Figure 1.

The β angle determines the symmetry of cell divisions in columnar cells, whereas α and β angles define hepatocytic cell divisions. Parameters that define spindle orientation in columnar (i.e., MDCK) or hepatocytic (i.e., WIF-B9, HepG2) metaphase cells. The β angle represents the angle between the spindle axis (SA) and the basal domain (BD) and defines division outcomes in both hepatocytic and columnar cells. The α angle measures the angle between the spindle axis (SA) and the apical–basolateral polarity axis (PA) in the x-y dimension and defines division outcome in hepatocytic cells, but is irrelevant for the inheritance of apical–basolateral domains in columnar cells. Similarly, the γ angle between the spindle axis (SA) and the apical–basolateral polarity axis (PA) in the x-z dimension is a predictor for the division outcome in hepatocytic cells. Because the cleavage furrow (black arrowheads) organizes perpendicular to the spindle pole, a β angle of 0° yields symmetric and a β angle of 90° asymmetric divisions in columnar cells. By contrast, small α angles favor asymmetric divisions in hepatocytic cells when the β and γ angles are also small. AD, apical domain.