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A F Moorman

Publications and source records attributed to A F Moorman.

At least 163 records · Page 9Linked to original sources
PubMed1990

Expression patterns of mRNAs for ammonia-metabolizing enzymes in the developing rat: the ontogenesis of hepatocyte heterogeneity.

The expression patterns of the mRNAs for the ammonia-metabolizing enzymes carbamoylphosphate synthetase (CPS), glutamine synthetase (GS) and glutamate dehydrogenase (GDH) were studied in developing pre- and neonatal rat liver by in situ hybridization. In the period of 11 to 14 embryonic days (ED) the concentrations of GS and GDH mRNA increases rapidly in the liver, whereas a substantial rise of CPS mRNA in the liver does not occur until ED 18. Hepatocyte heterogeneity related to the vascular architecture can first be observed at ED 18 for GS mRNA, at ED 20 for GDH mRNA and three days after birth for CPS mRNA. The adult phenotype is gradually established during the second neonatal week, i.e. GS mRNA becomes confined to a pericentral compartment of one to two hepatocytes thickness, CPS mRNA to a large periportal compartment being no longer expressed in the pericentral compartment and GDH mRNA is expressed over the entire porto-central distance, decreasing in concentration going from central to portal. Comparison of the observed mRNA distribution patterns in the perinatal liver, with published data on the distribution of the respective proteins, points to the occurrence of posttranslational, in addition to pretranslational control mechanisms in the period of ontogenesis of hepatocyte heterogeneity. Interestingly, during development all three mRNAS are expressed outside the liver to a considerable extent and in a highly specific way, indicating that several organs are involved in the developmentally regulated expression of the mRNAs for the ammonia-metabolizing enzymes, that were hitherto not recognized as such.

Ammonia↗
PubMed1990

Expression patterns of mRNAs for alpha-fetoprotein and albumin in the developing rat: the ontogenesis of hepatocyte heterogeneity.

In developing and normal adult rat liver the expression patterns of the mRNAs for alpha-fetoprotein (AFP) and albumin (ALB) were analysed by in situ hybridization using specific 35S-labelled complementary DNA probes. In the developing liver AFP and ALB mRNA are found from embryonic day (ED) 11 and 12, respectively, onward. At ED 20 the first signs of a zonal distribution of these mRNAs across the liver lobule can be observed, AFP mRNA concentration being higher in the pericentral area and ALB mRNA concentration higher in the periportal area. This distribution pattern of reciprocal, overlapping gradients of mRNA can be clearly recognized in the neonatal period. In the adult liver AFP mRNA can no longer be detected and similar to the neonatal situation, ALB mRNA is expressed across the entire porto-central distance decreasing in concentration going from the portal to the central area. Transient extra-hepatic expression of AFP mRNA is found in the embryonic heart and in the epithelial lining of intestine and lung; furthermore, AFP and ALB mRNA are found to be transiently expressed in the developing renal tubules. Similar expression patterns have been observed for other liver-characteristic mRNAs (Moorman et al., 1990), suggesting that common regulatory factors are operative during development.

Albumins↗
PubMed1990

Regulation of hepatocyte-specific gene expression in cultures of human embryonic hepatocytes.

The aim of this study was to see whether the rat embryo can serve as a model system for hepatocyte-specific gene expression in the human embryo. Carbamoylphosphate synthetase was used as a hepatocyte-specific marker molecule. Despite the earlier developmental appearance of this enzyme in human than in murine liver, the hormonal regulation of gene expression in cultures of embryonic hepatocytes was found to be the same. Therefore, a relatively early developmental appearance of regulatory hormones rather than differences in regulatory mechanisms of gene expression appears to be responsible for the early accumulation of the enzyme in human liver, when compared to murine liver.

Animals↗
PubMed1990

Histochemical and functional fibre typing of the rabbit masseter muscle.

The fibre-type distribution of the masseter muscle of the rabbit was studied by means of the myosin-ATPase and succinate dehydrogenase reactions. Six different fibre types were found and these were unequally distributed between and within the anatomical compartments of the muscle. Most of the masseter consists of slow- and fast-twitch oxidative fibres. The slow fibres increase in numbers in the deeper and more anterior regions of the muscle. Fast-twitch glycolytic fibres were almost exclusively found in the most posterior portions of the superficial and deep masseter. The fibre composition within the sagittally orientated anatomical compartments was found to be correlated with maximal contraction speeds during natural mastication as estimated from a mechanical model. However, the differences in fibre composition between the anatomical compartments (and hence between superficial and deep layers) appeared not to be correlated with contraction speed. The regional and compartmental specialisation within the masseter permits the muscle to perform many different functional roles in the generation and control of the jaw movements, jaw position and bite forces.

