Perlecan and Dystroglycan act at the basal side of theDrosophilafollicular epithelium to maintain epithelial organization

Abstract

Dystroglycan (Dg) is a widely expressed extracellular matrix (ECM) receptor required for muscle viability, synaptogenesis, basementmembrane formation and epithelial development. As an integral component of the Dystrophin-associated glycoprotein complex, Dg plays a central role in linking the ECM and the cytoskeleton. Disruption of this linkage in skeletal muscle leads to various types of muscular dystrophies. In epithelial cells, reduced expression of Dg is associated with increased invasiveness of cancer cells. We have previously shown that Dg is required for epithelial cell polarity in Drosophila, but the mechanisms of this polarizing activity and upstream/downstream components are largely unknown. Using the Drosophila follicle-cell epithelium (FCE) as a model system, we show that the ECM molecule Perlecan (Pcan) is required for maintenance of epithelial-cell polarity. Follicle cells that lack Pcan develop polarity defects similar to those of Dg mutant cells. Furthermore, Dg depends on Pcan but not on Laminin A for its localization in the basal-cell membrane, and the two proteins bind in vitro. Interestingly, the Dg form that interacts with Pcan in the FCE lacks the mucin-like domain, which is thought to be essential for Dg ligand binding activity. Finally, we describe two examples of how Dg promotes the differentiation of the basal membrane domain: (1) by recruiting/anchoring the cytoplasmic protein Dystrophin; and (2) by excluding the transmembrane protein Neurexin. We suggest that the interaction of Pcan and Dg at the basal side of the epithelium promotes basal membrane differentiation and is required for maintenance of cell polarity in the FCE.

Differential Expression of Dystroglycan-spliceforms With and Without the Mucin-Like Domain During Drosophila Embryogenesis

“…The same difference in abundance was found when using the anti-cyto antibody. 5 Taken together, these findings confirm the results of the Northern blot analysis and show that DG-C is expressed between 2.5 and 20 h of embryogenesis, while a shorter form of DG appears first after 6 h and represents the predominant form of DG during later stages of embryogenesis. The results from the Northern blot and the RNA in situ hybridization suggest that this short form of DG corresponds mainly to DG-B.…”

“…5 The findings presented in this report further supports the idea that DG-forms lacking the mucin-like domain serve a specific function in Drosophila.…”

“…13 For Western blotting, antibodies were used in the following concentrations: rabbit anti-DG ex8 , 1:1000, 1 and rabbit anti-DG Cterm , 1:200. 5 Histochemistry. Drosophila embryos were staged according to Campos-Ortega and Hartenstein.…”

“…We have previously shown that in embryonic protein extracts, two major forms of DG (200 and 120 kDa) can be detected by Western blotting. 5 The 200 kDa protein is recognized by all three antibodies and therefore corresponds to DG-C. The 120-kDa band is only recognized by anti-C-term and anti-cyto and represents DG-A and/or DG-B (DG-A/B hereafter).…”

“…11 However, our own findings suggest that at least in the follicle cell epithelium of Drosophila, the mucin-like domain is not required for interaction with Perlecan. 5 Splicing of Dg is developmentally controlled. To determine the expression profile of the Dg transcripts during embryogenesis, we used a probe common to all three Dg-mRNAs on a Northern blot that contained mRNA from 0-6 h, 6-12 h and 12-18 h old embryos (Fig.…”