Phenotypic analysis of null mutants for DE-cadherin and Armadillo in Drosophila ovaries reveals distinct aspects of their functions in cell adhesion and cytoskeletal organization

Background: DE-cadherin is an epithelial cadherin in Drosophila, and forms adherens junctions by associating with Armadillo (beta-catenin). To investigate its role in oogenesis, we generated germ-line clones homozygous for a null mutation in shotgun (shg) encoding this molecule, and examined their phenotypes, comparing with those of armadillo (arm) mutants, Results: In the wild-type ovaries, DE-cadherin was expressed by both the germ-line and somatic derivatives, colocalizing with Armadillo. In the shg mutant ovaries in which the mutation was restricted to the germ line, germ cells were rounded, and generated gaps between themselves, suggesting that their surface adhesiveness was reduced or lost. However, the positioning of germ cells in the egg chamber was normal. Two groups of somatic follicle cells-the border cells and centripetal follicle cells-frequently migrated along incorrect pathways, indicating that DE-cadherin is required for their appropriate migration. Notably, the shg phenotypes were distinct from those of arm null mutants. Intercellular adhesion appeared to be less severely affected by arm than by the shg mutation, and the actin-based cytoskeleton and cell arrangement were disorganized only in the arm mutants. Conclusions: These findings suggest that DE-cadherin is critical for cell-cell adhesion, and functional to a certain extent without Armadillo, whereas Armadillo is required for cytoskeletal organization and for the control of cell positioning. We therefore propose that the molecular complex of DE-cadherin and Armadillo which is present in normal cells is endowed with multiple functions derived from each molecule.