Biomedical subjects

J V Schmidt

Publications and source records attributed to J V Schmidt.

16 recordsLinked to original sources

PubMed2006

Parental regulation of central patterns of estrogen receptor alpha.

Reduced levels of estrogen receptor alpha (ERalpha) in the medial amygdala (MeA) and bed nucleus of stria terminalis (BST) have been hypothesized to play a significant role in the expression of male behaviors associated with monogamy. Therefore, the regulation of ERalpha could be a critical factor in determining male behavior and the evolution of monogamy. Central expression of ERalpha immunoreactivity was compared in hybrid offspring from crosses between two phenotypically distinct populations of prairie voles (Microtus ochrogaster). Illinois voles (IL) are socially monogamous and display low levels of ERalpha, while Kansas voles (KN) display some characteristics associated with polygyny and have higher levels of ERalpha. In offspring from hybrid crosses, the pattern of ERalpha expression was dependent upon parentage; the two types of hybrid crosses did not produce the same ERalpha pattern in the offspring. In the BST and MeA, hybrid males expressed ERalpha patterns consistent with those of males from their mother's population, while hybrid females had ERalpha patterns typical of females belonging to their father's population. The parental-specific patterns of ERalpha expression are suggestive of genomic imprinting, therefore, the vole ERalpha (Esr1) gene was cloned and sequenced, and examined for allele-specific expression. Results from this study indicate that while maternal factors may play a major role the expression of ERalpha in their male offspring, genomic imprinting is unlikely to be involved, suggesting another mechanism is responsible.

Amygdala↗

PubMed2001

Genomic imprinting of a placental lactogen gene in Peromyscus.

The mammalian genome contains over 30 genes whose expression is dependent upon their parent-of-origin. Of these imprinted genes the majority are involved in regulating the rate of fetal growth. In this report we show that in the deer mouse Peromyscusthe placental lactogen-1-variant ( pPl1-v) gene is paternally expressed throughout fetal development, whereas the linked and closely related pPl1gene is expressed in a biallelic manner. Neither the more distantly related pPl2Agene, nor the Mus Pl1gene displays any preferential expression of the paternal allele, suggesting that the acquisition of imprinting of pPl1-v is a relatively recent event in evolution. Although pPl1 expression is temporally mis-regulated in the dysplastic placentae of hybrids between two Peromyscus species, its over-expression cannot account for the aberrant phenotypes of these placentae. We argue that the species-specific imprinting of pPl1-v, encoding a growth factor that regulates nutrient transfer from mothers to their offspring, is consistent with the parent-offspring conflict model that has been proposed to explain the evolution of genomic imprinting.

Amino Acid Sequence↗

PubMed2001

Germ cell specific promoter drives ectopic transgene expression during embryogenesis.

In this study, we used the male germ cell-specific phosphoglycerate kinase 2 (Pgk2) promoter to generate Pgk2Cre transgenic mice to allow investigation of genes critically involved in meiosis. The Pgk2 promoter had been used previously to target transgene expression to spermatocytes and spermatids in several laboratories including ours. In several Cre targeting experiments using other promoters, ectopic Cre expression had been observed, but the timing and extent of this expression was not analyzed. We demonstrate that in adult mice the Pgk2Cre transgene is expressed specifically in spermatocytes and spermatids, as expected. However, in offspring from matings of Pgk2Cre mice and an H19loxP indicator strain, we discovered that recombination events had occurred in several, but not all, tissues to varying extents. The lacZ-loxP transgenic indicator strain was next used to uncover ectopic Cre expression even in single cells, which indicated that the Pgk2Cre transgene is expressed between days 11 and 15 during embryogenesis in several tissues and organs. Using an RT PCR assay we were unable to detect endogenous Pgk2 mRNA during embryogenesis or in adult tissues other than testis. In conclusion, the Pgk2 promoter is a valid choice for targeting gene expression to meiotic male germ cells, since transient ectopic expression is unlikely to have a discernable effect in most studies, but it may be inappropriate for utilization with Cre recombinase.

Animals↗

PubMed2000

The Dlk1 and Gtl2 genes are linked and reciprocally imprinted.

