Biomedical subjects

H Marshall

Publications and source records attributed to H Marshall.

At least 55 records · Page 3Linked to original sources

PubMed1996

Segmental expression of Hoxa-2 in the hindbrain is directly regulated by Krox-20.

The hindbrain is a segmented structure divided into repeating metameric units termed rhombomeres (r). The Hox family, vertebrate homologs of the Drosophila HOM-C homeotic selector genes, are expressed in rhombomere-restricted patterns and are believed to participate in regulating segmental identities. Krox-20, a zinc finger gene, has a highly conserved pattern of expression in r3 and r5 and is functionally required for their maintenance in mouse embryos. Krox-20 has been shown to directly regulate the Hoxb-2 gene and we wanted to determine if it was involved in regulating multiple Hox genes as a part of its functional role. Hoxa-2 is the only known paralog of Hoxb-2, and we examined the patterns of expression of the mouse Hoxa-2 gene with particular focus on r3 and r5 in wild type and Krox-20-/- mutant embryos. There was a clear loss of expression in r3, which indicated that Hoxa-2 was downstream of Krox-20. Using transgenic analysis with E. coli lacZ reporter genes we have identified and mapped an r3/r5 enhancer in the 5' flanking region of the Hoxa-2 gene. Deletion analysis narrowed this region to an 809 bp Bg/II fragment, and in vitro binding and competition assays with bacterially expressed Krox-20 protein identified two sites within the enhancer. Mutation of these Krox-20 sites in the regulatory region specifically abolished r3/r5 activity, but did not affect neural crest and mesodermal components. This indicated that the two Krox-20 sites are required in vivo for enhancer function. Furthermore, ectopic expression of Krox-20 in r4 was able to transactivate the Hoxa 2/lacZ reporter in this rhombomere. Together our findings suggest that Krox-20 directly participates in the transcriptional regulation of Hoxa-2 during hindbrain segmentation, and is responsible for the upregulation of the r3 and r5 domains of expression of both vertebrate group 2 Hox paralogs. Therefore, the segmental phenotypes in the Krox-20 mutants are likely to reflect the role of Krox-20 in directly regulating multiple Hox genes.

Animals↗

PubMed1996

Retinoids and Hox genes.

The vertebrate embryonic body plan is constructed through the interaction of many developmentally regulated genes that supply cells with the essential positional and functional information they require to migrate to their appropriate destination and generate the proper structures. Some molecular cues involved in patterning the central nervous system, particularly in the hindbrain, are interpreted by the Hox homeobox genes. Retinoids can affect the expression of Hox genes in cells lines and embryonic tissues; the hindbrain and branchial region of the head are particularly sensitive to the teratogenic effects of retinoic acid. The presence of endogenous retinoic acid, together with the distribution of retinoid binding proteins and nuclear receptors in the developing embryo, strongly suggest that retinoic acid is a natural morphogen in vertebrate development. The molecular basis for the interaction between retinoic acid and the Hox genes has been aided in part by approaches using deletion analysis in transgenic mice carrying lacZ reporter constructs. Such studies have identified functional retinoic acid response elements within flanking sequences of some of the most 3' Hox genes, suggesting a direct interaction between the genes and retinoic acid. Furthermore, as demonstrated using transgenic mice carrying Hoxb-1/lacZ constructs, multiple retinoic acid response elements may cooperate with positive and negative regulatory enhancers to specify pattern formation in the vertebrate embryo. These types of studies strongly support the normal roles of retinoids in patterning vertebrate embryogenesis through the Hox genes.

Animals↗

PubMed1995

The ideas and experiences of pregnancy and childbirth of Asian and non-Asian women in east London.

