Despite their barrier function, epithelial layers can locally lose their integrity to create physiological openings during morphogenesis. The cellular and molecular mechanisms driving the formation of these epithelial breaks are only starting to be investigated. Here, we studied the formation of the zebrafish nostril (the olfactory orifice), which opens in the skin epithelium to expose the olfactory neurons to external odorant cues. Combining live imaging, drug treatments, laser ablation and tissue-specific functional perturbations, we demonstrate that the formation of the orifice is driven by a mechanical interplay between the olfactory placode neurons and the skin: the neurons pull on the overlying skin cells in an actomyosin-dependent manner, thus triggering the opening of the orifice. This work unravels an original mechanism to break an epithelial sheet, in which an adjacent group of cells instructs and mechanically assists the epithelium to induce its local rupture.

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