Requirements for the cytoplasmic domain of the α_PS1, α_PS2 and β_PS integrin subunits during Drosophila development

The integrins are a family of transmembrane heterodimeric proteins that mediate adhesive interactions and participate in signaling across the plasma membrane. In this study we examine the functional significance of the cytoplasmic domains of the α_PS1, α_PS2 and β_PS subunits of the Drosophila Position Specific (PS) integrin family by analyzing the relationship between cytoplasmic domain structure and function in the context of a developing organism. By examining the ability of β_PS molecules lacking the cytoplasmic domain to rescue embryonic abnormalities associated with PS integrin loss, we find that although many embryonic events require the β_PS cytoplasmic domain, this portion of the molecule is not required for at least two processes requiring PS integrins: formation of midgut constrictions and maintaining germband integrity. Furthermore, our studies demonstrate that mutant proteins affecting four highly conserved amino acid residues in the cytoplasmic tail function with different efficiencies during embryonic development, suggesting that interaction of PS integrins with cytoplasmic ligands is developmentally modulated during embryogenesis.

We have also examined the ability of α_PS1 and α_PS2 to function without their cytoplasmic domains. By analyzing the ability of transgenes producing truncated α_PS molecules to rescue abnormalities associated with integrin loss, we find that the cytoplasmic tail of α_PS2 is essential for both embryonic and postembryonic processes, while this portion of α_PS1 is not required for function in the wing and in the retina. Furthermore, temperature-shift experiments suggest roles for the α_PS2 cytoplasmic domain in signaling events occurring in the developing wing.