FIGURE 2:

Chlamydomonas metaphase spindle. (A) Tomographic slice showing features of a metaphase half spindle. The nuclear envelope (NE) stays mostly intact during mitosis. Chromosomes with kinetochores (K) bind several MTs. Bar = 500 nm; 100 nm for insert. (B) The nucleus develops a fenestra at each pole (PF), through which spindle MTs project into the cytoplasm, ending in a region with no apparent structure. Meanwhile, the cell’s basal bodies (BB) remain at the plasma membrane. Bar = 200 nm. (C) Projection of a 3D model of a partial metaphase spindle reconstructed from four serial, 250-nm-thick sections. KMTs (yellow; n = 38), mcMTs (light blue; n = 68), and non-KMTs that either ended before reaching the chromosomes or went out of the volume of the reconstruction (red; n = 114). The mother basal bodies (pink cylinders) and forming daughters (blue cylinders) are some distance from the spindle pole. Bar = 500 nm. This reconstruction and its model are shown in Supplemental Movie S1. (D) The 3D model shown in C was resampled to display MT locations along the spindle axis from near the pole (i) to midspindle (ii and iii) to just beyond the metaphase plate (iv). mcMTs (light blue) commingle with KMTs (yellow) along their lengths. Supplemental Movie S2 displays this resampled model.