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Biomedical subjects

A F Moorman

Publications and source records attributed to A F Moorman.

At least 55 records · Page 3Linked to original sources
PubMed1999

Expression pattern of glutamine synthetase marks transition from collecting into conducting hepatic veins.

The expression of glutamine synthetase (GS) is confined to a rim of hepatocytes surrounding the efferent hepatic veins in all mammalian species investigated. In rat liver, a two- to three-cell thick layer of GS-positive (GS(+)) hepatocytes uniformly surrounds the two to four terminal branching generations of the hepatic vein that collect blood from sinusoids (central veins). With increasing diameter of the efferent vessel, this multilayered rim of GS(+) hepatocytes becomes confined to patches surrounding the decreasing number of central vein outlets. The remaining part of the wall of these sublobar hepatic veins is bordered by a one-cell thick layer of GS(+) hepatocytes. Around still larger veins, this single-cell layer of GS(+) hepatocytes gradually disappears. The expression pattern of GS is therefore a convenient biological parameter to delimit sinusoidal draining ("collecting") from nondraining ("conducting") surfaces in the wall of the efferent hepatic vessels. The hepatocytes surrounding a single tree of central veins together form a compound liver lobule. (J Histochem Cytochem 47:1507-1511, 1999)

Animals↗
PubMed1998

Sox4-deficiency syndrome in mice is an animal model for common trunk.

Embryonic mice lacking functional Sox4 transcription factor die from cardiac failure at embryonic day (ED) 14. Heart morphogenesis in these embryos was analyzed in hematoxylin-azophlochsin or immunohistochemically stained, 3-dimensionally reconstructed serial sections between ED12 and ED14. Although Sox4 is expressed in the endocardially derived tissue of both the outflow tract and atrioventricular canal, Sox4-deficient hearts only suffer from defective transformation of the endocardial ridges into semilunar valves and from lack of fusion of these ridges, usually resulting in common trunk, although the least affected hearts should be classified as having a large infundibular septal defect. The more serious cases are, in addition, characterized by an abnormal number and position of the semilunar valve-leaflet anlagen, a configuration of the ridges typical for transposition of the great arteries (with linear rather than spiral course of both ridges and posterior position of the pulmonary trunk at the level of the valve), and variable size of the aorta relative to the pulmonary trunk. The coronary arteries always originated from the aorta, irrespective of its position relative to the pulmonary trunk. The restriction of the malformations to the arterial pole implies that the interaction between the endocardially derived tissue of the outflow tract and the neural crest-derived myofibroblasts determines proper development of the arterial pole.

Actins↗
PubMed1998

Normal development of the outflow tract in the rat.

The outflow tract (OFT) provides the structural components forming the ventriculoarterial connection. The prevailing concept that this junction "rotates" to acquire its definitive topography also requires a concept of "counterrotation" and is difficult to reconcile with cell-marking studies. Rats between 10 embryonic days (EDs) and 2 postnatal days were stained immunohistochemically and by in situ hybridization. DNA replication was determined by incorporation of bromodeoxyuridine and apoptosis by the annexin V binding and terminal deoxynucleotidyl transferase-mediated dUTP-X nick end labeling (TUNEL) assays. Starting at ED12, cardiomyocytes in the distal (truncal) part of the OFT begin to shed their myocardial phenotype without proceeding into apoptosis, suggesting transdifferentiation. Myocardial regression is most pronounced on the dextroposterior side and continues until after birth, as revealed by the disappearance of the myocardial cuff surrounding the coronary roots and semilunar sinuses and by the establishment of fibrous continuity between mitral and aortic semilunar valves. Fusion of the endocardial ridges of the truncus on late ED13 is accompanied by the organization of alpha-smooth muscle actin-and nonmuscle myosin heavy chain-positive myofibroblasts into a central whorl and the appearance of the semilunar valve anlagen at their definitive topographical position within the proximal portion of the truncus. After fusion of the proximal (conal) portion of the endocardial ridges, many of the resident myofibroblasts undergo apoptosis and are replaced by cardiomyocytes. The distal myocardial boundary of the OFT is not a stable landmark but moves proximally over the spiraling course of the aortic and pulmonary routes, so that the semilunar valves develop at their definitive topographic position. After septation, the distal boundary of the OFT continues to regress, particularly in its subaortic portion. The myocardializing conus septum, on the other hand, becomes largely incorporated into the right ventricle. These opposite developments account for the pronounced asymmetry of the subaortic and subpulmonary outlets in the formed heart.

