Biochemistry of liver development in the perinatal period

Proteomics identifies the developmental regulation of HKDC1 in liver of pigs and mice

During the perinatal period, unique metabolic adaptations support energetic requirements for rapid growth. To gain insight into perinatal adaptations, quantitative proteomics was performed comparing the livers of Yorkshire pigs at postnatal day 7 and adult. These data revealed differences in the metabolic control of liver function including significant changes in lipid and carbohydrate metabolic pathways. Newborn livers showed an enrichment of proteins in lipid catabolism and gluconeogenesis concomitant with elevated liver carnitine and acylcarnitines levels. Sugar kinases were some of the most dramatically differentially enriched proteins compared with neonatal and adult pigs including galactokinase 1 (Galk1), ketohexokinase (KHK), hexokinase 1 (HK1), and hexokinase 4 (GCK). Interestingly, hexokinase domain containing 1 (HKDC1), a newly identified fifth hexokinase associated with glucose disturbances in pregnant women, was highly enriched in the liver during the prenatal and perinatal periods and continuously declined throughout postnatal development in pigs and mice. These changes were confirmed via Western blot and mRNA expression. These data provide new insights into the developmental and metabolic adaptations in the liver during the transition from the perinatal period to adulthood in multiple mammalian species.

N6-methyladenosine modification governs liver glycogenesis by stabilizing the glycogen synthase 2 mRNA

Hepatic glycogen is the main source of blood glucose and controls the intervals between meals in mammals. Hepatic glycogen storage in mammalian pups is insufficient compared to their adult counterparts; however, the detailed molecular mechanism is poorly understood. Here, we show that, similar to glycogen storage pattern, N6-methyladenosine (m6A) modification in mRNAs gradually increases during the growth of mice in liver. Strikingly, in the hepatocyte-specific Mettl3 knockout mice, loss of m6A modification disrupts liver glycogen storage. On the mechanism, mRNA of Gys2, the liver-specific glycogen synthase, is a substrate of METTL3 and plays a critical role in m6A-mediated glycogenesis. Furthermore, IGF2BP2, a "reader" protein of m6A, stabilizes the mRNA of Gys2. More importantly, reconstitution of GYS2 almost rescues liver glycogenesis in Mettl3-cKO mice. Collectively, a METTL3-IGF2BP2-GYS2 axis, in which METTL3 and IGF2BP2 regulate glycogenesis as "writer" and "reader" proteins respectively, is essential on maintenance of liver glycogenesis in mammals.

Temporal analyses of postnatal liver development and maturation by single-cell transcriptomics

The postnatal development and maturation of the liver, the major metabolic organ, are inadequately understood. We have analyzed 52,834 single-cell transcriptomes and identified 31 cell types or states in mouse livers at postnatal days 1, 3, 7, 21, and 56. We observe unexpectedly high levels of hepatocyte heterogeneity in the developing liver and the progressive construction of the zonated metabolic functions from pericentral to periportal hepatocytes, which is orchestrated with the development of sinusoid endothelial, stellate, and Kupffer cells. Trajectory and gene regulatory analyses capture 36 transcription factors, including a circadian regulator, Bhlhe40, in programming liver development. Remarkably, we identified a special group of macrophages enriched at day 7 with a hybrid phenotype of macrophages and endothelial cells, which may regulate sinusoidal construction and Treg-cell function. This study provides a comprehensive atlas that covers all hepatic cell types and is instrumental for further dissection of liver development, metabolism, and disease.

Transcriptome comparison between prenatal and postnatal Large White livers identifies differences in the expression level of genes related to metabolism and postnatal growth

The current study examined the liver transcriptomic profiles of the Large White different in developmental periods. It was performed on pigs of two developmental stages: 70-day fetus (P70) and 70-day piglets (D70). The objective of the study was to identify genes associated with Large White liver lipid metabolism, growth and development. We sequenced eight sRNA libraries of liver samples from four Large White at P70 and D70 respectively. We totally obtained 19,202 genes. 4916 of them were found to be differentially expressed (DEGs) (p < 0.05, fold change ≥ 1), of which 2502 were up-regulated and 2414 were down-regulated. GO enrichment and KEGG pathway analysis indicated that ACACA, ACADM, ACAA2 and HADH were simultaneously enriched in diverse pathways related to lipid metabolism, and so they were considered to be the promising candidate genes which could affect the porcine liver lipid metabolism. Notably, the gene insulin-like growth factor 1 (IGF1) which participated in somatotropic axis signaling was found to be up-regulated in D70 compared with P70. miRWalk and TargetScan softwares were used to screen the miRNAs which bound to the 3' untranslated region (3'UTR) of IGF1. After integration analysis with miRNAs sequencing data, miR-18b and miR-130b-3p were selected for further study. MiR-18b and miR-130b-3p were down-regulated in D70 compared with P70. Dual luciferase assays indicated that miR-18b and miR-130b-3p could obviously decrease (p < 0.05) the fluorescence activity of the group transfected with the wild-type vector of IGF1 3'UTR, while the relative luciferase activity of the group transfected with the mutant vector of IGF1 3'UTR did not change significantly. Taken together, it indicated that miR-18b and miR-130b-3p could target IGF1 directly.

