Synthesis of glutaminic and aspartic acids in mitochondria of the visual analyzer of the dog brain during postnatal ontogenesis

It is revealed that glutaminic acid (GA) synthesis by direct reductive amination proves to be the most rapid in the mitochondria of the outer geniculate body (OGB) from the 1st till the 45th day of the postnatal development, and beginning from the 45th day till the 3-month age in visual cortex (field 17) (VC) and bigeminal bodies (BB). It is stated that GA synthesis by transamination in the mitochondria of VC, OGB, and BB proceeds less intensively than by a direct reductive amination at the early stage of postnatal development, being more rapid during the period from the 12-16th till the 45th day of postnatal development. Unlike GA synthesis in the mitochondria of the studied visual analyzer structures of canine brain AsA synthesis is more rapid in transamination reaction at the early stage of postnatal development. The high level of AsA synthesis was observed on the day when the puppies' eyes began to see clearly. The level of AsA synthesis by reductive amination and transamination in the mitochondria of VC, BB, and OGB at the early stage of postnatal development is lower than that of GA synthesis.     

A Halothane-Related Effect on Rat Brain Myelination: A Comparison of Chronic Prenatal or Postnatal Exposure

Rats were exposed to 0.5% halothane in air for 8 h per day during the intervals (1) 5 days postconception to birth, (2) birth to 5 days postnatal age, or (3) birth to 10 days postnatal age. Controls were exposed to an equivalent flow of air. Prenatal exposure had no significant effect on body or brain weight and no subsequent effect on the relative synthesis of brain subcellular membranes. Five days of postnatal exposure caused a 10% reduction in body and brain weight and a 10% relative reduction in the synthesis of brain myelin. The effect persisted throughout the period of rapid postnatal brain myelination. Ten days of postnatal exposure produced equivalent, more severe effects on body and brain weights and a more severe effect on myelin synthesis. Postnatal exposure had no apparent effect on the relative synthesis of non-myelin particulate proteins.     

Histone H1 subtype synthesis in neurons and neuroblasts.

Rat cerebral cortex neurons contain the five histone H1 subtypes H1a-e and the subtype H1 zero present in other mammalian somatic tissues. The four subtypes H1a-d decay exponentially during postnatal development and are partially or totally replaced by H1e that becomes the major H1 subtype in adults. H1 zero accumulates in a period restricted to neuronal terminal differentiation. Here we study the synthesis of the H1 subtypes in cortical neurons and their neuroblasts by in vivo labeling with [14C]lysine. The subtype synthesis pattern of neuroblasts has been determined by labeling gravid rats during the period of proliferation of cortical neurons and synthesis in neurons has been studied by postnatal labeling. The subtype H1a is synthesized in neuroblasts but not in neurons and is therefore rapidly removed from neuronal chromatin. The synthesis of H1b and H1d is much lower in neurons than in neuroblasts so that these subtypes are replaced to a large extent during postnatal development. H1c is synthesized at levels much higher than the other subtypes both in neurons and neuroblasts, but its very high turnover, about one order of magnitude faster than that of H1e in neurons, favors its partial replacement during postnatal development. Comparison of the synthesis rates of H1 zero in newborn and 30-day-old rats shows that the accumulation of H1 zero in differentiating neurons is due to an increased level of synthesis.     

The effect of insulin and thyroxine on the age-related dynamics of synthesis and degradation of proteins in skeletal muscles of cattle

The intensity of sarcoplasmic and myofibrillar protein synthesis in skeletal muscle homogenates of the cattle aged from 45 to 360 days is 3.5 and 3.8 times reduced, respectively, and remains at the same level in the old beef cattle aged 540 days. Exogenous insulin and thyroxin increases the sarcoplasmic and myofibrillar protein synthesis in skeletal muscle homogenates of animal at certain stages of postnatal ontogenesis. The catepsin and neutral protease activities are 2.0 and 1.7 times as low in the skeletal muscle of the cattle aged from 45 to 360 days while in the subsequent period they change slightly. Exogenous insulin decreases the catepsin protease activities but does not change the neutral protease activities in the skeletal muscle of animal at the most stages of postnatal ontogenesis. Exogenous thyroxin increases the catepsin and neutral protease activities in skeletal muscle of animals at the some stages of postnatal ontogenesis.     

