Clinical teratology counseling and consultation report: high dose beta-carotene use during early pregnancy.
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Abnormalities, Drug-Induced↗
Biomedical subjects
J M Friedman
Publications and source records attributed to J M Friedman.
Aneuploidy in germ cells: etiologies and risk factors.
A 2 1/2-day workshop on germ cell aneuploidy was convened September 11-13, 1995 at the National Institute of Environmental Health Sciences in Research Triangle Park, North Carolina to discuss current understandings of the etiology and origin of human aneuploidy, especially in regard to potential environmental causes, and to identify gaps in our research knowledge. The workshop was designed to facilitate interactions among research experts conducting studies on the fundamental biology of chromosomal movement and segregation, on aneuploidy as a human clinical problem, and on toxicological aspects of aneuploidy induction. Overview presentations provided perspectives on aneuploidy as a human clinical problem, the genetics of aneuploidy, and the issues of concern in toxicological testing and regulatory risk assessment. The four chairs introduced the topics for each of their workgroups, setting the stage for subsequent, in-depth discussions on (1) chromosome mover components, (2) altered recombination, (3) parental age effects, and (4) differential chromosome susceptibility. From these discussions, gaps in our research knowledge related to the role of the environment in the etiology of aneuploidy and associated molecular, cellular, and genetic processes involved were identified, and will be used to establish a research agenda for filling those gaps.
Aneuploidy↗
Near-infrared spectra of Scapharca homodimeric hemoglobin: characterization of the deoxy and photodissociated derivatives.
The near-infrared charge transfer band at 760 nm (band III) has been investigated in deoxy and photodissociated dimeric Scapharca hemoglobin. At 300 K, the 10-ns spectrum of the carbonmonoxy derivative photoproduct is shifted by about 6 nm toward longer wavelengths with respect to the deoxy spectrum, both in buffer and in glycerol/buffer solutions. Moreover, the band III peak occurs at about the same wavelength at 300 K and at 10 K for the 10-ns photodissociated derivative, whereas in the deoxy derivative large changes in peak position and linewidth are observed as a function of temperature. These findings suggest that in dimeric Scapharca hemoglobin the photoproduct has not relaxed after 10 ns. The complete time dependence of the relaxation process has been studied both in buffer and in glycerol/buffer solutions at room temperature. The relaxation from the photoproduct to the deoxy species occurs on a microsecond time scale, in line with recent optical absorption and resonance Raman measurements.
Animals↗
Leptin activation of Stat3 in the hypothalamus of wild-type and ob/ob mice but not db/db mice.
Leptin, a hormone secreted by adipocytes, regulates the size of the adipose tissue mass through effects on satiety and energy metabolism. Leptin's precise sites of action are not known. The leptin receptor (Ob-R) is found in many tissues in several alternatively spliced forms raising the possibility that leptin exerts effects on many tissues including the hypothalamus. Ob-R is a member of the gp130 family of cytokine receptors which are known to stimulate gene transcription via activation of cytosolic STAT proteins. In order to identify the sites of leptin action in vivo, we assayed for activation of STAT proteins in mice treated with leptin. The STAT proteins bind to phosphotyrosine residues in the cytoplasmic domain of the ligand-activated receptor where they are phosphorylated. The activated STAT proteins dimerize and translocate to the nucleus where they bind DNA and activate transcription. The activation of STAT proteins in response to leptin was assayed in a variety of mouse tissues known to express Ob-R. Leptin injection activated Stat3 but no other STAT protein in the hypothalamus of ob/ob and wild-type mice but not db/db mice, mutants that lack an isoform of the leptin receptor. Leptin did not induce STAT activation in any of the other tissues tested. Activation of Stat3 by leptin was dose dependent and first observed after 15 minutes and maximal at 30 minutes. Our data indicate the hypothalamus is a direct target of leptin action and that this activation is critically dependent on the gp-130-like leptin receptor isoform missing in C57BLKS/J db/db mice. This is the first in vivo demonstration of leptin signal transduction.
