Biomedical Engineering Reference
In-Depth Information
In this chapter, we present an approach of multiscale analysis applied to the cell
peripheral movement. The methodology can successfully characterize the spatio-
temporally coordinated hierarchical behavior in the lamellipodial protrusion at the
leading edge of the cell. As described details in Chap.
1
, lamellipodial protrusion is
one of the fundamental steps of cell migration. Lamellipodial protrusion is essen-
tially driven by the actin polymerization at the cell periphery. The rate of polymer-
ization is regulated to be spatiotemporally coordinated, resulting in directed
peripheral movement of a migrating cell.
6.2
Experimental Design to Acquire Live Cell Imaging
Data for Multiscale Analysis
A major feature of the multiscale analysis explained here is that it adopts a top-down
approach to extract spatiotemporal hierarchical patterns of cell peripheral dynamics
from a sequence of micrographs by estimating cell protrusion rates at various
differential intervals. This strategy is useful for the characterization of complex
phenomena, especially in the case where we have incomplete pre-existing knowl-
edge about the molecular machines, such as proteins and small chemicals, and their
interactions underlying a particular phenomenon. Such interactions are included
implicitly in the pattern as the lumping together of multiple interactions (Satulovsky
et al.
2008
). Thus, the concept of image-based multiscale analysis is useful to cope
with the problem of inherent redundancy and heterogeneity associated with evolved
molecular machines.
In the image-based multiscale analysis, fi rst we design an experimental system
by choosing cell type, imaging systems (microscopes) and image acquisition set-
tings among multiple options. This section discusses how we choose the method
between multiple options at each step of the image-based multiscale analysis.
6.2.1
Choice of Model Cell Type
As a simple model, fi sh epidermal keratocyte is a suitable cell type for analysis of the
dynamic organization and mechanics of the actin cytoskeleton. Remarkably, kerato-
cytes are known as motile cells with no chemotactic behavior. Thus, their use allows
us to clearly focus on the role of mechanical factors in the actin cytoskeleton without
crosstalk from chemotaxis (Yam et al.
2007
). Furthermore, keratocytes can migrate
without microtubules (Euteneuer and Schliwa
1984
; Okeyo et al.
2009
), suggesting
that they possess a reduced complexity of the system network structure underlying
the intra- and inter-scale hierarchical interactions of the regulatory factors.
As seen in Fig.
6.1
, keratocytes show a non-polarized full-moon-shape as well as
a polarized crescent-shape. The full-moon-shaped keratocytes present hierarchical
motile behavior (Yam et al.
2007
) that involves balanced protrusion around the
