Patterning of wound-induced intercellular Ca²⁺flashes in a developing epithelium

Abstract

Differential mechanical force distributions are increasingly recognized to provide important feedback into the control of an organ’s final size and shape. As a second messenger that integrates and relays mechanical information to the cell, calcium ions (Ca2+) are a prime candidate for providing important information on both the overall mechanical state of the tissue and resulting behavior at the individual-cell level during development. Still, how the spatiotemporal properties of Ca2+ transients reflect the underlying mechanical characteristics of tissues is still poorly understood. Here we use an established model system of an epithelial tissue, the Drosophila wing imaginal disc, to investigate how tissue properties impact the propagation of Ca2+ transients induced by laser ablation. The resulting intercellular Ca2+ flash is found to be mediated by inositol 1,4,5-trisphosphate (IP3) and depends on gap junction communication. Further, we find that intercellular Ca2+ transients show spatially nonuniform characteristics across the proximal-distal (PD) axis of the larval wing imaginal disc, which exhibit a gradient in cell size and anisotropy. A computational model of Ca2+ transients is employed to identify the principle factors explaining the spatiotemporal patterning dynamics of intercellular Ca2+ flashes. The relative Ca2+ flash anisotropy is principally explained by local cell shape anisotropy. Further, Ca2+ velocities are relatively uniform throughout the wing disc, irrespective of cell size or anisotropy. This can be explained by the opposing effects of cell diameter and cell elongation on intercellular Ca2+ propagation. Thus, intercellular Ca2+ transients follow lines of mechanical tension at velocities that are largely independent of tissue heterogeneity and reflect the mechanical state of the underlying tissue.

Intercellular calcium signaling is regulated by morphogens duringDrosophilawing development

“…2G, Movie S5, S6). Additionally, we confirmed several of the components previously implicated in Ca 2+ signaling in the wing disc are required for ICW dynamics through RNAi experiments: ICWs require Ca 2+ release through IP 3 R, Ca 2+ recycle through SERCA and diffusion through gap junctions (9,14,16,30,36) (Movie S7-9). Ca 2+ channels Stim, Orai and PMCA did not qualitatively impact ICWs activity (Movie S10-12).…”

“…We have shown that ICWs can be stimulated by the release of compression in wing discs (Narciso et al, 2017). Laser ablation of cells leads to rapid dissipation of mechanical stress and Ca 2+ flashes in the wing discs cultured in fly extract-free medium (Narciso et al, 2015). In addition, it was shown that the myosin II inhibitor blebbistatin interrupted Ca 2+ oscillations in the wing disc (Balaji et al, 2017).…”

“…Spontaneous intercellular Ca 2+ waves (ICWs) occur in many tissue types. For example, ICWs are involved in ensuring robust wound healing and regeneration (7,9,14) and have been observed in multicellular developmental contexts such as butterfly pupal wings (15) and in Drosophila larval wing discs (9,16,17). However, how ICWs emerge or how they are controlled at the organ scale is largely unknown.…”

Growth control in the Drosophila wing disk

“…Ca 2+ is a second messenger, and Ca 2+ signaling networks often exhibit a “bow‐tie” structure in that the integrated effect of many inputs is governed by a small number of molecules in the calcium pathway, and they affect many outputs (Brodskiy & Zartman, ), similar to the way that many growth‐affecting factors impinge upon the Hippo kinase cascade. Like Hippo, growth and mechanical signals both affect Ca 2+ (Antunes, Pereira, Cordeiro, Almeida, & Jacinto, ; Balaji et al, ; Brodskiy et al, ; Narciso et al, ; Narciso, Contento, Storey, Hoelzle, & Zartman, ; Restrepo & Basler, ). Ca 2+ signaling in the wing disk exhibits a rich variety of dynamical behaviors.…”

Imaginal disc regeneration takes flight

“…In embryonic wounds, the NADPH oxidase DUOX, which acts as a source of H 2 O 2 , is activated by calcium, and Ca 2+ flashes have been found upon damage [43]. Intercellular Ca 2+ waves, propagated via gap junctions are triggered by injury to imaginal discs [44, 45]. …”