Differential positioning of adherens junctions is associated with initiation of epithelial folding

Differential positioning of adherens junctions is associated with initiation of epithelial folding

Yu-Chiun Wang, Zia Khan, Matthias Kaschube & Eric F. Wieschaus

Nature. 2012 Mar 28. doi: 10.1038/nature10938

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During tissue morphogenesis, simple epithelial sheets undergo
folding to form complex structures. The prevailing model underlying epithelial folding involves cell shape changes driven by
myosin-dependent apical constriction. Here we describe an
alternative mechanism that requires differential positioning of
adherens junctions controlled by modulation of epithelial apical–
basal polarity. Using live embryo imaging, we show that before the
initiation of dorsal transverse folds during Drosophila gastrulation, adherens junctions shift basally in the initiating cells, but maintain their original subapical positioning in the neighbouring cells.
Junctional positioning in the dorsal epithelium depends on the
polarity proteins Bazooka and Par-1. In particular, the basal shift
that occurs in the initiating cells is associated with a progressive
decrease in Par-1 levels. We show that uniform reduction of the
activity of Bazooka or Par-1 results in uniform apical or lateral
positioning of junctions and in each case dorsal fold initiation is
abolished. In addition, an increase in the Bazooka/Par-1 ratio
causes formation of ectopic dorsal folds. The basal shift of junctions
not only alters the apical shape of the initiating cells, but also forces
the lateral membrane of the adjacent cells to bend towards the
initiating cells, thereby facilitating tissue deformation. Our data
thus establish a direct link between modification of epithelial
polarity and initiation of epithelial folding.

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