Cloning and characterization of cDNAs encoding the integrin alpha2 and alpha3 subunits from Xenopus laevis

Integrins containing the alpha2 and alpha3 subunits associate with the beta1 subunit to form distinct receptors with partially overlapping adhesive specificities. We report the cloning and sequence of cDNAs that encode the Xenopus orthologues of integrins alpha2 and alpha3 and the expression of these subunits during embryogenesis. Integrin alpha2 and alpha3 mRNAs are first expressed in the dorsal mesoderm and developing notochord at gastrulation. We also show that alpha3 mRNAs are expressed in the entire marginal zone of gastrulae dorsalized with LiCl but that this localization is lost in embryos ventralized by ultraviolet light. Immunoblots reveal that the alpha3 protein is expressed throughout early development, however, the alpha2 protein is not detected until late tailbud stages. Injection of full-length alpha3 transcripts into the animal poles of fertilized eggs results in embryonic defects in paraxial mesoderm attributed to the failure of somites to form segments. Injection of the alpha3 transcripts into the vegetal pole and overexpression of a 5'-truncated alpha3 control construct have no apparent affect on development or somite formation. These data suggest that normal position-specific expression of integrins is important in maintaining the proper organization of tissues during early amphibian morphogenesis.