Biology subjects

Afify, A.

Publications and source records attributed to Afify, A..

4 recordsLinked to original sources

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↗

bioRxiv2020

A Feedback Mechanism Regulates Odorant Receptor Expression in the Malaria Mosquito, Anopheles gambiae

Mosquitoes locate and approach humans ( host-seek) when specific Olfactory Neurons (ORNs) in the olfactory periphery activate a specific combination of glomeruli in the mosquito Antennal Lobe (AL). We hypothesize that dysregulating proper glomerular activation in the presence of human odor will prevent host-seeking behavior. In experiments aimed at ectopically activating most ORNs in the presence of human odor, we made a surprising finding: ectopic expression of an AgOr (AgOr2) in Anopheles gambiae ORNs dampens the activity of the expressing neuron. This contrasts studies in Drosophila melanogaster, the typical insect model of olfaction, in which ectopic expression of non-native ORs in ORNs confers ectopic neuronal responses without interfering with native olfactory physiology. To gain insight into this dysfunction in mosquitoes, RNA-seq analyses were performed comparing wild-type antennae to those ectopically expressing AgOr2 in ORNs. Remarkably, almost all Or transcripts were significantly downregulated (except for AgOr2), and additional experiments suggest that it is AgOR2 protein rather than mRNA that mediates this downregulation. Our study shows that ORNs of Anopheles mosquitoes (in contrast to Drosophila) employ a currently unexplored regulatory mechanism of OR expression, which may be adaptable as a vector-control strategy. SIGNIFICANCE STATEMENTStudies in Drosophila melanogaster suggest that insect Olfactory Receptor Neurons (ORNs) do not contain mechanisms by which Odorant Receptors (ORs) regulate OR expression. This has proved useful in studies where ectopic expression of an OR in Drosophila ORNs confers responses to the odorants that activate the newly expressed OR. In experiments in Anopheles gambiae mosquitoes, we found that ectopic expression of an OR in most Anopheles ORNs dampened the activity of the expressing neurons. RNA-seq analyses demonstrated that ectopic OR expression in Anopheles ORNs leads to downregulation of endogenous Or transcripts. Additional experiments suggest that this downregulation required ectopic expression of a functional OR protein. These findings reveal that Anopheles mosquitoes, in contrast to Drosophila, contain a feedback mechanism to regulate OR expression. Mosquito ORNs might employ regulatory mechanisms of OR expression previously thought to occur only in non-insect olfactory systems.

neuroscience↗

bioRxiv2019

Genomics of Egyptian Healthy Volunteers: The EHVol Study

Comprehensive genomic databases offer unprecedented opportunities towards effective tailored strategies for the prevention and treatment of disease. The integration of genomic and phenotypic data from diverse ethnic populations is also key to advancements in precision medicine and novel diagnostic technologies. Current reference genomic databases, however, are not representative of the global human population, making variant interpretation challenging and uncertain, especially in underrepresented populations such as the North African population. To address this, a study of 391 Egyptian healthy volunteers (EHVols) was initiated as a milestone towards establishing the 1000 Egyptian Genomes project.

genomics↗

bioRxiv2017

A GAL80 collection to nullify transgenes in Drosophila olfactory sensory neurons

Fruit flies recognize hundreds of ecologically relevant odors and respond appropriately to them. The complexity, redundancy and interconnectedness of the olfactory machinery complicate efforts to pinpoint the functional contributions of any component neuron or receptor to behavior. Some contributions can only be elucidated in flies that carry multiple mutations and transgenes, but the production of such flies is currently labor-intensive and time-consuming. Here, we describe a set of transgenic flies that express the Saccharomyces cerevisiae GAL80 in specific olfactory sensory neurons (OrX-GAL80s). The GAL80s effectively and specifically subtract the activities of GAL4-driven transgenes that impart anatomical and physiological phenotypes. OrX-GAL80s can allow researchers to efficiently activate only one or a few types of functional neurons in an otherwise nonfunctional olfactory background. Such experiments will improve our understanding of the mechanistic connections between odorant inputs and behavioral outputs at the resolution of only a few functional neurons.

neuroscience↗