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A F Moorman

Publications and source records attributed to A F Moorman.

At least 181 records · Page 10Linked to original sources
PubMed1987

Reciprocal regulation of glutamine synthetase and carbamoylphosphate synthetase levels in rat liver.

In glucocorticosteroid-treated diabetic rats, glutamine synthetase enzyme levels in the liver are decreased 3-fold, whereas carbamoylphosphate synthetase enzyme levels are increased 2.3-fold. In addition, immunohistochemistry shows that under these conditions the distribution of carbamoylphosphate synthetase is expanded over the entire liver acinus, whereas that of glutamine synthetase is reduced to very few cells bordering the central (terminal hepatic) veins. Using a newly isolated cDNA complementary to rat liver glutamine synthetase mRNA, we show that this regulation is primarily effected at a pretranslational level. (For data on carbamoylphosphate synthetase mRNA levels, see De Groot et al. (1986) Biochim. Biophys. Acta 866, 61-67). Furthermore, hybridization studies show stimulatory effects of both glucocorticosteroids and thyroid hormone on the glutamine synthetase mRNA level. Attempts to localize glutamine synthetase mRNA within the liver acinus by selective destruction of the pericentral zone failed because of generally low levels of liver mRNAs after CCl4 poisoning. In contrast to the situation after birth, significantly higher glutamine synthetase mRNA/enzyme activity ratios in fetal rat liver point to the presence of additional post-transcriptional control mechanisms before birth. These findings complement similar observations on carbamoylphosphate synthetase gene expression (De Groot et al. (1986) Biochim. Biophys. Acta 866, 61-67).

Animals↗
PubMed1987

Acetylcholinesterase in prenatal rat heart: a marker for the early development of the cardiac conductive tissue?

In rat embryos, acetylcholinesterase (AChE, EC 3.1.1.7) activity is present in a continuous sleeve of myocytes that extends from the myocardium that is adjacent to the atrioventricular endocardial cushions via the ventricular trabeculae to the outflow tract. No activity is found in the atrial roof, in the ventricular walls and in the interventricular septum except for its subendocardial surface. AChE-positive cells are first identified in 11-day rat embryos, while the prototypical distribution is best demonstrable in 13-day embryos. Part of the AChE-positive cell system is identifiable as a precursor of the adult conduction system by topographical criteria in 16-day fetuses and by morphological criteria in 20-day fetuses. At birth (2 days later), AChE activity has disappeared from the cardiac myocytes except for a ring of tissue at the atrial side of the atrioventricular junction. These findings suggest that the embryonic heart can be divided into an upstream myocardium that has no AChE activity and a downstream myocardium that is characterized by the presence of AChE. Furthermore they suggest that an acetylcholine-dependent mechanism may be responsible for the retardation of the depolarization wave in the downstream parts of the heart. Finally they show that the adult conduction system is formed by a transdifferentiation of part of a far more extensive embryonic precursor system.

Acetylcholinesterase↗
PubMed1987

Isomyosin expression in developing chicken atria: a marker for the development of conductive tissue?

Isomyosin expression patterns in embryonic chicken atria during the first two weeks of development were analyzed immunohistochemically. In the 3-days embryonic chicken heart (HH19-20), strong coexpression of both isomyosins can be found as band-like zones at the lateral sides of the sinoatrial junction. The zones converge on the bottom of the atrium and continue as a band around the atrioventricular canal. In the 5-days heart (HH27-28) the coexpression area encompasses the entire sinoatrial junction and extends into parts of the sinus venosus and into the dorsocaudal atrial wall. In the 7-days heart (HH 32-33) the relative extension of coexpression areas reaches its maximum. Coexpression is also found in a ring-like band in the ventral (bottom) wall of the atria peripheral to the ring-like band in the atrioventricular junction. The latter band has now become continuous with the coexpression area in the bottom of the interatrial septum. Caudally coexpression extends behind the atrioventricular cushions towards the interventricular septum and cranially coexpression of the atrioventricular junction has become continuous with that of the ring around the outflow tract (cf Sanders et al. 1986). In the second week of incubation a decrease of coexpression is observed. The isomyosin expression pattern described in this study has put forward additional arguments that the conductive tissue originates from areas that continue to express both isomyosins relatively late in development.