Hepatic microRNAome reveals potential microRNA-mRNA pairs association with lipid metabolism in pigs

Objective

As one of the most important metabolic organs, the liver plays vital roles in modulating the lipid metabolism. This study was to compare miRNA expression profiles of the Large White liver between two different developmental periods and to identify candidate miRNAs for lipid metabolism.

Methods

Eight liver samples were collected from White Large of 70-day fetus (P70) and of 70-day piglets (D70) (with 4 biological repeats at each development period) to construct sRNA libraries. Then the eight prepared sRNA libraries were sequenced using Illumina next-generation sequencing technology on HiSeq 2500 platform.

Results

As a result, we obtained 346 known and 187 novel miRNAs. Compared with the D70, 55 down- and 61 up-regulated miRNAs were shown to be significantly differentially expressed (DE). Gene ontology and Kyoto encyclopedia of genes and genomes enrichment analysis indicated that these DE miRNAs were mainly involved in growth, development and diverse metabolic processes. They were predicted to regulate lipid metabolism through adipocytokine signaling pathway, mitogen-activated protein kinase, AMP-activated protein kinase, cyclic adenosine monophosphate, phosphatidylinositol 3 kinase/protein kinase B, and Notch signaling pathway. The four most abundantly expressed miRNAs were miR-122, miR-26a and miR-30a-5p (miR-122 only in P70), which play important roles in lipid metabolism. Integration analysis (details of mRNAs sequencing data were shown in another unpublished paper) revealed that many target genes of the DE miRNAs (miR-181b, miR-145-5p, miR-199a-5p, and miR-98) might be critical regulators in lipid metabolic process, including acyl-CoA synthetase long chain family member 4, ATP-binding casette A4, and stearyl-CoA desaturase. Thus, these miRNAs were the promising candidates for lipid metabolism.

Conclusion

Our study provides the main differences in the Large White at miRNA level between two different developmental stages. It supplies a valuable database for the further function and mechanism elucidation of miRNAs in porcine liver development and lipid metabolism.

High-resolution mapping of transcriptional dynamics across tissue development reveals a stable mRNA-tRNA interface

The genetic code is an abstraction of how mRNA codons and tRNA anticodons molecularly interact during protein synthesis; the stability and regulation of this interaction remains largely unexplored. Here, we characterized the expression of mRNA and tRNA genes quantitatively at multiple time points in two developing mouse tissues. We discovered that mRNA codon pools are highly stable over development and simply reflect the genomic background; in contrast, precise regulation of tRNA gene families is required to create the corresponding tRNA transcriptomes. The dynamic regulation of tRNA genes during development is controlled in order to generate an anticodon pool that closely corresponds to messenger RNAs. Thus, across development, the pools of mRNA codons and tRNA anticodons are invariant and highly correlated, revealing a stable molecular interaction interlocking transcription and translation.

Lactation Biology Symposium: role of colostrum and colostrum components on glucose metabolism in neonatal calves

