Involvement of laminin binding integrins and laminin-5 in branching morphogenesis of the ureteric bud during kidney development

Branching morphogenesis of the ureteric bud (UB) [induced by the metanephri c mesenchyme (MM)] is necessary for normal kidney development. The role of integrins in this complex developmental process is not well understood. How ever, the recent advent of in vitro model systems to study branching of UB cells and isolated UB tissue makes possible a more detailed analysis of the integrins involved. We detected integrin subunits alpha3, alpha6, beta1, a nd beta4 in both the UB and cells derived from the early UB. Blocking the f unction of each of these integrin subunits individually markedly inhibited branching morphogenesis in cell culture models. However, inhibiting individ ual integrin function with blocking antibodies in whole kidney and isolated UB culture only partially inhibited UB branching morphogenesis, suggesting that, in these more complex in vitro systems, multiple integrins are invol ved in the branching program. In whole or-an and isolated bud culture, mark ed retardation of UB branching was observed only when both alpha3 and alpha 6 integrin subunits were inhibited. The alpha6 integrin subunit can be expr essed as both alpha6 beta1 and alpha6 beta4, and both of these beta subunit s are important for UB branching morphogenesis in both cell and organ cultu re. Furthermore, laminin-5, a common ligand for integrins alpha3 beta1 and alpha6 beta4, was detected in the developing UB and shown to be required fo r normal UB branching morphogenesis in whole embryonic kidney organ culture as well as isolated UB culture. Together, these data from UB cell culture, organ culture, and isolated UB culture models indicate that both integrin alpha3 and alpha6 subunits play a direct role in UB branching morphogenesis , as opposed to being modulators of the inductive effects of mesenchyme on UB development. Furthermore the data are consistent with a role for laminin -5, acting through its alpha3 beta1 and/or alpha6 beta4 integrin receptors, in UB branching during nephrogenesis. These data may help to partially exp lain the renal phenotype seen in integrin alpha3 and alpha3/alpha6 subunit- deficient animals. (C) 2001 Academic Press.