Cell polarization and importance for cancer

Cells have an Apical and a Basal side in contact with the basal lamina (Basement membrane) (A, adapted from The Molecular Biology of the Cell).

Epithelial cells in Drosophila are similar in architecture to mammalian cells (see B, adapted from Humbert P. et al.) Common junctional complexes between insects and mammals are shown in the middle cells. Junctional proteins that are unique to Drosophila to the left and mammals to the right.

 
Adherense junctions form the Zonula adherens, an ultrastructural distinct belt surrounding the apical portion of the epithelial cells.The core components of the adherense junctions are transmembrane E-cadherin molecules (termed shotgun shg in Drosophila), alfa-catenin and beta-catenin (armadillo, arm in Drosophila).In mammalian cells a second complex, is localised to adherense junctions containing Nectin, Afadin (AF-6, Canoe in Drosophila).

Subapical region/marginal zone is localised in equivalent positions to the tight junctions in mammalian cells, just apically to the to adherense junctions. Two protein complexes are localised to this region: The Par3 (Bazooka in Drosophila), Par6, a PKC complex and Crumbs (transmembrane), Pals (Stardust in Drosophila), Patj (Disclost in Drosopila).

Septate junctions in insects is a solute barrier and is thought to be analogous to the tight junctions of mammalian cells.

In the Z section confocal picture above the stratified monolaer of cells of the wing puch of a wing imaginal disc is labeled with Actin (red) to visualize the adherense junctions and disc large (Dlg) to visualize the Septate junctions. DNA is labeled in green with TOTO-3 (molecular probes) 

Structure	Drosophila marker	Reference
Subapical region/Marginal zone	Bazooka/Par3 Disclost/Par6 Stardust/Pals
Adherense junctions	alfa-catenin armadillo/beta-catenin Canoe/Afadin
Drosophila septate junction	Neurexin IV Coracle Disc Large/Dlg Scribble/LAP4 Lethal Giant Larva/Lgl (exosyst t-snare binding) Camgurk (Cask)
Basement membrane	Laminin A Collagen IV RFP-enhancer trap	(Pagliarini RA. et al 2003) (Pagliarini RA. et al 2003)