Identifying the Molecular Phenotype of Renal Progenitor Cells

Although many of the molecular interactions in kid- ney development are now well understood, the molecules involved in the specification of the metanephric mesenchyme from surrounding intermediate mesoderm and, hence, the for- mation of the renal progenitor population are poorly charac- terized. In this study, cDNA microarrays were used to identify genes enriched in the murine embryonic day 10.5 (E10.5) uninduced metanephric mesenchyme, the renal progenitor pop- ulation, in comparison with more rostral derivatives of the intermediate mesoderm. Microarray data were analyzed using R statistical software to determine accurately genes differen- tially expressed between these populations. Microarray outliers were biologically verified, and the spatial expression pattern of these genes at E10.5 and subsequent stages of early kidney development was determined by RNA in situ hybridization. This approach identified 21 genes preferentially expressed by the E10.5 metanephric mesenchyme, including Ewing sarcoma homolog, 14-3-3 , retinoic acid receptor-, stearoyl-CoA de- saturase 2, CD24, and cadherin-11, that may be important in formation of renal progenitor cells. Cell surface proteins such as CD24 and cadherin-11 that were strongly and specifically expressed in the uninduced metanephric mesenchyme and mark the renal progenitor population may prove useful in the purification of renal progenitor cells by FACS. These findings may assist in the isolation and characterization of potential renal stem cells for use in cellular therapies for kidney disease. There is increasing evidence from a number of organ systems that cells with at least multipotentiality (1,2) and possibly pluripotentiality (3) exist in adult organs that previously were thought not to contain such populations. Although cell division is infrequent in the adult kidney, this organ possesses the capacity for regeneration as evidenced by the cellular prolif- eration observed during recovery from conditions such as acute tubular necrosis (4). Although cell lineage relationships during renal repair and regeneration are poorly defined, it is possible that these processes recapitulate some aspects of embryonic renal development. The permanent kidney (metanephros) arises via reciprocal interactions between two tissues, the ure- teric bud (UB) and the metanephric mesenchyme (MM) (5). Each of these tissues is initially derived from the intermediate mesoderm (IM), although the UB develops as a caudal out- growth from the nephric duct (ND), whereas the MM develops from the nephrogenic cord, the same block of tissue that gives rise to the pronephroi and the mesonephroi (5). After invasion by the UB, cells of the MM are induced to differentiate into specific renal lineages. The central dogma of kidney develop- ment suggests that the UB forms the ureter and collecting duct system of the mature kidney, whereas the MM gives rise to the