Biomedical Engineering Reference
In-Depth Information
7.6
Mechanochemical and Hierarchical Feedback
Mechanisms for Coordinated Cellular Protrusion:
Effect of Membrane Curvature on Actin Polymerization
Based on the results of the correlation between
v
ʔt
ƹ and
ʺ
ʔs
, we can hypothesize, as
summarized in Fig.
7.8
, the intra- and inter-scale feedback mechanism underlying
coordinated cellular protrusion. As illustrated in Fig.
7.8c
, at the molecular scale,
cellular protrusion is based on actin filament elongation by chemical polymerization
of actin monomers supplied by diffusion (Pollard and Cooper
2009
). At the subcel-
lular scale, as illustrated in Fig.
7.8b
, the elongating filaments assemble into a den-
dritically branched actin network (Svitkina et al.
1997
; Ridley
2011
; Chhabra and
Higgs
2007
; Svitkina and Borisy
1999
; Verkhovsky et al.
1999
). The local cell
peripheral activity in our analysis reflects the contribution of net actin elongation on
a
Cellular
b
Subcellular
c
Molecular
Membrane
curvature,
k
(
s
)
<
V
A
>
15 - 20
µ
m
Diffusion
s
2
< >
3
µ
m
s
2
V
A
∂
/
∂
Actin elongation,
V
< >
3
µ
m
V
A
< >
3
µ
m
< >
3
µ
m
V
A
V
A
≈
3
µ
m
Traveling wave
Global net actin elongation
+Retrograde flow
Traveling wave:
Local net actin elongation
Fig. 7.8
Hypothesized mechanochemical and hierarchical feedback underlying coordinated pat-
tern of the lamella-type cellular protrusion (Miyoshi and Adachi
2012
). (
a
) Cellular scale. The
red
arrows
indicate laterally travelling waves consisting of the sum of the global net actin elongation,
〈
V
A
〉
15 − 20ʼm
, and retrograde flow. (
b
) Subcellular scale. The
red arrows
indicate laterally travelling
wave of local net actin elongation, 〈
V
A
〉
3ʼm
. By the mechanical interaction among cell membrane
and the actin filaments, the membrane curvature,
ʺ
(
s
), decreases in the membrane domain under
which local net actin elongation, 〈
V
A
〉
3ʼm
, is a minimum value, as indicated by the
T-shaped
line. In
contrast,
ʺ
(
s
) increases in the membrane domain under which 〈
V
A
〉
3ʼm
is a maximum value, as
indicated by the
black arrows
. (
c
) Molecular scale. The actin elongation,
V
A
, which is indicated by
the
blue arrow
, is caused by chemical polymerization of actin monomers supplied by diffusion.
The membrane domains with higher membrane curvature on the subcellular scale has higher inhib-
itory effect on the actin elongation,
V
A
(Adapted with permission from The Royal Society of
Chemistry: [Integrative Biology], copyright (2012))
