Patronin stabilizes MT minus ends and is necessary for anaphase B spindle elongation. (A) Time-lapse images and spindle length plots of a representative embryo injected with anti-Patronin (arrow) at NEB (0 s) showing a gradient of phenotypes. Green, tubulin. Red, histone. Spindles close to the injection site (spindle 4 [s4] and spindle 5 [s5]) display normal metaphase length but no anaphase B spindle elongation, whereas distal spindles (spindle 1 [s1] and spindle 2 [s2]) show normal anaphase B. Repeated in >25 embryos. Bar, 10 µm. (B) Representative spindle after Patronin inhibition (bottom) compared with control (top). Black, time from NEB; red, time from anaphase A onset. See also Videos 3 and 4. (C) Plots of pole–pole (p-p) and chromosome to pole (chr-p) distances versus time for control and anti-Patronin (pat)–injected embryos. NEB = 0 s. Error bars show SDs. (D) Representative tubulin kymographs after Patronin inhibition (bottom) compared with control (top). (right) Yellow and green lines track tubulin speckles and spindle poles, respectively. Sharpen and low-pass filters were applied. (E) Quantitation (±SDs). Patronin inhibition decreased the anaphase B spindle elongation rate (P = 1.553 × 10⁻¹⁰) and increased the rate of anaphase B MT poleward flux (P < 2.2 × 10⁻¹⁶), without decreasing preanaphase B spindle length or the anaphase A chromosome to pole rate. For anaphase B measurements, we have included spindles in the gradient with suppressed anaphase B, which allowed us to distinguish anaphase B from preanaphase B. The number of embryos (first number), spindles (second number), and speckles (third number) analyzed are indicated in parentheses. (F) EB1-GFP localization in wild-type and Patronin-inhibited embryos during preanaphase (pre-ana) B and anaphase B. Red, tubulin; green, EB1. WT, wild type.