Aerobiosis↗
PubMed1989

Isomyosin expression patterns during rat heart morphogenesis: an immunohistochemical study.

An immunohistochemical study of cardiac alpha and beta myosin heavy chain (MHC) expression during rat heart morphogenesis was performed. In tubular hearts (embryonic days, ED10-11) coexpression of both cardiac alpha and beta MHC was found throughout the heart, except for the left free wall of the atrium, where only cardiac alpha MHC is detected. A transition of coexpression to single expression of either cardiac alpha or beta MHC begins at the same time in both atria and ventricles but requires a longer time for completion in the ventricules; in the atria transition takes place during the period ED 12-13 and in the ventricles during ED12-15. Furthermore, expression of cardiac alpha and beta MHC was detected in the sinus venosus, and cardiac alpha MHC expression was detected in the pulmonary veins. A comparison of the results obtained in chicken embryos revealed that in tubular hearts the expression pattern is similar, whereas in later developmental stages two major differences were observed: 1) transition of coexpression to single expression in rat ventricles appears to take a longer developmental period; 2) the persistence of areas of coexpression in the sinoatrial junction, dorsal mesocardium, atrioventricular junction, and outflow tract, as found in the chicken embryo in later developmental stages, is not found in the rat heart.

Animals↗
PubMed1989

Localization of ammonia-metabolizing enzymes in human liver: ontogenesis of heterogeneity.

Immunohistochemical analysis of human liver (8 to 94 years) shows a compartmentation of ammonia-metabolizing enzymes across the acinus. The highest concentration of carbamoylphosphate synthetase (ammonia) is found in the parenchymal cells around the terminal portal venules. Glutamine synthetase is found in a small pericentral compartment two to three cells thick. In contrast to observations in rat liver, in human liver a well-recognizable intermediate zone can be distinguished in which neither enzyme can be detected. This intermediate zone is not yet established at the age of 8 years but can be recognized in livers from 25 years onward. Carbamoylphosphate synthetase can already be detected in the liver of human fetuses at 5 weeks of development. The enzyme distribution reveals a random heterogeneity among the hepatocytes, suggesting that not all hepatocytes start to accumulate carbamoylphosphate synthetase at the same time. From 9 weeks of development onward, the enzyme becomes homogeneously distributed throughout the liver parenchyma until at least 2 days after birth. Glutamine synthetase cannot be detected during this period. In addition, the definitive architecture of the acinus is not yet completed at birth. These results therefore support the idea that in human liver, metabolic zonation with respect to NH3 metabolism exists as it does in rat liver. Furthermore, the data show that this functional compartmentation becomes established concomitant with the development of the acinar architecture.(ABSTRACT TRUNCATED AT 250 WORDS)

Ammonia↗
PubMed1989

Hepatic enzymic zonation: a reevaluation of the concept of the liver acinus.

The distribution pattern of a periportal enzyme (carbamoylphosphate synthetase) and a pericentral enzyme (glutamine synthetase) in human and rat liver has provided an objective parameter to delineate the zonal boundaries of the liver acinus. On sections, the pericental zone (zone 3) is circular and discrete rather than star-like and reticular, as predicted by the acinar concept, whereas the periportal zone (zone 1) is reticular, i.e. contiguous between adjacent acini rather than discrete. Three-dimensionally, the composite of pericentral zones (the pericentral compartment) follows the branching pattern of the terminal hepatic (central) vein, whereas the composite of periportal zones (the periportal compartment) envelops the pericentral compartment as a three-dimensional network (reticulum). This modified concept that is based upon the three-dimensional distribution of hepatocyte-specific enzymes is supported by data from the literature regarding the three-dimensional angioarchitecture of the liver, the perfusion pattern of the liver and the three-dimensional pattern of tissue oxygenation. Hence, a unified concept of the liver architecture that is based upon the observed distribution pattern of blood flow, of gene expression and of metabolism can be established.

Adult↗
PubMed1989

Creatine kinase isozyme expression in embryonic chicken heart.

