Biomedical Engineering Reference
In-Depth Information
microtubule length distribution and rearrange their organization depending
on the activity of the cell.
Figure 4.1.
Functional microtubule organization in cells. Microtubules are orga-
nized differently depending on the cell type or cell cycle state. (a) Mitotic spindle
in a first cell stage of a
Celegans
embryo. Microtubules are nucleated by centro-
somes. They keep the chromosomes aligned in the middle of the cell (arrows; not
visible) and interact with the cell cortex to keep the spindle asymmetrically posi-
tioned with respect to the posterior (P) and anterior (A) axis of the embryo. Scale
bar is 10 micron (approximately also the scale for b and c). Image adapted from [3].
Copyright (2001), with permission from Macmillan Publishers Ltd; (b) Microtubule
organization in an interphase motile mouse fibroblast. Microtubules are nucleated
by a single centrosome located near the nucleus on the right and interact with the
cortex at the leading edge of the cell (cell moves to the left) to help polarize the cell.
Image courtesy of Dr. Anna Akhmanova. (c) Microtubule array during interphase
in a fission yeast cell. Microtubules are nucleated by nucleation sites attached to the
nuclear membrane and interact with the cell ends to keep the nucleus positioned in
the middle of the cell. Image adapted from [4]. Copyright (2001), with permission
from The Rockefeller University Press.
Dynamic microtubules are furthermore capable of generating forces that
can be used to drive intracellular transport processes. A well-known exam-
ple is the microtubules that are attached to the kinetochores of chromosomes
during anaphase in dividing cells [5]. In this situation, shrinking microtubules
are involved in generating the pulling forces that move chromosomes to the
new cell poles. The growth of microtubules, in analogy to the growth of actin
filaments, can also generate forces that help position organelles and micro-
tubule-organizing centers within the cell. The biophysical aspects of how mi-
crotubules (and actin filaments) generate these forces have been studied in
experimental and theoretical work by several groups over the last ten years.
In this chapter, we summarize the current knowledge on microtubule struc-
ture and dynamics, and review our experimental work that has focused on the
force-generating properties of growing microtubules. We also discuss some of
