Acid-soluble Precursor Pools Research Articles

Stability of RNA synthesized by the mouse oocyte during its major growth phase

The RNA of growing mouse oocytes and ovulated ova was labeled by injection of a solution containing tritiated uridine into the ovarian bursa. The time course of incorporation into RNA by oocytes was followed by analysis of alkali-labile acid insoluble radioactivity and by autoradiography. The results show that most of the incorporation into RNA by growing oocytes takes place within one day of bursal injection of the precursor, reflecting the rapid fall of label in the acid soluble precursor pool. The RNA of growing oocytes of all sizes is unusually stable, at least 80% of the labeled RNA present two days after bursal injection being retained until ovulation 10 to 20 days later. The fraction of heterogeneous RNA in labeled RNA of ova was estimated as 20% by sucrose gradient analysis. It is likely that egg RNA is synthesized primarily during the period of oocyte growth one to three weeks before ovulation.

ACTH and Brain RNA: Changes in Content and Labelling of RNA in Rat Brain Stem

The influence of synthetic ACTH1-24 and ACTH1-10 on rat brain RNA was studied. ACTH1-24 (5 IU/100 g s.c.) treatment resulted in a small decrease in labelling of brain stem RNA (-12%), measured 30 min after the injection of [5-3H] uridine (100 muCi; s.c.), without affecting the distribution of radioactivity of the acid-soluble precursor pool. Furthermore, a small and transitional reduction of total brain stem RNA was found. Similar treatment of adrenalectomized rats (36 h after surgery) resulted in a marked increase (+ 40%) in labelling of brain stem RNA, without affecting the distribution of radioactivity in the acid-soluble pool. In both intact and adrenalectomized rats, treatment with ACTH1-24 did not affect RNA of cortex cerebrum and cerebellum. ACTH1-10, a fragment of ACTH without corticotropic activity in vivo, exhibited no effect on brain stem RNA in either intact or adrenalectomized rats, nor did corticosterone (1 mg/100 g) affect adrenalectomized rats.

A comparison of RNA metabolism in the visual cortex of sighted rats and rats with retinal degeneration

The RNA metabolism in the visual cortex of visually stimulated adult blind and sighted rats has been compared. The blind rats belonged to a strain suffering from an inherited retinal dystrophy. This condition renders them blind after the age of 3–4 weeks. There is no gross difference in the metabolic rate of the blind and sighted strains. No significant differences were seen in the RNA, DNA, and protein content per wet weight of the two types of visual cortex but the RNA DNA ratio was significantly lower in the blind animals. Intraventricularly administered ( 14C) orotic acid was incorporated into RNA to a lesser extent in the visual cortex of the blind animals. This could not be wholly attributed to a difference in the size of the acid soluble pool. Chromatographic studies on RNA hydrolysates and the acid soluble precursor pool indicated that the reduced labeling of RNA in the blind visual cortex was not due to a reduction in the rate of conversion of orotic acid to UTP and thus it would appear that the lowered rate of incorporation of label into RNA is due to a reduced rate of RNA synthesis. This was restricted to the visual cortex, no differences were observed in the frontal cortex. In vitro studies indicated that there were no differences in the total ribonuclease activity in the blind and sighted visual cortex but the RNA polymerase activity (but not the Poly C synthetase activity) was slightly lower in the visual cortex of the blind animals.

Development of rapid axonal flow in the chick embryo.

AbstractThe development of axonal transport in the optic nerve of the developing chick has been investigated. Following monocular injection of radioactive fucose and proline, the specific activity of protein from paired optic lobes was determined in chick embryos and new‐hatched chicks. In addition, the magnitude of the acid soluble precursor pool within lobes was assayed. The specific activity of protein in the optic lobe contralateral to (and innervated by) the injected eye relative to that of protein within the corresponding ipsilateral lobe (not innervated by the injected eye) was used as an index of axonal flow. In embryonic chicks from 8–12 days of age, four hours after injection of 3H‐fucase into a single eye, this ratio was somewhat above unity. In the 13‐day incubated embryo the ratio rose abruptly to over 10, and remained high throughout the period studied (up to one day after hatch). No similar sharp rise was found for the corresponding ratio for acid soluble radioactivity which remained under 2 in all ages of chicks examined. Parallel experiments with 14C‐proline resulted in a smaller and more gradual development of asymmetry of specific activity of protein from paired optic lobes.These data suggest that, at the 13th day of incubation, specialized mechanisms develop for the rapid distal transport of glycoprotein synthesized within the retinal ganglion cells to terminations in the optic tectum. This phenomenon follows the major development of cerebral oxidative metabolism, but precedes the appearance of spontaneous or evoked potentials within the chick brain.

The effect of polyinosinic:polycytidylic acid on tumor metabolism.

SummaryThe synthetic double-stranded RNA, polyinosinic: polycytidylic acid (poly I:poly C), strongly inhibits in vivo RNA and protein synthesis in three different tumors in mice. Macromolecule synthesis in normal organs of these mice may be inhibited or enhanced, depending to some extent on the strain of mouse. Administration of poly I:poly C to the mice also leads to alterations in the specific radioactivity of acid-soluble precursor pools, sometimes increasing and sometimes decreasing such specific activity. There was no discernible relationship between the nature of the alteration in precursor specific activity and the direction of effect on macro-molecule synthesis.

A comparative study of RNA synthesis in rat hepatic nuclei and mitochondria under the influence of cortisone

1. A mixture of labeled [ 3H]uridine and [ 14C]guanine was employed in 10-minute pulse labeling experiments in vivo to study the nature of RNA synthesis in hepatic nuclei and mitochondria of adrenalectomized rats under the influence of cortisone. 2. Ten minutes after cortisone treatment there was a change in the nature of the newly synthesized total hepatic RNA. Specific activity measurements indicated that the U/G base labeling ratio of the total RNA of hormonally treated rats was elevated relative to controls as a consequence of a concurrent stimulation of U-rich RNA synthesis and a diminution of G-rich RNA synthesis. 3. Four hours after hormonal treatment, with a 10-minute pulse labeling period, the U/G base labeling ratio of the total hepatic RNA was shifted downward as a consequence of cortisone enhancement of G-rich ribosomal precursor RNA synthesis in the nucleus. 4. Mitochondria actively synthesized U-rich RNA which was stimulated by a 10-minute cortisone treatment. However, there was no reversal of the RNA labeling pattern after four hours of hormone treatment, as evidenced by an unchanged high U/G base labeling ratio. It is therefore concluded that the mitochondrial ribosomal RNA genome is under a different mechanism of control than its nuclear counterpart. 5. In view of the fact that after a 10-minute pulse incorporation the U/G base labeling ratio of the RNA species was low in nuclei and high in cytoplasm, it is inferred that U-rich RNA synthesized in nuclei was rapidly transported into cytoplasm leaving behind the immature G-rich ribosomal RNA, whereas mitochondria retained their U-rich RNA. 6. Separate acid-soluble RNA precursor pools in nuclei and mitochondria seem to be present in liver cells, the former being high in U/G base ratio, the latter low. The U/G ratios of the acid-soluble precursor pools were relatively insensitive to cortisone both in nuclei and mitochondria after either 10 min or 4 h of hormonal treatment.