Actins↗
PubMed1998

Age-dependent changes in myosin composition correlate with enhanced economy of contraction in guinea-pig hearts.

1. The composition of myosin heavy chains (MHCs) was investigated in young (1- to 8-week-old) and mature (9- to 26-week-old) guinea-pigs using two monoclonal antibodies directed specifically against alpha-MHC and beta-MHC. In addition, maximum force and the rate of ATP consumption during isometric contraction were measured in chemically skinned trabeculae taken from the same hearts. 2. An age-dependent shift in the MHC composition was found. The alpha-MHC fraction decreased from 0.17 +/- 0.02 (mean +/- S.E.M.; n = 24) in young to 0.04 +/- 0.01 (n = 43) in mature hearts. This shift was correlated with a decrease in tension cost (i.e. ATP consumption per second per trabecula volume/force per cross-sectional area) from 4.1 +/- 0.2 mmol kN-1 m-1 s-1 (n = 23) in young to 2.5 +/- 0.1 mmol kN-1 m-1 s-1 (n = 57) in mature hearts. 3. From the results it follows that the slow beta-MHC isoform, which predominates in hearts of mature guinea-pigs, is about 5 times more economical than the fast alpha-MHC isoform. Calcium sensitivity of force and ATP consumption decreased with age, but stabilized within a few weeks after birth. The pronounced dependence of cardiac energetics on MHC composition should be taken into account in long-term studies of cardiac overload.

Adenosine Triphosphatases↗
PubMed1998

Heart defects in connexin43-deficient mice.

Cardiac malformation in connexin43 (CX43)-disrupted mice is restricted to the junction between right ventricle and outflow tract, even though CX43 is also expressed abundantly elsewhere. We analyzed cardiac morphogenesis in immunohistochemically and hybridohistochemically stained and three-dimensionally reconstructed serial sections of CX43-deficient embryos between embryonic day (ED) 10 and birth. The establishment of the D configuration in the ascending loop of CX43-deficient hearts is markedly retarded, so that the right ventricle retains a craniomedial position and is connected with the outflow tract by a more acute bend in ED10 and ED11 embryos. Because of the subsequent growth of the right ventricle, this condition usually evolves into a D loop, but when it persists, a "crisscross" configuration develops, with the atrioventricular cushions rotated 90 degrees, a horizontal muscular ventricular septum, and a parallel course of the endocardial ridges of the outflow tract. After ED12, large intertrabecular pouches develop at the ventricular side of both shelflike myocardial structures that support the endocardial ridges of the outflow tract, ie, at the location that was earlier characterized by the acute bend between the right ventricle and the outflow tract and that subsequently develops into the anterosuperior leaflet of the tricuspid valve. Retarded development of the D configuration in the ascending loop of the embryonic heart predisposes the myocardium at the junction of the right ventricle and outflow tract to excessive development of intertrabecular pouches during subsequent development.

Animals↗
PubMed1998

Changing patterns of gene expression in the pulmonary trunk-banded rat heart.

A pressure-overload model in the rat by banding the pulmonary trunk (PT) was developed to investigate alterations in gene expression in left- and right-ventricular compartments during the transition from compensated right-ventricular (RV) hypertrophy to right heart failure. Right heart failure in rat is characterized by liver cirrhosis, hydrothorax and ascites. The diameter of constriction was found to determine the time course of heart failure development. Only the RV free wall and the right atrium increased in weight, without a difference between compensated and failing RV. An increase in circulating ANP revealed a hypertrophic response of the myocardium, while increased circulating ammonia levels discriminated between compensated hypertrophy and failure. As parameters for stress, fibrosis and Ca2+-handling, changes in the pattern and level of the mRNAs encoding atrial natriuretic peptide (ANP), collagenIIIalpha1, and sarcoplasmic endoplasmic reticular calcium ATPase 2 (SERCA2), phospholamban (PLB) and calsequestrin (CSQ) were studied by Northern blot and in situ hybridization analyses. Pulmonary trunk banding resulted in an induction of ANP mRNA, a moderate increase in collagenIII alpha1 mRNA and a decrease in SERCA2 and PLB mRNA levels in both the left and right ventricles, but changes were most pronounced in the myocardium surrounding the RV cavity. Increased ammonia blood levels are a promising prognostic marker to detect the development of right heart failure.

Ammonia↗
PubMed1998

Expressional analysis of the cardiac Na-Ca exchanger in rat development and senescence.