In neonatal calves, nutrient intake shifts from continuous glucose supply via the placenta to discontinuous colostrum and milk intake with lactose and fat as main energy sources. Calves are often born hypoglycemic and have to establish endogenous glucose production (eGP) and gluconeogenesis, because lactose intake by colostrum and milk does not meet glucose demands. Besides establishing a passive immunity, colostrum intake stimulates maturation and function of the neonatal gastrointestinal tract (GIT). Nutrients and nonnutritive factors, such as hormones and growth factors, which are present in high amounts in colostrum of first milking after parturition, affect intestinal growth and function and enhance the absorptive capacity of the GIT. Likely as a consequence of that, colostrum feeding improves the glucose status in neonatal calves by increasing glucose absorption, which results in elevated postprandial plasma glucose concentrations. Hepatic glycogen concentrations rise much greater when colostrum instead of a milk-based colostrum replacer (formula with same nutrient composition as colostrum but almost no biologically active substances, such as hormones and growth factors) is fed. In contrast, first-pass glucose uptake in the splanchnic tissue tended to be greater in calves fed formula. The greater plasma glucose rise and improved energy status in neonatal calves after colostrum intake lead to greater insulin secretion and accelerated stimulation of anabolic processes indicated by enhanced maturation of the postnatal somatotropic axis in neonatal calves. Hormones involved in stimulation of eGP, such as glucagon and cortisol, depend on neonatal diet, but their effects on eGP stimulation seem to be impaired. Although colostrum feeding affects systemic insulin, IGF-I, and leptin concentrations, evidence for systemic action of colostral insulin, IGF-I, and leptin in neonatal calves is weak. Studies so far indicate no absorption of insulin, IGF-I, and leptin from colostrum in neonatal calves, unlike in rodents where systemic effects of colostral leptin are demonstrated. Therefore, glucose availability in neonatal calves is promoted by perinatal maturation of eGP and colostrum intake. There may be long-lasting effects of an improved colostrum supply and glucose status on postnatal growth and development, and colostrum supply may contribute to neonatal programming of performance (milk and growth) in later life, but data proving this concept are missing.

Energy metabolism in the newborn farm animal with emphasis on the calf: endocrine changes and responses to milk-born and systemic hormones

Neonatal mammals need adaption to changes in nutrient supply because energy intake shifts from continuous parenteral supply of nutrients (mainly glucose, lactate, and amino acids) via the placenta to discontinuous colostrum and milk intake with lactose and fat as main energy sources. Besides ingested lactose, endogenous glucose production is essential in the neonate to assure sufficient glucose availability. Fetal endogenous glucose production is low, but endocrine changes (especially the prenatal rise of glucocorticoid production) promote maturation of metabolic pathways that enable marked glycogen synthesis before and enhanced gluconeogenesis after birth to establish an adequate glucose status during postnatal maturation. In preterm born farm animals gluconeogenic activity is low, mainly because of a low glucocorticoid and thyroid status. In full-term neonates, endogenous glucose production increases with age. Colostral bioactive components (such as growth factors, hormones, bioactive peptides, and cytokines) do not have a direct effect on endogenous glucose production. However, colostrum feeding stimulates intestinal growth and development, an effect at least in part mediated by bioactive substances. Increased nutrient and glucose absorption thus allows increased glucose supply and hepatic glycogen storage, which improves the glucose status. The improved energetic status of colostrum-fed neonates is reflected by an accelerated maturation of the somatotropic axis, leading especially to enhanced production of IGF-I in the neonate. Secretion and production of hormones involved in the regulation of glucose and fat metabolism in neonates depend on the developmental stage and the response to feeding. In addition, many such hormones have actions in the neonate that differ from adult animals. Endocrine action to support endogenous energy supply in neonates is probably not fully established, and therefore, needs postnatal maturation. Therefore, our knowledge on energy metabolism in the neonate needs to be extended to better understand the function and the failure and to assess endocrine responses during the neonatal period.

Epigenetic Control of Circadian Clock Operation during Development

The molecular players of circadian clock oscillation have been identified and extensively characterized. The epigenetic mechanisms behind the circadian gene expression control has also been recently studied, although there are still details to be illucidated. In this review, we briefly summarize the current understanding of the mammalian clock. We also provide evidence for the lack of circadian oscillation in particular cell types. As the circadian clock has intimate interaction with the various cellular functions in different type of cells, it must have plasticity and specicity in its operation within different epigenetic environments. The lack of circadian oscillation in certain cells provide an unique opportunity to study the required epigenetic environment in the cell that permit circadian oscillation and to idenfify key influencing factors for proper clock function. How epigenetic mechansims, including DNA methylaiton and chromatin modifications, participate in control of clock oscillation still awaits future studies at the genomic scale.

