Abstract:Ionotropic Receptors (IRs) are a large subfamily of variant ionotropic glutamate receptors present across Protostomia. While these receptors are most extensively studied for their roles in chemosensory detection, recent work has implicated two family members, IR21a and IR25a, in thermosensation in Drosophila. Here we characterize one of the most evolutionarily deeply conserved receptors, IR93a, and show that it is co-expressed and functions with IR21a and IR25a to mediate physiological and behavioral responses… Show more
“…We observed robust, non-adapting increases in GCaMP fluorescence upon switching from low to high humidity air (7% to 90% relative humidity [RH]), and robust, non-adapting decreases in fluorescence upon switching from high to low humidity air (Figure 2b–d). These humidity-dependent calcium responses are opposite of those of IR40a-expressing dry cells (Enjin et al, 2016; Knecht et al, 2016), indicating that Ir68a-Gal4 neurons correspond to moist cells.10.7554/eLife.26654.004Figure 2. Ir68a is required for humidity detection by moist cells.( a ) Schematic of the Drosophila head (viewed from above) illustrating the projection of Ir68a-Gal4- labeled neurons (green) from the sacculus to the antennal lobes in the brain, visualized through a hole cut in the head cuticle. ( b ) Left panel: Raw fluorescence image of Ir68a -labeled axons (in an Ir68a-Gal4;UAS-GCaMP6m(III) animal) innervating the antennal lobe.…”
Section: Resultsmentioning
confidence: 98%
“…Importantly, these Ir68a-Gal4 -expressing cells are intermingled with, but distinct from Ir40a- expressing neurons (Figure 1c), consistent with a role as moist cells in the sensilla of chamber II.10.7554/eLife.26654.002Figure 1. Ir68a and Ir40a reporters are expressed by neighboring neurons in the Drosophila sacculus.( a ) Left: schematic of the adult Drosophila antenna, showing the location of the sacculus (red) inside the antenna. Right: the sacculus contains three chambers (I, II, III) lined with sensilla of various morphologies (modified from Shanbhag et al [1995]) and Knecht et al [2016]). ( b ) Immunostaining of the antenna of a Ir68a-Gal4/UAS-myr:GFP ( Ir68a>GFP ) fly (left).…”
Insects use hygrosensation (humidity sensing) to avoid desiccation and, in vectors such as mosquitoes, to locate vertebrate hosts. Sensory neurons activated by either dry or moist air (‘dry cells’ and ‘moist cells’) have been described in many insects, but their behavioral roles and the molecular basis of their hygrosensitivity remain unclear. We recently reported that Drosophila hygrosensation relies on three Ionotropic Receptors (IRs) required for dry cell function: IR25a, IR93a and IR40a (Knecht et al., 2016). Here, we discover Drosophila moist cells and show that they require IR25a and IR93a together with IR68a, a conserved, but orphan IR. Both IR68a- and IR40a-dependent pathways drive hygrosensory behavior: each is important for dry-seeking by hydrated flies and together they underlie moist-seeking by dehydrated flies. These studies reveal that humidity sensing in Drosophila, and likely other insects, involves the combined activity of two molecularly related but neuronally distinct hygrosensing systems.DOI:
http://dx.doi.org/10.7554/eLife.26654.001
“…We observed robust, non-adapting increases in GCaMP fluorescence upon switching from low to high humidity air (7% to 90% relative humidity [RH]), and robust, non-adapting decreases in fluorescence upon switching from high to low humidity air (Figure 2b–d). These humidity-dependent calcium responses are opposite of those of IR40a-expressing dry cells (Enjin et al, 2016; Knecht et al, 2016), indicating that Ir68a-Gal4 neurons correspond to moist cells.10.7554/eLife.26654.004Figure 2. Ir68a is required for humidity detection by moist cells.( a ) Schematic of the Drosophila head (viewed from above) illustrating the projection of Ir68a-Gal4- labeled neurons (green) from the sacculus to the antennal lobes in the brain, visualized through a hole cut in the head cuticle. ( b ) Left panel: Raw fluorescence image of Ir68a -labeled axons (in an Ir68a-Gal4;UAS-GCaMP6m(III) animal) innervating the antennal lobe.…”
Section: Resultsmentioning
confidence: 98%
“…Importantly, these Ir68a-Gal4 -expressing cells are intermingled with, but distinct from Ir40a- expressing neurons (Figure 1c), consistent with a role as moist cells in the sensilla of chamber II.10.7554/eLife.26654.002Figure 1. Ir68a and Ir40a reporters are expressed by neighboring neurons in the Drosophila sacculus.( a ) Left: schematic of the adult Drosophila antenna, showing the location of the sacculus (red) inside the antenna. Right: the sacculus contains three chambers (I, II, III) lined with sensilla of various morphologies (modified from Shanbhag et al [1995]) and Knecht et al [2016]). ( b ) Immunostaining of the antenna of a Ir68a-Gal4/UAS-myr:GFP ( Ir68a>GFP ) fly (left).…”
