Figure 5.

Magnified time-lapse record showing the creation of a birefringent fiber and filopodium. The retardance magnitude is in pseudocolor; the numbers below each record give the time in seconds elapsed since the first record. The formation of the filopodium is preceded by the appearance of a birefringent spot at the leading edge of the growth cone (arrow in the 5-sec record). The spot elongates into a filopodium and generates a visible actin bundle (arrow in the 55-sec record) that extends toward the center of the lamellipodial region. The newly formed filopodium and fiber are tilted to one side, move laterally, and fuse with a neighboring, stable filopodium (85- to 105-sec records). In the 5- to 95-sec records, the same stable filopodium is seen to fuse with another filopodium and fiber, generated earlier. Lower right, pseudocolor retardance scale in nanometers. Bar, 2 μm.