Effect of polyamines on ribosomal RNA synthesis during sea urchin development

Effects of polyamine limitation on nucleolar development and morphology in early chick embryos

Inhibition of polyamine synthesis in early chick embryos by in ovo treatment with DL-alpha-difluoromethylornithine (DFMO), injected beneath the blastoderm after 5 h of incubation, permanently blocks post-gastrular development. After the first day of polyamine limitation, the embryos possess a thickened primitive streak. Further morphogenesis is blocked and the ectoderm and mesoderm are condensed around the streak. There is obvious suppression of nucleolar formation in 24 h DFMO-treated embryos. In the mesoderm obliquely in front of Hensen's node the frequency of nucleolus-possessing cells is only a few percent lower in DFMO-treated than in control embryos. However, in the same area the frequency of mesoderm cells possessing multiple nucleoli is about 50% lower in the polyamine-depleted embryos. At the ultrastructural level, mesoderm cells from 24 h DFMO-treated embryos show a reduction of the fibrillar component of the nucleolus with a resulting segregation of the nucleolar material. Our data indicate that stimulation of polyamine synthesis is an obligatory step in the differentiation of epiblast cells into mesoderm cells.

Relationship between polyamine accumulation and RNA biosynthesis and content during the cell cycle

Polyamine accumulation was related to RNA biosynthesis and content during the cell cycle of CHO-K1 and HeLa cells. The highest correlations were observed between polyamine accumulation and RNA content. Feeding, serum-starved cultures of embryonic chick fibroblasts, which exhibit a 3-fold increase in RNA content, demonstrated that RNA content was most closely paralleled by spermidine content.

Possible involvement of putrescine in nucleolar formation in early embryos

Continuous treatment of developing eggs of the polychete Ophryotrocha labronica with alpha-methylornithine, which inhibits synthesis of putrescine, led to arrest of development at gastrulation. The present ultrastructural analysis suggests that the arrest of development is due to failure to form nuclei, and thus reveals a possible role for putrescine in nucleolar formation. Further support for this contention was provided by means of electron-microscopical autoradiography. It was found that newly synthesized putrescine, derived from administered 3H-ornithine, labeled the nucleoli intensely at the time of their normal appearance during gastrulation, the time at which the rate of endogenous putrescine synthesis is maximal. These observations have led to the conclusion that putrescine synthesis may be directly involved in formation of nucleoli.

Studies on sex-organ development. Oestrogenic effect on ornithine decarboxylase activity in the differentiating Müllerian ducts and other organs of the chick embryo

The activity of ornithine decarboxylase in the differentiating left and right Müllerian ducts was assayed and compared with that in other embryonic organs, i.e. the liver and the brain throughout the stages of development. In general the enzyme activity was high in the early stages and decreased extensively in the late stages of development. Specifically, in the left and righ Müllerian ducts, the enzyme activity was high from day 8 to day 9 of incubation. In the right duct the enzyme activity started to decline on day 9 and then continuously decreased to an almost undetectable value on day 18 of incubation. In the left duct the enzyme activity also decreased slightly from day 9 to day 12; however, it increased from day 13 to day 15 and finally decreased to a constant value from day 18 until hatching. The alteration in enzyme activity in the Müllerian duct as assayed in vitro during development is not due to the effect of the size of the endogenous ornithine pool. When the enzyme activity was subjected to oestrogen stimulation, an increase of 5--10-fold for the left duct and of 5--3-fold for the right duct was observed during the course of development. No such stimulation was observed with the treatment of progesterone. Testosterone consistently caused a 25--30% inhibition of the enzyme activity in the Müllerian duct. Oestrogen slightly stimulated the enzyme activity in the developing liver but inhibited that of the brain. The concentration of the three polyamines measured in the Müllerian duct corresponds to the activity of the enzyme determined.

