Dissecting Complex Mechanisms of Calcium Influx in a Simple Wound System

Abstract

In normal epithelial wound repair, cells across an epithelial sheet begin a coordinated process of re-epithelialization within minutes of wounding. These coordinated behaviors are driven by a calcium wave, a rise in cytosolic calcium expanding away from the wound in a wave-like fashion. The calcium wave is evolutionarily conserved and is the earliest detectable wound response. Understanding the mechanisms of calcium influx and propagation may reveal fundamental aspects of wound detection and of cell coordination. We observed multiple, distinct mechanisms of calcium influx and propagation around reproducible wounds in the Drosophila notum. First, extracellular calcium flows directly into cells through micro-tears on the cell surface. We were able to assess the role of micro-tears in calcium dynamics by using pulsed laser ablation, a common wounding method that generates exaggerated micro-tears. Pulsed laser ablation creates a cavitation bubble, which forms and collapses within microseconds of ablation and damages the plasma membranes of cells tens of microns away from the wound. Once inside the cells, our model predicts calcium diffuses to neighboring cells via gap junctions. Next, we observed a larger, wound-induced calcium wave that is driven by an unknown extracellular signal. This signal activates a Gαq mediated signaling cascade and induces calcium release from intracellular ER stores. Our simple, pulsed laser ablation wounding model recapitulates a complex damage profile and reveals multiple patterns of calcium influx and propagation around a single wound. For this reason, this model has the potential to unite previous, and seemingly contradictory, findings regarding calcium dynamics in the wound healing field.