Biomedical Engineering Reference
In-Depth Information
inability of the lamellipodia to attach to the substrate may cause depolymerization
of the actin network after polymerization-driven extension, resulting in lamellipo-
dial retraction.
To demonstrate the effect of activating actomyosin contractility on lamellipodial
protrusion during cell migration on a micropattern, let us consider the migration of
keratocytes treated with calyculin A, which is a myosin II activator. This drug inhibits
serine/threonine phosphatase thereby up-regulating myosin light chain phosphory-
lation, leading to the activation of actomyosin contractility (Ishihara et al.
1989
;
Okeyo et al.
2009
). Details of cell treatment with the drug can be found in Chap.
5
.
Both calyculin-treated and untreated cells exhibit temporal changes in lamellipodial
length which conform to a bell-shape distribution (Fig.
8.2d
), suggesting that varia-
tions in lamellipodial length occurs randomly due to alternating cycles of protrusion
and retraction. Remarkably, as illustrated in Fig.
8.2d
, the distribution curve for
calyculin-treated cells is shifted to the right compared to that of untreated control
cells, demonstrating that the length of the lamellipodia increases in response to
enhanced actomyosin contractility. Quantitatively, the mean length of the lamellipodia
is 3.4
m after
calcyculin addition (
p
< 0.001, t-test), as shown in the inset of Fig.
8.2d
. Thus, the
result demonstrates that contractility plays a role in the protrusion dynamics of the
lamellipodia.
Indeed, the percentage of cells migrating across the micropattern increases
from ~ 30 % to 50 % in the case of
d
= 3
ʼ
m before calyculin addition but increases signifi cantly to 4.5
ʼ
ʼ
m, and from ~12 % to ~20 % in the case
of
d
= 5
m (Fig.
8.3
). Moreover, a higher number of calyculin-treated cells are
capable of migrating even on a micropattern with
d
= 7
ʼ
m, for which migration of
untreated cells does not occur. This is supported by the observation that activating
ʼ
Fig. 8.3
Relation between adhesion barrier gap length and the percentage of cell migrating across
fi bronectin micropatterns (Okeyo et al.
2011
). Cell migration was monitored in the presence and
absence of calyculin. The percentage of migrating cells increased signifi cantly after actomyosin
activation with calyculin on each micropattern (Adapted with permission from Springer, Part of
Springer Science + Business Media: [Cellular and Molecular Bioengineering], copyright (2011))