The effect of arginine deprivation on the cytopathogenic effect and replication of human cytomegalovirus

Arginine is necessary for the development of the cytopathogenic effect of human cytomegalovirus in human embryonic fibroblasts. It is also required, though in greater concentrations, for the production of infective virions, the requirement being at an early stage of replication. Inhibitor studies suggested that this block in replication caused by arginine deficiency was prior to the formation of viral DNA. Withdrawal of arginine from the medium 24 or 48 hours after infection resulted in a decline in virus production indicating that the continued presence of the amino acid is necessary for constant virus production. Infected cultures deprived of arginine could be stimulated to produce cytopathic effects and infective virions by replacement of the amino acid even eight days after inoculation, demonstrating that the information for cytomegalovirus replication remains intact within the cell. This establishment of latency in vitro may be related to the ability of the virus to establish a similar state in vivo.

Inhibition of spermidine formation in rat liver and kidney by methylglyoxal bis(guanylhydrazone)

The effect of methylglyoxal bis(guanylhydrazone), a substance known to inhibit putrescine-dependent S-adenosyl-l-methionine decarboxylase, on polyamine metabolism in liver and kidney was investigated. Almost complete inhibition of the incorporation of putrescine into spermidine was obtained up to 8h after administration of 80mg of methylglyoxal bis(guanylhydrazone)/kg body wt. by intraperitoneal injection. However, by 20h after administration of the inhibitor spermidine synthesis was resumed. Considerable accumulation of putrescine occurred during this period (up to 3 times control concentrations in both tissues), but there was only a slight fall in the spermidine content. These results suggest that the putrescine-activated S-adenosyl-l-methionine decarboxylase plays an essential role in spermidine biosynthesis in rat liver and kidney, and the possibility of using methylglyoxal bis(guanylhydrazone) to study the role of polyamine synthesis in growth is discussed.

Ornithine decarboxylase in cardiac hypertrophy in the rat

Ornithine decarboxylase, a possible rate-limiting enzyme in the synthesis of polyamines, was assayed in hearts of normal rats, sham-operated rats, and rats subjected to aortic constriction. In the hearts of rats with constricted aortas, significantly increased enzyme activity compared with that in the hearts of sham-operated rats was observed 2, 4, 6, and 8 hours and 3, 5, and 10 days after operation, and two peaks in activity occurred--one at 4 hours and the other at 5-10 days. Increased ornithine decarboxylase activity was one of the earliest changes associated with cardiac hypertrophy. The changes in enzyme activity correlated well with the subsequent hypertrophy in the hearts of rats with aortic constriction and with the regression in the hearts of sham-operated rats, suggesting a role for polyamines in the regulation of cardiac growth. The early increase in ornithine decarboxylase activity in hearts of rats with aortic constriction was inhibited by actinomycin D, 8-azaguanine, and cycloheximide, indicating that RNA and protein synthesis are involved in the process. Actinomycin D given 30 minutes after operation or even at the time of aortic constriction failed to inhibit the increase in the enzyme activity, suggesting that the transcription required for the increase occurs early after operation. Cycloheximide given 1 hour before the rats were killed markedly decreased the enzyme activity, and the estimated half-life of cardiac ornithine decarboxylase was comparable to that of the reported short-lived liver ornithine decarboxylase. The study suggests that the synthesis of ornithine decarboxylase is influenced at the stage of transcription by mechanical stress on the myocardium and that polyamines might have a regulatory role in cardiac hypertrophy and regression.

Effect of polyamines on the stability of brain-cortex ribosomes

1. Ribosomes isolated from the cortex tissue of goat brain contain very small amounts of spermidine and spermine. Ribosomes isolated from spermidine-treated slices have a higher spermidine content. 2. The polyamines partially prevent the temperature-dependent breakdown of ribosomes into acid-soluble nucleotides. 3. The ;melting' temperature of ribosomes rises slightly when the ribosomes are heated slowly in the presence of polyamines. 4. The pH-dependent breakdown of ribosomes into protein, RNA and acid-soluble nucleotide is markedly decreased by polyamines present in media in which ribosomes are suspended. 5. The breakdown of ribosomes in the presence of high concentrations of salts and EDTA is partially checked by the concurrent presence of polyamines. 6. Spermidine and spermine make ribosomes less susceptible to enzymic digestion by crystalline trypsin and ribonuclease.