Metanephric rat-mouse chimeras to study cell lineage of the nephron

The nephron is derived from the ureteric bud and metanephric mesenchyme and develops into a complex epithelial structure with a wide variety of phenotypes along its length. This segmental variation in expression of molecules provides an approach to understand the lineage of unique segments. The present study evaluated the expression of four relatively well-localized molecules--renin, Tamm-Horsfall protein (THP), oxytocin receptor (OTR), and the vasopressin type 2 receptor (V2R)--in cultured mouse-rat chimeric metanephric kidneys using reverse transcription-polymerase chain reaction (RT-PCR). Chimeric kidneys were formed by 1) separating the ureteric bud (U) from the metanephric mesenchyme (M) of mouse (m) at E11 and rat (r) at E13 days of gestation and 2) recombining the ureteric bud of one species with the metanephric mesenchyme of the other species (i.e., UrMm and UmM(r), followed by filter culture until differentiated. Species-specific restriction enzymes for all four genes were chosen to digest the PCR product from either rat or mouse. RT-PCR was performed for each mRNA species and the products digested. The V2R product from the UrMm chimera was cleaved by a restriction enzyme known to digest only rat product, suggesting the PCR product was produced predominantly by cells derived from the ureteric bud. The renin, OTR, and THP products from both chimeras were cleaved equally well by species-specific restriction enzymes, suggesting the products were made by cells originating from both the ureteric bud and the metanephric mesenchyme. These studies demonstrate that the cultured chimeric metanephric model is useful to study segment lineage. The results suggest that the lineage of at least certain portions of the nephron is heterogenous.