Boundaries to Epithelial Movement - Mechanisms of Morphogenesis - page 261

FIGURE 21.4 The role of tension in straightening and maintaining a border. In wild-type D. melanogaster ,
compartment boundaries are typically associated with the presence of thick, tense acto-myosin fibre bundles. In
zipper mutants have lost myosin II function, the actomyosin bundles are absent and the boundary becomes rough
with cell mixing.
described here and Harris' model for cell tension-mediated sorting described in Chapter 14.
In the boundary system described in this current chapter, high tension is generated locally in
response to signalling events at heterotypic cell contacts.
The importance of high tension being induced by heterotypic cell contact underlines the
necessity for recognition and signal transduction. This could take place, for example, by sig-
nalling systems such as Notch/Delta and Eph/Ephrin, the elements of which will be
expressed differently in cells of the two compartments, and then use the detection of unlike
neighbours to drive the production of tensile filaments, probably via the small GTPase Rho. 17
It is also possible that heterotypic cadherin recognition can organize the fibres, which would
provide a different explanation for the requirement for cadherins in the neocortex d basal
ganglion neurepithelium sorting phenomenon described above.
FIGURE 21.5 Tension organized along borders of unlike cells acts to repel invasion (from either side).