DEVELOPMENT OF THE KIDNEY - RECENT MOLECU LAR-BIOLOGY DATA

Three renal anlages form successively from the cephalic to the caudal part of the intermediary mesoderm of the embryo. Differentiation of th e permanent kidney, or metanephros, begins during the fifth week when the ureteric bud reaches the nephrogenic blastema, and continues throu ghout most of the gestational period. When it comes in contact with th e blastema, the ureteric bud grows and divides to form the collecting system, from the renal pelvis? to the cortical collecting ducts. Start ing at the eighth week, the blastema cells in contact with the ends of the ureteric divisions differentiate into nephrons. This process occu rs centripetally, in successive waves that develop in lockstep with th e growth of the ureteric bud. The fetal kidney is therefore a heteroge neous organ, containing both structurally and functionally mature neph rons and immature nephrons. Models of organotypic cultures of whole or dissociated renal anlages have demonstrated reciprocal induction betw een the ureteric bud and the blastema. Recent technological advances, most notably in molecular genetics, have provided valuable insights in to the molecular mechanisms involved in these interactions, although g aps persist in our knowledge of renal development. These new data sugg est new approaches to abnormalities of renal development occurring alo ne or as part of a complex malformation syndrome.