Histological observations on cell death in the developing kidneys of the fetal and newborn mice, with special reference to differentiation of nephron-forming cells in the renal cortex*
Cell death occurring in developing kidneys was examined light microscopically in 30 ICR-mice. The kidneys were removed at 18 days of gestation, 0 and 2 days after birth, fixed in Karnowsky's fluid and embedded in glycolmetacrylate mixture for 1 μm semithin sections. Distribution of apoptotic cells was also examined by the TUNEL (TdT-mediated dUTP nick end-labeling) method in paraffin section. Between 18 days of gestation and 2 days after birth, the kidneys contained not only numerous mitotic figures but also dying cells with pyknotic and fragmented nuclei. After birth, number of dying cells per unit area slightly increased, and its 3fold increase was observed in the medulla. Dying cells could be recognized in both nephron-forming cell clusters and mesenchymal cell clusters, and numerous dying cells could be detected in the outer cortex beneath the capsule and the medullary papilla. Since cleareul positive staining appeared in the TUNEL assey, the cell death was shown to be through apoptosis. In the process of nephron development in the cortex, metanephric cap, i.e. the cell mass of mesoderm, was first formed around the tips of the two branches of ureteric ducts, then the cell mass became comma-shaped. As the glomerular apparatus of the nephron took shape, a slit formed in the comma-shaped metanephric vesicle, transforming it into an S-shaped structure, and the metanephric vesicles were invaded by capillaries through the slit. The apoptotic cells in the nephron-forming cell clusters appeared at an S-shaped metanephric vesicle stage and were localized in the cell layerof future glomerular capsules. The relationship between programmed cell death and nephron-forrming cell differentiation in the renal cortex was discussed. (Accepted on April 30, 1998) Kawasaki Igakkaishi 24(1) : 7-15, 1998