This study examined differences between the ideas and experiences of pregnancy and childbirth of Asian and non-Asian women giving birth in East London, and sources of variability in Asian women's accounts. In line with the findings of previous research, Asian women's ideas about diet in pregnancy, the gender of their children and postnatal care (e.g. the need for rest and recovery, and restrictions on their activities) were influenced by cultural beliefs and practices. However, in other ways Asian women demonstrated a strong commitment to Western maternity care. In contrast to some other studies Asian women wanted their husbands or partners present at delivery, indicating the extent to which traditional ideas are being modified. Qualitative analysis of Asian women's fuller accounts indicated that women subscribed to traditional practice as well as Western maternity care. Acculturation or familiarity with Western ideas about maternity care was associated with variability in Asian women's ideas and experiences, in line with previous research. However, in spite of frequent assumptions about its significance, religion was not associated with variability in Asian women's ideas and experiences. Parity, however, was a major variable, for Asian and for non-Asian women, suggesting that the first birth has different significance for parents than subsequent births. The implications for the provision of maternity care are discussed, especially the need to go beyond stereotypical views based on women's ethnicity or religion to consider the beliefs and preferences of women as individuals and their personal circumstances.

Adolescent↗

PubMed1995

Medicaid costs of live births from unintended pregnancies in Florida.

The Florida Pregnancy Risk Assessment Monitoring System (PRAMS) survey, a population-based, random sample mail-telephone query of new mothers of live-born infants, includes questions about pregnancy timing and wantedness, sources of payment for care, other related topics, mother's risk behaviors, satisfaction with prenatal care, and the newborn's health. There were 2,059 completed responses in 1993. Results are weighted for factors affecting response rates to reflect all births. An estimated 13.8% (95% confidence interval 11.7, 15.9) of all Florida babies in 1993 were unwanted at conception, and 20.3% (16.5, 24.1) of those whose deliveries were paid for by Medicaid were unwanted. The Medicaid program currently pays for the prenatal, intrapartum, delivery and infant health care of an estimated 16,000 pregnancies and newborns each year that were unwanted at conception. The total annual cost is estimated at $401 million, or over 8% of all 1992-93 Medicaid costs.

Adolescent↗

PubMed1994

Role of a conserved retinoic acid response element in rhombomere restriction of Hoxb-1.

After activation in mesoderm and neuroectoderm, expression of the Hoxb-1 gene is progressively restricted to rhombomere (r) 4 in the hindbrain. Analysis of the chick and mouse Hoxb-1 genes identified positive and negative regulatory regions that cooperate to mediate segment-restricted expression during rhombomere formation. An enhancer generates expression extending into r3 and r5, and a repressor limits this domain to r4. The repressor contains a conserved retinoic acid response element, point mutations in which allow expression to spread into adjacent rhombomeres. Retinoids and their nuclear receptors may therefore participate in sharpening segment-restricted expression of Hoxb-1 during rhombomere boundary formation.

Animals↗

PubMed1994

A conserved retinoic acid response element required for early expression of the homeobox gene Hoxb-1.

Within the Hoxb homeobox gene complex, Hoxb-1 is the earliest member expressed in the mesoderm and neuroectoderm of primitive streak and presomite embryos, preceding rhombomere-restricted expression in the hindbrain. Ectopic exposure of embryos to retinoic acid alters spatial aspects of Hox gene expression patterns. However, the role of retinoids in regulating these genes during normal development is unclear. We have now identified two enhancers, 3' of the mouse Hoxb-1 gene, which together reconstruct the early endogenous expression pattern and mediate the early ectopic response to retinoic acid. Furthermore, these regions are functionally conserved in both chicken and pufferfish (Fugu rubripes) Hoxb-1 genes. The enhancer that controls the retinoic acid response, and regulates expression predominantly in neuroectoderm, contains a retinoic acid response element (RARE). Point mutations in the RARE abolish expression in neuroectoderm. Therefore, this RARE is not only involved in the ectopic response to retinoic acid, but is also essential for establishing aspects of the early Hoxb-1 expression pattern.

Animals↗

PubMed1994

Ectopic Hoxa-1 induces rhombomere transformation in mouse hindbrain.