Animals↗
Weight-reducing effects of the plasma protein encoded by the obese gene.
The gene product of the ob locus is important in the regulation of body weight. The ob product was shown to be present as a 16-kilodalton protein in mouse and human plasma but was undetectable in plasma from C57BL/6J ob/ob mice. Plasma levels of this protein were increased in diabetic (db) mice, a mutant thought to be resistant to the effects of ob. Daily intraperitoneal injections of either mouse or human recombinant OB protein reduced the body weight of ob/ob mice by 30 percent after 2 weeks of treatment with no apparent toxicity but had no effect on db/db mice. The protein reduced food intake and increased energy expenditure in ob/ob mice. Injections of wild-type mice twice daily with the mouse protein resulted in a sustained 12 percent weight loss, decreased food intake, and a reduction of body fat from 12.2 to 0.7 percent. These data suggest that the OB protein serves an endocrine function to regulate body fat stores.
Adipose Tissue↗
Increased expression in adipocytes of ob RNA in mice with lesions of the hypothalamus and with mutations at the db locus.
The gene product of the recently cloned mouse obese gene (ob) is important in regulating adipose tissue mass. ob RNA is expressed specifically by mouse adipocytes in vivo in each of several different fat cell depots, including brown fat. ob RNA is also expressed in cultured 3T3-442A preadipocyte cells that have been induced to differentiate. Mice with lesions of the hypothalamus, as well as mice mutant at the db locus, express a 20-fold higher level of ob RNA in adipose tissue. These data suggest that both the db gene and the hypothalamus are downstream of the ob gene in the pathway that regulates adipose tissue mass and are consistent with previous experiments suggesting that the db locus encodes the ob receptor. In db/db and lesioned mice, quantitative differences in expression level of ob RNA correlated with adipocyte lipid content. The molecules that regulate expression level of the ob gene in adipocytes probably are important in determining body weight, as are the molecules that mediate the effects of ob at its site of action.
Adipocytes↗
The human obese (OB) gene: RNA expression pattern and mapping on the physical, cytogenetic, and genetic maps of chromosome 7.
The recently identified mouse obese (ob) gene apparently encodes a secreted protein that may function in the signaling pathway of adipose tissue. Mutations in the mouse ob gene are associated with the early development of gross obesity. A detailed knowledge concerning the RNA expression pattern and precise genomic location of the human homolog, the OB gene, would facilitate examination of the role of this gene in the inheritance of human obesity. Northern blot analysis revealed that OB RNA is present at a high level in adipose tissue but at much lower levels in placenta and heart. OB RNA is undetectable in a wide range of other tissues. Comparative mapping of mouse and human DNA indicated that the ob gene is located within a region of mouse chromosome 6 that is homologous to a portion of human chromosome 7q. We mapped the human OB gene on a yeast artificial chromosome (YAC) contig from chromosome 7q31.3 that contains 43 clones and 19 sequence-tagged sites (STSs). Among the 19 STSs are eight corresponding to microsatellite-type genetic markers, including seven (CA)n repeat-type Genethon markers. Because of their close physical proximity to the human OB gene, these eight genetic markers represent valuable tools for analyzing families with evidence of hereditary obesity and for investigating the possible association between OB mutations and human obesity.
Adipose Tissue↗
Positional cloning of the mouse obese gene and its human homologue.
The mechanisms that balance food intake and energy expenditure determine who will be obese and who will be lean. One of the molecules that regulates energy balance in the mouse is the obese (ob) gene. Mutation of ob results in profound obesity and type II diabetes as part of a syndrome that resembles morbid obesity in humans. The ob gene product may function as part of a signalling pathway from adipose tissue that acts to regulate the size of the body fat depot.
Adipose Tissue↗
Structural basis of asymmetry in the human immunodeficiency virus type 1 reverse transcriptase heterodimer.
