Biology Reference
In-Depth Information
FIGURE 16.9
The signalling system implicated in passing planar polarity information to convergent extension.
(a) The two arms of the key pathway, one of which activates actin-myosin contraction and the other of which
discourages junction assembly (including replacement of junctions). (b) The activation of these systems on the
North border of a cell results in that cell shortening and dismantling its junctions: the next cell along loses its
junctions because these complexes are stable only when they interact with another cell.
which are absent fromD. melanogaster so cannot be involved in its biology, are very important
to the way that mammalian epithelia make use of polarity information in their own plane,
particularly to build specialized structures. These issues are important to many human
congenital diseases but lie beyond the remit of this topic.
Epithelial convergent extension, depending as it does on the polarized, boundary-
changing activity of individual cells, is another example of the self-organizing of morpho-
genetic change by a multitude of autonomous agents, each of which follows simple rules.
What is slightly unusual is that the morphological change of each cell does not reflect the
resulting change of the tissue in microcosm, as is the case when tissues extend because their
constituent cells do (
Figure 16.1
, top) or when each cell moves in the direction that the
population as a whole moves during cell migration. It therefore serves as a reminder to
researchers attempting to find a cellular explanation of a morphogenetic change at the tissue
level, that the relationship between events at the two levels may involve complex geometrical
transformations rather than a simple scaling up of the same change of shape.
Reference List
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3. Munro EM, Odell GM. Polarized basolateral cell motility underlies invagination and convergent extension of
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