Biomedical subjects

J C Smith

Publications and source records attributed to J C Smith.

At least 217 records · Page 12Linked to original sources

PubMed1996

Xom: a Xenopus homeobox gene that mediates the early effects of BMP-4.

Bone morphogenetic protein-4 (BMP-4) is thought to play an important role in early Xenopus development by acting as a "ventralizing factor' and as an epidermal determinant: local inhibition of BMP-4 function in whole embryos causes the formation of an additional dorsal axis, and inhibition of BMP-4 function in isolated ectodermal cells causes the formation of neural tissue. In this paper we describe a homeobox-containing gene whose expression pattern is similar to that of BMP-4, whose expression requires BMP-4 signalling and which, when over-expressed, causes a phenotype similar to that caused by over-expression of BMP-4. We suggest that this gene, which we call Xom, acts downstream of BMP-4 to mediate its effects.

Amino Acid Sequence↗

PubMed1996

Inhibition of Xbra transcription activation causes defects in mesodermal patterning and reveals autoregulation of Xbra in dorsal mesoderm.

The Brachyury (T) gene is required for formation of posterior mesoderm and for axial development in both mouse and zebrafish embryos. In this paper, we first show that the Xenopus homologue of Brachyury, Xbra, and the zebrafish homologue, no tail (ntl), both function as transcription activators. The activation domains of both proteins map to their carboxy terminal regions, and we note that the activation domain is absent in two zebrafish Brachyury mutations, suggesting that it is required for gene function. A dominant-interfering Xbra construct was generated by replacing the activation domain of Xbra with the repressor domain of the Drosophila engrailed protein. Microinjection of RNA encoding this fusion protein allowed us to generate Xenopus and zebrafish embryos which show striking similarities to genetic mutants in mouse and fish. These results indicate that the function of Brachyury during vertebrate gastrulation is to activate transcription of mesoderm-specific genes. Additional experiments show that Xbra transcription activation is required for regulation of Xbra itself in dorsal, but not ventral, mesoderm. The approach described in this paper, in which the DNA-binding domain of a transcription activator is fused to the engrailed repressor domain, should assist in the analysis of other Xenopus and zebrafish transcription factors.

Animals↗

PubMed1996

Temporal consistency and stability of three scales for measuring stress in adults.

We investigated the 30-min. temporal consistency and temporal stability of three focal scales for measuring stress: the Cognitive Anxiety Scale-State, the Focusing Inventory Scale-State, and the Somatic Symptom Scale-State. These scales are applicable for individually measured reduction in stress in research on outcome with older adolescents and adults. All possess excellent internal consistency. All manifested significant temporal consistency and good to excellent temporal stability over 30 min. in a nonclinical sample of 60 undergraduates. Small significant differences in means on the Cognitive Anxiety Scale-State and the Somatic Symptom Scale-State were noted. The phenomenological states associated with stress were stable and consistent over 30 min., the optimal time interval used in research on stress.

Adult↗

PubMed1996

Pathways for conformational change in seryl-tRNA synthetase from Thermus thermophilus.

Seryl t-RNA synthetase of the bacterium Thermus thermophilus contains a long arm, consisting of an antiparallel coiled coil, that is involved in binding of tRNA. Two crystallographic structures exist for this protein, in which the arm is in different conformations. Here, we use computational methods employing an empirical potential energy function to investigate the flexibility of the long arm. A conformational pathway is calculated between the 2 crystallographic structures using a method based on molecular dynamics simulation. The pathway is analyzed in terms of sequential phi and psi backbone angle changes. Several transient phi and psi displacements are present along the pathway that are not visible in the end states and may be required for transition between them. Energy maps are constructed by rotating the arm around its principal axes of inertia and energy minimizing. The map identifies 2 regions of relatively low energy which might be accessible to the arm.

In Vitro Techniques↗

PubMed1996

Poisoning of wildlife in South Africa.

Over a period of 7 years the Toxicology Diagnostic Laboratory at the Onderstepoort Veterinary Institute investigated 370 suspected incidents of poisoning of wildlife. A diagnosis was made in 166 of the outbreaks. Synthetic organic pesticides were responsible for 82.5% of the poisonings. More than 90% of the poisonings were maliciously intended and monocrotophos was the chemical most often used. The data were derived from authenticated outbreaks of poisoning and indicate the chemicals most often incriminated in acute poisoning of wildlife. Of all wild animals, birds are the most frequent victims of poisoning. Uncommon toxicities such as ionophore, cardiac glycoside poisoning and chronic fluorosis are also described.