Circadian rhythms of fetal liver transcription persist in the absence of canonical circadian clock gene expression rhythms in vivo

The cellular circadian clock and systemic cues drive rhythmicity in the transcriptome of adult peripheral tissues. However, the oscillating status of the circadian clocks in fetal tissues, and their response to maternal cues, are less clear. Most clock genes do not cycle in fetal livers from mice and rats, although tissue level rhythms rapidly emerge when fetal mouse liver explants are cultured in vitro. Thus, in the fetal mouse liver, the circadian clock does not oscillate at the cellular level (but is induced to oscillate in culture). To gain a comprehensive overview of the clock status in the fetal liver during late gestation, we performed microarray analyses on fetal liver tissues. In the fetal liver we did not observe circadian rhythms of clock gene expression or many other transcripts known to be rhythmically expressed in the adult liver. Nevertheless, JTK_CYCLE analysis identified some transcripts in the fetal liver that were rhythmically expressed, albeit at low amplitudes. Upon data filtering by coefficient of variation, the expression levels for transcripts related to pancreatic exocrine enzymes and zymogen secretion were found to undergo synchronized daily fluctuations at high amplitudes. These results suggest that maternal cues influence the fetal liver, despite the fact that we did not detect circadian rhythms of canonical clock gene expression in the fetal liver. These results raise important questions on the role of the circadian clock, or lack thereof, during ontogeny.

Transcriptome comparison between fetal and adult mouse livers: implications for circadian clock mechanisms

Microarray transcriptome analyses of fetal mouse liver did not detect circadian expression rhythms of clock genes or clock-controlled genes, although some rhythmic transcripts that were likely not driven by endogenous cellular clocks were identified. This finding reveals a key distinction between the circadian oscillators in fetal and adult mouse livers. Thus, in this study, the transcriptomes of fetal and adult livers were systematically compared to identify differences in the gene expression profiles between these two developmental stages. Approximately 1000 transcripts were differentially enriched between the fetal and adult livers. These transcripts represent genes with cellular functions characteristic of distinct developmental stages. Clock genes were also differentially expressed between the fetal and adult livers. Developmental differences in liver gene expression might have contributed to the differences in oscillation status and functional states of the cellular circadian clock between fetal and adult livers.

The health implications of birth by Caesarean section

Since the first mention of fetal programming of adult health and disease, a plethora of programming events in early life has been suggested. These have included intrauterine and postnatal events, but limited attention has been given to the potential contribution of the birth process to normal physiology and long-term health. Over the last 30 years a growing number of studies have demonstrated that babies born at term by vaginal delivery (VD) have significantly different physiology at birth to those born by Caesarean section (CS), particularly when there has been no exposure to labour, i.e. pre-labour CS (PLCS). This literature is reviewed here and the processes involved in VD that might programme post-natal development are discussed. Some of the effects of CS are short term, but longer term problems are also apparent. We suggest that VD initiates important physiological trajectories and the absence of this stimulus in CS has implications for adult health. There are a number of factors that might plausibly contribute to this programming, one of which is the hormonal surge or "stress response" of VD. Given the increasing incidence of elective PLCS, an understanding of the effects of VD on normal development is crucial.

Metabolic programming of long-term outcomes due to fatty acid nutrition in early life

Understanding of the importance of dietary fatty acids has grown beyond a simple source of energy to complex roles in regulating gene expression and cell and intracellular communication. This is important because the metabolic and neuroendocrine environment of the fetus and infant plays a key role in guiding the set point of neural receptors that regulate energy homeostasis and expression of genes that control energy storage and oxidation. Early deviations in these pathways have the potential to lead to lasting adaptations, termed metabolic programming, which may combine to increase the risk of metabolic syndrome in later life. The quality of fatty acids in human diets has undergone major changes in the last 50 years, characterized by an increase in ω-6 and decrease in ω-3 fatty acids. Evidence is accumulating to support the concept that the maternal intake of ω-6 and ω-3 fatty acids in gestation and lactation, possibly involving both excess ω-6 and inadequate ω-3 fatty acids, can impact the developing infant tissue lipids and neuroendocrine and metabolic pathways relevant to metabolic programming. Further work is needed to understand the needs for different ω-6 and ω-3 fatty acids during fetal and infant life, and their roles with respect to development of energy homeostasis and metabolism.

