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An important role of Ionotropic receptors in insect chemosensation D1 楊 斌

2012/10/25 20:09 に Takashi Matsuo が投稿
2012年10月19日(金) 
 
    Insect chemosensory receptors have been perfectly characterized at a molecular level in many species. Recently, a third family of Drosophila chemosensory receptors-the ionotropic receptors (IRs)-has been identified besides ORs and GRs in coeloconic sensilla [1, 2], and were named for their homology to Ionotropic glutamate receptors (iGluRs) [3]. Importantly, IRs contain divergent ligand-binding domains that lack glutamate-interacting residues which suggesting that they recognize distinct ligands. IRs are expressed in a combine torial fashion in sensory neurons that respond to many distinct odors but do not express either insect odorant receptors (ORs) or gustatory receptors (GRs) [1]. So IRs may be equally important with ORs in chemoreception.
Comparison of chemosensory receptors in insects and mammals showed that IRs are only found in insects but not mammals [4]. A farther study of evolution on IRs indicated that IRs are found across the protostomian branch of the animal kingdom. The evolutionary forces acting on the IR gene subfamilies parallel those on the ORs and GRs and appear to correlate with their putative distinct chemosensory functions in olfaction and gestation. Moreover, whereas OR repertoires are primarily species specific, many IRs are conserved in most or all insects [5]. The deeper conservation of IRs offers a possibility to consider how the stepwise expansion of this receptor repertoire during evolution is linked to the functional and anatomical diversification of this olfactory subsystem [6].
    Functional analyses of IRs indicated that IRs affect environment explorational and sexual behaviors of insects. IRs are specific for selecting amines and acids, which complements the broader tuning of ORs for esters and alcohols [6]. Olfactory sensory neurons in the fruitfly, Drosophila melanogaster, express an ionotropic receptor IR64a that is highly selective for acidity [7]. Besides, IRs also affect insect sexual behaviors. IR84a, an olfactory receptor for food-derived odours, the aromatic odours phenylacetic acid and phenylacetaldehyde, was found to promote male courtship in Drosophila [8].
    Because of the importance of IRs on insect environment-detecting, candidates of IRs have been identified in several moth species [9, 10]. Studies of IRs will make a deep understanding on insect communication in future.
 
References:
[1] Benton et al. (2009) Variant Ionotropic Glutamate Receptors as Chemosensory Receptors in Drosophila. Cell: 136 , 149-162
[2] Maria L. Spletter and Liqun Luo. (2009) A New Family of Odorant Receptors in Drosophila. Cell 136
[3] L. Abuin et al. (2011) Functional Architecture of Olfactory Ionotropic Glutamate Receptors. Neuron: 69, 44-60
[4] A.F. Silbering & R. Benton. (2010) Ionotropic and metabotropic mechanisms in chemoreception: ‘chance or design’? EMBo reports.
[5] V. Croset et al. (2010) Ancient Protostome Origin of Chemosensory Ionotropic Glutamate Receptors and the Evolution of Insect Taste and Olfaction. PLoS Genetics: Volume 6
[6] A.F. Silbering et al. (2011) Complementary Function and Integrated Wiring of the Evolutionarily Distinct Drosophila Olfactory Subsystems. The Journal of Neuroscience. 31(38): 13357-13375
[7] Minrong Ai et al. (2010) Acid sensing by the Drosophila olfactory system. NATURE. VOL 468
[8] Y. Grosjean et al. (2011) An olfactory receptor for food-derived odours promotes male courtship in Drosophila. NATURE. VOL 478:13
[9] J. M. Bengtsson et al. (2012) Putative Chemosensory Receptors of the Codling Moth, Cydia pomonella, Identified by Antennal Transcriptome Analysis. PLoS ONE: Volume 7
[10] V. Olivier et al. (2011) Candidate chemosensory ionotropic receptors in a Lepidoptera. Insect Molecular Biology.  20(2), 189-199

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