Genes subject to genomic imprinting exist in large chromosomal domains, probably reflecting coordinate regulation of the genes within a cluster. Such regulation has been demonstrated for the H19, Igf2, and Ins2 genes that share a bifunctional imprinting control region. We have identified the Dlk1 gene as a new imprinted gene that is paternally expressed. Furthermore, we show that Dlk1 is tightly linked to the maternally expressed Gtl2 gene. Dlk1 and Gtl2 are coexpressed and respond in a reciprocal manner to loss of DNA methylation. These genes are likely to represent a new example of coordinated imprinting of linked genes.

Animals↗

PubMed2000

High risk pregnancy in the workplace. Influencing positive outcomes.

Childbearing employees are well served by the occupational health nurse who promotes optimal preconceptual and pregnancy health practices, uses community resources, and maintains current knowledge about high risk pregnancy prevention and care. These broad goals of care can lead to decreased absenteeism, healthier and happier employees, and more positive outcomes of pregnancy. For employees with high risk pregnancies, the role of the occupational health nurse includes, but is not limited to, facilitating awareness with the employer, making suggestions for adjusting working conditions, making frequent assessments of the employee's needs, and communicating with prenatal health care providers. Occupational health nurses should never underestimate their role and potential influence on the mother, and on her significant other, for a positive outcome of her pregnancy.

Adult↗

PubMed1999

Enhancer competition between H19 and Igf2 does not mediate their imprinting.

The linked H19 and Igf2 genes on mouse distal chromosome 7 are subject to genomic imprinting. Competition between the promoters of the genes for transcription from shared enhancers has been proposed as an explanation for the coordinate expression and reciprocal imprinting of these two genes. To test this model, we have used Cre-loxP technology to generate in mice a conditional deletion of the H19 promoter and structural gene that leaves no transcription unit in the locus. Contrary to the prediction of enhancer competition we find that transcriptional activity from the H19 promoter is not required for the imprinted silencing of the Igf2 gene.

Alleles↗

PubMed1997

Abnormal angiogenesis and responses to glucose and oxygen deprivation in mice lacking the protein ARNT.

The arylhydrocarbon-receptor nuclear translocator (ARNT) is a member of the basic-helix-loop-helix-PAS family of heterodimeric transcription factors which includes the arylhydrocarbon receptor (AHR), hypoxia-inducible factor-1alpha (HIF-1alpha) and the Drosophila single-minded protein (Sim). ARNT forms heterodimeric complexes with the arylhydrocarbon receptor, HIF-1alpha, Sim and the PAS protein Per. In response to environmental pollutants, AHR-ARNT heterodimers regulate genes involved in the metabolism of xenobiotics, whereas ARNT-HIF-1alpha heterodimers probably regulate those involved in the response to oxygen deprivation. By generating a targeted disruption of the Arnt locus in the mouse, we show here that Arnt-/- embryonic stem cells fail to activate genes that normally respond to low oxygen tension. Arnt-/- ES cells also failed to respond to a decrease in glucose concentration, indicating that ARNT is crucial in the response to hypoxia and to hypoglycaemia. Arnt-/- embryos were not viable past embryonic day 10.5 and showed defective angiogenesis of the yolk sac and branchial arches, stunted development and embryo wasting. The defect in blood vessel formation in Arnt-/- yolk sacs is similar to the angiogenic abnormalities reported for mice deficient in vascular endothelial growth factor or tissue factor. On the basis of these findings, we propose a model in which increasing tissue mass during organogenesis leads to the formation of hypoxic/nutrient-deprived cells, the subsequent activation of ARNT, and a concomitant increase in the expression of genes (including that encoding vascular endothelial growth factor) that promote vascularization of the developing yolk sac and solid tissues.

Animals↗

PubMed1996

Characterization of a murine Ahr null allele: involvement of the Ah receptor in hepatic growth and development.

The Ah receptor (AHR) is a ligand-activated transcription factor that mediates a pleiotropic response to environmental contaminants such as benzo[a]pyrene and 2,3,7,8-tetrachlorodibenzo-p-dioxin. In an effort to gain insight into the physiological role of the AHR and to develop models useful in risk assessment, gene targeting was used to inactivate the murine Ahr gene by homologous recombination. Ahr-/- mice are viable and fertile but show a spectrum of hepatic defects that indicate a role for the AHR in normal liver growth and development. The Ahr-/- phenotype is most severe between 0-3 weeks of age and involves slowed early growth and hepatic defects, including reduced liver weight, transient microvesicular fatty metamorphosis, prolonged extramedullary hematopoiesis, and portal hypercellularity with thickening and fibrosis.

