| Description |
The first division of Pelvetia zygotes is an unequal division which produces two cells with two distinct developmental fates. The smaller rhizoid cell gives rise to the holdfast of the mature plant, and the larger thallus cell gives rise to the stripe and fronds. We have been investigating the role of the cytoskeleton in determining the orientation of this invariant division. Prior to mitosis, microtubule organizing centers (MtOCs) associated with the nuclear envelope undergo a precise realignment from transverse to axial with respect to the rhizoid/thallus axis. This is accomplished by a 90 degree rotation of the entire nuclear MtOC complex. After rotation, each MtOC serves as a spindle pole during mitosis, and the subsequent wall forms bisecting the spindle. Both of the cytoskeletal inhibitor drugs, cytochalasin D and nocodazole, cause incorrect alignment of MtOCs, indicating that both microtubules and microfilaments (respectively( are required for nuclear MtOC rotation. These inhibitors also result in mispositioning of the first division plane. Microtubules visualized by confocal microscopy connect the rotating nucleus to the apical cortex which contains an accumulation of cortical microfilaments. A model is presented in which cortical microfilaments provide positional information and microtubules provide force for rotation of the nuclear MtOC complex. |