The reverse transcriptase from human immunodeficiency virus type 1 is a heterodimer consisting of one 66-kDa and one 51-kDa subunit. The p66 subunit contains both a polymerase and an RNase H domain; proteolytic cleavage of p66 removes the RNase H domain to yield the p51 subunit. Although the polymerase domain of p66 folds into an open, extended structure containing a large active-site cleft, that of p51 is closed and compact. The connection subdomain, which lies between the polymerase and RNase H active sites in p66, plays a central role in the formation of the reverse transcriptase heterodimer. Extensive and very different intra- and intersubunit contacts are made by the connection subdomains of each of the subunits. Together, contacts between the two connection domains constitute approximately one-third of the total contacts between subunits of the heterodimer. Conversion of an open p66 polymerase domain structure to a closed p51-like structure results in a reduction in solvent-accessible surface area by 1600 A2 and the burying of an extensive hydrophobic surface. Thus, the monomeric forms of both p66 and p51 are proposed to have the same closed structure as seen in the p51 subunit of the heterodimer. The free energy required to convert p66 from a closed p51-like structure to the observed open p66 polymerase domain structure is generated by the burying of a large, predominantly hydrophobic surface area upon formation of the heterodimer. It is likely that the only kind of dimer that can form is an asymmetric one like that seen in the heterodimer structure, since one dimer interaction surface exists only in p51 and the other only in p66. We suggest that both p51 and p66 form asymmetric homodimers that are assembled from one subunit that has assumed the open conformation and one that has the closed structure.
Antibodies, Viral↗
Stability of a potential blood substitute, HbXL99 alpha, under high pressure.
One important criteria for a plasma circulating hemoglobin blood substitute is resistance to subunit dissociation. For this reason, cross-linked hemoglobins (with low oxygen affinities) are being specifically designed to serve as potential blood substitutes. An example is HbXL99 alpha, cross-linked between the alpha-subunits [PNAS (1987) 84:7280]. In the study presented here, the effects of up to 2 kilobars of pressure on the intrinsic fluorescence of HbXL99 alpha, HbA, and myoglobin were compared. Hemoglobin solutions were studied between 0.01-0.1g% in potassium phosphate or Hepes buffers, pH 7.4. Results show HbA exhibits a decrease in fluorescence intensity as a function of pressure. In contrast, HbXL99 alpha as well myoglobin (a monomer) show essentially no significant intrinsic fluorescence changes as a function of pressure. These results suggest that HbXL99 alpha is stable as a tetramer up to approximately 2 kilobars of pressure. In addition, high pressure intrinsic fluorescence studies provide a suitable technique for determining the subunit stability of hemoglobins.
Animals↗
Structure of the binding site for nonnucleoside inhibitors of the reverse transcriptase of human immunodeficiency virus type 1.
The dipyridodiazepinone Nevirapine is a potent and highly specific inhibitor of the reverse transcriptase (RT) from human immunodeficiency virus type 1 (HIV-1). It is a member of an important class of nonnucleoside drugs that appear to share part or all of the same binding site on the enzyme but are susceptible to a variety of spontaneous drug-resistance mutations. The co-crystal-structure of HIV-1 RT and Nevirapine has been solved previously at 3.5-A resolution and now is partially refined against data extending to 2.9-A spacing. The drug is bound in a hydrophobic pocket and in contact with some 38 protein atoms from the p66 palm and thumb subdomains. Most, but not all, nonnucleoside drug-resistance mutations map to residues in close contact with Nevirapine. The major effects of these mutations are to introduce steric clashes with the drug molecule or to remove favorable protein-drug contacts. Additionally, four residues (Phe-227, Trp-229, Leu-234, and Tyr-319) in contact with Nevirapine have not been selected as sites of drug-resistance mutations, implying that there may be limitations on the number and types of resistance mutations that yield viable virus. Strategies of inhibitor design that target interactions with these conserved residues may yield drugs that are less vulnerable to escape mutations.
Amino Acid Sequence↗
Alteration of tryptophan fluorescence properties upon dissociation of Lumbricus terrestris hemoglobin.
