Figure 5.
Figure 5. KLP10A inhibition converts MT poleward flux to spindle elongation, mimicking the anaphase B switch. (A) Representative tubulin kymograph from an embryo sequentially injected with cyclin B and anti-KLP10A to monitor poleward flux. Yellow and green lines track tubulin speckles and spindle poles, respectively. Sharpen and low-pass filters were applied. (B) Comparison of spindle elongation and poleward flux rates in wild-type and injected embryos (±SDs; cyc B only, injected with only cyclin B; cyc B+anti-10A, sequentially injected with cyclin B and anti-KLP10A). KLP10A inhibition significantly decreased MT poleward flux rate (P < 2.2 × 10−16), as observed at anaphase B onset in wild-type embryos (P < 2.2 × 10−16). P-values and dip values from Hartigan’s dip test reveal unimodal flux data, except for wild-type (WT) preanaphase B spindles, in which it is bimodal (P < 0.05). The number of embryos (first number), spindles (second number), and speckles (third number) analyzed are indicated in parentheses. (C) MT poleward flux and spindle elongation rates in B are inversely correlated in both wild-type anaphase B switch and treated embryos. Error bars show SDs. (D) Histograms of the MT poleward flux rates shown in B (counts in B). The curves show the best-fit normal distributions. ana, anaphase. (E) Model of anaphase B induction in Drosophila syncytial embryos in which kinesin-5 persistently slides apart antiparallel ipMTs, and anaphase B spindle elongation is induced by a Patronin-mediated spindle pole–associated switch. During preanaphase B, KLP10A depolymerizes the minus ends of outward sliding ipMTs at the spindle poles, producing poleward flux in spindles maintained at a constant length. Cyclin B degradation induces an unknown Patronin modification that enhances its activity to protect ipMT minus ends from KLP10A-induced depolymerization at the poles, thus allowing outwardly sliding ipMTs to exert force and push apart the spindle poles. (top) Simplified model showing a single ipMT bundle, with minus ends reaching the poles. (bottom) More realistic model in which Patronin-bound ipMT minus ends localize all over the spindle, kinesin-5 slides antiparallel MTs apart, and KLP10A concentrates at spindle poles.

KLP10A inhibition converts MT poleward flux to spindle elongation, mimicking the anaphase B switch. (A) Representative tubulin kymograph from an embryo sequentially injected with cyclin B and anti-KLP10A to monitor poleward flux. Yellow and green lines track tubulin speckles and spindle poles, respectively. Sharpen and low-pass filters were applied. (B) Comparison of spindle elongation and poleward flux rates in wild-type and injected embryos (±SDs; cyc B only, injected with only cyclin B; cyc B+anti-10A, sequentially injected with cyclin B and anti-KLP10A). KLP10A inhibition significantly decreased MT poleward flux rate (P < 2.2 × 10−16), as observed at anaphase B onset in wild-type embryos (P < 2.2 × 10−16). P-values and dip values from Hartigan’s dip test reveal unimodal flux data, except for wild-type (WT) preanaphase B spindles, in which it is bimodal (P < 0.05). The number of embryos (first number), spindles (second number), and speckles (third number) analyzed are indicated in parentheses. (C) MT poleward flux and spindle elongation rates in B are inversely correlated in both wild-type anaphase B switch and treated embryos. Error bars show SDs. (D) Histograms of the MT poleward flux rates shown in B (counts in B). The curves show the best-fit normal distributions. ana, anaphase. (E) Model of anaphase B induction in Drosophila syncytial embryos in which kinesin-5 persistently slides apart antiparallel ipMTs, and anaphase B spindle elongation is induced by a Patronin-mediated spindle pole–associated switch. During preanaphase B, KLP10A depolymerizes the minus ends of outward sliding ipMTs at the spindle poles, producing poleward flux in spindles maintained at a constant length. Cyclin B degradation induces an unknown Patronin modification that enhances its activity to protect ipMT minus ends from KLP10A-induced depolymerization at the poles, thus allowing outwardly sliding ipMTs to exert force and push apart the spindle poles. (top) Simplified model showing a single ipMT bundle, with minus ends reaching the poles. (bottom) More realistic model in which Patronin-bound ipMT minus ends localize all over the spindle, kinesin-5 slides antiparallel MTs apart, and KLP10A concentrates at spindle poles.

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