Drosophilasensory receptors—a set of molecular Swiss Army Knives

Abstract

Genetic approaches in the fruit fly, Drosophila melanogaster, have led to a major triumph in the field of sensory biology—the discovery of multiple large families of sensory receptors and channels. Some of these families, such as transient receptor potential channels, are conserved from animals ranging from worms to humans, while others, such as “gustatory receptors,” “olfactory receptors,” and “ionotropic receptors,” are restricted to invertebrates. Prior to the identification of sensory receptors in flies, it was widely assumed that these proteins function in just one modality such as vision, smell, taste, hearing, and somatosensation, which includes thermosensation, light, and noxious mechanical touch. By employing a vast combination of genetic, behavioral, electrophysiological, and other approaches in flies, a major concept to emerge is that many sensory receptors are multitaskers. The earliest example of this idea was the discovery that individual transient receptor potential channels function in multiple senses. It is now clear that multitasking is exhibited by other large receptor families including gustatory receptors, ionotropic receptors, epithelial Na+ channels (also referred to as Pickpockets), and even opsins, which were formerly thought to function exclusively as light sensors. Genetic characterizations of these Drosophila receptors and the neurons that express them also reveal the mechanisms through which flies can accurately differentiate between different stimuli even when they activate the same receptor, as well as mechanisms of adaptation, amplification, and sensory integration. The insights gleaned from studies in flies have been highly influential in directing investigations in many other animal models.

Mechanism for food texture preference based on grittiness

“…S-and L-type sensilla contain four GRNs, whereas I-type sensilla contain two GRNs. 1 Most GRNs respond to multiple stimuli but for simplicity are referred to as: (A) sweet, (B) bitter, (C) water, (D) cation, and (E) low salt. 1 All A-D GRNs appeared to express the tmem63 reporter (Figures 3G-3R; Table 1).…”

“…1 Most GRNs respond to multiple stimuli but for simplicity are referred to as: (A) sweet, (B) bitter, (C) water, (D) cation, and (E) low salt. 1 All A-D GRNs appeared to express the tmem63 reporter (Figures 3G-3R; Table 1). We did not examine overlap with E GRNs, which are specific tmem63 required in md-L neurons for attraction to particles in food The observations that tmem63 is expressed in multiple types of neurons raised the question as to which type functions in detecting particles in food.…”

“…Genotype: tmc-QF,tmem63 2 /UAS-GCaMP6f,UAS-tdTomato,tmem63 1 ;QUAS-Gal4/+. Pseudo color of GCaMP6f and tdTomato pre-stimuli (0) and at peak levels of mechanical stimulation (1)(2)(3)(4). Scale bar, 20 mm.…”

“…(I) Testing for rescue of tmem63 1/2 defect by expressing UAS-tmem63 in md-L. Genotype: tmc-QF,tmem63 2 /UAS-GCaMP6f,UAS-tdTomato,tmem63 1 ;QUAS-Gal4/UAS-tmem63. J, tmc 1 . (K and L) Extracellular recordings of md-L responses to 10-mm or 20-mm cuticle deformation.…”

“…Multiple classes of chemosensory receptors have been defined in flies, mice, and other animals that contribute to the discrimination of nutritious from noxious foods. [1][2][3] In humans and other mammals, the textural features of food also have a major impact on food appeal. 4 The texture of food is influenced by its hardness and viscosity, as well as the size of food particles.…”