Mutations in the Drosophila alpha PS2 integrin subunit uncover new features of adhesion site assembly

The Drosophila alpha PS2 beta PS integrin is required for diverse development events, including muscle attachment. We characterized six unusual mutations in the alpha PS2 gene that cause a subset of the null phenotype. One mutation changes a residue in aPS2 that is equivalent to the residue in alpha V that contacts the arginine of RGD. This change severely reduced alpha PS2 beta PS affinity for soluble ligand, abolished the ability of the integrin to recruit laminin to muscle attachment sites in the embryo and caused detachment of integrins and talin from the ECK Three mutations that alter different parts of the alpha tPS2 beta-propeller, plus a fourth that eliminated a late phase of alpha PS2 expression, all led to a strong decrease in alpha PS2 beta PS at muscle ends, but, surprisingly, normal levels of talin were recruited. Thus, although talin recruitment requires alpha PS2 beta PS, talin levels are not simply specified by the amount of integrin at the adhesive junction. These mutations caused detachment of talin and actin from integrins, suggesting that the integrin-talin link is weaker than the ECM-integrin link.