Fig. 5.

The case for reduced intrakinetochore stretch in generating a wait-anaphase signal. (A) Schematic adaptation of data from Clute and Pines (adapted with permission) (Clute and Pines, 1999). Cyclin-B1—GFP levels begin declining after alignment of the last chromosome, indicating SAC satisfaction, and anaphase onset ensues (blue line). However, even after the SAC has been satisfied, addition of 10 μM taxol reinitiates an active wait-anaphase signal and cyclin-B1—GFP degradation ceases within minutes (red line). (B) However, data from an electron microscopy study by McEwen et al. (reproduced with permission) (McEwen et al., 1997) concluded that taxol treatment did not cause a significant decrease in kinetochore microtubule number and, in fact, slightly more kinetochore microtubules were observed after a 10 minute treatment with 1 μM taxol. (C) High-resolution mapping of the kinetochore by Wan et al. (Wan et al., 2009) found that delta (δ) was reduced within 5 minutes of addition of 10 μM taxol. In this schematic, we highlight the response of the same Ndc80 attachment site (with examples of either a kinked Ndc80 molecule or a stiff Ndc80 complex with a flexible linker — for details, refer to key in Fig. 2) under conditions of full intrakinetochore stretch, relaxing to reduced intrakinetochore stretch following a 5 minute taxol treatment. We envision that this reduction of intrakinetochore stretch is a result of reduced flux and/or straightening of the microtubule lattice owing to loss of bending protofilaments. Thus, reduction of intrakinetochore stretch, not kinetochore microtubule number, occurs on the same timescale (minutes) as generation of a wait-anaphase signal in response to taxol.