differences in drosophilid species. Nat Ecol Evol 2022; 6:1343-1353. [PMID: 35864227 DOI: 10.1038/s41559-022-01830-y] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2022] [Accepted: 06/15/2022] [Indexed: 11/09/2022]
Abstract
Despite numerous examples of chemoreceptor gene family expansions and contractions, how these relate to modifications in the sensory neuron populations in which they are expressed remains unclear. Drosophila melanogaster's odorant receptor (Or) family is ideal for addressing this question because most Ors are expressed in distinct olfactory sensory neuron (OSN) types. Between-species changes in Or copy number may therefore indicate increases or reductions in the number of OSN populations. Here we investigated the Or67a subfamily, which exhibits copy number variation in D. melanogaster and its closest relatives: D. simulans, D. sechellia and D. mauritiana. These species' common ancestor had three Or67a paralogues that had already diverged adaptively. Following speciation, two Or67a paralogues were lost independently in D. melanogaster and D. sechellia, with ongoing positive selection shaping the intact genes. Unexpectedly, the functionally diverged Or67a paralogues in D. simulans are co-expressed in a single neuron population, which projects to a glomerulus homologous to that innervated by Or67a neurons in D. melanogaster. Thus, while sensory pathway neuroanatomy is conserved, independent selection on co-expressed receptors has contributed to species-specific peripheral coding. This work reveals a type of adaptive change largely overlooked for olfactory evolution, raising the possibility that similar processes influence other cases of insect Or co-expression.
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13
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Xu P, Choo YM, Leal WS. Odorant inhibition in mosquito olfaction mediated by inverse agonists. Biochem Biophys Res Commun 2022; 609:156-162. [PMID: 35430419 PMCID: PMC10540603 DOI: 10.1016/j.bbrc.2022.04.015] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2022] [Accepted: 04/05/2022] [Indexed: 11/02/2022]
Abstract
The insect repellent methyl salicylate elicits excitatory responses upon interaction with CquiOR32, an odorant receptor (OR) from the southern house mosquito, Culex quinquefasciatus. By contrast, eucalyptol binds to CquiOR32 to generate electrophysiological and behavioral inhibitory responses. In an attempt to identify CquiOR32 variants displaying more robust inhibitory responses for more accurate current-voltage analysis, we sequenced 31 CquiOR32 clones. In the Xenopus oocyte recording system, CquiOR32V2/CquiOrco-expressing oocytes yielded eucalyptol-elicited outward (inhibitory) currents relatively larger than methyl salicylate-generated inward (excitatory) currents. Rescuing experiments showed that two of the amino acid substitutions in CquiOR32V2 located in a predicted transmembrane helix of the receptor are determinants of the outward/inward ratios. These findings, along with co-stimulus assays, suggest that odorant and inhibitor may bind to the same binding pocket. Current-voltage relationships obtained with standard perfusion buffer and those devoid of Na+ or Cl- indicated that both excitatory and inhibitory currents are mediated, at least in part, by cation. We then concluded that eucalyptol is an inverse agonist, which shifts the open ⇔ closed equilibrium of the receptor toward the closed conformation, thus reducing the spontaneous activity. By contrast, the binding of methyl salicylate shifts the equilibrium towards the open conformation and, consequently, leads to an increase in cation influx.
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Affiliation(s)
- Pingxi Xu
- Department of Molecular and Cellular Biology, University of California-Davis, Davis, CA, 95616, USA
| | - Young-Moo Choo
- Department of Molecular and Cellular Biology, University of California-Davis, Davis, CA, 95616, USA
| | - Walter S Leal
- Department of Molecular and Cellular Biology, University of California-Davis, Davis, CA, 95616, USA.
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