Maternal high-fat diet triggers lipotoxicity in the fetal livers of nonhuman primates

Maternal obesity is thought to increase the offspring's risk of juvenile obesity and metabolic diseases; however, the mechanism(s) whereby excess maternal nutrition affects fetal development remain poorly understood. Here, we investigated in nonhuman primates the effect of chronic high-fat diet (HFD) on the development of fetal metabolic systems. We found that fetal offspring from both lean and obese mothers chronically consuming a HFD had a 3-fold increase in liver triglycerides (TGs). In addition, fetal offspring from HFD-fed mothers (O-HFD) showed increased evidence of hepatic oxidative stress early in the third trimester, consistent with the development of nonalcoholic fatty liver disease (NAFLD). O-HFD animals also exhibited elevated hepatic expression of gluconeogenic enzymes and transcription factors. Furthermore, fetal glycerol levels were 2-fold higher in O-HFD animals than in control fetal offspring and correlated with maternal levels. The increased fetal hepatic TG levels persisted at P180, concurrent with a 2-fold increase in percent body fat. Importantly, reversing the maternal HFD to a low-fat diet during a subsequent pregnancy improved fetal hepatic TG levels and partially normalized gluconeogenic enzyme expression, without changing maternal body weight. These results suggest that a developing fetus is highly vulnerable to excess lipids, independent of maternal diabetes and/or obesity, and that exposure to this may increase the risk of pediatric NAFLD.

Generalized Two-Dimensional Correlation Analysis of NMR and Raman Spectra for Structural Evolution Characterizations of Silk Fibroin

Generalized two-dimensional (2D) correlation spectroscopy was used to characterize the structural evolution of silk fibroin as the pH changed from 6.8 to 4.8, demonstrating that the conformational transitions of silk fibroin are induced step by step as the pH decreases. 2D homo- and hetero-spectral correlation spectroscopy was used to establish the relationship between information extracted from NMR and Raman spectroscopy. This novel method reveals the structural evolution using two probes with different frequency scales (10(5-9) Hz for nuclear spin motion and 10(12-14) Hz for molecular vibration motion), reflecting the different spatial scale sensitivity to the molecular conformational change. The transition order is identified as silk I state (helix dominant) --> silk I intermediate state --> silk II intermediate state --> silk II state (beta-sheet dominant), as the pH decreases. The results may rationalize the silkworm spinning process, which undergoes the conformational transition steadily from the soluble helix state to the insoluble beta-sheet state as the pH decreases from the posterior to anterior glands.

Effect of subchronic exposure to malathion on glycogen phosphorylase and hexokinase activities in rat liver using native PAGE

The aim of this study was the evaluation of the effects of a subchronic exposure to malathion, an organophosphorus (OP) insecticide, on plasma glucose and hepatic enzymes of glycogenolysis and glycolysis in rats in vivo. Malathion was administered intragastrically by stomach tube in the amount of 1 ml corn oil containing 100mg/kg body weight (BW) daily for 32 days. At the end of the experiment, the liver was removed. The activities of glycogen phosphorylase (GP) and hexokinase (HK) were analysed in the homogenate. The methodology employed was a non-denaturing electrophoresis followed by activity-staining (native PAGE). Malathion decrease GP activity by 50% and increase HK activity by 10%. In addition, an hepatomegaly was recorded with a rise in the hepatic glycogen rate in malathion-treated rats. Moreover, subchronic administration of malathion has no effect on blood glucose concentration. The storage of glycogen in liver may be due to a stimulation of insulin secretion after the inhibition of acethylcholinesterase activity in pancreatic beta cells by malathion. These findings were in favour of an activation of glycogen storage by malathion.

Metabolic consequences of hypoxia from birth and dexamethasone treatment in the neonatal rat: comprehensive hepatic lipid and fatty acid profiling

Neonatal hypoxia is a common condition resulting from pulmonary and/or cardiac dysfunction. Dexamethasone therapy is a common treatment for many causes of neonatal distress, including hypoxia. The present study examined the effects of dexamethasone treatment on both normoxic and hypoxic neonatal rats. We performed comprehensive hepatic fatty acid/lipid profiling and evaluated changes in pertinent plasma hormones and lipids and a functional hepatic correlate, i.e. hepatic lipase activity. Rats were exposed to hypoxia from birth to 7 d of age. A 4-d tapering dose regimen of dexamethasone was administered on: postnatal day (PD)3 (0.5 mg/kg), PD4 (0.25 mg/kg), PD5 (0.125 mg/kg), and PD6 (0.05 mg/kg). The most significant finding was that dexamethasone attenuated nearly all hypoxia-induced changes in hepatic lipid profiles. Hypoxia increased the concentration of hepatic triacylglyceride and free fatty acids and, more specifically, increased a number of fatty acid metabolites within these lipid classes. Administration of dexamethasone blocked these increases. Hypoxia alone increased the plasma concentration of cholesterol and triacylglyceride, had no effect on plasma glucose, and only tended to increase plasma insulin. Dexamethasone administration to hypoxic pups resulted in an additional increase in plasma lipid concentrations, an increase in insulin, and a decrease in plasma glucose. Hypoxia and dexamethasone treatment each decreased total hepatic lipase activity. Normoxic pups treated with dexamethasone displayed increased plasma lipids and insulin. The effects of dexamethasone on hepatic function in the hypoxic neonate are dramatic and have significant implications in the assessment and treatment of metabolic dysfunction in the newborn.