Animal Diseases↗

PubMed1995

Structural basis of antibody cross-reactivity: solution conformation of an immunogenic peptide fragment containing both T and B epitopes.

A synthetic octadecapeptide with the amino acid sequence of residues 23-40 of toxin alpha from Naja nigricollis, cyclized with a disulfide bridge between residues 23 and 40, induces antibodies that cross-react with toxin alpha. We report a structural analysis of this peptide in aqueous solution using NMR spectroscopy and molecular modeling. Structures compatible with the 151 obtained NMR distance restraints were generated using a random simulated annealing protocol followed by restrained high-temperature dynamics and energy minimization. The generated structures are compared with that of the corresponding sequence in the native toxin. The two stretches 23-28 and 37-40 adopt a canonical beta-strand structure in the toxin but are disordered in the peptide. The region 28-36 is ordered in both the peptide and the toxin. Residues 28-30 and 34-36 adopt beta-strand structures in the toxin but loop structures in the peptide. Residues 30-33 form a reverse turn in both the peptide and the toxin. Residues Val-27, Trp-28, Ile-35, and Ile-36 form a hydrophobic cluster. The similar, reverse-turn fold of residues 30-33 in the peptide and the toxin may be associated with the immunogenic cross-reactivity.

Amino Acid Sequence↗

PubMed1995

Isolation, structural elucidation, and partial synthesis of lutein dehydration products in extracts from human plasma.

All-E-(3R,6'R)-3-hydroxy-3',4'-didehydro-beta,gamma-carotene (anhydrolutein I) and all-E-(3R,6'R)-3-hydroxy-2',3'-didehydro-beta,epsilon-carotene (2',3'-anhydrolutein II) have been isolated and characterized from extracts of human plasma using semipreparative high-performance liquid chromatography (HPLC) on a C18 reversed-phase column. The identification of anhydroluteins was accomplished by comparison of the UV-Vis absorption and mass spectral data as well as HPLC-UV-Vis-mass spectrometry (MS) spiking experiments using fully characterized synthetic compounds. Partial synthesis of anhydroluteins from the reaction of lutein with 2% H2SO4 in acetone, in addition to anhydrolutein I (54%) and 2',3'-anhydrolutein II (19%), also gave (3'R)-3'-hydroxy-3,4-dehydro-beta-carotene (3',4'-anhydrolutein III, 19%). While anhydrolutein I has been shown to be usually accompanied by minute quantities of 2',3'-anhydrolutein II (ca. 7-10%) in human plasma, 3',4'-anhydrolutein III has not been detected. The presence of anhydrolutein I and II in human plasma is postulated to be due to acid catalyzed dehydration of the dietary lutein as it passes through the stomach. These anhydroluteins have also been prepared by conversion of lutein diacetate to the corresponding anhydrolutein acetates followed by alkaline hydrolysis. However, under identical acidic conditions, loss of acetic acid from lutein diacetate proceeded at a much slower rate than dehydration of lutein. The structures of the synthetic anhydroluteins, including their absolute configuration at C(3) and C(6') have been unambiguously established by 1H NMR and in part by 13C NMR, and circular dichroism.

Chromatography, High Pressure Liquid↗

PubMed1995

Mesoderm induction in Xenopus caused by activation of MAP kinase.

