Biomedical subjects

S S Tan

Publications and source records attributed to S S Tan.

At least 55 records · Page 3Linked to original sources

PubMed1995

Lineage specification of neuronal precursors in the mouse spinal cord.

We have investigated the differentiation potential of precursor cells within the developing spinal cord of mice and have shown that spinal cord cells from embryonic day 10 specifically give rise to neurons when plated onto an astrocytic monolayer, Ast-1. These neurons had the morphology of motor neurons and > 83% expressed the motor neuron markers choline acetyltransferase, peripherin, calcitonin gene-related peptide, and L-14. By comparison, < 10% of the neurons arising on monolayers of other neural cell lines or 3T3 fibroblasts had motor neuron characteristics. Cells derived from dorsal, intermediate, and ventral regions of the spinal cord all behaved similarly and gave rise to motor neuron-like cells when plated onto Ast-1. By using cells that expressed the lacZ reporter gene, it was shown that > 93% of cells present on the Ast-1 monolayers were motor neuron-like. Time-lapse analysis revealed that the precursors on the Ast-1 monolayers gave rise to neurons either directly or following a single cell division. Together, these results indicate that precursors in the murine spinal cord can be induced to differentiate into the motor neuron phenotype by factors produced by Ast-1 cells, suggesting that a similar factor(s) produced by cells akin to Ast-1 may regulate motor neuron differentiation in vivo.

Animals↗

PubMed1995

Transformation of astrocytes in transgenic mice expressing SV40 T antigen under the transcriptional control of the glial fibrillary acidic protein promoter.

There are many animal models of glioma, but few that represent the biology of low-grade tumors and allow the study of the genetic mechanisms of glial oncogenesis. We report the in vivo transformation of astrocytic cells in transgenic mice by the SV40 T antigen under the control of the 5'-flanking sequence of the murine glial fibrillary acidic protein (GFAP) gene. High levels of T antigen expression were detectable in a tissue distribution that mirrored the normal expression of GFAP. This was associated with a consistent phenotype in the founder mice. Diffuse proliferation occurred in cells of the periventricular subependymal zone with diffuse invasion into the brain parenchyma, leading to death by 19-30 days postnatally. Transformed cells exhibited secondary structuring, a typical histopathological feature of human astrocytomas. Early passage cultures of these cells expressed GFAP in vitro and were transformed on the basis of tumor formation after transplantation into nude mice. These results demonstrate the susceptibility of periventricular astrocytic cells in the immature brain to malignant transformation. Furthermore, this study demonstrates the potential of the transgenic approach for the in vivo determination of genetic events involved in astrocyte transformation and for the development of novel models of astrocytoma.

Animals↗

PubMed1995

Radial and tangential dispersion patterns in the mouse retina are cell-class specific.

The retina is derived from a pseudostratified germinal zone in which the relative position of a progenitor cell is believed to determine the position of the progeny aligned in the radial axis. Such a developmental mechanism would ensure that radial arrays of cells which comprise functional units in the mature central nervous system are also clonally related. The present study has tested this hypothesis by using X chromosome-inactivation transgenic mosaic mice. We report that the retina shows a conspicuous distinction for clonally related neuroblasts of different laminar and functional fates: the rod photoreceptor, Müller, and bipolar cells are aligned in the radial axis, whereas the cone photoreceptor, horizontal, amacrine, and ganglion cells are tangentially displaced with respect to them. These results indicate that the dispersion of cell classes across the retinal surface is differentially constrained. Some classes of retinal neuroblast exhibit a significant tangential, as well as radial, component in their dispersion from the germinal zone, whereas others disperse only in the radial dimension. Consequently, the majority of radial columns within the mature retina must be derived from multiple progenitors. Because the cone photoreceptor, horizontal, amacrine, and ganglion cells establish nonrandom matrices in their cellular distributions within the respective retinal layers, tangential dispersion may be the means by which these matrices are constructed.