The cardiac Na-Ca exchanger (NCX) serves as the main calcium extrusion mechanism in heart muscle and is important in maintaining intracellular calcium homeostasis. The accumulations of NCX RNA and protein are known to be regulated in cardiac hypertrophy, by thyroid hormone and during postnatal development. In this study the temporal and spatial patterns of NCX mRNA and protein accumulations were examined, and nuclear run-on assays performed. NCX is highly expressed in late fetal and neonatal rat hearts, decreasing to adult levels by 20 days after birth for RNA (P < 0.05, fetal and 1 neonatal day old (1 ND) versus 20 day old (20 ND)). Maximal protein expression is seen in 19 embryonic day (ED) old hearts, and reaches adult levels sometime after 20 neonatal days. (P < 0.05, fetal versus adult). Spatially, NCX is homogenously expressed in early embryonic and fetal heart, followed by a decline after birth. The protein levels decline more slowly suggesting a long protein half-life. The lowest level of mRNA accumulation is seen in 6 and 18 month old animals (P < 0.05 for all time points before 10 neonatal days). In the 24 month old senescent rat, NCX transcripts are increased by almost 50% above that seen at 6 and 18 months (P < 0.05) but are not different from those at 15 neonatal days. Perinatal NCX expression is regulated transcriptionally: late fetal and neonatal hearts have high transcriptional activity but by 20 postnatal days, no detectable transcriptional activity can be demonstrated. Throughout development, at least five transcription start sites are used, and no significant difference in the 5' untranslated or 3' coding splice sites could be demonstrated, although several new cardiac splicing variants were identified. We also report the cloning of a 3.7 kb fragment containing the cardiac NCX1 promoter which is transcriptionally active in neonatal cardiomyocytes.

Aging↗
PubMed1998

Regulation of the spatiotemporal pattern of expression of the glutamine synthetase gene.

Glutamine synthetase, the enzyme that catalyzes the ATP-dependent conversion of glutamate and ammonia into glutamine, is expressed in a tissue-specific and developmentally controlled manner. The first part of this review focuses on its spatiotemporal pattern of expression, the factors that regulate its levels under (patho)physiological conditions, and its role in glutamine, glutamate, and ammonia metabolism in mammals. Glutamine synthetase protein stability is more than 10-fold reduced by its product glutamine and by covalent modifications. During late fetal development, translational efficiency increases more than 10-fold. Glutamine synthetase mRNA stability is negatively affected by cAMP, whereas glucocorticoids, growth hormone, insulin (all positive), and cAMP (negative) regulate its rate of transcription. The signal transduction pathways by which these factors may regulate the expression of glutamine synthetase are briefly discussed. The second part of the review focuses on the evolution, structure, and transcriptional regulation of the glutamine synthetase gene in rat and chicken. Two enhancers (at -6.5 and -2.5 kb) were identified in the upstream region and two enhancers (between +156 and +857 bp) in the first intron of the rat glutamine synthetase gene. In addition, sequence analysis suggests a regulatory role for regions in the 3' untranslated region of the gene. The immediate-upstream region of the chicken glutamine synthetase gene is responsible for its cell-specific expression, whereas the glucocorticoid-induced developmental appearance in the neural retina is governed by its far-upstream region.

Aging↗
PubMed1998

WHSC1, a 90 kb SET domain-containing gene, expressed in early development and homologous to a Drosophila dysmorphy gene maps in the Wolf-Hirschhorn syndrome critical region and is fused to IgH in t(4;14) multiple myeloma.

Wolf-Hirschhorn syndrome (WHS) is a malformation syndrome associated with a hemizygous deletion of the distal short arm of chromosome 4 (4p16.3). The smallest region of overlap between WHS patients, the WHS critical region, has been confined to 165 kb, of which the complete sequence is known. We have identified and studied a 90 kb gene, designated as WHSC1 , mapping to the 165 kb WHS critical region. This 25 exon gene is expressed ubiquitously in early development and undergoes complex alternative splicing and differential polyadenylation. It encodes a 136 kDa protein containing four domains present in other developmental proteins: a PWWP domain, an HMG box, a SET domain also found in the Drosophila dysmorphy gene ash -encoded protein, and a PHD-type zinc finger. It is expressed preferentially in rapidly growing embryonic tissues, in a pattern corresponding to affected organs in WHS patients. The nature of the protein motifs, the expression pattern and its mapping to the critical region led us to propose WHSC1 as a good candidate gene to be responsible for many of the phenotypic features of WHS. Finally, as a serendipitous finding, of the t(4;14) (p16.3;q32.3) translocations recently described in multiple myelomas, at least three breakpoints merge the IgH and WHSC1 genes, potentially causing fusion proteins replacing WHSC1 exons 1-4 by the IgH 5'-VDJ moiety.