Insects use hygrosensation (humidity sensing) to avoid desiccation and, in vectors such as mosquitoes, to locate vertebrate hosts. Sensory neurons activated by either dry or moist air (‘dry cells’ and ‘moist cells’) have been described in many insects, but their behavioral roles and the molecular basis of their hygrosensitivity remain unclear. We recently reported that Drosophila hygrosensation relies on three Ionotropic Receptors (IRs) required for dry cell function: IR25a, IR93a and IR40a (Knecht et al., 2016). Here, we discover Drosophila moist cells and show that they require IR25a and IR93a together with IR68a, a conserved, but orphan IR. Both IR68a- and IR40a-dependent pathways drive hygrosensory behavior: each is important for dry-seeking by hydrated flies and together they underlie moist-seeking by dehydrated flies. These studies reveal that humidity sensing in Drosophila, and likely other insects, involves the combined activity of two molecularly related but neuronally distinct hygrosensing systems.DOI:
http://dx.doi.org/10.7554/eLife.26654.001
Insects comprise the most diverse and successful animal group with over one million described species that are found in almost every terrestrial and limnic habitat, with many being used as important models in genetics, ecology, and evolutionary research. Genome sequencing projects have greatly expanded the sampling of species from many insect orders, but genomic resources for species of certain insect lineages have remained relatively limited to date. To address this paucity, we sequenced the genome of the banded demoiselle, Calopteryx splendens, a damselfly (Odonata: Zygoptera) belonging to Palaeoptera, the clade containing the first winged insects. The 1.6 Gbp C. splendens draft genome assembly is one of the largest insect genomes sequenced to date and encodes a predicted set of 22,523 protein-coding genes. Comparative genomic analyses with other sequenced insects identified a relatively small repertoire of C. splendens detoxification genes, which could explain its previously noted sensitivity to habitat pollution. Intriguingly, this repertoire includes a cytochrome P450 gene not previously described in any insect genome. The C. splendens immune gene repertoire appears relatively complete and features several genes encoding novel multi-domain peptidoglycan recognition proteins. Analysis of chemosensory genes revealed the presence of both gustatory and ionotropic receptors, as well as the insect odorant receptor coreceptor gene (OrCo) and at least four partner odorant receptors (ORs). This represents the oldest known instance of a complete OrCo/OR system in insects, and provides the molecular underpinning for odonate olfaction. The C. splendens genome improves the sampling of insect lineages that diverged before the radiation of Holometabola and offers new opportunities for molecular-level evolutionary, ecological, and behavioral studies.
“…The sensor(s) that allow mosquitoes to detect attractive heat cues are still unknown. Ionotropic Receptors (IRs) that are temperature responsive have been found in Drosophila [25, 26]. Further studies are needed to identify whether these receptors or others are important for mosquitoes to detect the temperature of their hosts.…”
Section: Human Cuesmentioning
confidence: 99%
“…Drosophila IRs respond primarily to amines and acids while ORs respond to esters and alcohols [47]. Beyond olfaction, Drosophila IRs play a role in taste [48, 49], moisture and temperature sensing [25, 26], and possibly in the auditory system [50]. Although GRs are usually involved in taste [35], specialized GRs have been implicated in other sensory modalities in insects including light sensing [51], warmth sensing [52], and CO 2 detection [53] .…”
Section: Molecular Sensors Of Human Cuesmentioning
Mosquitoes detect the presence of humans by integrating chemosensory, thermal, and visual cues. Among these, odors are crucial for mosquito host detection. Insects have evolved a diverse repertoire of receptors to detect their plant and animal hosts. Genetic analysis of these receptors in Drosophila has set the stage for similar studies in mosquitoes. The diversity of the cues involved in mosquito host-seeking has made designing behavioral control strategies a challenge. The sensory receptors that are most important for mosquito detection of humans can now be determined using genome editing. Here, we will review our current understanding of the salient cues that attract mosquitoes, their receptors, and suggest ways forward for novel olfaction-based vector control strategies.
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