Apical restriction of DE-Cadherin (green, left) is lost in baz mutants (right).
Polarized epithelia are characterized by complexes that provide tight adhesions between neighboring cells. These complexes, known as adherens junctions (AJs), contain transmembrane cadherins that link adjacent cells. Cadherin is anchored to the actin cytoskeleton through the AJ proteins Armadillo and α-catenin.
The building of AJs is normally considered the earliest known event in establishing apicobasal polarity. Looking for polarity in the absence of AJs, however, is tricky; sheet architecture falls apart if AJs are removed, so the cells are no longer epithelial. But Harris and Peifer find that, in the developing fly, enough epithelial cells stay in place to determine that a polarized epithelium can develop without AJs.
The signs...
