AIP1-Mediated Actin Dynamics Is Essential For Adherens Junction Remodeling During Drosophila Eye Development

Dynamic assembly and disassembly of the actin cytoskeleton are required for such essential processes as cell division, cell motility, endocytosis and morphogenesis. Actin interacting protein1(AIP1) was first identified in yeast and was later shown to collaborate with cofilin to disassemble F-actin in vitro. It is a WD-repeat protein (-67-kD), and like cofilin it is highly conserved across species.Drosophila AIP1is encoded by the gene flare (flr). Recently, mutations of flr have been reported to affect planar polarity and morphogenesis of wing hairs. We show here that epithelial morphogenesis is severely affected in the larval eye discs of flr mutants. Specifically, adherens junctions (AJ, E-cadherin/β-catenin/a-catenin complex) within ommatidial preclusters and clusters are severely altered in flr mutant tissues, while other epithelial polarity markers, including the apical Par3/Par6/aPK.C complex, and the basalateral Dlg complex (septate junction) do not show gross defects. Immuno-staining study shows that AIP1is preferentially expressed behind the MF, and it specifically colocalizes with the AJ within ommatidial clusters. Furthermore, F-actin level is dramatically increased in the mutant flr clones behind the MF but not anterior to it, indicating AIP1is required for F-actin disassembly and its actin depolymerizing activity is mostly required in regions of epithelia that undergo active morphogenesis (eg. dynamic rearrangement of AJ). These F-actin and AJ defects could also be detected in tsr (encoding cofilin) temperature-sensitive alleles. Overexpressing cofilin in flr.RNAi flip-out clones rescued AJs structure, suggesting that AIP1enhance the efficiency of cofilin-induced actin depolymerization specifically around AJs. At last, the actin drug experiments on the eye discs illuminate that actin dynamics is essential for A(?)remodeling after the MF. Taken together, our results suggest that AIP1and cofilin-mediated actin dynamics is required in AJ formation and rearrangement during epithelial morphogenesis in the eye.