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

Chris Q. Doe,Roger Albertson,Chiswili Chabu,Amy Sheehan

doi:10.1242/jcs.01525

Abstract

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.

Highlights

The establishment of polarized cortical protein domains is essential for both asymmetric cell division and proper function of many cell types, such as epithelia, neurons and muscle
Loss of Scrib, Lethal giant larvae (Lgl) or Discs large (Dlg) leads to a disruption of septate junctions causing apical proteins such as Par3-Par6-aPKC to diffuse from the apical cortex to the basolateral cortex, resulting in defects in junctional complexes, cell morphology, and growth control in Drosophila epithelia (Bilder and Perrimon, 2000; Bilder et al, 2003)
The scrib gene encodes a 1766 amino acid protein that contains 16 leucine rich repeats (LRRs), LAPSDa/b domains and four PDZ domains; this is the form of the protein we have worked with in this investigation

Summary

Introduction

The establishment of polarized cortical protein domains is essential for both asymmetric cell division and proper function of many cell types, such as epithelia, neurons and muscle. Studies in Drosophila, C. elegans and mammalian epithelial cells have demonstrated that apical/basal cell polarity is created through membrane domains and junctional complexes with characteristic positions along the apical/basal axis (Bryant, 1997). In vertebrates, these are the tight junctions, adherens junctions and a basolateral domain, from apical to basal, respectively. Loss of Scrib, Lgl or Dlg leads to a disruption of septate junctions causing apical proteins such as Par3-Par6-aPKC to diffuse from the apical cortex to the basolateral cortex, resulting in defects in junctional complexes, cell morphology, and growth control in Drosophila epithelia (Bilder and Perrimon, 2000; Bilder et al, 2003)

Methods

Results

Discussion

Conclusion