Condensation of Cells - Mechanisms of Morphogenesis - page 164

FIGURE 14.3 Tangential forces (those actin along the plane of the membrane) due to adhesion and actin/
myosin contraction.

two different cells, A and B, that exert different contractile forces the interface force
will be:

g AB ¼ F csk A F csk B F adh AB

þ

AB , cells will show no inclination to sort. If the
interfacial forces are different, though, junctions between cells of different types will be
subjected to forces that will encourage cells of one type to slip between cells of the other
type. A simple illustration of this, for an idealized junction between four cells, is shown in
Figure 14.4 . The position of the 4-way junction is controlled by the balance of the interfa-
cial forces. If g

AA is identical to g

If the interfacial force g

AA , the interface will be drawn downwards until the angle at which
the A cells penetrate the B cells is acute enough for the forces to balance. If the structure of
the A cells will not permit an acute enough angle ( f ) to form, the envelopment of A cells
in type B cells will continue. It does not matter to this model whether the differences in
interfacial force are due to forces of adhesion, cytoskeletal forces modulated by adhesion,
or both.

BB

> g

FIGURE 14.4 Interfacial
tensions at an interface between
two A cells and two B cells.
(Diagram based loosely on
discussion in Brodland and
Chen 14 ).