Development of the Metanephric Kidney

Abstract

The metanephric kidney was studied in fetal and older mice beginning at 16 days after mating of the parents. Polyribosomes from fetal kidneys labeled in vitro with 4C-labeled amino acids had 10-20 times more acid-precipitable radioactivity associated with them than polysomes from adult kidneys similarly labeled. Between 3 and 6 days after birth the rate incorporation of labeled amino acids by polyribosomes from neonatal kidneys declined sharply to only twice the value found for adult kidneys. There was no change in the shape of the polyribosome profile with increasing age, but before birth few, if any, ribosomes were bound to membranes compared with 20% 2 days after birth and between 20 and 30% in the adult. Total protein represented less than 10% of the wet weight in the fetal kidney but increased to 17 % of the wet weight in the adult kidney. There was a steady decline in the concentration of RNA and DNA with respect to dry weight throughout kidney development. DNA concentration declined more rapidly than RNA concentration, so that the milligram to milligram ratio of RNA to DNA increased. In males the RNA/DNA ratio was stable at 1.3 at 40 days after birth; but in females the decline in DNA concentration was more protracted, and at 200 days after birth the RNA/DNA ratio was only 0.99. Thus, total nucleic acids show only gradual changes in concentration throughout development of the kidney, but a sharp change in the synthetic activity of the ribosomes and in their binding to membranes occurs in kidneys scon after birth.The biochemistry of development has been studied most extensively in echinoderm and amphibian eggs, in which changes in nucleic acid and protein metabolism can be related to distinct phases of morphogenesis. The heterogeneity and the complex stimuli governing the growth of most mammalian organs make them less convenient for biochemical investigation. Nonetheless, the synthesis of ribosomes, ribosomal RNA (rRNA), and messenger RNA (mRNA) during compensatory growth can be analyzed in an organ as heterogeneous as the kidney (1-3).In this paper we describe the patterns of protein and nucleic acid synthesis in the metanephros of the mouse during rapid normal growth from fetal to adult life. An intense synthesis of protein on free, i.e. not membrane-bound, polysomes during late fetal and early neonatal life ends abruptly between 3 and 6 days after birth; at the same time, membrane-bound ribosomes increase at the expense of free ribosomes. Thereafter, protein accumulates with little increase in DNA and with production of RNA proportionate only to maintaining a stable concentration of RNA in the organ. A preliminary statement of some of these findings has appeared (4). MATERIALS AND METHODS KidneysMice used in this study were Ham/ICR albinos (Charles River Breeding Laboratories, North Wilmington, Mass.). For experiments with fetal and juvenile kidneys, a single group of females were mated 42 days after their birth. The appearance of a vaginal plug in the mother was regarded as the first day of fet...

Compensatory Renal Hypertrophy in Fetal Lambs

“…Because there is no statistical difference between mean body wt, kidney wt, and renal cortical RNA and DNA content for the twin fetuses, changes in these parameters after removal of one fetus represent a reasonable estimate of the rate of intrauterine growth for the period of observation. Our studies were performed at an earlier gestational age, and in sheep, but are in agreement with the results of Winick and Noble (21) and of Priestly and Malt (18) in demonstrating that, in utero, normal renal growth is mainly by cell division. It should be noted that removal of the first twin in the control studies is a stimulus for noncompetitive enhanced growth, and the observed results are greater than the normal.…”

Protein and nucleic acid metabolism in organs from mice selected for larger and smaller body size

“…(iii) Biochemical methods Techniques used to estimate tissue constituents were essentially those described in Priestley & Malt (1968). Water content was determined when weighed organs were dried to constant weight under vacuum.…”

“…Free amino acid concentrations were measured in postmitochondrial supernatants (20 000 g for 5 min, Sorvall RC 2 centrifuge) by the ninhydrin method of Moore & Stein (1948), as described in Priestley & Malt (1968), using a sample:reagent ratio of 1:10 by volume, and 50 % aqueous ethanol as diluent. The standard curve was prepared with leucine and results were expressed relative to that amino acid.…”

The bigger the better: determining nephron size in kidney

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“…Hypertrophy has also been suggested to play an instrumental role in the development of glomeruli and the proximal tubules [11, 21, 22]. Yet, an in depth analysis of this process and its underlying mechanism is still lacking.…”