Amino Acid Sequence↗
PubMed1998

Arginine-metabolizing enzymes in the developing rat small intestine.

Before weaning, arginine biosynthesis from citrulline most likely takes place in the small intestine rather than in the kidney. We studied the expression of ornithine cycle enzymes in the rat small intestine during perinatal development. The spatiotemporal patterns of expression of ornithine aminotransferase, carbamoylphosphate synthetase, ornithine transcarbamoylase, argininosuccinate synthetase, argininosuccinate lyase, and arginase mRNAs were studied by Northern blot analysis and in situ hybridization. In addition, the expression of carbamoylphosphate synthetase and argininosuccinate synthetase protein was studied by immunohistochemistry. Before birth, the developmentally more mature proximal loops of the intestine expressed the mRNAs at higher concentrations than the more distal loops. After birth, this difference was no longer obvious. The mRNAs of argininosuccinate synthetase and argininosuccinate lyase, the enzymes that metabolize citrulline to arginine, were detectable only in the upper part of the villi, whereas the other mRNAs were concentrated in the crypts. The distribution of argininosuccinate synthetase protein corresponded with that of the mRNA, whereas carbamoylphosphate synthetase protein was present in all enterocytes of the crypts and villi. Hepatic arginase mRNA could not be detected in the enterocytes. The spatial distribution of the respective mRNAs and proteins along the villus axis of the suckling small intestine indicates that the basal enterocytes synthesize citrulline, whereas the enterocytes in the upper half of the villus synthesize arginine.

Animals↗
PubMed1997

Developmental appearance of ammonia-metabolizing enzymes in prenatal murine liver.

To resolve an apparent discrepancy in the developmental appearance of glutamine synthetase (GS) protein in rat [Gaasbeek Janzen et al. (1987) J. Histochem, Cytochem., 35:49-54] and mouse [Bennett et al. (1987) J. Cell Biol., 105:1073-1085] liver, we have investigated its expression during liver development in the mouse and compared it with that of carbamoylphosphate synthetase I (CPS). The expression of glutamate dehydrogenase was used as a marker to identify all hepatocytes in these strongly hematopoietic livers. GS protein accumulation starts in mouse hepatocytes at embryonic day (ED) 15. The first hepatocytes in which the enzyme accumulates were found around the major hepatic veins. CPS protein was found to accumulate in mouse hepatocytes from ED 13 onward: first, at the center of the median and lateral lobes, but temporarily not at the periphery of these lobes and not at the caudate lobe. The initial phase of accumulation of GS and CPS protein was characterized by a heterogeneity in enzyme content between hepatocytes. By ED 17, both enzymes were detectable in all hepatocytes at the center of the median and lateral lobes. This event marked the onset of the development of the complementary distribution of the enzymes typical of zonal heterogeneity in the adult mammalian liver. However, during the perinatal period, the pericentral hepatocytes temporarily accumulated CPS protein. We also observed heterochrony between species in the appearance of CPS protein in the small intestine.

Ammonia↗
PubMed1997

Organ-specific activity of the 5' regulatory region of the glutamine synthetase gene in developing mice.

Glutamine synthetase (GS) converts ammonia and glutamate into glutamine. We assessed the activity of the 5' regulatory region of the GS gene in developing transgenic mice carrying the chloramphenicol acetyltransferase (CAT) gene under the control of 3150 bp of the upstream sequence of the rat GS gene to obtain insight into the spatiotemporal regulation of its pattern of expression. To determine the organ-specific activity of the 5' regulatory region CAT and GS mRNA expression were compared by ribonuclease-protection and semi-quantitative in situ hybridization analyses. Three patterns were observed: the 5' region is active and involved in the regulation of GS expression throughout development (pericentral hepatocytes, intestines and epididymis); the 5' region shows no activity at any of the ages investigated (periportal hepatocytes and white adipose tissue); and the activity of the 5' region becomes repressed during development (stomach, muscle, brown adipose tissue, kidney, lung and testis). In the second group, an additional element must be responsible for the activation of GS expression. The last group included organs in which the 5' regulatory region is active, but not in the cells that express GS. In these organs, the activity of the 5' regulatory region must be repressed by other regulatory regions of the GS gene that are missing from the transgenic construct. These findings indicate that in addition to the 5' regulatory region, at least two unidentified elements are involved in the spatiotemporal pattern of expression of GS.