Mesoderm induction is a critical early step in vertebrate development, involving changes in gene expression and morphogenesis. In Xenopus, normal mesoderm formation depends on signalling through the fibroblast growth factor (FGF) tyrosine kinase receptor. One important signalling pathway from receptor tyrosine kinases involves p21ras (ref. 5). Ras associates with the serine kinase c-Raf-1 in a GTP-dependent manner, and this complex phosphorylates and activates MAPK/ERK kinase (MEK), a protein kinase with dual specificity. MEK then activates p42mapk and (at least in mammals) p44mapk, members of the mitogen-activated protein (MAP) kinase family. FGF activates MAP kinase during mesoderm induction, and the use of dominant-negative constructs suggests that mesoderm induction by FGF requires both Ras and Raf. However, these experiments do not reveal whether Ras and Raf do act through MAP kinase to induce mesoderm or whether another pathway, such as the phosphatidylinositol 3-kinase cascade, is involved. Here we show that expression of active forms of MEK or of MAP kinase induces ventral mesoderm of the kind elicited by FGF. Overexpression of a Xenopus MAP kinase phosphatase blocks mesoderm induction by FGF, and causes characteristic defects in mesoderm formation in intact embryos, whereas inhibition of the P13 kinase and p70 S6 kinase pathways has no effect on mesoderm induction by FGF. FGF induces different types of mesoderm in a dose-dependent manner; strikingly, this is mimicked by expressing different levels of activated MEK. Together, these experiments demonstrate that activation of MAP kinases is necessary and sufficient for mesoderm formation.

Actins↗

PubMed1995

Inductive signals. Revolving vertebrates.

An old idea about the relationship between arthropod and vertebrate body plans has been given new life by studies of the signalling genes controlling dorsal and ventral development in Drosophila and Xenopus.

Amino Acid Sequence↗

PubMed1995

Surveillance of family planning services at Title X clinics and characteristics of women receiving these services, 1991.

PROBLEM/CONDITION: Public health surveillance data describing family planning services at Title X clinics and characteristics of women receiving these services during 1991 are contained in this report. These data update previously published information concerning characteristics of women and services at such clinics during 1981. REPORTING PERIOD COVERED: 1991. DESCRIPTION OF SYSTEM: Data characterizing patients and services were reported by family planning clinics to Title X grantees. These data for 1991 were provided by all 75 grantees to CDC's Family Planning Services Surveillance (FPSS) project. RESULTS: In 1991, 4.2 million women received services at Title X clinics. Overall, 69.5% of family planning patients had chosen oral contraceptives as their method of contraception, and 64.7% of patients were at or below the federal poverty level. In addition to information characterizing patients and services at Title X clinics, this report also evaluated current data-collection methods used by Title X grantees. Complexities in the analysis reflected variations in the quality and availability of data, including differences in definitions, data-collection instruments at the clinic level, and data categories. INTERPRETATION: The number and characteristics of family planning patients receiving services at Title X clinics during 1991 were similar to the number and characteristics during 1981. Furthermore, these results underscore the need to improve the quality and timeliness of family planning data and to facilitate program planning and operations at the grantee level. ACTIONS TAKEN: These surveillance findings have been communicated to state family planning administrators and to national Title X program administrators. This information will be used to assess how publicly funded family planning clinics currently contribute to health-care delivery and how these clinics might contribute to a national system of reproductive health-care services in the future.

Adolescent↗

PubMed1995

Abortion surveillance--United States, 1991.

PROBLEM/CONDITION: From 1980 through 1991, the number of legal induced abortions reported to CDC remained stable, varying each year by < or = 5%. REPORTING PERIOD COVERED: This report summarizes and reviews information reported to CDC regarding legal induced abortions obtained in the United States during 1991. DESCRIPTION OF SYSTEM: For each year since 1969, CDC has compiled abortion data received from 52 reporting areas: 50 states, the District of Columbia, and New York City. RESULTS: In 1991, 1,388,937 abortions were reported--a 2.8% decrease from 1990. The abortion ratio was 339 legal induced abortions per 1,000 live births, and the abortion rate was 24 per 1,000 women 15-44 years of age. Women who were undergoing an abortion were more likely to be young, white, and unmarried; most had had no previous live births and had been obtaining an abortion for the first time. More than half (52%) of all abortions were performed at or before the 8th week of gestation, and 88% were before the 13th week. Younger women (i.e., women < 19 years of age) were more likely to obtain abortions later in pregnancy than were older women. INTERPRETATION: Since 1980, the number and rate of abortions have remained relatively stable, with only small year-to-year fluctuations of < or = 5%. However, since 1987, the abortion-to-live-birth ratio has declined; in 1991, the abortion ratio was the lowest recorded since 1977. An increasing rate of childbearing may partially account for this decline. ACTIONS TAKEN: An accurate assessment of the number and characteristics of women who obtain abortions in the United States is necessary both to monitor efforts to prevent unintended pregnancy and to identify and reduce preventable causes of morbidity and mortality associated with abortions.

