Fig. 4. Comparison of microtubule distribution in wt (A) and KO (B) growth cones. (A) A wt growth cone triple stained for actin (red), myosin IIA (green) and microtubules (blue). The insert shows only the microtubule staining. Microtubules penetrate the base of F-actin-rich structures. (B) A KO growth cone stained as in A. Microtubules penetrate into peripheral structures, but these often appear to have reduced staining for F-actin compared with wt. (C) Higher magnification example of multiple (1-4) microtubule ends interacting with actin containing protrusive structures. The average distance between microtubule ends and the tips of protrusive structures is greater for the KO examples. The overlap of color makes identification of microtubules difficult so the microtubule staining is also shown by itself (black and white image; contrast enhancement has produced a thickening of microtubules). B, Bar, 4.3 µm; C, the vertical Bar in No. 4=1.8 µm.