Fig. 3. Growth cone turning of retinal axons after contact with an ephrin-A5-coated bead. (Top, left) Xenopus retinal growth cone filopodia contact an ephrin-A5-Fc coated bead. The bead is located slightly to the right of the pathway of the growth cone. (Top, right) The growth cone has moved slowly forward and has made extensive filopodial and lamellipodial contact to the bead. (Bottom, left) The growth cone has started to detach from the bead, the central domain of the growth cone has moved away from the bead. (Bottom, right) The growth cone has almost detached from the bead. Part of the growth cone previously in contact with the bead appears to be collapsed. There are only very few filopodial contacts left with the bead. Its growth direction has changed by an angle of –41° to the left (away from the bead). New filopodia have been formed on the side opposite to the bead. In total, a mean turning angle of –41°±2.6° was determined for experiments with ephrin-A5-coated beads (n=8). In control experiments with non-coated or protein A-coated beads (n=10), growth cones did not show a change in growth direction (–6°±0.4°; n=10). As schematised in the picture (bottom, right), turning angles were measured by determining the angle between the axon shaft before bead contact and after passing the bead. Experiments were performed using laminin as an outgrowth promoting substratum. The pictures were taken using a Zeiss inverted phase contrast microscope with a magnification of 63. The beads were 4.5 µm diameter.

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