Animals↗
PubMed1987

Isomyosin expression patterns in tubular stages of chicken heart development: a 3-D immunohistochemical analysis.

The 3-D distribution of atrial and ventricular isomyosins is analysed in tubular chicken hearts (stage 12+ to 17 (H/H)) using antibodies specific for adult chicken atrial and ventricular myosin heavy chains, respectively. At stage 12+ (H/H) all myocytes express the atrial isomyosin; furthermore, all myocytes except those originally situated in the dorsolateral wall of the sinu-atrium coexpress the ventricular isomyosin as well. Moreover, it appears that recently incorporated myocardial cells at both ends of the heart tube start with a coexpression of both isomyosins. From stage 14 (H/H) onwards a regional loss of expression of one of either isomyosins is observed in the atrial and ventricular compartment. In this way the single isomyosin expression types that are characteristic for the adult working myocardium of the atria and ventricles arise. So, the isomyosin expression patterns are, unexpectedly, hardly useful to discriminate the different heart parts of the tubular heart. The ventricle, defined by its adult type of isomyosin expression, is even not detectable before stage 14 (H/H). Interestingly, interconnected coexpression areas, which may be precursor conductive tissues, are still present at stage 17 (H/H) in the outflow tract, the ventricular trabeculae, the atrio-ventricular transitional zone and in the sinu-atrium. The pattern of isomyosin coexpression was found to correlate with a peristaltoid contraction and a slow conduction velocity, whereas single expression areas correlate with a synchronous contraction and a relatively fast conduction velocity. The possible implications of the changing isomyosin pattern for the differentiation of the tubular myocardium, in particular in relation to the development of the conductive tissues, will be discussed.

Animals↗
PubMed1987

Immunohistochemical analysis of the distribution of histone H5 and hemoglobin during chicken development.

We used immunohistochemical procedures to investigate embryonic erythropoiesis in serial sections of chicken embryos after 2-13 days of incubation. Antibodies specific for the erythrocyte-specific histone H5, for embryonic hemoglobin, and for adult hemoglobin were used as markers for general, primitive, and definitive erythropoiesis, respectively. Histone H5 was present in erythrocytes at all of the stages studied, i.e., in both the primitive and definitive cells. Cell of the definitive lineage were first detected, at about 5-6 days of incubation, in erythroid foci in the mesenchyme around the vitelline stalk. At 7-9 days of incubation, a massive mesenchymal conglomeration of erythropoietic cells developed, extending from the cervical to the abdominal region and ventrally to the vertebral body, with its largest extensions being around the arteries in the mediastinum. Immunostaining revealed that these erythroid cells belonged to the definitive erythropoietic lineage. These cells had disappeared completely after 12 days of incubation, i.e., before erythropoiesis is visible in the bone marrow. These observations are consistent with the notion that the yolk sac is essential for the formation of the definitive erythroid lineage.

Animals↗
PubMed1987

The histone H1(0)/H5 variant and terminal differentiation of cells during development of Xenopus laevis.

The maintenance of the differentiated condition is supposed to be associated with the presence of a histone of the H1(0)/H5 subclass. If the H1(0)/H5 variant has an important role in differentiation distinct from that of H1, it should display differential expression in time and position during development. Here we report that this prediction is verified during Xenopus laevis development, in which tadpoles exhibit a very characteristic, developmentally regulated pattern of histone H1(0)/H5 expression that is different for the derivatives of each embryonic germ layer. However, the pattern of appearance of this variant during development does not reflect a simple correlation between its presence and the state of differentiation. Therefore, these results are pertinent to current ideas on differentiation and the involvement of lysine-rich histones in the repression of eukaryotic genes.

Aging↗
PubMed1987

Development of enzymic zonation in liver parenchyma is related to development of acinar architecture.

The appearance of the distribution patterns of the NH3-metabolizing enzymes carbamoylphosphate synthetase, glutamate dehydrogenase, and glutamine synthetase in the developing liver of an altricial species (rat) was compared with that in the developing liver of a closely related, precocial species (spiny mouse). The comparison showed that the development of hepatic acinar architecture, rather than perinatal adaptation, is responsible for the development of periportal and pericentral compartments of gene expression. Conditions that confine the expression of specific enzymes to the pericentral compartment of the acinus originate before conditions that confine the expression of (other) specific enzymes to the periportal compartment. However, whether or not the site of gene expression is restricted to specific compartments within the liver acinus, the rate of expression of the gene involved can also be adaptively regulated. Therefore, different factors appear to control the site and the rate of gene expression within one tissue.

