Cited1 and Cited2 are differentially expressed in the developing kidney but are not required for nephrogenesis

Early kidney development in mammals is characterized by reciprocal tissue interaction between the ureteric bud and the metanephric mesenchyme. The coordinated response to this interaction is regulated largely at the transcriptional level. Here, we investigate the expression and function of Cited1, a transcriptional cofactor that we have previously implicated in kidney development. We show that Cited1 is expressed in the metanephric mesenchyme after invasion of the ureteric bud and that its expression is limited to the cap mesenchyme, those cells that aggregate most tightly around the tip of the ureteric bud and give rise to nephronic epithelium of the adult kidney. Cited1 is down-regulated during the initial stages of epithelial conversion and is not expressed past this progenitor stage. Despite its unique expression pattern, deletion of Cited1 does not disrupt kidney development. We hypothesized that this finding was due to functional redundancy with other members of this gene family. The expression pattern of Cited2 overlaps that of Cited1, but its deletion, either alone or in combination with Cited1, does not disrupt epithelial differentiation of the metanephric mesenchyme. From these studies, we conclude that Cited1 and 2 are dynamically expressed during kidney development, but are not required for nephrogenesis.