Ionotropic receptors (IRs): chemosensory ionotropic glutamate receptors in Drosophila and beyond.

TLDR: The expression and function of IRs in Drosophila are reviewed, highlighting similarities and differences with iGluRs, and an evolutionarily conserved role for these receptors in chemosensation in insects and other protostomes is implied.

About: This article is published in Insect Biochemistry and Molecular Biology.The article was published on 2013-09-01 and is currently open access. It has received 364 citations till now. The article focuses on the topics: Ionotropic glutamate receptor & Class C GPCR.

Figures

Fig. 4. Evolution and phylogeny of IR repertoires across protostomes. (A) Left: Table illustrating the presence and number of orthologous sequences to D. melanogaster olfactory IRs identified in the genome sequence (colored boxes) or in EST datasets (lighter shaded boxes) of the indicated protostome species, ordered according to the cladogram on the far left. Colors distinguish insect orders or other groups of species. Predicted pseudogenes are indicated by a “p”. IR60a and IR68a are included in this table because of their phylogenetic relatedness to other olfactory IRs, although there is no available evidence for antennal expression or function (Croset et al., 2010). Right: Histogram representing the total number of olfactory IR-like receptors (defined by their homology to D. melanogaster sequences) and other e mostly species-specific e IRs in each genome-sequenced species (numbers for species for which only EST data are available are not included). (B) Phylogenetic tree showing the relationships between all IR protein sequences from the species shown in (A),

Fig. 3. Neuroanatomy of IR olfactory circuits. (A) Antennal lobe glomerular innervations of t neurons (PNs) in the higher olfactory centers (mushroom body and lateral horn), color-co mushroom body and project directly to the lateral horn are shown in lighter shades. (D: dor with permission.

Frequently asked questions

Q1. What contributions have the authors mentioned in the paper "Ionotropic receptors (irs): chemosensory ionotropic glutamate receptors in drosophila and beyond" ?

Here, the authors review the expression and function of IRs in Drosophila, highlighting similarities and differences with iGluRs. The authors also briefly describe the organization of the neuronal circuits in which IRs function, comparing and contrasting them with the sensory pathways expressing ORs. 

Q2. What are the future works mentioned in the paper "Ionotropic receptors (irs): chemosensory ionotropic glutamate receptors in drosophila and beyond" ?

The clear homology of IRs and iGluRs has helped to address molecular mechanisms by which odor recognition is converted into neuronal depolarization by these receptors ewhich are issues that still remain unclear for ORs ( Nakagawa and Vosshall, 2009 ) e and further advancement in the future seems likely. Intriguingly, one of these receptors, IR94b, was recently implicated in auditory system function ( Senthilan et al., 2012 ), raising the possibility that IRs may also have non-chemosensory roles. Beyond Drosophila, large repertoires of IR sequences in molluscs, annelids, nematode worms, crustaceans and diverse insects remain to be characterized, and it will be exciting to see the functional conservation and divergence of this repertoire across these ecologically disparate species. The revelation of a progressive expansion of the olfactory IR repertoire across protostomes ( Fig. 4A ) e whose resolution will certainly be increased with additional insect genomes, particularly from orthopteran species ( Hansson and Stensmyr, 2011 ; Rebora et al., 2012 ) e invites comparative analyses both between individual receptors/circuits within a particular species, and between presumed conserved receptors in different species. 

Q3. What is the IRs of Anopheles gambiae?

Acids and amines, for example, are key host-seeking signals in mosquitoes (van der Goes van Naters and Carlson, 2006), and it is highly likely that the Anopheles gambiae IRs (Liu et al., 2010) underlie the acid and amine responses in grooved peg sensilla OSNs in the adult antenna (Qiu et al., 2006). 

Q4. How many IRs are not detected in the D. melanogaster antenna?

The 41 intact IRs whose expression is not detected in the D. melanogaster antenna display a more dynamic pattern of evolution within drosophilids. 

Q5. What is the role of IRs in Drosophila?

Within D. melanogaster, the olfactory IRs represent just a quarter of the entire repertoire, so definition of the site of expression and function of the remaining larger fraction represents a key area of interest. 

Q6. What is the role of IRs in D. melanogaster?

The arista contains thermosensory and not olfactory neurons, but the heat-sensing function is thought to be mediated by TRP channels (Foelix et al., 1989; Gallio et al., 2011) and the role of these IRs is unknown. 

Q7. How many IRs are found in Drosophila?

Within the 12 species whose genomes were first available, IR repertoires range in size from 58 genes in Drosophila pseudoobscura, Drosophila virilis and Drosophila grimshawi to 69 in Drosophila simulans and Drosophila sechellia (Croset et al., 2010). 

Q8. What is the sequence homology of iGluRs?

Within the Drosophila IR repertoire, sequence homology ranges from 10 to 70%, strongly suggesting functional diversity (Benton et al., 2009). 

Q9. What are some examples of IR genes that might have species-specific functions?

There are also several examples of lineage specific expansions of IR genes, for example, the IR317 subfamily in the ant Camponotus floridanus (Zhou et al., 2012), which might have species-specific functions. 

Q10. How many of these genes are expressed in the antenna?

Comprehensive expression analysis of these genes by RT-PCR, fluorescence RNA in situ hybridization and/or using transgenic reporters has shown that 16 of these are expressed in the antenna. 

Q11. What is the reason for the segregation of IR olfactory neurons?

Nevertheless it is likely that while sensory input within these two olfactory subsystems is segregated in the antennal lobe, integration of sensory information occurs in the central brain to ultimately produce a co-ordinated behavioral response.