Visualization of γ-tubulin-independent MT nucleation. (A and B) MT nucleation in the presence (A) or absence (B) of γ-tubulin. Images were acquired every 2 s with oblique illumination fluorescence microscopy, which allows the detection of individual γ-tubulin complexes. (C) Time of first MT appearance after drug washout in the presence (1.4 ± 1.5 min [SD], n = 17) or absence (8.3 ± 4.8 min, n = 23) of γ-tubulin. An MT was counted when the first SiR-tubulin signal stronger than the background was detected in three consecutive frames (i.e., 6 s). P < 0.0001 (unpaired t test with Welch’s correction). **, P < 0.01. (D) Two examples of nucleating MTs in the absence of γ-tubulin. The minus ends of nucleating MTs are marked with arrows. MT loop is formed in the second example (84–92 s).