Animals↗

PubMed1995

Taste receptor cells arise from local epithelium, not neurogenic ectoderm.

Except for taste bud cells, all sensory receptor cells and neurons have been shown to originate from neurogenic ectoderm (i.e., neural tube, neural crest, or ectodermal placodes). Descriptive studies on taste buds indicate that they, however, may arise from local epithelium. To determine whether taste receptor cells originate from neurogenic ectoderm or from local epithelium, the tongues of X chromosome-inactivation mosaic mice were examined. Results of this analysis show that taste bud cells and their surrounding epithelium always match in terms of the mosaic marker. This suggests that taste cells and epithelial cells arise from a common progenitor and that taste receptor cells originate from local tissue elements. Since taste buds are widespread in the oropharynx, they lie in epithelium derived from both ectoderm and endoderm. Therefore, taste receptor cells can be induced in tissue from two different germ layers. Thus in terms of tissues of origin, taste receptor cells are unlike other cells with neuronal characteristics.

Animals↗

PubMed1995

Expression of a gastric autoantigen in pancreatic islets results in non-destructive insulitis after neonatal thymectomy.

Autoimmune gastritis, induced by day-3 thymectomy of BALB/c mice, is a destructive CD4+ T cell-mediated disease characterized by leukocyte infiltrates in the gastric mucosa, loss of parietal and chief cells and anti-gastric H/K ATPase autoantibodies. Our previous studies have indicated that a T cell response to the H/K ATPase beta subunit is required for the onset of autoimmune gastritis (Alderuccio, F., Toh, B. H., Tan, S. S., Gleeson, P. A. and van Driel, I. R., J. Exp. Med. 1993. 178: 419). To determine whether a response to the beta subunit autoantigen is alone sufficient to induce autoimmunity, or whether other tissue-specific factors are required, we have generated transgenic mice expressing the gastric H/K ATPase beta subunit in beta islet cells of the pancreas (RIP-H/K beta). RIP-H/K beta mice developed autoimmune gastritis and insulitis after day-3 thymectomy. Significantly, insulitis, observed as a peri-islet infiltrate, was only detected in thymectomized mice with autoimmune gastritis. There was no apparent immune destruction of the pancreas as insulitis did not progress to invasion of the islets or diabetes. Double transgenic mice, expressing the gastric H/K ATPase beta subunit in the thymus and in the pancreas, were protected from both gastritis and insulitis after day-3 thymectomy. Therefore, insulitis in the RIP-H/K beta mice appears to be dependent on a T cell response to the H/K ATPase beta subunit. This is the first example where an organ-specific initiating autoantigen has been expressed in another peripheral tissue. Autoimmune destruction in the stomach, but not the pancreas, indicates that tissue-specific factors play a fundamental role in the development of organ-specific autoimmunity.

Animals↗

PubMed1995

Mouse endogenous X-linked genes do not show lineage-specific delayed inactivation during development.

X chromosome inactivation (XCI) has been assumed to be complete in all cells of female mouse embryos at about 6 d post coitum (dpc). However, a recent study on beta-galactosidase expression of an X-linked lacZ transgene suggests that XCI is probably not complete several days after this time in some lineages. To help resolve this issue, we analysed XCI in embryos which carry the T(X;16)16H (Searle's) translocation and are heterozygous at the X-linked Hprt and Pgk-1 genes. The quantitative RT-PCR single nucleotide primer extension (SNuPE) assay was used to measure Hprt and Pgk-1 allele-specific transcripts in embryos 9.5 dpc. No transcripts from the normal X chromosome were found in any of the tissues tested, indicating that inactivation was complete for these endogenous genes.

Alleles↗

PubMed1995

Pharmacokinetics of propofol infusion in Asian patients undergoing coronary artery bypass grafting.

