Development of the renal corpuscle and occurrence of apoptosis in the newborn mouse kidney – an ultrastructural study – *
Apoptosis occurring in the developing renal corpuscle of fetal and neonatal ICR-mice was ultrastructurally examined. Kidneys were removed at 18 days of gestation and at 0 and 2 days after birth, fixed in Karnowsky's fluid and embedded in Epon 812 for ultrathin sections. Renal corpuseles at various developmental stages could be observed in the cortex of the newborn kidneys. Mctanephric caps were located in the subcapsular cortex, and the superficial cortex contained comma-shaped and S-shaped metanephric vesicles. Immature and mature renal corpuscles could be seen in the deep cortex near the cortico-medullary junction. In both S-shaped metanephric vesicles and immature renal corpuscles, dead cells appeared among Bowman's epithelial cells. Dead cells could be recognized in both the visceral and parietal epithelial cell layers. Both epithelial layers often contained large heterophagosomes containing cell debris derived from apoptotic cells. The nuclei of dying cells became very condensed, and the heterochromatin aggregated, Apoptotic cells were fragmented, forming apoptotic bodies to be phagocytosed by neighboring cells. Apoptotic cells were frequently recognized near the border of the visceral and parietal epithelium. In immature renal corpuscles, some dead cells also appeared within Bowman's space, and their ultrastructures suggested that they were of parietal epithelial cell origin. Based on our ultrastructual observations, programmed cell death in the neonatal renal cortex is considered to appear in relation to development of the renal corpuscle. In particular, apoptosis may play an active role in the differentiation and maturation of Bowman's epithelial cells and formation of the Bowman's space. (Accepted on September 22, 1998) Kawasaki Igakkaishi 24(3) : 141-148, 1998