Homeobox genes are expressed with a specific spatial and temporal order, which is essential for pattern formation during the early development of both invertebrates and vertebrates. Here we show that widespread ectopic expression of the Hoxa-1 (Hox 1.6) gene directed by a human beta-actin promoter in transgenic mice is embryolethal and produces abnormal phenotypes in a subset of domains primarily located in anterior regions. Interestingly, this abnormal development in the Hoxa-1 transgenic mice is associated with ectopic expression of the Hoxb-1 (Hox 2.9) gene in select hindbrain regions. At gestation day 9.5, two domains of strong Hoxb-1 expression are found in the anterior region of the hindbrains of Hoxa-1 transgenic embryos. One region represents the normal pattern of Hoxb-1 expression in rhombomere 4 and its associated migrating neural crest cells, while another major domain of Hoxb-1 expression consistently appears in rhombomere 2. Similar ectopic domains of beta-galactosidase activity are detected in dual transgenic embryos containing both beta-actin/Hoxa-1 transgene and a Hoxb-1/lacZ reporter construct. Expression of another lacZ reporter gene that directs beta-galactosidase activity predominantly in rhombomere 2 is suppressed in the Hoxa-1 transgenic embryos. We have also detected weaker and variable ectopic Hoxb-1 expression in rhombomeres 1, 3 and 6. No ectopic Hoxb-1 expression is detected in rhombomere 5 and the expression of Hoxa-3 and Krox-20 in this region is unchanged in the Hoxa-1 transgenic embryos. While no obvious change in the morphology of the trigeminal or facial-acoustic ganglia is evident, phenotypic changes do occur in neurons that emanate from rhombomeres 2 and 3 in the Hoxa-1 transgenic embryos. Additionally, alterations in the pattern of Hoxa-2 and Hoxb-1 expression in a subpopulation of neural crest cells migrating from the rhombomere 2 region are detected in these transgenics. Taken together, these data suggest that ectopic Hoxa-1 expression can reorganize select regions of the developing hindbrain by inducing partial transformations of several rhombomeres into a rhombomere-4-like identity.

Actins↗

PubMed1993

The zinc finger gene Krox20 regulates HoxB2 (Hox2.8) during hindbrain segmentation.

The zinc finger gene Krox20 and many Hox homeobox genes are expressed in segment-restricted domains in the hindbrain. The restricted expression patterns appear before morphological segmentation, suggesting that these transcription factors may play an early role in the establishment and identity of rhombomeric segments. In this paper, we show that the HoxB2 (Hox2.8) gene is normally upregulated in rhombomeres (r) 3, 4, and 5, and we identify an enhancer region upstream of the gene that imposes r3/r5 expression in transgenic mice. This enhancer contains three Krox20-binding sites required in vitro for complex formation with Krox20 protein and in vivo for rhombomere-restricted expression. In transgenic mice, Krox20 expressed in ectopic domains can transactivate a reporter construct containing the HoxB2 r3/r5 enhancer. These data demonstrate that Krox20 is a part of the upstream transcriptional cascade that directly regulates HoxB2 expression during hindbrain segmentation.

Animals↗

PubMed1993

Hox homeobox genes and regionalisation of the nervous system.

The Hox family of homeobox-containing genes are intimately associated with the processes of axial patterning in vertebrate embryos. This family of transcription factors is widely conserved in evolution and by analogy with their Drosophila counterparts, the HOM-C homeotic genes, may play a role in establishing regional identity in a number of embryonic systems, including the CNS. The patterns of expression of these genes are linked with the generation of rhombomeres and neural crest in the developing hindbrain, and suggest that they provide a molecular system for generating a combinatorial patterning mechanism. Analysis of mouse Hox mutants generated by homologous recombination have clearly demonstrated that the genes have important roles in normal regionalisation of the hindbrain and branchial arches, and this has lead to interest in how their early patterns are established in the nervous system. The Hox genes and their relation to hindbrain segmentation therefore provide a means of examining the cascade of events which regulates pattern formation in early neural development.

