Cellular Differentiation in the Kidneys of Newborn Mice Studied With the Electron Microscope

Abstract

Renal structure and function are incompletely developed at birth in a number of mammals, including the rat and man. Functional immaturity manifests itself as an inability on the part of the kidney to vary the volume and concentration of the urine (McCance, 1948). I n the rat, renal function matures during the first few weeks after birth (Falk, 1955). Detailed studies of the structural changes in kidneys of newborn animals have been confined largely to the rat.During the first few weeks after birth, the rat kidney grows as a result of the formation of new nephrons in the peripheral zone of the cortex (Kittelson, 1917;Arataki, 1926), and at the same time the cells of the kidney acquire their specific cytological characteristics. Stergios, in an unpublished thesis (1933), has described the development of the brush border in the proximal tubules and the formation of basal striations, the Stabchen of Heidenhain (1874), in proximal and distal tubules. At birth the proximal tubules possess a homogeneous cuticular border which acquires the appearance of a brush border during the first 2 weeks after birth. The basal striations develop during this time by a process of alignment of the mitochondria, which were randomly arranged at birth, into rows perpendicular to the basement membrane. Between 4 and 9 days after birth, the brush border and basal striations achieve a state of organization which renders them birefringent (Olivecrona and Hillarp, 1949). Coincident with the development of the brush border, the cells of the proximal tubules acquire the ability to stain intravitally with trypan blue (Baxter and Yoffey, 1948). The alkaline phosphatase reaction and the periodic acid-Schiff staining properties of the brush border continue to differentiate for several months after birth in the mouse (Longley and Fisher, 1956) Cytoplasmic droplets that stain with the periodic acid-Schiff technique occur in the proximal tubules of a variety of mammalian fetuses, including the rat and man (Davies, 1954). Their presence is associated with proteinuria, and both droplets and proteinuria disappear soon after birth in most animals. Similar droplets have been produced in the proximal tubules of adult rats by the administration of certain

Mitophagy Plays an Essential Role in Reducing Mitochondrial Production of Reactive Oxygen Species and Mutation of Mitochondrial DNA by Maintaining Mitochondrial Quantity and Quality in Yeast

“…Although the presence of mitochondria in lysosomes or vacuoles was first reported in 1957 in mammalian cells (22) and in 1992 in yeast (23), the physiological relevance of mitochondrial degradation by autophagy has been unclear. Very recently, in mammalian cells, several studies have suggested that PINK1/ parkin-dependent mitophagy selectively degrades depolarized mitochondria (12,18,19), implying that mitophagy contributes to mitochondrial quality control.…”

The Ingestion of Proteins and Colloidal Materials by Columnar Absorptive Cells of the Small Intestine in Suckling Rats and Mice

“…Excess membrane derived from the fusion and dehydration of vacuoles might be the source of the complex arrays of parallel membranes found associated with these inclusions. The combination of a microvillous cell border, subcuticular tubules, apical vacuoles, and dense inclusions is characteristic not only of intestinal cells in suckling animals, but of the visceral epithelium of the mammalian yolk sac (Dempsey, 1953) and the proximal tubular epithelium of the kidney (Rhodin, 1954;Clark, 1957). Both the yolk sac and the proximal tubular epithelium ingest vital dyes and proteins.…”

The pathways of mitophagy for quality control and clearance of mitochondria

“…Accordingly, entire mitochondrial organelles were often observed in yeast vacuoles and mammalian lysosomes in electron microscopy studies. 10,11 Bulk degradation of cellular contents occurs through a regulated process called autophagy (reviewed elsewhere in this issue); however, a selective form of autophagy, termed mitophagy, is chiefly responsible for elimination of damaged or superfluous mitochondria. In this process, mitochondria are sequestered in doublemembrane vesicles and delivered to lysosomes for hydrolytic degradation.…”