THE METANEPHRIC BLASTEMA DIFFERENTIATES INTO COLLECTING SYSTEM AND NEPHRON EPITHELIA IN-VITRO

The kidney forms from two tissue populations derived from intermediate mesoderm, the ureteric bud and metanephric mesenchyme. It is currentl y accepted that metanephric mesenchyme is committed to differentiating into nephrons while the ureteric bud is restricted to forming the ren al collecting system. To test this hypothesis, we transferred lacZ int o pure metanephric mesenchyme isolated from gestation day 13 rat embry os, The fate of tagged mesenchymal cells and their progeny was charact erized after co-culture with isolated ureteric buds. When induced to d ifferentiate by the native inducer of kidney morphogenesis, lineage-ta gged mesenchymal cells exhibit the potential to differentiate into col lecting system epithelia, in addition to nephrons, The fate of cells d eriving from isolated ureteric buds was also examined and results of t hese lacZ gene transfer experiments indicate that the majority of uret eric bud cells differentiate into the renal collecting system, These c ell fate studies combined with in situ morphological observations rais e the possibility that collecting system morphogenesis in vivo occurs by growth of the ureteric bud and recruitment of mesenchymal cells fro m the metanephric blastema. Thus, metanephric mesenchyme may be a plur ipotent renal stem population.