Biology subjects

Menuz, K.

Publications and source records attributed to Menuz, K..

4 recordsLinked to original sources

bioRxiv2021

Evaluation of a high-throughput deorphanization strategy to identify cytochrome p450s important for odor degradation in Drosophila

Members of the cytochrome p450 (CYP) enzyme family are abundantly expressed in insect olfactory tissues, where they are thought to act as Odorant Degrading Enzymes (ODEs). However, their contribution to olfactory signaling in vivo is poorly understood. This is due in part to the challenge of identifying which of the dozens of antennal-expressed CYPs might inactivate a given odorant. Here, we tested a high-throughput deorphanization strategy in Drosophila to identify CYPs that are transcriptionally induced by exposure to a plant volatile. We discovered three CYPs selectively upregulated by the odorant using transcriptional profiling. Although these CYPs are shown to be broadly expressed in the antenna in non-neuronal cells, electrophysiological recordings from CYP mutants did not reveal any changes in olfactory neuron responses to the odorant. Neurons were desensitized by pre-exposing flies to the odorant, but this effect was similar in CYP mutants. Together, our data suggest that this transcriptomic approach may not be useful for identifying CYPs that contribute to olfactory signaling. We go on to show that some CYPs have highly restricted expression patterns in the antenna, and suggest that such CYPs may be useful candidates for further studies on olfactory CYP function.

neuroscience↗

bioRxiv2021

Functional characterization of odor responses and gene expression changes in olfactory co-receptor mutants in Drosophila

Two large families of olfactory receptors, the Odorant Receptors (ORs) and the Ionotropic Receptors (IRs), mediate responses to most odors in the insect olfactory system. Individual odor binding "tuning" OR receptors are expressed by olfactory neurons in basiconic and trichoid sensilla and require the co-receptor Orco to function. The situation for IRs is more complex. Different tuning IR receptors are expressed by olfactory neurons in coeloconic sensilla and rely on either the Ir25a or Ir8a co-receptors; some evidence suggests that Ir76b may also act as a coreceptor, but its function has not been systematically examined. This is particularly important as recent data indicate that nearly all coeloconic olfactory neurons co-express Ir25a, Ir8a, and Ir76b. Here, we report the effects of Drosophila olfactory co-receptor mutants on odor detection by coeloconic olfactory neurons and determine their broader impact on gene expression through RNASeq analysis. We demonstrate that Ir76b and Ir25a function together in all amine-sensing olfactory receptor neurons. In most neurons, loss of either co-receptor abolishes amine responses, whereas in ac1 sensilla, amine responses persist in the absence of Ir76b or Ir25a, but are lost in a double-mutant. Such responses do not require Ir8a. Conversely, acid-sensing ORNs require Ir8a, but not Ir76b or Ir25a. Using antennal transcriptional profiling, we find that the expression of acid-sensing IR receptors is significantly reduced in Ir8a mutants, but is unaffected by the loss of Ir25a or Ir76b. Similarly, select OR tuning receptors are also downregulated in Orco2 mutants. In contrast, expression of amine-sensing IR receptors is mostly unchanged in Ir25a and Ir76b mutants. Together, our data reveal new aspects of co-receptor function in the olfactory system. SummaryInsect vectors of human disease rely on their sense of smell to locate humans for blood meals. A critical first step in olfaction is the odorant-induced activation of receptors on olfactory neurons. There are two major olfactory receptor families in insects, with each species having dozens of different odorant-binding "tuning" receptors. The receptor complexes also contain non-tuning co-receptors, which are highly conserved across insect species and are required for function. Here we characterize co-receptor mutants with electrophysiological recordings and transcriptome analysis in Drosophila. Our findings resolve the differential co-receptor dependence of olfactory neuron responses to volatile amines and acids. We also report changes in antennal gene expression that result from the absence of these co-receptors. Most notably, the absence of some co-receptors leads to a selective loss of transcript expression for the tuning olfactory receptors whose function depends on the missing co-receptors. Together our data provide new insight into the roles of co-receptors in insect olfaction.

neuroscience↗

bioRxiv2021

An ammonium transporter is a non-canonical olfactory receptor for ammonia

Two families of ligand-gated ion channels function as olfactory receptors in insects. Here, we show that these canonical olfactory receptors are not necessary for responses to ammonia, a key ecological odor that is attractive to many insects including disease vectors and agricultural pests. Instead, we show that a member of the ancient electrogenic ammonium transporter family, Amt, is a new type of olfactory receptor. We report two hitherto unidentified olfactory neuron populations that mediate neuronal and behavioral responses to ammonia. Their endogenous ammonia responses are Amt-dependent, and ectopic expression of either Drosophila or Anopheles Amt confers ammonia sensitivity. Amt is the first transporter known to function as an olfactory receptor in animals, and its role may be conserved across insect species.

neuroscience↗

bioRxiv2020

Widespread Polymodal Chemosensory Receptor Expression in Drosophila Olfactory Neurons

Drosophila melanogaster olfactory neurons have long been thought to express only one chemosensory receptor gene family. There are two main olfactory receptor gene families in Drosophila, the Odorant Receptors (ORs) and the Ionotropic Receptors (IRs). The dozens of odorant binding receptors in each family require at least one co-receptor gene in order to function: Orco for ORs, and Ir25a, Ir8a, and Ir76b for IRs. Using a new genetic knock-in strategy, we targeted the four co-receptors representing the main chemosensory families in Drosophila (Orco, Ir8a, Ir76b, Ir25a). Co-receptor knock-in expression patterns were verified as accurate representations of endogenous expression. We find extensive overlap in expression among the different co-receptors. As defined by innervation into antennal lobe glomeruli, Ir25a is broadly expressed in 88% of all olfactory sensory neuron classes and is co-expressed in 82% of Orco+ neuron classes, including all neuron classes in the maxillary palp. Orco, Ir8a, and Ir76b expression patterns are also more expansive than previously assumed. Single sensillum recordings from Orco-expressing Ir25a mutant antennal and palpal neurons identify changes in olfactory responses. These results suggest co-expression of chemosensory receptors is common in olfactory neurons. Together, our data present the first comprehensive map of chemosensory co-receptor expression and reveal their unexpected widespread co-expression in the fly olfactory system.

neuroscience↗