Fluorescence analysis has been used to study dissociation of the dodecameric 3.8 kDa Lumbricus terrestris hemoglobin. Since tryptophan intrinsic fluorescence has been used as a reporter group to study Lumbricus hemoglobin, it is of interest to study dissociation perturbed properties of the tryptophan residues. Shifts in the fluorescence emission maximum to longer wavelengths upon dissociation at pH 9.2 suggest that tryptophans buried at the subunit interface(s) become more exposed. Fluorescence lifetime and quenching studies are employed in this present investigation as a means to confirm the location of tryptophan residues at the subunit interfaces. Acrylamide titration (to 2.5 M) indicate only a fraction of the residues can be quenched at either pH. At pH 7.0, the Stern-Volmer plot has downward curvature, while at pH 9.2 there is slight upward curvature, again indicating a change in environment. The intrinsic fluorescence decay requires at least four exponentials at both pHs. The mean fluorescence lifetime of CO Lumbricus hemoglobin increases from 1.1 ns at pH 7 to 3.3 ns at pH 9.2. The lifetime data can be further interpreted as a decrease in the quenching of residues with a approximately 30 ps lifetime, and a concomitant increase in the longer lifetime components. This is consistent with interface tryptophans becoming exposed to solvent upon dissociation, and loss of quenching by intersubunit hemes. The overall results suggest that in the dodecamer, most of the tryptophans are located in a hydrophobic environment, not all of which are located at the subunit interface.
Acrylamide↗
A reevaluation of risk of in utero exposure to lithium.
OBJECTIVE: To reevaluate the risk associated with in utero exposure to lithium. DATA SOURCES AND STUDY SELECTION: Data were obtained from all published studies, in multiple languages, referenced in MEDLINE, Toxline, and the Lithium Information Center databases. Unpublished studies were not included. The search terms were lithium, pregnancy, teratogen, abnormalities (drug induced), Ebstein's anomaly, and adverse effects. DATA EXTRACTION AND SYNTHESIS: In the 1970s a very strong association was suggested between maternal lithium treatment during pregnancy and Ebstein's anomaly of the heart in the offspring. The relative risk for Ebstein's anomaly among such children was estimated to be 400 on the basis of data collected from a registry of voluntarily submitted cases. More recent controlled epidemiologic studies have consistently shown a lower risk. No women who took lithium during pregnancy were found among four case-control studies of Ebstein's anomaly involving 25, 34, 59, and 89 affected children, respectively. In two cohort studies, risk ratios of 3.0 (95% confidence interval [CI], 1.2 to 7.7) and 1.5 (95% CI, 0.4 to 6.8) for all congenital anomalies have been observed. The risk ratios for cardiac malformations in these studies were 7.7 (95% CI, 1.5 to 41.2) and 1.2 (95% CI, 0.1 to 18.3), respectively. CONCLUSION: While initial information regarding the teratogenic risk of lithium treatment was derived from biased retrospective reports, more recent epidemiologic data indicate that the teratogenic risk of first-trimester lithium exposure is lower than previously suggested. The clinical management of women with bipolar disorder who have childbearing potential should be modified with this revised risk estimate.
Abnormalities, Drug-Induced↗
Time-resolved resonance Raman spectroscopy as probe of structure, dynamics, and reactivity in hemoglobin.
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Heme↗
Molecular genetics of the brown (b)-locus region of mouse chromosome 4. I. Origin and molecular mapping of radiation- and chemical-induced lethal brown deletions.
Over a period of many years, germ-cell mutagenesis experiments using the mouse specific-locus test have generated numerous radiation- and chemical-induced alleles of the brown (b; Tyrp 1) locus in mouse chromosome 4. We describe here the origin, maintenance and initial molecular characterization of 28 b mutations that are prenatally lethal when homozygous. Each of these mutations is deleted for Tyrp 1 sequences, and each of 25 mutations tested further is deleted for at least one other locus defined by molecular clones previously found to be closely linked to b by interspecific backcross analysis. A panel of DNAs from mice carrying a lethal b mutation and a Mus spretus chromosome 4 was used in the fine structure mapping of these molecularly defined loci. The deletional nature of each of these prenatally lethal mutations is consistent with the hypothesis that the null phenotype at b has an effect only on the quality (color) of eumelanin produced in melanocytes. The resulting deletion map provides a framework on which to build future molecular-genetic and biological analyses of this region of mouse chromosome 4.