Aging↗
PubMed1987

Heterogeneous distribution of glutamine synthetase during rat liver development.

Two days before birth, immunohistochemical detection of glutamine synthetase already reveals a heterogeneous distribution pattern related to the vascular architecture of the liver. Only a small number of hepatocytes in the vicinity of the efferent venules show relatively high staining intensity. Before that age, only megakaryocytes show intense staining, while liver parenchyma is only faintly stained. The developmental profile of glutamine synthetase activity shows two periods of increasing enzyme activity: one in the perinatal period and one in the second and third postnatal week. Both periods are correlated with high levels of circulating corticosteroid hormones. Although the relative number of intensely stained hepatocytes increases during the first rise in enzyme activity, the second rise is correlated with a decreasing number of glutamine synthetase-positive hepatocytes which, however, show a considerable increase in staining intensity. Carbamoylphosphate synthetase shows a homogeneous distribution pattern in the perinatal period. Conditions that lead during development to a relatively high level of glutamine synthetase expression in the pericentral compartment apparently originate before the appearance of conditions that lead to a relatively high level of carbamoylphosphate synthetase gene expression in the periportal compartment. Our results indicate that downstream localization of glutamine synthetase in liver acinus is essential from the perinatal period onwards, whereas reciprocal distribution of glutamine synthetase and carbamoylphosphate synthetase gene expression (that is found in adult rat liver) is not.

Animals↗
PubMed1986

Developmental and hormonal regulation of carbamoyl-phosphate synthase gene expression in rat liver: evidence for control mechanisms at different levels in the perinatal period.

Carbamoyl-phosphate synthase gene expression is found to be primarily regulated by conditions that enhance hepatic glucocorticosteroid levels (hormone injections) and cyclic AMP levels (induction of diabetes). After birth, changes in the level of carbamoyl-phosphate synthase protein follow changes in the level of carbamoylphosphate synthase mRNA, suggesting a pretranslational control mechanism. In fetal rats, carbamoyl-phosphate synthase gene expression is regulated by the same factors as in adults. However, both the level to which carbamoyl-phosphate synthase mRNA can accumulate and the extent to which mRNA can be translated appear to be limited, indicating control mechanisms at the pretranslational and translational level. Finally, in the immediate postnatal period, a transient but pronounced decrease in the rate of degradation of carbamoyl-phosphate synthase protein may play a role in the accumulation of the enzyme.

Adrenalectomy↗
PubMed1986

The local expression of adult chicken heart myosins during development. II. Ventricular conducting tissue.

The development of the ventricular conducting tissue of the embryonic chicken heart has been studied using a previous finding that morphologically recognizable atrial conducting tissue coexpresses the atrial and the ventricular myosin isoforms. It is found that, by these criteria, at 9 days part of the ventricular conduction system consists of a myocardial ring located around the infundibula of the aorta and truncus pulmonalis. Part of this ring is formed by the retro-aortic root branch. The ring continues via the septal branch into the atrioventricular bundle and its branches, that all express both myosin isoforms. The retro-aortic root branch could be traced back as a part of the myocardial wall of the truncus arteriosus at the 4 days embryonic stage. At the 16th day of development, the septal branch, atrioventricular bundle and left and right bundle branches no longer express the atrial isomyosin, but two bundles originating from the septal branch still express both isomyosins, one being the retro-aortic root branch, the other being only immunologically recognizable and directed to the ventral side of the truncus pulmonalis; this latter we call the pulmonary root branch. Both bundles are remnants of the myocardial ring.

Animals↗
PubMed1986

Immunological evidence for an H1(0) type of histone protein in chicken liver.

We prepared monoclonal antibodies against chicken histone H5. These antibodies could be divided into two classes, and we present the results obtained with one representative antibody of each class. One class reacted exclusively with chicken H5, whereas the other additionally cross-reacted with rat H1(0) and with material present in adult but not embryonic chicken liver. The cross-reacting material in adult liver was identified by Western blotting as representing a minor band in histone preparations. The protein was not present in histone extracts from chicken erythrocytes. It is likely that this newly identified protein is a chicken H1(0) histone.

