Membrane potential regulates Hedgehog signalling in the Drosophila wing imaginal disc.

Maya Emmons‐Bell,Iswar K Hariharan

doi:10.15252/embr.202051861

Abstract

While the membrane potential of cells has been shown to be patterned in some tissues, specific roles for membrane potential in regulating signalling pathways that function during development are still being established. In the Drosophila wing imaginal disc, Hedgehog (Hh) from posterior cells activates a signalling pathway in anterior cells near the boundary which is necessary for boundary maintenance. Here, we show that membrane potential is patterned in the wing disc. Anterior cells near the boundary, where Hh signalling is most active, are more depolarized than posterior cells across the boundary. Elevated expression of the ENaC channel Ripped Pocket (Rpk), observed in these anterior cells, requires Hh. Antagonizing Rpk reduces depolarization and Hh signal transduction. Using genetic and optogenetic manipulations, in both the wing disc and the salivary gland, we show that membrane depolarization promotes membrane localization of Smoothened and augments Hh signalling, independently of Patched. Thus, membrane depolarization and Hh‐dependent signalling mutually reinforce each other in cells immediately anterior to the compartment boundary.

Highlights

During the development of many organisms, boundaries between different groups of cells function as developmental organizers, serving as sources of morphogens, molecules that diffuse from their source and specify cell fates in a dose-dependent manner (reviewed by (Blair, 2003; Irvine & Rauskolb, 2001))
We show that Vmem is patterned in a spatiotemporal manner during development of the wing disc of Drosophila, and that it regulates Hedgehog signaling, compartment boundary maintenance, and the differential ability of cells to survive in the two compartments
We found that the expression of at least two regulators of Vmem, the ENaC channel Ripped Pocket (Rpk) and the alpha subunit of the Na+/K+ ATPase are expressed at higher levels in this same portion of the disc

Summary

Introduction

During the development of many organisms, boundaries between different groups of cells function as developmental organizers, serving as sources of morphogens, molecules that diffuse from their source and specify cell fates in a dose-dependent manner (reviewed by (Blair, 2003; Irvine & Rauskolb, 2001)). One of the best studied examples of this phenomenon is the anteroposterior (A-P) compartment boundary in the wing-imaginal disc of Drosophila The wing disc arises from a population of approximately 20-30 embryonic cells in the second thoracic segment that straddle the parasegment boundary (Madhavan and Schneiderman, 1977; Worley, et al, 2013; Requena et al, 2017). These cells represent the primordium of the adult wing and the thoracic tissue to which it is attached. During the larval stage of development, these cells proliferate to generate a structure, the wing imaginal disc, that is composed of approximately 40,000 cells (Martin et al, 2009). During the later stages of larval development, the A-P boundary appears to be reinforced by an intracellular actomyosin cable that runs within cells that abut the boundary (Umetsu et al, 2014)

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