Figure 6.

spc110-226 cells (HSY83) contain an abnormal nuclear microtubule array. (A and B) 3-D EM models show the microtubules form an aster-like array within the nucleus, with their ends converging in a ring at its center. Videos 4 and 5 show the projected 3-D models in A and B. (C) Example of a tomographic slice showing two side-by-side SPBs separated by a mass of electron-dense material (short arrow), nuclear envelope, cytoplasmic microtubules (arrowheads), and a portion of the nuclear microtubule aster containing a spherical core at its center (long arrow). The complete tomographic volume from this cell is shown in Video 6. (D) Projected 3-D model of this cell showing the boundary of the nuclear envelope (yellow) and the SPBs (light blue) separated by an electron-dense mass (tan). Nuclear microtubules (green) are shown forming an aster-like array with their ends (orange spheres) pointed toward a small spherical core (red). Video 7 shows the rotating model. (E-I) Representative images of microtubule ends in nuclear aster arrays from spc110-226 cells. Microtubule ends pointing toward the center of the aster have a closed, capped morphology (arrowheads). In one example, an electron-dense spherical core could be detected (G; long arrow). Filamentous material could also be seen at the ends of the capped microtubule ends (H, arrow). (J) An example of nuclear microtubules in wild-type cells shows a similar capped morphology (O'Toole et al., 1999). Here, however, the nuclear microtubules are tethered to the SPB by fine filaments (arrows). Bar, 50 nm.