Expression and binding properties of the two mannose-6-phosphate receptors differ during perinatal development in rat liver

Mammalian tissues express both cation-dependent (CD-MPR) and cation-independent (CI-MPR) mannose-6-phosphate receptors, which mediate the targeting of acid hydrolases to lysosomes. The coexistence of the two receptors in all cell types and tissues is still poorly understood. To determine whether these receptors might play a role in maturation, we studied their expression and binding properties in rat liver during perinatal development. CI-MPR expression decreases progressively from 18-day fetuses to adults, whereas the CD-MPR showed a transient decrease in newborn and at the 5th day after birth. Immunostaining of the tissues showed that both receptors localize to hepatocytes at all the ages and, additionally, the CD-MPR was reactive in megakaryocytes at early stages. Binding assays showed differences in the B(max) and K(D) values between the ages studied. These results demonstrate that both receptors change differentially during perinatal development, suggesting that they play distinct roles during organ maturation.

GLUT-1 and GLUT-2 mRNA, protein, and glucose transporter activity in cultured fetal and adult hepatocytes

To understand glycogenesis in the fetal hepatocyte, we examined glucose transport in cultured fetal and adult male rat hepatocytes. GLUT-1 mRNA was detected in fetal hepatocytes at isolation but in adult hepatocytes only after culture. GLUT-1 mRNA was more abundant in fetal than in adult hepatocytes (P < 0.005). GLUT-1 protein paralleled its message. GLUT-2 mRNA was more abundant in adult than in fetal hepatocytes (P < 0.05), and abundance did not change during culture, but GLUT-2 protein was discordantly regulated. There was more GLUT-2 protein in fetal hepatocytes at 45 h (P < 0.025). An Eadie-Hofstee plot of 3-O-methylglucose transport appeared to have two linear components. One component was presumed to be GLUT-1 [variable Michaelis constant (Km) approximating 6-8 mM, maximal uptake rate (Vmax) for fetal vs. adult hepatocytes 106 vs. 35 nmol.min-1.mg protein-1], and a second was presumed to be GLUT-2 (Km of 23 mM, Vmax for fetal vs. adult hepatocytes 198 vs. 92 nmol.min-1.mg protein-1). Early phosphorylation of 2-deoxyglucose was greater in fetal than in adult hepatocytes, but transport was always greater than phosphorylation. Increased expression of both GLUT-1 and GLUT-2 by fetal hepatocytes permits greater glucose uptake and positions the fetal rat hepatocyte for efficient glycogenesis at low plasma glucose concentration.

Transcription induction of c-Ki-ras with the tumour promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) in normal and transformed liver cells

Results from nuclear run-off assays show that exposure of hepatocytes and Reuber H35B hepatoma cells to the tumour promoter, 12-O-tetradecanoylphorbol-13-acetate (TPA), leads to enhanced transcription of c-Ki-ras gene. This increase in transcription in turn results in an accumulation of the functionally active c-Ki-ras message. The half life of c-Ki-ras message in both normal and transformed livers cells is not altered by TPA and is determined to be 3.5 hr. The induction of c-Ki-ras message is accompanied by an increase in the level of c-Ki-ras protein.

Levels of Cu-Zn and Mn superoxide dismutases in rat liver during development

Superoxide dismutase is the main scavenger of superoxide radicals in the mammalian body. The liver has high levels of two types of superoxide dismutase enzymes, cytosolic Cu-Zn and mitochondrial Mn enzymes. The aim of the present study was to investigate the content of two distinct superoxide dismutases in liver during the perinatal transition from a hypoxic to a hyperoxic environment. Both isozymes were purified to homogeneity and used as immunogens in rabbits. Antisera raised were found to recognize only polypeptides of molecular weight 16,900 or 23,400, which correspond to Cu-Zn and Mn superoxide dismutases, respectively. It was found that the level of Cu-Zn superoxide dismutase enzymatic activity and protein as assessed by immunoquantitation increased 10-fold during the postnatal period, reaching adult levels by 3 weeks. In contrast, the amount of Mn superoxide dismutase content increased only twofold to adult levels during the first week of life. Neither of the superoxide dismutases showed an alteration in specific activity or apparent molecular weight in rat livers during ontogeny. These results show that the levels of two intracellular superoxide dismutases are differentially elevated during the perinatal period. It is suggested that each dismutase plays a different physiological role for superoxide scavenging in liver as a function of the hypoxic/hyperoxic environment at birth.