The pharmacokinetics of propofol was studied in 11 Asian patients with fentanyl-isoflurane anaesthesia during cardiopulmonary bypass (CPB) and undergoing elective coronary artery bypass grafting (CABG). Instead of the usual increments of morphine and a benzodiazepine, propofol (4 mg/kg/h) was initiated at the start of CPB and ceased at CPB separation. Whole blood propofol concentrations were determined during and postinfusion using high-performance liquid chromatography with fluorescence detection. Data from four patients seemed to fit a two-compartment model, whereas those from seven patients were significantly (F test, p < 0.05) better fitted to a three-compartment model. The pharmacokinetic parameters were as follows: The mean (SD) of the initial distribution phase t1/2 pi, intermediate distribution phase t1/2 alpha, and elimination phase t1/2 beta were 2.22 (1.04) min, 42.9 (16.4) min, and 370 (138) min, respectively. The mean clearance of 1.31 (0.50) L/min was lower than those reported from other studies, whereas the mean blood concentration of 2.2 (1.0) mg/L at the 1-h infusion period was higher. The mean calculated apparent Css was 3.9 (1.5) mg/L. The low clearance is likely to be due to hemodynamic changes during CPB and CABG, thereby affecting drug distribution and blood flow to the liver.

Aged↗

PubMed1995

Renal expression of the gene encoding the gastric H(+)-K(+)-ATPase beta-subunit.

The gastric mucosal parietal cells and cells of the renal collecting duct both possess H(+)-K(+)-adenosinetriphosphatase (H(+)-K(+)-ATPase) activities. In the stomach, the H(+)-K(+)-ATPase (EC 3.6.1.3) is responsible for acidification of luminal contents. The kidney H(+)-K(+)-ATPase protein(s) contribute to potassium reabsorption and secretion of hydrogen ions to maintain potassium and acid-base homeostasis. The stomach H(+)-K(+)-ATPase is well defined and consists of an alpha-catalytic subunit of apparent molecular mass of 95 kDa and a highly glycosylated beta-subunit of 60-90 kDa. The molecular identity of the protein that mediates the H(+)-K(+)-ATPase activity in the kidney has been addressed in this paper. A combination of RNA hybridizations, polymerase chain reaction analysis of kidney RNA, and sequence analysis of cDNAs indicated that gastric H(+)-K(+)-ATPase beta-subunit mRNA is present in kidney. Immunoblotting with antibodies specific for the gastric H(+)-K(+)-ATPase beta-subunit detected proteins, which, after deglycosylation, had the same molecular mass as the gastric beta-subunit in membrane protein preparations from rabbit, pig, rat, and mouse kidneys. Furthermore, we have used transgenic mice to demonstrate that the gastric H(+)-K(+)-ATPase beta-subunit gene contains cis-acting regulatory sequences that are active in both gastric parietal cells and the renal collecting ducts. Overall, these data indicate that the gastric H(+)-K(+)-ATPase beta-subunit is found in the kidney and probably associates with the gastric H(+)-K(+)-ATPase alpha-subunit and/or other P-type ATPase alpha-subunits, thus contributing to acid-base and potassium homeostasis.

Animals↗

PubMed1995

Effect of propofol infusion on the endocrine response to cardiac surgery.

The effect of propofol infusion on the stress response was studied in patients undergoing coronary artery bypass graft (CABG). Ten patients received propofol infusion during cardiopulmonary bypass (CPB) and ten controls received diazepam. Blood levels of cortisol, adrenaline and noradrenaline were sampled. There was a significant reduction in all three hormones (P < 0.05) in the study group. In addition, the amount of sodium nitroprusside used during CPB was significantly reduced (P < 0.05).

Analgesics, Opioid↗

PubMed1995

Neuroectodermal fate of epiblast cells in the distal region of the mouse egg cylinder: implication for body plan organization during early embryogenesis.