Gamma- and UV-induced DNA synthesis in neurons of the rat neocortex

Nuclear DNA synthesis in neocortex neurons of neonatal 14- and 60-day rats after in vitro irradiation of isolated sections was estimated by the incorporation of a labeled precursor into DNA. gamma- and UV-radiation increased the rate of DNA synthesis in the cells of animals of all studied age groups. However, the level of the UV-induced synthesis sharply dropped during the postnatal ontogenesis while gamma-radiation-induced synthesis decreased slightly. The peculiarities revealed in the repair DNA synthesis seem to be influenced by the process of postnatal differentiation of a neuron accompanied by the nucleosome length shortening and the decrease in the DNA-polymerase alpha content.     

Proteochondroitin sulfate is the main proteoglycan synthesized in fetal hepatocytes

The synthesis of total and specific types of glycosaminoglycans (GAG) with emphasis on proteochondroitin sulfate (PCS) was studied in late embryonic and early postnatal liver parenchymal cells. In contrast to adult hepatocytes, which synthesize almost exclusively proteoheparan sulfate (PHS), PCS proved to be the major type of GAG synthesized in fetal hepatocytes (more than 60% of total GAG) whereas PHS contributes less than 40% of total GAG synthesis. Starting immediately after birth PCS synthesis in hepatocytes declines progressively, at the 6th postnatal day PCS formation is one-fifteenth of that measured in embryonic liver cells. Adult levels are reached around the 10th postnatal day. A significant portion of plasma membrane-associated proteoglycans in fetal hepatocytes is represented by PCS, its fraction declines in early postnatal life. Between the synthesis rate of PCS and [3H]thymidine incorporation into DNA exists a strong positive statistic correlation (r = 0.949). In conclusion, fetal hepatocytes have a completely different profile of GAG synthesis characterized by preponderant production of PCS. This ability is lost early after birth but might be regained in hepatocellular carcinoma cells and parenchymal cells in chronically injured liver tissue developing fibrosis.     

The Rate of Tau Synthesis Is Differentially Regulated During Postnatal Development in Mouse Cerebellum

1. Tau, which is a microtubule-associated protein, with mRNA targeted to the axon and growth cone, is involved in axonal elongation. During postnatal development in mouse, Tau expression in cerebellar granule cells is reduced after the second postnatal week. The aim of this work was to study the regulation of the rate of the synthesis of Tau protein during the period of granule cell axonal growth in mouse cerebellum.2. We found four [³⁵S]methionine-labeled isoforms of Tau synthesized postnataly. Their levels remain constant from postnatal day 9 to 12 (P9–P12), and decreased by P20.3. The rate of Tau synthesis showed differences with the rate of synthesis of total proteins. They also differ from proteins phosphatases 2A and 2B, both associated with the regulation of Tau function. In addition, the turnover of newly synthesized Tau increased at P20, compared with P9 and P12.4. These results imply a specific developmental regulation of mRNA translation of Tau, and indicate that, after the period of synapse formation is complete, and therefore axonal growth has finished (P20), only a limited number of new Tau molecules are synthesized. This might reflect that, after synapse formation is complete, newly synthesized Tau molecules are not longer needed.     