The effect of dexamethasone and glucagon on the expression of hepatocyte plasma membrane proteins during development

The regulation of different maturational processes in the liver is believed to be influenced by the hormonal system. The aim of this study was to investigate the effect of two hormones, glucagon and dexamethasone, on levels of plasma membrane proteins in rat liver cells during late fetal and early postnatal stages of development. For this purpose, 18-day-old rat fetuses and 1-day-old newborns were treated with glucagon or dexamethasone and killed at 22 days of gestation and 3, 5 and 7 days of age, respectively. Postnuclei liver membranes were isolated using a sucrose gradient method and assessed for levels of specific membrane proteins. Asialoglycoprotein receptor and 110,000 Mr glycoprotein, denoted GP 110, representing the sinusoidal and bile canalicular domains, respectively, were quantitated using the immunoblot method. Membrane enzymes alkaline phosphatase, leucine aminopeptidase and gamma-glutamyl transferase were evaluated using enzymatic methods. The data showed that glucagon and dexamethasone have a differential effect on membrane constituents according to the stage of development. Glucagon increased the levels of membrane enzymes during the late fetal stage but had no effect on liver membrane proteins in the newborn animal. In contrast, although dexamethasone elevated GP 110 in fetal rat livers, none of the other marker proteins was significantly affected. On the other hand, in newborns dexamethasone reduced the amount of asialoglycoprotein receptor and alkaline phosphatase and leucine aminopeptidase enzyme activities but greatly augmented the level of gamma-glutamyl transferase. Thus, glucagon primarily affects plasma membrane proteins in late gestation while dexamethasone does so during the early postnatal period. The roles that these two hormones may play during ontogeny is discussed with respect to liver development.

Developmental changes in rat hepatic casein kinases 1 and 2

Cytosolic histone kinase and casein kinase activities varied considerably in the late fetal and postnatal periods of liver development. Both activities showed a maximum at day 21 of gestation and decreased at birth to values close to those of adult rats. The changes in total casein kinase activity were due to variations of casein kinase 1 and casein kinase 2. Similarly the activities of both the cyclic-AMP-dependent protein (histone) kinase and the cyclic-AMP-independent histone kinase varied during development. Besides the changes in total activity, the affinity of casein kinases 1 and 2 for casein also varied in fetal and postnatal development. The Km values of casein kinase 2 increased from day 18, reached a maximum at day 20 of gestation and then started to decrease until one day after birth. In contrast the Km values of casein kinase 1 decreased from day 18, reached its lowest value at day 21 of gestation and attained values similar to those in the adult at the day of birth. Changes in this parameter were also observed when insulin (3 IU/kg) was administered by intraperitoneal injection to one-day-old rats. The Km values of casein kinase 1 decreased while those of casein kinase 2 increased after administration of this hormone. On the other hand, the Km values for ATP of casein kinases 1 and 2 as well as their apparent molecular masses and sensitivity to heparin and GTP did not significantly change during ontogeny of rat liver.

Changes in kidney transaminase activity during development in male and female rats

The developmental changes in the activity of kidney transamidinase in male and female rats were investigated. The activity in both sexes increased rapidly after birth, reaching adult levels at 4 days of age. After weaning, the activity in male rats remained constant, while in female rats it declined to 60% of that in males. Thus, transamidinase is in the neonatal cluster of enzyme differentiation.

Aldose metabolism in developing human fetal brain and liver

Aldose reductase, sorbitol dehydrogenase, and glucose-6-phosphate dehydrogenase enzyme activities were studied in human foetal brain and liver at different periods of gestation. Aldose reductase activity in liver disappears after 16 weeks of gestation whereas sorbitol dehydrogenase keeps on increasing in liver as well as in brain. In utero, some glucose metabolism may be mediated through an active sorbitol pathway in human fetuses.