Biology Reference
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Figure 13.2 Microtubules are required for leading edge protrusion in epithelial cells.
(A) The PtK1 cell on the right (arrowhead) was injected with a phosphorylation-site-
deficient, dominant active Op18/stathmin protein resulting in depolymerization of most
microtubules. The pair of cells was then observed by time-lapse phase contrast microscopy.
Shown are three representative frames. Note the extensive protrusive activity of the control
cell on the left. Elapsed time is indicated in minutes. Bar, 20 mm. (B) Kymograph analysis
shows the position of the leading edge over time of a control PtK1 cell compared with a cell
injected with dominant active Op18/stathmin. While the control cell undergoes multiple
cycles of protrusion and retraction during the course of 2 h, the edge of the injected cell is
almost completely quiescent
Storer et al., 1999; Wittmann and Waterman-Storer, 2001). Accordingly, we
also observed that microtubule depolymerization in PtK1 cells, a rat-
kangaroo kidney epithelial cell line, by either nocodazole or microinjection
of a dominant active mutant of the microtubule-destabilizer Op18/stathmin
(Cassimeris, 2002) severely altered leading edge dynamics (Figure 13.2). In
control PtK1 cells, large protrusions develop at random sites along the cell's
leading edge and extend for several minutes up to 10 mm before retracting
again. In the absence of microtubules, however, only minor membrane ru
es
form at the extreme periphery of the lamellipodium and are distributed evenly
all along the free edge of these cells.
Like actin, microtubule organization and dynamics are polarized in
migrating cells. In most cells, microtubules are organized in a radial array
by the centrosome in the cell centre, where they are nucleated and most
microtubule minus ends are anchored. Microtubule plus ends emanate out to
the cell periphery, where they undergo stochastic changes between polymer-
ization and depolymerization, a property known as dynamic instability (Desai