Alleles↗

PubMed1996

Ah receptor signaling pathways.

The aryl hydrocarbon (Ah) receptor has occupied the attention of toxicologists for over two decades. Interest arose from the early observation that this soluble protein played key roles in the adaptive metabolic response to polycyclic aromatic hydrocarbons and in the toxic mechanism of halogenated dioxins and dibenzofurans. More recent investigations have provided a fairly clear picture of the primary adaptive signaling pathway, from agonist binding to the transcriptional activation of genes involved in the metabolism of xenobiotics. Structure-activity studies have provided an understanding of the pharmacology of this receptor; recombinant DNA approaches have identified the enhancer sequences through which this factor regulates gene expression; and functional analysis of cloned cDNAs has allowed the characterization of the major signaling components in this pathway. Our objective is to review the Ah receptor's role in regulation of xenobiotic metabolism and use this model as a framework for understanding the less well-characterized mechanism of dioxin toxicity. In addition, it is hoped that this information can serve as a model for future efforts to understand an emerging superfamily of related signaling pathways that control biological responses to an array of environmental stimuli.

Amino Acid Sequence↗

PubMed1994

Potent transactivation domains of the Ah receptor and the Ah receptor nuclear translocator map to their carboxyl termini.

The Ah receptor (AHR) is a ligand-activated transcription factor that is structurally related to its dimerization partner, the Ah receptor nuclear translocator (ARNT), and two Drosophila proteins, SIM and PER. All four proteins contain a region of homology now referred to as a PAS homology domain. In addition, the AHR, ARNT, and SIM harbor a basic region helix-loop-helix motif in their N termini, whereas PER does not. Previous mapping studies of the AHR have demonstrated that the PAS domain contains sequences required for ligand recognition, dimerization, and interaction with the 90-kDa heat shock protein. They also have confirmed that the basic region helix-loop-helix domain plays a role in both dimerization and sequence-specific DNA binding. To identify domains involved in transactivation of target genes, we generated chimeras of AHR/ARNT deletion mutants with the DNA binding region of the yeast Gal4 protein, transiently expressed these in COS-1 cells, and monitored their capacity to activate the chloramphenicol acetyltransferase reporter gene under the control of a minimal promoter driven by enhancer elements recognized by Gal4. Extensive analysis of these fusions revealed that the AHR and ARNT harbor potent transactivation domains within their C termini. Importantly, the amino-terminal halves of both the AHR and ARNT were found to be devoid of transactivation activity.

Amino Acid Sequence↗

PubMed1994

Chromosomal localization of the human AHR locus encoding the structural gene for the Ah receptor to 7p21-->p15.

The AHR locus encodes the structural gene for the Ah receptor, a ligand activated transcription factor that regulates the expression of a number of enzymes involved in the metabolism of chemical carcinogens and that appears to mediate the tumor promoting properties of compounds such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Using polymerase chain reaction (PCR), we amplified exon-10 and intron-D of the AHR gene from human genomic DNA. By using PCR analysis of somatic cell hybrids and fluorescence in situ hybridization of metaphase cells, we localized AHR to human chromosome 7, bands p21-->p15. This mapping data should prove useful in determining the role that the AHR locus plays in human cancer incidence and in the identification of human populations with altered susceptibilities to the toxic/carcinogenic effects of planar aromatic hydrocarbons.

Animals↗

PubMed1993

Molecular characterization of the murine Ahr gene. Organization, promoter analysis, and chromosomal assignment.

The AH receptor is a ligand-activated transcription factor that mediates the biological effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin. The AH receptor has primary sequence homology to its dimerization partner the AH receptor nuclear translocator, and to the Drosophila proteins Sim and Per. Characterization of the gene encoding the murine AH receptor (Ahr gene) reveals that its structural organization is also conserved with respect to the sim gene, since 6 of 11 Ahr exons are spliced at homologous sites. Interestingly, little splicing homology was observed between the Ahr and per genes. The promoter of the Ahr gene is GC-rich and contains no TATA or CCAAT boxes; however, sequence analysis has shown several binding sites for the transcription factor Sp1 (GC boxes). Additionally we have identified a potential cAMP response element, AP-1 and E box sites, and two elements demonstrated in other genes to confer placenta-specific expression. Using a restriction fragment length polymorphism in exon 7 and recombinant inbred mouse lines, the Ahr gene was found to be concordant with the phenotypically defined Ahr locus, supporting the identity of these two genetic elements.