The distribution pattern of creatine kinase (EC 2.7.3.2) isozymes in developing chicken heart was studied by immunohistochemistry. Creatine kinase M, which is absent from adult heart, is transiently expressed between 4 and 11 days of incubation. During that period, numerous muscular cells in the roof and septum of the atrium, in the interventricular septum and on top of the trabeculae cordis and at the rim of the outflow tract stain strongly with a polyclonal antibody that is specific for the M subunit. In the ventricle and outflow tract, the M-positive cells are found mainly subendocardially and in the right half, at the transition of conducting and working myocytes. Creatine kinase B, which is the predominant adult isozyme, is initially expressed to a high concentration in a small group of disperse myocardial cells in upstream part of the inflow tract. When compared to the expression pattern of cardiac myosin heavy chains, the observed creatine kinase expression pattern suggests that M-positive cells are mainly found in areas that participate in the formation of cardiac conductive tissue, whereas B-positive cells are first found in areas that are involved in the generation of cardiac rhythm.

Animals↗
PubMed1989

Induction of glutamine synthetase and transient co-expression with carbamoylphosphate synthetase in hepatocytes transplanted into fat pads of syngeneic hosts.

Isolated rat hepatocytes were transplanted into the interscapular and both anterior lateral fat pads of hepatectomized syngeneic rats. At various time points following transplantation, the fat pads were removed, fixed and embedded in paraffin. Serial sections were stained for glutamine synthetase (GS) and carbamoylphosphate synthetase (CPS) using specific antisera and the PAP technique. The initially low fraction of GS+-heptatocytes remained low up to the fourth day, then increased strikingly up to almost 100% and declined gradually after the 14th day. In contrast, the number of CPS+-cells declined continuously to about 30% after 28 days. If the animals were exposed to CCl4 prior to the isolation of the hepatocytes in order to reduce the number of GS+-cells in the initial cell suspension similar results were obtained and no difference in the probability of the colony formation was noted between this and the normal hepatocyte suspensions indicating that the appearance of the GS+-phenotype was not due to a selective survival of these cells. Analysis of the staining intensity of the transplanted hepatocytes revealed the appearance of two populations of GS+-hepatocytes, one with a strong and one with a weak staining, during the course of formation of larger nodules, while only a single weakly stained population could be discerned with respect to the staining for CPS. These results demonstrate that all hepatocytes or at least their descendents can be induced to express GS by the environmental conditions of the fat pads, and that GS and CPS can be co-expressed with an apparently reciprocal relationship.

Animals↗
PubMed1989

The gamma-glutamyltransferase/glutamine synthetase activity ratio. A powerful marker for the acinar origin of hepatocytes.

The activity of glutamine synthetase (GS) in hepatocytes isolated by digitonin-collagenase perfusion from the perivenous region was more than 10-times higher than in cells isolated from the periportal region. This distribution was confirmed by immunohistochemical staining for GS of cells separated from either region. In contrast, in periportal hepatocytes, the activity of gamma-glutamyltransferase (GGT) was 3-4 times as high as in perivenous hepatocytes. This acinar distribution was also confirmed histochemically. The striking reciprocal acinar distribution of these two enzymes, now observed by direct biochemical analysis of selectively isolated hepatocytes, confirms the earlier qualitative differences observed by histochemistry and immunohistochemistry. The GGT/GS ratio seems to serve as a powerful marker of the acinar origin of isolated hepatocyte populations. Preliminary data describing glutamine synthetase activity in plasma of some subjects with suspected liver dysfunction suggests this enzyme as a marker for pericentral damage.

Animals↗
PubMed1989

Normal-sized thyroglobulin messenger ribonucleic acid in Dutch goats with a thyroglobulin synthesis defect is translated into a 35,000 molecular weight N-terminal fragment.

The translation product of the thyroglobulin (Tg) mRNA in Dutch goats with a Tg synthesis defect has been characterized. The Tg mRNA has a normal size of 8.4 kilobases. Translation of goitrous polysomal Tg mRNA resulted, after immunoprecipitation with polyclonal rabbit antigoat Tg antibodies, in a single 35,000 mol wt (Mr) Tg fragment. To characterize the Tg antigens produced in vivo, thyroid hormone release by the goiter was suppressed by injecting T4 sc in newborn goitrous goats. Immunohistochemical studies showed the presence of Tg antigens almost solely in the colloidal lumen. Electrophoresis of the reduced thyroid proteins demonstrated the presence of two Tg fragments with Mr of 40,000 and 32,000, respectively; the latter is probably a breakdown product of the 40,000 Mr fragment. The difference in Mr between the in vivo and in vitro translation products (40,000 and 35,000 Mr, respectively) can be explained by the carbohydrate content (10% wt/wt) of the in vivo product, as was shown by periodic acid-Schiff-positive staining. Using monoclonal antibodies against the hormonogenic sites at the first and last parts of the Tg molecule, we demonstrated that only the first part of the Tg molecule is present. Both in vivo and in vitro 10% of the goitrous Tg mRNA molecule is translated, resulting in an N-terminal Tg fragment that easily aggregates to large S-S complexes in the colloidal lumen of goiter by H2O2 oxidation.