Animals↗
PubMed1986

The cellular distribution of histone H5 in embryonic and adult tissues of Xenopus laevis and chicken.

The cellular distribution of histone H5 in embryonic and adult tissues of Xenopus laevis and chicken has been established with monoclonal antibodies to histone H5. Both in Xenopus and in chicken, the protein has presumably a more widespread cellular distribution than hitherto expected but is absent in most embryonic tissues. At least in Xenopus its presence seems not to be restricted to amitotic cells. Arguments will be put forward histone H5 in these animals should be considered as a H1(0) type of histone and that analogous to mammalian H1 degree this protein plays a role in differentiation.

Aging↗
PubMed1985

The conducting tissue in the adult chicken atria. A histological and immunohistochemical analysis.

A three-dimensional reconstruction from serial sections of adult chicken heart was made to verify whether Purkinje cells, that can be recognized by a number of well-known histological criteria, form specialized tracts in the adult chicken atria. This reconstruction revealed a loosely arranged network of Purkinje cells connecting the two atria. This network has not been described before. No tracts could be detected between the sinoatrial and the atrioventricular nodes. These atrial Purkinje cells express the atrial and ventricular myosin isoform, as determined by the use of monoclonal antibodies that were prepared against atrial and ventricular myosin isoform, respectively. Some atrial myocytes that are topographically closely related to the Purkinje cells and that cannot be distinguished from the surrounding myocytes with conventional histological criteria, express, apart from the atrial myosin isoform, also the ventricular myosin isoform. The similar expression pattern of these two cell types and their close topographical relationship suggest the presence of a more elaborate system specialized in conduction than the well-known conductive system found with conventional histological techniques.

Animals↗
PubMed1985

Immunohistochemical distribution of the histone H1(0)/H5 variant in various tissues of adult Xenopus laevis.

The cellular distribution of the histone H1(0)/H5 variant has been examined immunohistochemically in various tissues of adult Xenopus laevis, using monoclonal antibodies against this variant that was isolated from erythrocyte nuclei. The H1(0)/H5 variant appears not to be erythrocyte-specific and appears to be present in all cell types of liver, stomach, and skin. In contrast, in oocyte nuclei the H1(0)/H5 variant cannot be detected, whereas they do contain H1; the nuclei of spermatogenic cells contain the H1(0)/H5 variant, but probably less than the somatic cells. In Xenopus no H1(0) variant distinct from H5 seems to occur and the H1(0)/H5 variant apparently may perform a functional role related to mammalian H1(0).

Animals↗
PubMed1985

Development of the heterogeneous distribution of carbamoyl-phosphate synthetase (ammonia) in rat-liver parenchyma during postnatal development.

Carbamoyl-phosphate synthetase (ammonia) is homogeneously distributed in rat-liver parenchyma at birth, as demonstrated by immunohistochemistry. A heterogeneous distribution can first be demonstrated at 6 days post partum, but can be masked by use of a too sensitive detection system. This heterogeneity is established by a decrease in enzyme content around the hepatic venules and a considerable increase in enzyme content in the remaining parenchyma. The perivenous decrease in enzyme content does not occur in all hepatocytes synchronously. The adult type of heterogeneity is characterized by a perivenous layer, only two to three cells thick, in which carbamoyl-phosphate synthetase can no longer be detected, irrespective of the sensitivity of the assay used. This situation is fully established at the age of two months.

Aging↗
PubMed1984

Regulation of mRNA levels of rat liver carbamoylphosphate synthetase by glucocorticosteroids and cyclic AMP as estimated with a specific cDNA.

The construction and cloning of a cDNA complementary to the mRNA of rat liver carbamoylphosphate synthetase (ammonia) is described. Using this cDNA, the size of the mature, cytosolic carbamoylphosphate synthetase (ammonia) mRNA is estimated to be 6.0 Kb. The levels of carbamoylphosphate synthetase (ammonia) mRNA in liver are shown to be regulated by glucocorticosteroids and cyclic AMP. By studying mRNA levels of carbamoylphosphate synthetase, albumin and phosphoenolpyruvate carboxykinase, using specific cDNA clones, we show that carbamoylphosphate synthetase gene expression, like that of albumin is liver-specific.

Animals↗