The developmental fate of cells in the distal region (distal cap) of the epiblast was analysed by fate mapping studies. The displacement and differentiation of cells labelled in situ with carbocyanine dyes and lacZ-expressing cells grafted to the distal cap were studied over a 48-hour period of in vitro development. The distal cap epiblast differentiates predominantly into neurectodermal cells. Cells at the anterior site of the distal cap colonise the fore-, mid- and hindbrain and contribute to non-neural ectoderm cells of the amnion and craniofacial surface ectoderm. Those cells in the most distal region of the epiblast contribute to all three brain compartments as well as the spinal cord and the posterior neuropore. Cells at the posterior site of the distal cap are mainly localised to the caudal parts of the neural tube. A minor contribution to the embryonic (paraxial and lateral) and extraembryonic (allantoic and yolk sac) mesoderm is also found. Epiblast cells located outside the distal cap give rise to surface ectoderm and other non-ectodermal derivatives, with only a minor contribution to the neuroectoderm. Results of this study provide compelling evidence that the precursor population of the neural tube is contained in the distal cap epiblast of the early-primitive-streak-stage embryo. Furthermore, the regionalisation of cell fate within this small population suggest that a preliminary craniocaudal patterning may have occurred in the neural primordium before neurulation.

Animals↗

PubMed1995

Cell dispersion patterns in different cortical regions studied with an X-inactivated transgenic marker.

Inactivation of the X-linked lacZ transgene provides a novel and powerful way of distinguishing between clonally related cellular populations in X inactivation mosaics. This ability to distinguish between clonal populations of cells in the mature cortex permits inferences to be made about cellular dispersion patterns during cortical development. The present study addresses the extent to which radial and tangential dispersion patterns contribute to different regions of the cerebral cortex by quantifying the extent of cellular mixing between clonally distinct cells in separate domains of the medial, dorsolateral and lateral cortices. We show that stripes running perpendicular to the cortical layers are more likely to be seen in the medial and dorsolateral regions, and that the appearance of a stripe is attributed to about two-thirds of the cells being of the same colour. Both neurons and glia appeared to exhibit the same ratio of cell mixing. In the lateral regions of the cortex, stripes were not apparent, and cell mixing was roughly equal. In the barrel-field region of the somatosensory cortex we looked for a correspondence between cytoarchitectural features and clonal borders but found no correlation. These results demonstrate, first, that although there is widespread radial dispersion, no cortical region is composed of radially arrayed stripes of cells in which all members of a stripe are derived from a single progenitor. Second, they demonstrate that, within regions containing a sizeable fraction of cells that do migrate radially, the boundaries of individual stripes do not always coincide with single anatomical units of cortical specialization, such as individual barrels.

Animals↗

PubMed1995

Diagnosis of deep venous thrombosis: accuracy of colour doppler ultrasound compared with venography.

Doppler ultrasound is becoming increasingly accepted as an accurate, non-invasive means of imaging in suspected deep venous thrombosis (DVT). Several studies done abroad have reported (combined) sensitivity of 95% and specificity of 98%. Locally, however, we have still been relying primarily on venography to diagnose lower limb DVT. We performed a prospective study to assess the accuracy of ultrasound compared to venography, in the local context. Forty-one limbs were studied by ultrasound within 24 hours of a venogram examination. We assessed grey-scale appearance, compressibility, presence or absence of flow, and flow characteristics. Seventeen venograms were positive for DVT, and ultrasound was positive in all seventeen cases. There were two false positive ultrasound examinations. Two cases of small localised thrombi in the superficial femoral vein only were accurately detected by ultrasound. One case of isolated calf thrombosis was also successfully diagnosed. Overall, sensitivity and specificity for detection of lower limb DVT was 100% and 91.7% respectively. Overall accuracy was 95.1%.

Adult↗

PubMed1994

The engraftment of transplanted primary neuroepithelial cells within the postnatal mouse brain.

