During the final stages of nuclear division
a cleavage furrow
the surface of the dividing cell and
encircles it at the midline of the spindle.
The cleavage furrow deepens
and pinches the plasma membrane
as though it were being tightened
by an invisible rubber band. Microfilaments
of actin are present just
beneath the surface in the furrow
between the cells. Interaction with
myosin, similar to that which occurs
when muscle cells contract,
draws the furrow inward. Finally, the
infolding edges of the plasma membrane
meet and fuse, completing cell
division. As with other aspects of the
cytoskeleton, such as the spindle, the
centrosomes are responsible for locating
and contracting microfilaments
equidistant between them and at right
angles to the spindle.
|Figure 3-24 Stages of mitosis in whitefish.