Search

During the first 48h of compensatory renal hypertrophy induced by unilateral nephrectomy, RNA content per cell increased by 20-40%. During this period, rates of RNA synthesis derived from the rates of labelling of UTP and RNA after a single injection of [5-(3)H]uridine showed no change in the rate of RNA synthesis (3.1nmol of UTP incorporated into RNA/min per mg of RNA). ATP and ADP pools were not changed. The rate of RNA synthesis was considerably in excess of the increment of total RNA appearing in the kidneys. With [5-(3)H]uridine as label, only continuous infusion for 24h could produce an increase (60%) in the specific radioactivity of renal rRNA in mice with contralateral nephrectomies. With a single injection of [methyl-(3)H]methionine used to identify methyl groups inserted into newly synthesized rRNA, the specific radioactivity of this rRNA was unchanged 5h after contralateral nephrectomy, increased by 60% at 9-48h, and returned to normal values at 120h. Most RNA synthesized in both nephrectomized and sham-nephrectomized mice has a short half-life. Since total cellular RNA content increases in compensatory hypertrophy despite unchanged rates of rRNA synthesis, the accretion of RNA might involve conservation of ribosomal precursor RNA or a change in rate of degradation of mature rRNA.

Much of the RNA in mouse kidneys is not recovered when they are extracted with phenol-SDS at 60 degrees C. Better recovery is achieved by extracting in hypertonic buffer with phenol-SDS, chloroform, and isoamyl alcohol after treatment with DNase. 1. Among the polydisperse RNA in the renal nuclei are small amounts of 45S RNA and large amounts of 32S RNA; the latter first appear when 18S RNA is detectable in the cytoplasm 10 min after administration of undine-H(3). 2. In the cytoplasm rapidly labeled 18S RNA is transported as part of a 45S particle to which mRNA is attached. 3. Compared to HeLa cells in culture, normal mouse kidney is poor in the polydisperse nuclear precursors of rRNA and rich in the cytoplasmic polydisperse RNA that sediments like mRNA.

The labile precursors of ribosomal RNA in mouse kidney are preserved when nuclei rapidly isolated after sieving through multiple screens are swollen and cleansed in the presence of an RNase inhibitor before digestion with DNase and phenol extraction. The kinetics of nucleolar labeling analyzed on polyacrylamide gels show that 36S RNA is the major intermediate product in the catabolism of the original 45S RNA precursor to 32S RNA, from which 28S RNA is derived. Each kidney nucleus contains about 200-600 molecules of 45S RNA; the turnover time of the 45S pool is about 3 +/- 2 min. Compared with HeLa cells, kidney nuclei have a different major intermediate product and a much smaller and more rapidly turning-over pool of ribosomal precursor RNA.

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 14C-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 soon after birth.