Series of schematic diagrams depicting the morphological events during mammalian kidney development. The mammalian organism forms three excretory organs, all of which are derived from the intermediate mesoderm. (A, B): The first and most primitive organ, the pronephros, becomes functional in some fish although it has no obvious function in the mammalian embryo and after a short time it disappears. Longitudinal (A) and cross section (B) of the pronephros. (C, D): The pronephros is replaced by the mesonephros, which is found in high fishes and amphibians, whereas it degenerates and is replaced by the definitive kidney, the metanephros, in mammals. Longitudinal (C) and cross section (D) of the mesonephros. (E): The metanephros generates when the Wolffian duct elongates posteriorly and encounters the metanephric mesenchyma where the ureteric bud emerges. The metanephros and its generation of adult mammalian kidney is shown in a longitudinal section. (F): Scheme of a mature nephron and its developmental origin: the glomerulus, proximal tubule, Henle's loop, distal tubule, and connecting tubule derive from the metanephric mesenchyme, whereas the collecting ducts derive from the ureteric bud.

Hierarchical distribution of renal progenitors in adult human glomeruli. CD24⁺CD133⁺ renal progenitors (red) are localized at the urinary pole and are in close contiguity with podocytes (blue) at one extremity (the vascular stalk) and with tubular renal cells (white) at the other extremity. A transitional cell population (CD24⁺CD133⁺PDX⁺, red/blue) displays features of either renal progenitors (red) or podocytes (blue) and localizes between the urinary pole and the vascular pole. At the vascular stalk of the glomerulus, the transitional cells are localized in close continuity with cells that lack progenitor markers but exhibit the podocyte markers and the phenotypic features of differentiated podocytes (blue). Endothelial cells: yellow; mesangial cells: green; podocytes: blue; proximal tubular cells: white; renal progenitors: red.

Series of schematic diagrams depicting the morphological events and the localization of CD24⁺CD133⁺ renal progenitors during the different phases of nephron development. Mesenchymal cells near the tips of the branching ureteric bud are induced and differentiate through a series of forms: aggregate (A), renal vesicle (B), comma-shaped bodies (C), and S-shaped bodies (D). Also shown is the developing vasculature within the glomerular cleft of an S-shaped body (E) and the glomerulus in a more mature nephron (F). The tubular segments of the mature nephrons empty into the collecting ducts and eventually the ureter. Development proceeds in a radial manner so that older nephrons are centrally located and newer nephrons are added at the periphery as indicated. Cells of the ureteric bud are stained in green. CD24⁺CD133⁺ renal progenitors are stained in red. (A): CD24⁺CD133⁺ renal progenitors (red) localize in the condensed mesenchyme but not in the uninduced mesenchyme (white) or in the ureteric bud (green). (B): CD24⁺CD133⁺ renal progenitors localize in a primary vesicle but not in the uninduced mesenchyme (white) or in the ureteric bud (green). (C): CD24⁺CD133⁺ renal progenitors localize in the comma bodies but not in the uninduced mesenchyme (white) or in the ureteric bud (green). (D): CD24⁺CD133⁺ renal progenitors localize in the S-shaped body, in the proximal loop, as well as in the distal loop, but not in the uninduced mesenchyme (white) or in the ureteric bud (green). (E): CD24⁺CD133⁺ renal progenitors (red) localize in an S-shaped body after colonization by primordial capillaries and mesangium. (F): In maturing glomeruli, CD24⁺CD133⁺ renal progenitors (red) selectively persist as a subset of cells of the Bowman's capsule localized opposite to the vascular pole.