Axonal and Schwann cell behaviors at the point of neurectomy. Three days post fertilization transgenic Tg(neurod:TagRFP;foxd3:GFP) zebrafish larvae were neurectomized and imaged from 5 hpn to 11 hpn every 2 min following complete nerve transection (axons in red and Schwann cells in green). In all panels, the arrows show the behavior of axons and Schwann cells proximal to the gap whereas the arrowhead shows the behavior of Schwann cells distal to the gap. (A, B) A few hours after neurectomy, distal (denervated) Schwann cells extend their processes within the gap and show an exploratory behavior, whereas proximal Schwann cells are less motile. (C) At 6.5 hpn, the regrowing axons have contacted distal Schwann cells and have formed a bridge across the gap (asterisk). (D, E) After 7 hpn, the axons complete the crossing of the gap; often, the first axon to navigate the gap stops growing and another axon takes the lead. (F) After 11 hpn, the regrowing nerve has grown past the gap enabling the reconnection between proximal and distal Schwann cells in 100% of neurectomized larvae.