Scribble protein domain mapping reveals a multistep localization mechanism and domains necessary for establishing cortical polarity

The Drosophila tumor suppressor protein Scribble is required for epithelial polarity, neuroblast polarity, neuroblast spindle asymmetry and limiting cell proliferation. It is a member of the newly described LAP protein family, containing 16 leucine rich repeats (LRRs), four PDZ domains and an extensive carboxyl-terminal (CT) domain. LRR and PDZ domains mediate protein-protein interactions, but little is know about their function within LAP family proteins. We have determined the role of the LRR, PDZ and CT domains for Scribble localization in neuroblasts and epithelia, and for Scribble function in neuroblasts. We found that the LRR and PDZ domains are both required for proper targeting of Scribble to septate junctions in epithelia; that the LRR domain is necessary and sufficient for cortical localization in mitotic neuroblasts, and that the PDZ2 domain is required for efficient cortical and apical localization of Scribble in neuroblasts. In addition, we show that the LRR domain is sufficient to target Miranda protein to the neuroblast cortex, but that LRR+PDZ will exclude Miranda from the cortex. Our results highlight the importance of both LRR and PDZ domains for the proper localization and function of Scribble in neuroblasts.