Shooting Fruit Flies with Lasers: Cell Fusion in Response to Laser Wounding of Drosophila

To repair a wound, cells drastically reorient their normal functions. Cells that were originally fated to hold on to their neighbors to maintain a stable tissue instead become mobile and initiate adaptive responses to restore tissue integrity. Studying wound healing helps us understand the underlying mechanisms that allow a wound to close. We study wound healing in Drosophila pupae in an epithelial monolayer called the notum, wounding and imaging this flat sheet of cells to study how cells coordinate at a tissue level in order to close up a wound in a living organism. Neighboring cells will often fuse, breaking down their borders, sharing cytoplasm and forming larger cells with multiple nuclei. We probe this adaptive behavior via laser ablation, which causes quantifiable and repeatable damage. The central ablation region resembles puncture damage out to the wound’s leading edge, but cells beyond that edge also suffer crush-like damage from the laser-generated cavitation bubble. To probe the extent of this damage, we ablated Drosophila pupae that had been modified with a fluorescent reporter of intracellular Ca2+, measured the Ca2+ response immediately post-wound, then tracked the integrity of the cell borders for up to 2 hours. In order to study the correlation between wound size and cell fusion rates, we made wounds of varying sizes to study the correlation between wound size, damage, and cell fusion rates. We find a potential threshold for wound size below which cell fusion no longer happens.