Cellular energy metabolism during fetal development. V. Fatty acid synthesis by the developing heart

We have investigated fatty acid synthesis by the developing heart. The only system for fatty acid synthesis in the heart is the mitochondrial elongation pathway. Myocardial fatty acid elongation was very low prenatally but increased rapidly during the first week of life. Coincident with weaning there was a sharp drop in elongation activity possibly related to a shift from the high fat intake provided by the milk to the carbohydrate diet provided by standard laboratory chow. Either NADH or NADPH could provide reducing equivalents for myocardial fatty acid elongation. The presence of a long-chain fatty acid primer in the medium resulted in a higher incorporation of acetyl-CoA throughout the developmental period. However, the ratio of endogenous fatty acid elongation activity to that in the presence of an added primer increased with age presumably in relation to the postnatal increase in the availability of long-chain fatty acid primers. Products of fatty acid elongation in postnatal rats included a range of saturated and unsaturated fatty acids with major peaks of stearic acid (18:0) and 20- and 22-carbon unsaturated fatty acids suggesting elongation of the palmityl-CoA primer by the-two carbon units of acetyl-CoA. Decarboxylation of fatty acid products indicated that all synthesis could be accounted for by chain elongation. The observed developmental changes in myocardial fatty acid elongation may be related to functional, structural, and nutritional adaptations of the cell to the postnatal environment.     

Albumin and transferrin synthesis during development in the rat

In this study, the incorporation of [(14)C]leucine into albumin and transferrin in early rat foetuses, vitelline plus amniotic membranes, chorioallantoic placenta and perinatal rat liver slices was measured and used to detect and compare the rates of synthesis of the two proteins. Albumin synthesis was detected in the body of foetuses from 13 days gestation onwards. Transferrin synthesis was detected only after day 15. Transferrin synthesis was demonstrable in the membranes but not in the chorioallantoic placenta of all the animals investigated, i.e. from 13 to 19 days gestation. Synthesis of albumin and transferrin by the liver of near-term and postnatal animals was shown to correlate with published data on the parenchymal cell number/unit wet wt. of liver. Near-term foetuses synthesized relatively more transferrin than albumin when compared with 10-day postnatal animals. The serum concentrations of the two plasma proteins were also determined. These increased before term whereas the rate of synthesis of albumin and transferrin declined. Postnatally, plasma albumin concentration increased but transferrin concentration decreased, yet the rates of synthesis of both proteins by the liver increased with age. This lack of correlation between the rates of synthesis of the two proteins and their respective plasma concentrations could be explained in part by their increased stability after birth. There was also evidence that the liver haemopoietic cells took up transferrin although they do not synthesize the protein. Thus the decrease in this population of cells during development could also contribute to the discrepancy between liver synthesis and serum concentrations of transferrin.     

Hyperthermia Induces the Synthesis of a Heat Shock Protein by Polysomes Isolated from the Fetal and Neonatal Mammalian Brain

Abstract: Analysis of the cell-free translation products of polysomes isolated from fetal brain and other organs indicates that elevation of maternal body temperature induces the synthesis of a heat shock protein of molecular weight 74,000 (74K). The newborn mammal is particularly sensitive to induction of the 74K protein. As early postnatal development proceeds, higher body temperatures are required to induce synthesis of the 74K heat shock protein.     

Fatty acid synthesis in the brown fat and liver of foetal and newborn rabbits (Short Communication)

The postnatal fall in fatty acid synthesis in the liver and brown fat of newborn rabbits is accompanied in both tissues by a decrease in the capacities of the enzymes of fatty acid synthesis and an apparent increase in the degree of inhibition of one or more of these enzymes.     

Effect of undernutrition on DNA and RNA synthesis in subcellular fractions from different regions of the developing rat brain

The effect of undernutrition on the incorporation of [methyl-³H]thymidine into DNA and of 5-[³H]uridine into RNA of cerebral hemispheres, cerebellum, and brain stem was studied in vivo and in vitro in rats. The labeling of DNA from nuclei and mitochondria and of RNA from nuclei, mitochondria, microsomes, and soluble fractions, was also measured in vitro. The results demonstrate that nucleic acid synthesis is impaired and delayed during undernutrition. Specific effects were observed for the different brain regions and subcellular fractions: at 10 days nuclear and mitochondrial DNA and RNA synthesis was impaired, whereas at 30 days only the mitochondrial nucleic acid synthesis was affected.The delay of DNA and RNA labeling, caused by undernutrition, was most evident in the cerebellum, probably due to its intense cell proliferation during postnatal development. The specific sensitivity of mitochondria as compared to other subcellular fractions, may be due to the intense biogenesis and/or turnover of nucleic acids in brain mitochondria not only during postnatal development, but also in the adult animal.     

