Fig. 3. Comparison of filopodia protrusion from wt (A) and KO (B) growth cones. (A) A sequence (10 second intervals) showing the extension of a filopodia near the leading edge of a wt growth cone. The filopodia grows in length, but some retraction of the lamellipodia at the base of the filopodia adds to the appearance of length increase. (B) A sequence as in A, but from a KO growth cone. The filopodium extends at a similar rate to the wt filopodium in A. A common feature of growing KO filopodia are the small bumps or protrusions that form. They sometimes lead to branching and appear to undergo retrograde movements. Bar, 3 µm.