FIGURE 6.

Accessory cells of touch receptors in Drosophila. (A) Depiction of a bristle, the major type of touch receptor in the adult of Drosophila. The hair shaft of the bristle is connected to the dendrite of a sensory neuron via physical contact, thus transducing the hair deflection into activation of mechanosensitive channels in the neuron. The dendrite of the neuron bathes in an endolymph characterized by a high concentration of K⁺ and a low concentration of Ca²⁺ (Grunert and Gnatzy, 1987; Eberl, 1999; Roy et al., 2013). The sensory neuron is surrounded by four accessory cells: the thecogen, the trichogen, the tomogen, and the F-cell, which is of epidermal origin. (B) Schematic depiction of the need for F-cells for response to bristle deflection. Due to the high K⁺ concentration of the endolymph, the transepithelial potential (TEP) is normally ∼ + 50 mV (left panel). Upon hair deflection, the activation of the mechanosensitive channel in the neuron induces repolarization of the TEP. In Drosophila mutants in which the F-cells are either genetically ablated or do not develop, TEP is ∼ + 25 mV and deflection of the hair shaft causes smaller changes in the TEP [adapted from Mangione et al. (2023)].