Animals↗

PubMed1993

Repression of stromelysin metalloprotease expression in rat fibrosarcoma cells by dimethylsulfoxide.

Metalloproteases are implicated in conferring invasive properties to tumor cells. We show here that treatment of ras-oncogene-transformed rat fibroblasts with dimethylsulfoxide (DMSO) results in a reversible decrease in stromelysin mRNA. Furthermore, stromelysin expression was found to be repressed by DMSO, but not by glucocorticoid hormone, in a fibrosarcoma cell line showing low AP-1 (fos/jun) transcription factor activity. In two fibrosarcoma cell lines which express high levels of stromelysin and low levels of 68 kDa type IV collagenase, the DMSO-induced decrease in stromelysin expression was paralleled by a decreased invasive propensity.

Animals↗

PubMed1993

Lack of c-jun expression in a transformed cell line isolated by glucocorticoid promotion of ras-transfected rat embryo fibroblasts.

Rat embryo fibroblasts (REFs) are inefficiently transformed by the T24-ras oncogene. A contributing factor to cellular resistance to transformation is the limited tolerance to p21-ras oncoprotein expression. Here we present data suggesting that long-term glucocorticoid treatment of ras oncogene-transfected REFs results in increased tolerance to p21-ras oncoproteins, leading to expression of the transformed phenotype. Stably transformed cell lines that expressed high levels of H-ras and could be maintained in the absence of hormone were isolated. In three out of four lines studied, the AP-1-dependent collagenase gene was expressed at a low level. In one of these lines, low collagenase expression was paralleled by lack of c-jun mRNA. Immunochemical analysis revealed that progression to hormone independence was not paralleled by mutations in the p53 gene. We propose that a decreased expression of AP-1-driven genes may result in increased tolerance to p21-ras oncoprotein.

Animals↗

PubMed1992

Neuroblastoma. Effect of genetic factors on prognosis and treatment.

BACKGROUND AND METHODS. Genetic analysis of tumor tissue has provided considerable insight into mechanisms of malignant transformation and progression. Neuroblastomas have been studied by cytogenetics, flow cytometry, and molecular genetic techniques, and these studies have identified several specific abnormalities that allow subclassification of these tumors into genetic/clinical subtypes. RESULTS AND DISCUSSION. Four genetic abnormalities have been identified that are characteristic of certain neuroblastomas. These include: (1) loss of heterozygosity (LOH) for the short arm of chromosome 1, including band 1p36; (2) amplification of the N-myc protooncogene; (3) hyperdiploidy, or near triploidy; and (4) defects in expression or function of the nerve growth factor receptor (NGFR). Abnormalities of the NGFR are found in virtually all neuroblastoma cell lines, and some primary tumors. The latter have not been studied extensively. Hyperdiploidy is associated with lower stages of disease and with a favorable outcome in infants. LOH for chromomors. The latter have not been studied extensively. Hyperdiploidy is associated with lower stages of disease and with a favorable outcome in infants. LOH for chromosome 1, band p36, and N-myc amplification are more common in patients older than 1 year of age with advanced stages of disease. The latter two genetic abnormalities may be related, and LOH for 1p36 may precede the development of amplification. When these abnormalities are combined with assessment of DNA content, three distinct genetic subsets of neuroblastomas can be identified. The first is characterized by a hyperdiploid or near-triploid modal karyotype, with few if any cytogenetic rearrangements. These patients generally are younger than 1 year of age with localized disease and a good prognosis. The second has a near-diploid karyotype, with no consistent abnormality identified currently. These patients generally are older with more advanced stages of disease that progress slowly and are often fatal. The third group has a near-diploid or tetraploid karyotype, with deletions or LOH for 1p36, amplification of N-myc, or both. These patients generally are older with advanced stages of disease that rapidly are progressive. Thus, genetic analysis of neuroblastoma cells provides information that has prognostic significance and can direct a more appropriate choice of treatment.