Animals↗
PubMed1988

Noradrenergic innervation of developing rat and spiny mouse liver. Its relation to the development of the liver architecture and enzymic zonation.

The development of noradrenergic innervation of rat liver was studied with a polyclonal antiserum against noradrenaline. Nerves are first seen in the larger portal vessels at day 1 after birth and reach their final distribution at 5 days after birth i.e. at the same time as the establishment of the acinar architecture and the heterogeneous distribution of NH3-metabolizing enzymes. The latter distribution of nerves is already seen at birth in the liver of the closely related but precocial spiny mouse. This shows that the onset of extrinsic sympathetic innervation is regulated by the developmental stage of the animal rather than by adaptation to extrauterine life. Chemical sympathectomy at birth with 6-hydroxydopamine did not eliminate the developmental appearance of heterogeneous distributions of NH3-metabolizing enzymes.

Ammonia↗
PubMed1988

Immunohistochemical localization of glutamate dehydrogenase in rat liver: plasticity of distribution during development and with hormone treatment.

In adult rat liver, glutamate dehydrogenase is present in high concentrations around the terminal portal (zone 1) and hepatic (zone 3) veins, whereas its concentration is low in the intermediate zone. Although the size and staining intensity of the periportal glutamate dehydrogenase-positive compartment are less than those of the pericentral compartment, it can expand under appropriate endocrine conditions, leading to a homogeneous distribution. At birth, glutamate dehydrogenase is also homogeneously distributed. Glutamate dehydrogenase disappears from the periportal compartment during the first postnatal week and reappears in that compartment after weaning. These observations indicate an independent regulation of glutamate dehydrogenase levels in the periportal and pericentral zone. The size of the periportal glutamate dehydrogenase-containing zone is appreciably smaller than that of carbamoylphosphate synthetase, whereas the pericentral glutamate dehydrogenase-containing zone is appreciably larger than that of glutamine synthetase. The heterogeneous distribution of glutamate dehydrogenase suggests the possibility that, under normal conditions, deamination of glutamate prevails in the periportal compartment and amination of glutamate in the pericentral compartment.

Aging↗
PubMed1988

Gene expression in derivatives of embryonic foregut during prenatal development of the rat.

Proteins characteristic for the adult cellular phenotype, i.e., carbamoylphosphate synthetase (CPS) for liver and small intestine, arginase for liver, glutamate dehydrogenase (GLDH) for pancreas, liver, and small intestine, and amylase for pancreas were studied immunohistochemically in rat embryos and fetuses. At distinct developmental stages, subsets of enzymes appear synchronously in the foregut derivatives, suggesting that gene expression in the different organs is regulated by common factors. In contrast to the long-held opinion that fetal hepatocytes are a homogeneous cell population, it is shown that arginase and CPS are heterogeneously distributed between ED 16 and ED 20. This heterogeneity is related to the vascular architecture of the liver and disappears perinatally as the result of strong stimulation of enzyme synthesis. In addition, an intercellular heterogeneity in CPS content that is not related to the vasculature is observed between ED 14 and ED 20. This "random" heterogeneity reflects temporal differences in the onset of CPS accumulation in individual cells.

Amylases↗
PubMed1988

Complementary distribution of carbamoylphosphate synthetase (ammonia) and glutamine synthetase in rat liver acinus is regulated at a pretranslational level.

We studied the distribution of the mRNAs for carbamoylphosphate synthetase (ammonia) and glutamine synthetase in frozen sections of adult rat liver by in situ hybridization to [35S]-labeled cDNA probes. The density of silver grains resulting from hybridization to the labeled cDNA probe for carbamoylphosphate synthetase is highest around the portal venules, decreases towards the central venule, and is virtually absent from an area two to three cells wide that lines the central venules in which mRNA for glutamine synthetase is predominantly localized. Therefore, both mRNAs show the same complementary distribution within the liver acinus that was found for the proteins they encode, demonstrating that compartmentalization of the expression of these enzymes is controlled at a pretranslational level. In addition, we found that carbamoylphosphate synthetase mRNA is present mainly in the epithelium of the crypts of the proximal part of the small intestine, whereas carbamoylphosphate synthetase protein is present in the epithelium of both crypts and villi.

Animals↗