Free amino acids in rat ocular tissues during postnatal development

Amino acid changes in the retina, vitreous, lens, iris-ciliary body and cornea of the rat eye were determined during postnatal growth. The amino acid concentrations of the ocular tissues showed varying profiles at various developmental stages. These results suggest a different timetable for development of each ocular tissue or indicate a synthesis of specific proteins in the postnatal period. Adult amino acid levels appeared to be fully reached on the 30th day after birth at the latest. Quantitatively the greatest changes were observed in taurine concentrations, which increased in all five ocular tissues during maturation. GABA changes paralleled those of taurine in the retina, whereas in the other ocular tissues GABA changes were very low. The greatest decrease in glutamic acid and aspartic acid concentration during postnatal development was in the lens, where these amino acids probably are needed for the synthesis of the lenticular proteins, the alpha-, beta-, and gamma-crystallines.     

Preferential utilization of ketone bodies in the brain and lung of newborn rats

Persistent mild hyperketonemia is a common finding in neonatal rats and human newborns, but the physiological significance of elevated plasma ketone concentrations remains poorly understood. Recent advances in ketone metabolism clearly indicate that these compounds serve as an indispensable source of energy for extrahepatic tissues, especially the brain and lung of developing rats. Another important function of ketone bodies is to provide acetoacetyl-CoA and acetyl-CoA for synthesis of cholesterol, fatty acids, and complex lipids. During the early postnatal period, acetoacetate (AcAc) and beta-hydroxybutyrate are preferred over glucose as substrates for synthesis of phospholipids and sphingolipids in accord with requirements for brain growth and myelination. Thus, during the first 2 wk of postnatal development, when the accumulation of cholesterol and phospholipids accelerates, the proportion of ketone bodies incorporated into these lipids increases. On the other hand, an increased proportion of ketone bodies is utilized for cerebroside synthesis during the period of active myelination. In the lung, AcAc serves better than glucose as a precursor for the synthesis of lung phospholipids. The synthesized lipids, particularly dipalmityl phosphatidylcholine, are incorporated into surfactant, and thus have a potential role in supplying adequate surfactant lipids to maintain lung function during the early days of life. Our studies further demonstrate that ketone bodies and glucose could play complementary roles in the synthesis of lung lipids by providing fatty acid and glycerol moieties of phospholipids, respectively. The preferential selection of AcAc for lipid synthesis in brain, as well as lung, stems in part from the active cytoplasmic pathway for generation of acetyl-CoA and acetoacetyl-CoA from the ketone via the actions of cytoplasmic acetoacetyl-CoA synthetase and thiolase.     

Age-related changes in the rates of polypeptide chain elongation

The time of an average polypeptide chain synthesis, ts, in the liver and brain cortex of rats of various age--from the 17th day of prenatal life up to the 24th month of the postnatal period--was estimated. At the end of the prenatal period the value of t is much higher than in postnatal life. In newborns, the t value is minimal, showing a gradual increase during the postnatal development. Determination of an average molecular mass of newly synthesized polypeptides demonstrated that the increase of t in postnatal life is due to the decrease of the rate of polypeptide chain elongation.     