Cell Line↗

PubMed1992

Arctic terrestrial ecosystem contamination.

Limited data have been collected on the presence of contaminants in the Arctic terrestrial ecosystem, with the exception of radioactive fallout from atmospheric weapons testing. Although southern and temperate biological systems have largely cleansed themselves of radioactive fallout deposited during the 1950s and 1960s, Arctic environments have not. Lichens accumulate radioactivity more than many other plants because of their large surface area and long life span; the presence and persistence of radioisotopes in the Arctic is of concern because of the lichen----reindeer----human ecosystem. Effective biological half-life of cesium 137 is reckoned to be substantially less than its physical half-life. The database on organochlorines in Canadian Arctic terrestrial mammals and birds is very limited, but indications are that the air/plant/animal contaminant pathway is the major route of these compounds into the terrestrial food chain. For terrestrial herbivores, the most abundant organochlorine is usually hexachlorobenzene followed by hexachlorocyclohexane isomers. PCB accumulation favours the hexachlorobiphenyl, pentachlorobiphenyl and heptachlorobiphenyl homologous series. The concentrations of the various classes of organochlorine compounds are substantially lower in terrestrial herbivore tissues than in marine mammal tissues. PCBs and DDT are the most abundant residues in peregrine falcons (a terrestrial carnivore) reaching average levels of 9.2 and 10.4 micrograms.g-1, respectively, more than 10 times higher than other organochlorines and higher than in marine mammals, including the polar bear. Contaminants from local sources include metals from mining activities, hydrocarbons and waste drilling fluids from oil and gas exploration and production, wastes from DEW line sites, naturally occurring radionuclides associated with uranium mineralization, and smoke containing SO2 and H2SO4 aerosol from the Smoking Hills at Cape Bathurst, N.W.T.

Animals↗

PubMed1992

Elevated stromelysin-1 and reduced collagenase-IV expression in invasive rat embryo fibroblasts expressing E1A deletion mutants + T24-H-ras.

We have studied the in vitro invasive properties of 3 cell lines derived from the co-transfection of rat embryo fibroblasts (REF) with EIA genes deficient in exon 2 and T24-ras. All 3 cell lines showed invasive properties at passage 10 after isolation. Invasive cells expressed elevated levels of stromelysin-1 and reduced levels of 68-kDa type-IV collagenase compared with untransfected REF. In 2 cell lines the invasive capacity increased during in vitro propagation. The expression of stromelysin-1 increased during this process, whereas 68-kDa type-IV collagenase was persistently expressed at reduced levels. In the third clone analyzed, the invasive capacity decreased during culture, in parallel with decreased expression of stromelysin-1. The low level of stromelysin-1 expression observed in this cell line did not result from loss of AP-1-transcription-factor activity, and was not reversed by phorbol-ester treatment.

Adenovirus Early Proteins↗

PubMed1992

Neuroectodermal autonomy of Hox-2.9 expression revealed by rhombomere transpositions.

Involvement of the Hox genes in regional specifications of the vertebrate body axis is suggested by sequence similarity with the homeotic selector genes of Drosophila, the conservation of a collinear relationship between genomic organization and site of expression, and mutational analysis. Subdivision of vertebrate embryo hindbrain neuroepithelium into lineage compartments (rhombomeres) underlies segmental patterning of neuronal differentiation. The rhombomere boundaries delimit domains of expression of Hox genes, presumed to be determinants of rhombomere phenotype, suggesting that Hox genes confer positional value; the formation of rhombomere 4 (r4) is followed by strong expression of Hox-2.9 within its confines. If the Hox genes are determinants, their expression should be autonomous from the developmental stage at which regional commitment becomes fixed and irreversible. We have transplanted the future r4 region (from state-9-chick embryos) into the more anterior position of r2 and probed for Hox-2.9 transcripts. We report here that Hox-2.9 was expressed in the ectopic r4 as strongly as in the normal r4, whereas reciprocal grafts of future r2 to r4 position did not express Hox-2.9. The phenotype of ectopic rhombomeres developed according to their original position, as demonstrated by retrograde tracing of efferent cranial nerve nuclei. As early as stage-9-(six somites), both Hox-2.9 expression and segment identity are autonomous in the chick embryo hindbrain, independent both of position in the neuroepithelium and of signals from the underlying mesoderm.

