A Putative Src Homology 3 Domain Binding Motif but Not the C-terminal Dystrophin WW Domain Binding Motif Is Required for Dystroglycan Function in Cellular Polarity in Drosophila

Abstract

The conserved dystroglycan-dystrophin (Dg⅐Dys) complex connects the extracellular matrix to the cytoskeleton. In humans as well as Drosophila, perturbation of this complex results in muscular dystrophies and brain malformations and in some cases cellular polarity defects. However, the regulation of the Dg⅐Dys complex is poorly understood in any cell type. We now find that in loss-of-function and overexpression studies more than half (34 residues) of the Dg proline-rich conserved C-terminal regions can be truncated without significantly compromising its function in regulating cellular polarity in Drosophila. Notably, the truncation eliminates the WW domain binding motif at the very C terminus of the protein thought to mediate interactions with dystrophin, suggesting that a second, internal WW binding motif can also mediate this interaction. We confirm this hypothesis by using a sensitive fluorescence polarization assay to show that both WW domain binding sites of Dg bind to Dys in humans (K d ‫؍‬ 7.6 and 81 M, respectively) and Drosophila (K d ‫؍‬ 16 and 46 M, respectively). In contrast to the large deletion mentioned above, a single proline to an alanine point mutation within a predicted Src homology 3 domain (SH3) binding site abolishes Dg function in cellular polarity. This suggests that an SH3-containing protein, which has yet to be identified, functionally interacts with Dg.

RETRACTED: Dystroglycan and Perlecan Provide a Basal Cue Required for Epithelial Polarity during Energetic Stress

“…One copy of the mRpL34 transgene rescues this phenotype completely (Figure 3D). This result was surprising since it has been reported that expression of a Dg transgene also rescues the Dg 248 polarity phenotype (Yatsenko et al., 2007). We therefore reproduced this experiment and confirmed that Dg expression is sufficient to suppress the polarity defects associated with Dg 248 (Figure 3E).…”

Functional diversity of dystroglycan

“…Although no other extracellular partners have been identified so far besides the C-terminal domain of α-DG, possible interactions of the β-DG ectodomain with other extracellular proteins cannot be ruled out. In line with this dynamic view of the DG complex is the observation that in Drosophila also the affinity between the cytodomain of β-DG and dystrophin peptides is in the micromolar range (Yatsenko et al, 2007).…”

Loss-of-Function Screen Reveals Novel Regulators Required forDrosophilaGermline Stem Cell Self-Renewal

“…A group of genes, including POSH , UbcD10 , and pie , came to our interest. POSH and UbcD10 , respectively, encode for Drosophila E3 and E2 ubiquitin ligase (Figure 2B) (Tsuda et al 2005; Yatsenko et al 2007); whereas pie , with predicted RING/PHD domains, shares highly conserved sequence with a human E3 ubiquitin ligase G2E3 (Shi et al 2003; Brooks et al 2008) The authors of a recent study have demonstrated that another ubiquitin-conjugating enzyme, Effete, maintains Drosophila GSCs through regulating cyclin A degradation (Chen et al 2009). The finding of this group of ubiquitin ligase genes to be essential for GSC maintenance suggests a potentially conserved role of ubiquitin-mediated proteolysis in stem cell self-renewal and tissue homeostasis.…”