Kidney development in cadherin-6 mutants: Delayed mesenchyme-to-epithelialconversion and loss of nephrons

During nephrogenesis, dynamic changes in the expression of cell adhesion mo lecules are evident as epithelial structures differentiate from the induced mesenchyme. The cadherins are thought to play an important role in the met anephric mesenchyme, when cells aggregate to form the renal vesicle, a pola rized epithelial structure which eventually fuses with the ureteric bud to generate a continuous nascent nephron. We have generated and analyzed mice with a targeted mutation in the gene encoding cadherin-6 (Cad-6), a type II cadherin expressed during early stages of nephrogenesis. These mice are vi able and fertile, and they complete both early and late aspects of nephroge nesis. However, upon closer examination in vitro and in vivo, a fraction of the induced metanephric mesenchyme in Cad-6 mutant kidneys fails to form a fully polarized epithelium on schedule. Moreover, a significant number of the renal vesicles in Cad-6 mutant kidneys apparently fail to fuse to the u reteric bud. These alterations in epithelialization and fusion apparently l end to a loss of nephrons in the adult. These studies support the idea that cadherins play an essential role in the formation of epithelial structures and underscore the importance of timing in orchestrating the morphogenesis of complex epithelial tissues. (C) 2000 Academic Press.