A Key Function for αv Containing Integrins in Mesodermal Cell Migration duringPleurodeles waltlGastrulation

Abstract

During cleavage ofPleurodeles waltlamphibian embryos, inner cells of the blastocoel roof (presumptive ectodermal and mesodermal cells) organize a fibrillar extracellular matrix (ECM) containing fibronectin on their basal surface by a β1-integrin-dependent process. This matrix is used as a migratory substrate by mesodermal cells during gastrulation. While α5β1 integrin is expressed on both ectodermal and mesodermal cell surface, we have shown previously that αv containing integrins are essentially restricted to the surface of mesodermal cells (Alfandari, D., Whittaker, C. A., DeSimone, D. W., and Darribère, T.,Dev. Biol.170, 249–261, 1995). To investigate the function of αv integrins during gastrulation, we have generated a function blocking antibody directed against the extracellular domain of thePleurodelesintegrin αv subunit. The antibody did not prevent fibronectin fibril formation, whereas an antibody against the α5β1 integrin did. When injected into the blastocoel, the antibody against integrin αv subunit perturbed gastrulation and further development in a stage-dependent manner. Developmental defects were correlated to an abnormal positioning of the mesoderm layer.In vitro,the antibody blocked spreading of mesodermal cell to fibronectin or blastocoel roof ECM but not their attachment. In contrast, the antibody directed against the α5β1 integrin inhibited both cell attachment and spreading to the same substrates. We propose that the α5β1 integrin is required for fibronectin assembly into fibrils and mesodermal cell attachment to the blastocoel roof ECM, while the αv containing integrins are necessary for cell spreading, and possibly migration, on this complex network.