Down-regulation of the chicken α₅β₁ integrin fibronectin receptor during development

We have characterized the diversity of the chicken β₁ integrin family and studied the expression of individual receptors during development. The diversity of the β₁ integrin family was investigated by affinity purifying the β₁ integrins from a variety of adult and embryonic tissues. These purifications reveal the relative levels of expression and also the differential expression of the α subunits in those tissues. Monoclonal antibodies were generated against the prominent 'band 1' of the embryonic chicken integrins and used to characterize the expression of this α subunit in embryonic and adult tissues. This α subunit is shown to be the chicken homologue of human α₅ fibronectin receptor. The chicken α₅β₁ integrin is the most prominent β₁ integrin in the embryo and is expressed on the majority of cell types through the day 17 stage. The distribution of this receptor in the embryo closely parallels the distribution of its ligand, fibronectin. In adult tissues, expression of this receptor is greatly diminished relative to the expression of other α subunits. The cell type distribution is highly restricted: limited primarily to the vasculature and to connective tissue regions. These studies reveal a prominent role for the α₅β₁ integrin in embryonic cell types and a down-regulation of this receptor on many cell types during development.