Biomedical Engineering Reference
In-Depth Information
Considering that the lamellipodia of fi sh keratocytes undergo ruffl ing and retraction
when they are not properly anchored to the substrate (Fig.
8.2b
), the inability of
untreated cells to migrate across adhesion barriers implies that the rigidity of the
actin network in the lamellipodia is insuffi cient to counter the shortening effects
of ruffl ing and retraction. It has been established that lamellipodial stability is
weakened when polymerization-induced leading edge extension is not followed
immediately by attachment to the substrate (Craig and Chen
2003
; Libotte et al.
2001
). This scenario is illustrated in Fig.
8.5a
where the tip of the lamellipodia lifts
off the substrate to form ruffl es because the lamellipodia is not fi rmly adhered to the
PLL-g-PEG adsorbed gap.
a
Lamellipodium
Actin monomer
F-actin
Myosin II
Focal
adhesion
Adhesive region
Adhesion suppressed region
b
Fig. 8.5
Illustration of lamellipodial protrusion across an adhesion-suppressed gap (Okeyo et al.
2011
). (
a
) Ruffl ing of a lamellipodium during protrusion across a gap in the absence of calyculin.
Due to inability to attach fi rmly on the adhesion-suppressed gaps, ruffl ing occurs, resulting in the
formation of an unstable lamellipodium whose actin network lacks the meshwork lattice. Such a
cell would remain immobilized on the fi bronectin micropattern. (
b
) Lamellipodial protrusion
across a gap in the presence of calyculin. Elevated actomyosin contractility by calyculin treatment
induces the formation of a more stable lamellipodium probably by increasing the structural integ-
rity of the actin cytoskeleton, as well as by inducing focal adhesion formation on the gaps. Such a
cell can migrate normally from one pattern to another (Adapted with permission from Springer,
Part of Springer Science + Business Media: [Cellular and Molecular Bioengineering], copyright
(2011))
