FIGURE 1:

Diagram illustrating some of the forces present in small (≤2 µm) metaphase spindles. Each spindle pole body (yellow and blue) nucleates MTs, some of which bind kinetochores (red), while others overlap with MTs from opposite pole to form an interpolar spindle (green). Pole-directed forces act on sister kinetochores (red arrowheads in chromatin) and equal forces pull the poles inward (purple arrowheads at poles), so the net force on each KMT is zero. The overlapping ipMTs (green) provide an outward push on the poles, counterbalancing the inward pull on the poles by KMTs. In some cell types, an additional outward force is provided by astral MTs (black arrows at poles).