Pulmonary nerves extend to the budding epithelial tips and may regulate airway branching via secreted growth factors, structural cues, or cellular interactions. (A) In wholemount cultured explants, nerve fibres are visible reaching peripheral epithelium (anti-β3-tubulin immunostaining, green, indicated by arrowheads). In tissue sections (B), tiny nerve fibres can be seen bordering terminal airway buds. The images are individual adjacent slices of a z-stack obtained with confocal microscopy of sectioned explants. The terminal border of the explant is outlined with yellow dashes for clarity. Scale bars = 100 μm. (C) Diagram of possible mechanisms by which nerves may regulate airway branching, including via secreted growth factors, direct cellular interactions or intermediary interactions with other tissues.