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Fig. 3. Growth cone dynamics within the stop zone of shallow and steep
gradients. (A)Growth cones display an explorative equilibrium of
forward and backward movements within the stop zone of a shallow gradient. A
temporal growth cone approaches the gradient. After 15 minutes it pauses,
rearranges its lamellipodia and starts to retract to the beginning of the
gradient (30 minutes). Between 45 and 60 minutes the growth cone advances anew
in the gradient and subsequently pauses (65 minutes). Small side branches
appear along the axon shaft and a growth cone like structure builds at the
beginning of the gradient (70 minutes). The axon shaft left deeper in the
gradient retracts. Between 80 and 120 minutes the growth cone pauses under
continued filopodial activity within the gradient. (B) Steep ephrin
gradients can cause more pronounced reactions, including transient, partial
growth cone collapse and change of growth cone morphology within the stop
zone. A temporal growth cone entering a steep gradient starts withdrawing its
lamellipodia (4 minutes), and retracts completely from the gradient (5
minutes). After 15 minutes the growth cone marked by an arrow recovers from
the transient collapse and invades the gradient anew. A second growth cone
(arrowhead) advances. Between 20 and 22 minutes the growth cone marked by an
arrow undergoes a rapid change in morphology and realigns its filopodia along
the printed ephrin pattern. The same happens to the growth cone marked by an
arrowhead between 20 and 30 minutes. Afterwards, both growth cones remain
stationary and undergo only small morphological changes, adhering partially to
the lines of the gradient. Antibody-stained ephrin is shown in red; axons are
shown in phase contrast. Scale bar: 20 µm.
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