RNA METABOLISM IN ISOLATED MOUSE BRAIN NUCLEI DURING EARLY POSTNATAL DEVELOPMENT

—RNA metabolism in isolated brain nuclei has been shown to be dramatically altered during early postnatal brain development. The present study involved an examination of the RNA products synthesized by nuclei at various stages of postnatal neural maturation. In all cases, the majority of the RNA appeared to be heterodisperse, non-ribosomal and non-tRNA in nature. In comparison to the RNA isolated from nuclei of neonatal tissue, the RNA from nuclei of 12-day and 30-day-old mouse brain was found to be of smaller molecular weight. Despite the heterodisperse nature of these RNA molecules, the addition of α-amanitin did not completely inhibit nuclear synthesis. An investigation of RNA synthesis in isolated neuronal and glial cell nuclei revealed that nucleic acid metabolism in these respective cell populations had different and distinct developmental patterns. Preparations enriched with glial cell nuclei were found to be most active at birth and then decreased in activity (3–4-fold) during neural maturation. On the other hand, the rate of RNA synthesis in fractions enriched in neuronal cell nuclei was observed to increase dramatically in activity (4–5-fold) until 14 days of age. From 14 days of age until adulthood, RNA synthetic activity remained essentially the same.     

Factors influencing the development of urea-synthesizing enzymes in rat liver

1. The activities of enzymes of the urea cycle, carbamoyl phosphate synthetase, ornithine transcarbamoylase, argininosuccinate synthetase, argininosuccinase (the last two comprising the arginine synthetase system) and arginase, were measured in the liver during development of the rat. All five enzymes exhibited relatively low activities in foetal liver and a rapid postnatal increase was found. The rate-limiting enzyme of urea synthesis in the rat, the condensing enzyme of the arginine synthetase system, showed the lowest activity at birth and the most rapid postnatal increase, a fivefold increase within 24hr. after birth. A second increase of activity was noted after the tenth day. These results suggest that the postnatal increase of arginine synthetase activity initiates the ability for urea synthesis in the rat. 2. Some factors influencing the development of the rate-limiting arginine synthetase system were studied in more detail. (a) Intraperitoneal administration of puromycin inhibited the postnatal increaseof the enzyme activity. (b) Starvation of newborn animals for 24hr. after birth had no effect on the postnatal development of the enzyme. (c) Bilateral adrenalectomy at birth caused a marked diminution in the postnatal increase of the enzyme activity and injections of triamcinolone were effective in preventing the effect of adrenalectomy. (d) Administration of triamcinolone alone had a marked stimulatory effect on the postnatal development of this enzyme. (e) Premature and postmature birth had virtually no effect on the developmental pattern of the arginine synthetase activity, suggesting that the increase of this enzyme activity after birth is not initiated by the birth process.     

Myofilament incorporation determines the stoichiometry of troponin I in transgenic expression and the rescue of a null mutation

The highly organized contractile machinery in skeletal and cardiac muscles requires an assembly of myofilament proteins with stringent stoichiometry. To understand the maintenance of myofilament protein stoichiometry under dynamic protein synthesis and catabolism in muscle cells, we investigated the equilibrium of troponin I (TnI) in mouse cardiac muscle during developmental isoform switching and in under- and over-expression models. Compared with the course of developmental TnI isoform switching in normal hearts, the postnatal presence of slow skeletal muscle TnI lasted significantly longer in the hearts of cardiac TnI (cTnI) knockout (cTnI-KO) mice, in which the diminished synthesis was compensated by prolonging the life of myofilamental TnI. Transgenic postnatal expression of an N-terminal truncated cTnI (cTnI-ND) using α-myosin heavy chain promoter effectively rescued the lethality of cTnI-KO mice and shortened the postnatal presence of slow TnI in cardiac muscle. cTnI-KO mice rescued with different levels of cTnI-ND over-expression exhibited similar levels of myocardial TnI comparable to that in wild type hearts, demonstrating that excessive synthesis would not increase TnI stoichiometry in the myofilaments. Consistently, haploid under-expression of cTnI in heterozygote cTnI-KO mice was sufficient to sustain the normal level of myocardial cTnI, indicating that cTnI is synthesized in excess in wild type cardiomyocytes. Altogether, these observations suggest that under wide ranges of protein synthesis and turnover, myofilament incorporation determines the stoichiometry of troponin subunits in muscle cells.