Alleles↗
Occurrence of chickenpox during pregnancy in women seropositive for varicella-zoster virus.
In a group of 21 women counseled after exposure to chickenpox during pregnancy, 4 developed varicella despite initial studies showing that preinfection sera were varicella-zoster virus (VZV)-seropositive by fluorescent anti-membrane antibody, latex agglutination, ELISA, and VZV glycoprotein immunoblot assay. Further investigations showed that 2 of the 4 had low-titer (1/100), low-avidity, VZV-reactive IgG3 antibodies by ELISAs of preinfection sera. After chickenpox, these women developed primary-like serologic responses to VZV. Two women with high-titer (1/1600, 1/3200), high-avidity, IgG1 antibodies showed anamnestic serologic responses after reinfection. The criteria of protective VZV immunity remain ill-defined.
Adult↗
Crystal structures of the Klenow fragment of DNA polymerase I complexed with deoxynucleoside triphosphate and pyrophosphate.
Crystal structures of the Klenow fragment (KF) of DNA polymerase I from Escherichia coli complexed with deoxynucleoside triphosphate (dNTP) or with pyrophosphate (PPi) determined to 3.9-A resolution by X-ray crystallography show these molecules binding within the cleft of the polymerase domain and surrounded by residues previously implicated in dNTP binding. The dNTP binds adjacent to the O-helix [Ollis, D. L., Brick, P., Hamlin, R., Xuong, N. G., & Steitz, T. A. (1985a) Nature 313, 762-766] with its triphosphate moiety anchored by three positively charged residues, Arg 754, Arg 682, and Lys 758, plus His 734 and Gln 708. The dNTP binding site observed in the crystal is consistent with the results of chemical modification including cross-linking and is also near many of the amino acid residues whose mutation affects catalysis [Polesky, A. H., Steitz, T. A., Grindley, N. D. F., & Joyce, C. M. (1990) J. Biol. Chem. 265, 14579-14591; Polesky, A. H., Dahlberg, M. E., Benkovic, S. J., Grindley, N. D. F., & Joyce, C. M. (1992) J. Biol. Chem. 267, 8417-8428]. However, we conclude that the position of at least the dNMP moiety of dNTP in the binary complex is not likely to be the same as in its catalytically relevant complex with primer-template DNA.
Binding Sites↗
Absence of ligand binding-induced tertiary changes in the multimeric earthworm Lumbricus terrestris hemoglobin. A resonance Raman study.
In vertebrate hemoglobins, changes in protein tertiary structure induced by either ligand binding or changes in quaternary state are manifested at the heme as reflected in resonance Raman spectral changes involving the iron-proximal histidine stretching mode. No such changes are observed for Lumbricus terrestris hemoglobin. The iron-histidine stretching mode and the porphyrin breathing motion in the deoxy-, oxy-, or CO-photodissociated forms of Lumbricus hemoglobin and human hemoglobin A (pH 7.0 and 9.2, the latter to effect Lumbricus hemoglobin subunit dissociation) were studied using pulsed (10 ns) light at 435 nm. In contrast to that observed for hemoglobin A, a comparison of the spectra of the deoxy and photoproduct forms of Lumbricus hemoglobin reveal minimal differences in the region of the iron-histidine and the pi electron distribution in the heme moiety. The spectral frequencies are similar to that observed in R-state vertebrate hemoglobins. Such average behavior of the approximately 192 hemes present in Lumbricus hemoglobin is more analogous to the Raman spectral properties observed in myoglobin.
Animals↗