Primary neuroepithelial precursor cells carrying the reporter gene lacZ were transplanted into postnatal murine brain and assessed for their engraftment capacity. Freshly dissected precursors, derived from lacZ transgenic embryonic day 10 mouse brain, predominantly engrafted as discrete clusters, whereas the same precursors cultured in vitro with fibroblast growth factor-2, engrafted as single cells within the parenchyma of the hippocampus. Approximately 0.5% of the transplanted cells survived in the host brain for up to 3 months. Many of these cells displayed neuronal and astrocyte morphologies. These observations suggest that transplanted primary precursors derived from the embryonic brain can engraft and commit in situ to a variety of developmental fates.

Animals↗

PubMed1994

Simultaneous detection of beta-galactosidase activity and surface antigen expression in viable haematopoietic cells.

The quantitation of intracellular beta-galactosidase activity has been described for viable cells. By using the fluorogenic substrate fluorescein-di-beta-D-galactopyranoside (FDG) in conjunction with flow cytometry, the proportion of positive cells as well as the level of expression can be determined. In this paper we describe beta-galactosidase expression in lymphoid and myeloid cells from transgenic mice that widely express beta-galactosidase from an inserted lacZ transgene. Both foetal and adult haematopoietic tissues are able to express beta-galactosidase. The intracellular fluorescence reflecting beta-galactosidase activity can be readily combined with fluorescently labelled antibodies against cell surface antigens. Thus, beta-galactosidase can be used as a marker in transplantation experiments to study the development of lymphoid and myeloid precursor cells.

Animals↗

PubMed1994

Expression of an X-linked HMG-lacZ transgene in mouse embryos: implication of chromosomal imprinting and lineage-specific X-chromosome activity.

X-chromosome activity in female mouse embryos was studied at the cellular level using an X-linked lacZ transgene which encodes beta-galactosidase (beta-Gal). Translation of maternal RNA in oocytes is seen as beta-Gal activity that persists into early cleavage-stages. Zygotic transcription of the transgene from the maternal X chromosome (Xm) is first found at about the 8-cell stage. By contrast, expression of the lacZ transgene on the paternal X chromosome (Xp) is not seen until later at the 16-32-cell stage. Preferential inactivation of Xp occurs in the mural trophectoderm, the primitive endoderm, and derivatives of the polar trophectoderm, but a small number of cells in these lineages may still retain an active paternal X chromosome. X inactivation begins at 3.5 days in the inner cell mass but contrary to previous findings the process is not completed in the embryonic ectoderm by 5.5 to 6.0 days. Regional variation in beta-Gal activity is also observed in the embryonic ectoderm during gastrulation which may be related to the specification of cell fates. Random inactivation of Xp and Xm ensues in all somatic tissues but the process is completed at different times in different tissues. The slower progression of X inactivation in tissues such as the notochord, the heart, and the embryonic gut is primarily due to the persistent maintenance of two active X chromosomes in a significant fraction of cells in these tissues. Recent findings on the methylation of endogenous X-linked genes suggest that the prolonged expression of beta-Gal might also be due to the different rate of spreading of inactivation along the X chromosome to the lacZ transgene locus in different tissues.

Animals↗

PubMed1994

X-chromosome activity of the mouse primordial germ cells revealed by the expression of an X-linked lacZ transgene.