Animals↗

PubMed1992

Thrombolysis-related early patency reduces ECG late potentials after acute myocardial infarction.

To assess the effects of thrombolysis and reperfusion on late potentials after myocardial infarction, 101 patients (79 men, age 63.2 +/- 10.5 years) underwent signal-averaged ECG studies at 10.7 +/- 9.2 days, with the use of a 40 to 250 Hz band-pass filter. Patients were divided into four groups: (1) 54 patients treated with thrombolytic agents at 2.8 +/- 1.1 hours, with 81% "early" patency/reperfusion (TIMI grades 2 and 3); (2) 47 patients treated conventionally with 45% "late" patency/reperfusion; (3) 56 patients with patency (TIMI grades 2 and 3); and (4) 26 patients without patency (TIMI grades 0 and 1). A late potential was present when greater than or equal to 2 of 3 defined criteria were present. There was a significant difference in the incidence of late potentials between groups 1 and 2 (22% vs 43%, respectively; p = 0.048) and between groups 3 and 4 (18% vs 50%, respectively; p = 0.006). Late potentials also tended to occur less often after "early" than after "late" patency/reperfusion (12.5% vs 25%). The odds ratio for developing a late potential was 0.39 for thrombolysis versus no thrombolysis (p less than 0.05) and 0.22 for patency/reperfusion (TIMI grades 2 and 3) versus no patency/reperfusion (TIMI grades 0 and 1) (p less than 0.05). By analysis of covariance the effects of thrombolysis on late potentials were entirely explained by reperfusion. Thus the risk of late potentials after myocardial infarction is high but is reduced by thrombolysis and reperfusion. In addition, the effectiveness of "early" reperfusion appears to be greater than that of "late" but requires further clarification.

Adult↗

PubMed1992

Enhanced invasive properties of rat embryo fibroblasts transformed by adenovirus E1A mutants with deletions in the carboxy-terminal exon.

E1A genes deficient in the carboxy-terminal exon can cooperate with activated ras oncogenes to induce transformation of rat embryo fibroblasts. However, the resulting transformed foci show a distinct appearance characterized by a decreased adhesion of the cells to the substrate. Here, we demonstrate that cell lines derived from foci showing the variant morphology are defective in down-regulation of stromelysin 1 metalloprotease expression and show an increased invasive propensity compared with cells transformed by wild-type E1A. The altered focus morphology, the high invasive propensity and the elevated stromelysin 1 expression were abrogated by glucocorticoid treatment. Our results show that E1A functions necessary for transformation and inhibition of invasive properties may be separated, and indicate that a 23 amino acid serine/threonine-rich region within the E1A carboxy-terminal exon is required for efficient repression of metalloprotease expression in transformed cells.

Adenovirus Early Proteins↗

PubMed1991

Pulse oximetry during apparent tonic-clonic seizures.

A pulse oximeter was used to monitor arterial oxygen saturations in 11 patients during apparent tonic-clonic seizures. 8 had a clinical diagnosis of genuine fits, 6 of whom showed striking falls in oxygen saturation during the seizures. 3 had a clinical diagnosis of pseudoseizures, none of whom had hypoxia during these episodes. Pulse oximetry during apparent tonic-clonic seizures may help to identify patients with low arterial oxygen tension who need immediate intervention.

Adolescent↗