Abortion, Legal↗

PubMed1995

Mesoderm formation in response to Brachyury requires FGF signalling.

BACKGROUND: The Brachyury (T) gene is required for the formation of posterior mesoderm and for axial development in both mouse and zebrafish embryos. In these species, and in Xenopus, the gene is expressed transiently throughout the presumptive mesoderm, and transcripts then persiste in notochord and posterior tissues. In Xenopus embryos, expression of the Xenopus homologue of Brachyury, Xbra, can be induced in presumptive ectoderm by basic fibroblast growth factor (FGF) and activin; in the absence of functional FGF or activin signalling pathways, expression of the gene is severely reduced. Ectopic expression of Xbra in presumptive ectoderm causes mesoderm to be formed. As Brachyury and its homologues encode sequence-specific DNA-binding proteins, it is likely that each functions by directly activating downstream mesoderm-specific genes. RESULTS: We show that expression in Xenopus embryos of RNA encoding a dominant-negative FGF receptor inhibits the mesoderm-inducing activity of Xbra. We demonstrate that ectopic expression of Xbra activates transcription of the embryonic FGF gene, and that embryonic FGF can induce expression of Xbra. This suggests that the two genes are components of a regulatory loop. Consistent with this idea, dissociation of Xbra-expressing cells causes a dramatic and rapid reduction in levels of Xbra, but the reduction can be inhibited by addition of FGF. CONCLUSION: Formation of mesoderm tissue requires an intact FGF signalling pathway downstream of Brachyury. This requirement is due to a regulatory loop, in which Brachyury activates expression of a member of the FGF family, and FGF maintains expression of Brachyury.(ABSTRACT TRUNCATED AT 250 WORDS)

Activins↗

PubMed1995

Mesenchymal stem cells reside within the connective tissues of many organs.

Previous studies have noted the presence of mesenchymal stem cells located within the connective tissue matrices of avian skeletal muscle, dermis, and heart. In these studies, clonal analysis coupled with dexamethasone treatment revealed the presence of multiple populations of stem cells composed of both lineage-committed progenitor mesenchymal stem cells and lineage-uncommitted pluripotent mesenchymal stem cells. The present study was undertaken to assess the distribution of these stem cells in the connective tissues throughout various regions of the body. Day 11 chick embryos were divided into 26 separate regions. Heart, limb skeletal muscle, and limb dermis were included as control tissues. Cells were harvested enzymatically and grown using conditions optimal for the isolation, cryopreservation, and propagation of avian mesenchymal stem cells. Cell aliquots were plated, incubated with various concentrations of dexamethasone, and examined for differentiated phenotypes. Four recurring phenotypes appeared in dexamethasone-treated stem cells: skeletal muscle myotubes, fat cells, cartilage nodules, and bone nodules. These results suggest that progenitor mesenchymal stem cells and putative pluripotent mesenchymal stem cells with the potential to form at least four tissues of mesodermal origin have a widespread distribution throughout the body, being located within the connective tissue compartments of many organs and organ systems.

Animals↗

PubMed1995

Low-frequency vibrations in alpha-helices: helicoidal analysis of polyalanine and deoxymyoglobin molecular dynamics trajectories.

We present an approach to the analysis of low-frequency (0-200 cm-1) alpha-helix vibrations in molecular dynamics simulations. The approach employs the P-Curves algorithm [H. Sklenar, C. Etchebest, and R. Lavery, (1989) Proteins: Structure, Function and Genetics, Vol. 6, pp. 46-60] to determine the helical axis and a set of helicoidal parameters describing the axis curvature and the position of the repeating units with respect to the axis and each other. The vibrations are analyzed in terms of time correlation functions of the fluctuations of P-Curves parameters and their Fourier transforms. Simulations of polyalanine and myoglobin are analyzed. For polyalanine, global twisting, bending, and stretching vibrations are found at 11, 20, and 40 cm-1, respectively. In myoglobin, the spectra of the global helix vibrations are qualitatively different from those of polyalanine and considerably more complicated. Local vibrations of individual amino acid units in the helix backbones are also analyzed with P-Curves and compared.

Algorithms↗

PubMed1995

Lutein, lycopene, and their oxidative metabolites in chemoprevention of cancer.