We have determined the timing of the inactivation and reactivation of the X chromosome in the mouse primordial germ cells (PGCs) by monitoring the expression of an X-linked HMG-lacZ reporter gene. PGCs were identified by their distinct alkaline phosphatase activity and they were first localised in the primitive streak and allantoic bud of the 7.5-day gastrulating embryo. Although inactivation of the transgene was found in some PGCs at these sites, at least 85% of the population were still expressing the lacZ gene. This suggests that, although X-inactivation has commenced during gastrulation, the majority of PGCs still possess two active X chromosomes. Transgene activity remained unchanged during the relocation of PGCs to the hindgut endoderm, but decreased abruptly when PGCs left the hindgut and migrated through the mesentery. X-inactivation was completed during the migration of PGCs, but not simultaneously for the whole population. The first wave of PGCs entering the genital ridge at 9.5 days did not immediately re-activate the silent transgene until about 24 hours later. Re-activation of the transgene took place in over 80% of PGCs entering the genital ridge at 10.5-13.5 days p.c., preceding the entry into meiosis. About 90% of the meiotic germ cells in the 14.5-15.5 day fetal ovary expressed the transgene. Similar profiles of transgene activity were observed in PGCs of embryos that have inherited the lacZ transgene from different parents, showing unequivocally that X-inactivation in the germ cell lineage is not related to parental legacy.(ABSTRACT TRUNCATED AT 250 WORDS)

Alkaline Phosphatase↗

PubMed1994

Cranial paraxial mesoderm: regionalisation of cell fate and impact on craniofacial development in mouse embryos.

A combination of micromanipulative cell grafting and fluorescent cell labelling techniques were used to examine the developmental fate of the cranial paraxial mesoderm of the 8.5-day early-somite-stage mouse embryo. Mesodermal cells isolated from seven regions of the cranial mesoderm, identified on the basis of their topographical association with specific brain segments were assessed for their contribution to craniofacial morphogenesis during 48 hours of in vitro development. The results demonstrate extensive cell mixing between adjacent but not alternate groups of mesodermal cells and a strict cranial-to-caudal distribution of the paraxial mesoderm to craniofacial structures. A two-segment periodicity similar to the origins of the branchial motor neurons and the distribution of the rhombencephalic neural crest cells was observed as the paraxial mesoderm migrates during formation of the first three branchial arches. The paraxial mesoderm colonises the mesenchymal core of the branchial arches, consistent with the location of the muscle plates. A dorsoventral regionalisation of cell fate similar to that of the somitic mesoderm is also found. This suggests evolution has conserved the fate of the murine cranial paraxial mesoderm as a multiprogenitor population which displays a predominantly myogenic fate. Heterotopic transplantation of cells to different regions of the cranial mesoderm revealed no discernible restriction in cell potency in the craniocaudal axis, reflecting considerable plasticity in the developmental fate of the cranial mesoderm at least at the time of experimentation. The distribution of the different groups of cranial mesoderm matches closely with that of the cranial neural crest cells suggesting the two cell populations may share a common segmental origin and similar destination.

Animals↗

PubMed1993

An autoimmune disease with multiple molecular targets abrogated by the transgenic expression of a single autoantigen in the thymus.

Many autoimmune diseases are characterized by autoantibody reactivities to multiple cellular antigens. Autoantigens are commonly defined as targets of the autoimmune B cell response, but the role, if any, of these autoantigens in T cell-mediated autoimmune diseases is generally unknown. Murine experimental autoimmune gastritis is a CD4+ T cell-mediated organ-specific autoimmune disease induced by neonatal thymectomy of BALB/c mice. The murine disease is similar to human autoimmune gastritis and pernicious anemia, and is characterized by parietal and chief cell loss, submucosal mononuclear cell infiltrates, and autoantibodies to the alpha and beta subunits of the gastric H/K ATPase. However, the specificity of T cells that cause the disease is not known. To examine the role of the H/K ATPase in this T cell-mediated disease, transgenic mice were generated that express the beta subunit of the H/K ATPase under the control of the major histocompatibility complex class II I-Ek alpha promoter. We show that transgenic expression of the gastric H/K ATPase beta subunit specifically prevents the onset of autoimmune gastritis after neonatal thymectomy. In addition, thymocyte transfer experiments suggest that tolerance of pathogenic autoreactive T cells is induced within the thymus of the transgenic mice. We conclude that the beta subunit of the gastric H/K ATPase is a major T cell target in autoimmune gastritis and that thymic expression of a single autoantigen can abrogate an autoimmune response to multiple autoantigens.

Animals↗