The Baz (fly PAR-3) complex (cytoplasmic Baz, PAR-6, aPKC and Cdc42) and the Crumbs (Crb) complex (transmembrane Crb, and cytoplasmic Stardust and Patj) are apical cues, whereas the Discs large (Dlg) complex (cytoplasmic Dlg, Lethal giant larvae and Scribble) is a basolateral cue.
19 Domains of the plasma membrane are regulated by Par and Crumbs for the apical domain and Scribble for the basolateral domain.
Finally, although additional polarity complexes are known in epithelial cells (the apical Crumbs complex and the basolateral Scribble complex) where they also contribute to TJ formation and regulation, no similar observations have been reported, to our knowledge, in brain endothelial cells.
Recently, Bilder et al (Bilder and Perrimon, 2000) identified the basolateral protein scribble that determines the localisation of the apical epithelial determinants.
To establish cell polarity, cells have the separated plasma membrane of apical domain, regulated by Par (Par3, Par6, aPKC) and Crumbs (Crumbs, PALS/Stardust, PATJ/Discs) and basolateral domain regulated by Scribble (Scribble, LGL, DLG).
Members of the Scribble group (SCRIB/DLG/LGL) localize to the basolateral side and promote basolateral identity, while the apically localized PAR (PAR-3/PAR-6/aPKC) and Crumbs (CRB/PALS1/LIN-7/PATJ) complexes define apical identity.
Human scribble localised at the broad basolateral membrane in the epithelial MDCK cell line and human endocervical tissues as expected.
Three major complexes involved in the regulation of apical basal cell polarity of epithelial cells have been described: The Crumbs-Pals1 (Stardust -Patj-Lin-7 (CrumbStardust -Patj-Lin-7(Bazooka)-Par6-aPKC (Par complex) complexeStardust -Patj-Lin-7pically, and the lethal giant larvae (Lgl)-Stardust -Patj-Lin-7Crumbse (Dlg) proteins (Scomplex complex) thandlocalise at the basolateral membrane.
In support of this hypothesis, a previous study observed that CRB-1 can provide a positional cue for the localization of DLG-1 after inactivation of the basolateral regulator let-413 Scribble and the junctional component hmp-1 α-Catenin (Segbert et al., 2004).
So, scribble is not only an apical-basolateral polarity determinant but also a tumour suppressor.