Numerous epidemiological studies have demonstrated that consuming large quantities of fruits and vegetables reduces the risk for several types of human cancers. Carotenoids are abundant in fruits and vegetables and have been extensively studied as cancer preventive agents. A proposed mechanism of action for the protective effect of carotenoids against cancer is based on their antioxidant capability. Recently, we have isolated and characterized 14 new carotenoids, including seven metabolites from the extracts of human serum/plasma. This brings the total number of identified blood carotenoids to 21. Lutein and lycopene, abundant in most fruits and vegetables as well as human serum, have been shown to possess strong antioxidant capability. Among the metabolites of lutein, four results from oxidation and two from non-enzymatic dehydration. The metabolite of lycopene has been identified as 5,6-dihydroxy-5,6-dihydrolycopene, which apparently results from oxidation of lycopene to an intermediate, lycopene epoxide. This intermediate may undergo metabolic reduction to form the lycopene metabolite. Although in vivo oxidation of lutein to its metabolites has been demonstrated based on data obtained from two human studies, in vivo oxidation of lycopene to its metabolite has not yet been established. Recent preliminary studies involving healthy subjects ingesting purified lutein and zeaxanthin (a dietary dihydroxycarotenoid isomeric to lutein) are presented. We propose a possible antioxidant mechanism of action for lutein and lycopene that leads to formation of the oxidation products of these promising chemopreventive agents.

Anticarcinogenic Agents↗

PubMed1995

Unusual retention of introns in CD44 gene transcripts in bladder cancer provides new diagnostic and clinical oncological opportunities.

Increased and disorganised expression of CD44 variant exons has been demonstrated in biopsy samples of several types of human malignancy by many groups. This abnormality can be used to detect exfoliated tumour cells in the urine of bladder cancer patients. The present report demonstrates that the deranged activity of this gene in neoplasia also results in the accumulation of immature mRNA transcripts containing non-coding sequences (introns) from this gene in cancer tissues and cells. There is simultaneous overexpression of a newly identified 437 bp exon (coding sequence) located in the variably active region of the gene and of many abnormal variant exon combinations. This is the first report describing the specific retention of introns in gene transcripts in clinical diagnostic samples of tumour tissues and cells. The phenomenon was seen repeatedly in samples from cancer patients and in a cancer cell line, and thus could form the basis for a unique new and specific method of cancer diagnosis.

Aged↗

PubMed1995

Structural model of the photosynthetic reaction center of Rhodobacter capsulatus.

The reaction center (RC) from the photosynthetic bacterium Rhodobacter (Rb.) capsulatus has been the subject of a considerable amount of molecular biological and spectroscopic work aimed at improving our understanding of the primary steps of photosynthesis. However, no three-dimensional structure is available for this protein. We present here a model obtained by combining information from the structure of the highly homologous RC from Rhodopseudomonas (Rps.) viridis with molecular mechanics and simulated annealing calculations. In the Rb. capsulatus model the orientations of the bacteriochlorophyll monomer and the bacteriopheophytin on the branch inactive in electron transfer differ significantly from those in the RCs of Rps. viridis and Rb. sphaeroides. The bacteriopheophytin orientational difference is in good accord with previous linear dichroism measurements. A comparison is made of interactions between the pigments and the protein environment that may be of functional significance in Rps. viridis, Rb. sphaeroides, and Rb. capsulatus.

Amino Acids↗

PubMed1995

Atypical aortic coarctation and innominate artery stenosis associated with clubfoot and lower leg ischemia in an infant.

We report findings in a male infant born with talipes equinovarus and ischemic necrosis of the left lower leg and foot associated with atypical coarctation of the ascending aorta and stenosis and hypoplasia of the proximal innominate artery. We hypothesize that a vasculopathy of unknown etiology occurred in utero that resulted in ascending aortic arch coarctation and innominate artery stenosis. The presence of a thrombus in the coarcted segment suggests that one or more emboli could have been responsible for vascular compromise and subsequent clubfoot deformity and lower leg ischemia. Alternatively, a vasculopathy similar to that hypothesized as occurring in the aorta might also have occurred in the left anterior tibial artery, causing structural deformity and soft tissue ischemia of the left lower leg and foot. We believe that this is the first report of this association of findings.

Abnormalities, Multiple↗