Intracellular signals direct integrin localization to sites of function in embryonic muscles

Abstract

In the Drosophila embryo, the α(PS2)β(PS) integrin heterodimer is localized tightly at the termini of the multinucleate muscles where they attach to the α(PS1)β(PS)-containing epidermal tendon cells. Here we examine the basis for α(PS2)β(PS) integrin subcellular localization. We show that the β(PS) cytoplasmic tail is sufficient to direct the localization of a heterologous transmembrane protein, CD2, to the muscle termini in vivo. This localization does not occur via an association with structures set up by the endogenous β(PS) integrins, since it can occur even in the absence of the β(PS) protein. Furthermore, the subcellular localization of the α(PS2)β(PS) integrin is not dependent on any other interactions between the muscles and the tendon cells. In embryos that lack the segmental tendon cells, due to a mutation removing the related segment polarity genes engrailed and invected, α(PS2)β(PS) is still localized to the muscle termini even though the ventral longitudinal muscles are not attached to the epidermis, but instead are attached end to end. Thus the α(PS2)β(PS) integrin can be localized by an intracellular mechanism within the muscles. Our results challenge the view that the transmission of signals from the extracellular environment via integrins is required for the organization of the cytoskeleton and the resultant cellular polarity.