Adipose Tissue↗
PubMed1997

Regionalized transcriptional domains of myosin light chain 3f transgenes in the embryonic mouse heart: morphogenetic implications.

Within the embryonic heart, five segments can be distinguished: two fast-conducting atrial and ventricular compartments flanked by slow-conducting segments, the inflow tract, the atrioventricular canal, and the outflow tract. These compartments assume morphological identity as a result of looping of the linear heart tube. Subsequently, the formation of interatrial, interventricular, and outflow tract septa generates a four-chambered heart. The lack of markers that distinguish right and left compartments within the heart has prevented a precise understanding of these processes. Transgenic mice carrying an nlacZ reporter gene under transcriptional control of regulatory sequences from the MLC1F/3F gene provide specific markers to investigate such regionalization. Our results show that transgene expression is restricted to distinct regions of the myocardium: beta-galactosidase activity in 3F-nlacZ-2E mice is confined predominantly to the embryonic right atrium, atrioventricular canal, and left ventricle, whereas, in 3F-nlacZ-9 mice, the transgene is expressed in both atrial and ventricular segments (right/left) and in the atrioventricular canal, but not in the inflow and outflow tracts. These lines of mice illustrate that distinct embryonic cardiac regions have different transcriptional specificities and provide early markers of myocardial subdivisions. Regional differences in transgene expression are not detected in the linear heart tube but become apparent as the heart begins to loop. Subsequent regionalization of transgene expression provides new insights into later morphogenetic events, including the development of the atrioventricular canal and the fate of the outflow tract.

Animals↗
PubMed1997

Role of the 5' enhancer of the glutamine synthetase gene in its organ-specific expression.

In mammals, glutamine synthetase (GS) is expressed in a large number of organs, but the precise regulation of its expression is still obscure. Therefore a detailed analysis of the activity of the upstream regulatory element of the GS gene in the transcriptional regulation of its expression was carried out in transgenic mice carrying the chloramphenicol acetyltransferase (CAT) gene under the control of the upstream regulatory region of the GS gene. CAT and GS mRNA expression were compared in liver, epididymis, lung, adipocytes, testis, kidney, skeletal muscle and gastrointestinal tract, both quantitatively by ribonuclease-protection analysis and topographically by in situ hybridization. It was found that the upstream regulatory region is active with respect both to the level and to the topography of GS gene expression in liver, epididymis, gastrointestinal tract (stomach, small intestine and colon) and skeletal muscle. On the other hand, in the kidney, brain, adipocytes, spleen, lung and testis, GS gene expression is not or only partly regulated by the 5' enhancer. A second enhancer, identified within the first intron, may regulate GS expression in the latter organs. Furthermore, CAT expression in the brain did not co-localize with that of GS, showing that the 5' regulatory region of the GS gene does not direct its expression to the astrocytes.

Adipose Tissue↗
PubMed1997

Expression of the cholinergic signal-transduction pathway components during embryonic rat heart development.

BACKGROUND: Previous studies showed that acetylcholinesterase (AChE) activity is present in the downstream (arterial) part of the embryonic chick and rat heart, but its functional significance was unclear. To establish whether other components of a cholinergic signal-transduction pathway are present in the embryonic heart, we localised the mRNAs encoding choline acetyltransferase (ChAT), acetylcholinesterase (AChE), and the muscarinic receptor isoforms (mAChRs; m1-m5). METHODS: Messenger RNA detection and localisation by in situ hybridisation and reverse transcriptase-polymerase chain reaction were employed. RESULTS: Expression of ChAT and AChE mRNAs was observed from 15 embryonic days onward in the neural tissue covering the dorsocranial wall of the atria. Muscarinic receptors (m1, m2, m4) were observed at the same localisation as AChE and ChAT mRNAs, both during embryogenesis and after birth. In addition, m1 and m4 mAChRs showed a low level of expression in the atrial myocardium during the fetal period. No expression of the m3 or the m5 mAChRs was observed in or near the embryonic hearts. ChAT, AChE, and mAChRs (m1, m2, m4) mRNAs always colocalised in the cardiac ganglia. However, none of these mRNAs was found at a detectable level in the outflow tract and/or the ventricular trabeculations. CONCLUSIONS: The AChE activity in the arterial part of the embryonic heart is probably synthesised elsewhere and subserves a function different from the hydrolysis of locally produced acetylcholine.

Acetylcholinesterase↗