Amino Acid Sequence↗

PubMed1993

Cloning and expression of a human Ah receptor cDNA.

In this report, we describe the cloning and expression of a cDNA encoding a human Ah receptor, a basic/helix-loop-helix protein that mediates the toxic effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin. A comparison of this human cDNA with a murine homologue (Ahb1 allele) indicates that the molecular mass variation observed between the receptors found in these two species results from hypervariability of amino acid sequences in the carboxyl termini (< 60% conserved over 450 amino acids). Differential usage of stop codons generates proteins with molecular masses that differ by 6 kDa. In contrast, the amino-terminal halves of these proteins are highly conserved and show 90% amino acid sequence identity. Northern blot analysis indicates that the human Ah receptor mRNA is expressed at its highest levels in placenta and is also highly expressed in lung, heart, pancreas, and liver, with lower levels of expression found in brain, kidney, and skeletal muscle. Expression of the human cDNA in a rabbit reticulocyte lysate system allowed functional analysis of ligand binding, agonist-induced and Ah receptor nuclear translocator-dependent DNA binding, and receptor stabilization by sodium molybdate.

Amino Acid Sequence↗

PubMed1992

Rat urate oxidase produced by recombinant baculovirus expression: formation of peroxisome crystalloid core-like structures.

Urate oxidase (EC 1.7.3.3), which catalyzes the oxidation of uric acid to allantoin, is present in most mammals but absent in humans and hominoid primates. In rats and most other mammals that catabolize uric acid to allantoin, this enzyme is localized within the crystalloid cores of peroxisomes present in liver parenchymal cells. To determine whether urate oxidase forms these crystalloid cores or whether core-forming protein(s) exist in association with urate oxidase, a baculovirus expression vector system was used to overproduce the full-length rat urate oxidase in Spodoptera frugiperda cells. Urate oxidase was expressed to a level of approximately 30% of the total protein in this system. Immunoblot analysis demonstrated that the baculovirus-generated protein had electrophoretic and immunologic properties similar to those of urate oxidase expressed in rat liver. Immunofluorescence and electron microscopic examination revealed that the overexpressed recombinant urate oxidase is present in both the cytoplasm and the nucleus of infected insect cells as numerous 1- to 3-microns discrete particles. These insoluble protein aggregates, which were positively stained for urate oxidase by protein A-gold immunocytochemical approach, did not appear to be delimited by a single membrane. They revealed a crystalloid structure reminiscent of rat peroxisomal core consisting of bundles of tubules with an inner diameter of approximately 50 A. The recombinant urate oxidase particles, isolated by a single-step procedure, were composed entirely of 35-kDa urate oxidase subunit. These studies indicate that rat urate oxidase is capable of forming insoluble crystalloid core-like structures.

Animals↗

PubMedDate not supplied

History and development of fetal heart assessment: a composite.

Methods of assessing the fetal heart remained unchanged for approximately 150 years until the first commercial monitor suitable for clinical practice was sold in 1968. The impact and events of the last 30 to 40 years surrounding fetal heart assessment are revealed in perspectives of the past, present, and near future. Assessment practices have been shaped by the development of biotechnology, unrealistic expectations, interpretation disagreement, consumer response, and the practice and educational resources written by nursing and medicine.

Cardiotocography↗

PubMedDate not supplied

The development of AWHONN's fetal heart monitoring principles and practices workshop. Association of Women's Health, Obstetric and Neonatal Nurses.

The Fetal Heart Monitoring Principles and Practices (FHMPP) workshop was designed at the request of AWHONN's Committee on Education to meet member requests for standardized education in fetal heart assessment, including didactic and psychomotor skill content. Events and decisions are chronicled, from inception of the FHMPP program to development, evaluation, and revision. Current statistics and participation demonstrate the success of the workshop and its ongoing need. Today, as the project continues to grow and improve, its primary strength lies in member involvement and support.

Clinical Competence↗