FIGURE 1.

Metaphase and anaphase A chromatid motility in Drosophila embryos; qualitative and force-balance model. (A) Dynamics of spindle poles and chromatids in Drosophila embryos. During metaphase (∼80–135 s), the chromatids remain at the spindle equator, and do not exhibit oscillations between the spindle poles as observed in some other organisms. During anaphase A (∼135–175 s), chromatids move steadily and rapidly toward the spindle poles, which are held at constant spacing at ∼10 μm (14,18). (B) Kinetochore-MT interface in Drosophila embryos, adapted from Maiato (5) and Rogers et al. (18). A kinetochore inner (red) and outer plate (black) along with the fibrous corona (black), a dynein (pink), and a cenpE (orange) motor generating antagonistic forces at the kinetochore, the KLP59C motors (blue) depolymerizing MT's (green) plus end inserted into the kinetochore, a centrosome (green circle), and the KLP10A motors (purple) depolymerizing the minus end of the MT at the spindle pole are shown. The direction of the velocities of motors, kinetochore and MT, and the position of the spindle equator (x = 0), the kinetochore plate, the plus end of the kMT, and the right spindle pole (x = 5) are indicated. (C) Force-balance model. Forces acting on the kinetochore and the kMT are shown. For simplicity, only a single kMT is shown bound to the kinetochore, and only a single spindle MT impinging on the chromosome arm generating polar ejection forces is shown.