Biomedical subjects

T E Johnson

Publications and source records attributed to T E Johnson.

At least 109 records · Page 6Linked to original sources

PubMed1993

Speciation of plutonium in potato and the gastrointestinal transfer of plutonium and americium from potato.

Complexation of Pu(IV) and Am(III) by naturally occurring agents such as citrate and phytate might enhance their uptake from the digestive tract. However, the extent to which they enhance the gastrointestinal uptake of actinides from foodstuffs is far from resolved, as this study shows. Investigations of the chemical forms of Pu(IV) and Am(III), by gel permeation chromatography, in simulated digests of potato tubers naturally radiolabelled with 239Pu(IV) and 241Am(III) have shown that neither citrate nor phytate appear to determine their chemical forms. Therefore, it is possible that these are not the complexing anions which determine the gastrointestinal transfer of these radioelements from potato meal. Isotachophoretic analyses of the juices pressed from tubers and solutions prepared by simulated digestion of potato tubers have demonstrated the presence of several low molecular weight anions. These anions might be complexing agents because they possess an isotachophoretic mobility similar to that of citrate; some of these anions remain unidentified. Whereas 239Pu and 241Am were used in the foregoing studies, 238Pu and 241Am were used to produce either in vitro or naturally radiolabelled potatoes for gastrointestinal transfer measurements using rats and hamsters. Gastrointestinal transfer values of 0.13 +/- 0.05% (mean +/- standard error of mean) and 0.16 +/- 0.06% were determined with rats for the uptake of 238Pu and 241Am, respectively, from naturally labelled potato meal. Higher gastrointestinal transfer values were obtained for hamsters: for 238Pu and 241Am the transfer values from naturally labelled meal were 0.25 +/- 0.08% and 0.33 +/- 0.07%, respectively. Similar values were observed for uptake from in vitro labelled potato meal. On the basis of the similarity of the values for the naturally labelled potato meal and for the 'spiked' potato meal it would appear that biological incorporation is not necessary for the binding of the actinides to the ligands which will determine gastrointestinal transfer.

Americium↗

PubMed1993

Comparing mutants, selective breeding, and transgenics in the dissection of aging processes of Caenorhabditis elegans.

The genetic analysis of aging processes has matured in the last ten years with reports that long-lived strains of both fruit flies and nematodes have been developed. Several attempts to identify mutants in the fruit fly with increased longevity have failed and the reasons for these failures are analyzed. A major problem in obligate sexual species, such as the fruit fly, is the presence of inbreeding depression that makes the analysis of life-history traits in homozygotes very difficult. Nevertheless, several successful genetic analyses of aging in Drosophila suggest that with careful design, fruitful analysis of induced mutants affecting life span is possible. In the nematode Caenorhabditis elegans, mutations in the age-1 gene result in a life extension of some 70%; thus age-1 clearly specifies a process involved in organismic senescence. This gene maps to chromosome II, well separated from a locus (fer-15) which is responsible for a large fertility deficit in the original stocks. There is no trade-off between either rate of development or fertility versus life span associated with the age-1 mutation. Transgenic analyses confirm that the fertility deficit can be corrected by a wild-type fer-15 transformant (transgene); however, the life span of these transformed stocks is affected by the transgenic array in an unpredictable fashion. The molecular nature of the age-1 gene remains unknown and we continue in our efforts to clone the gene.

Aging↗

PubMed1993

FRAR course on laboratory approaches to aging. Genetic influences on aging in mammals and invertebrates.

A central theme underlies this review: "Genetics offers an important tool for identifying key molecular events that are involved in specifying biological functions." This approach has been used repeatedly to understand such diverse biological phenomena as oncogenesis, development, and the cell cycle, but has only recently been applied to the analysis of organismic aging and senescence. The power of the genetic approach lies in the ability to integrate phenomena that are displayed at multiple observational levels (i.e., from the molecular to the whole organism), and the power to reveal causal factors that are not dependent upon the prejudice of the investigator. I discuss several areas where genetics has been fruitfully applied to the study of the aging processes: human genes identified by "segmental progeroid" mutations; neurological diseases of the elderly; the limited proliferative life span of human somatic cells in tissue culture; studies on the life span of the mouse; and genetic analysis of life span in shorter-lived metazoans (Drosophila melanogaster and Caenorhabditis elegans), and the yeast Saccharomyces cerevisiae.

Aging↗

PubMed1993

The diagnostic histopathologic features of ocular malaria.

BACKGROUND: The ocular complications in patients with malaria have been studied clinically by many investigators, but the histopathologic changes were rarely described and generally regarded as nonspecific. METHODS: The eye of a 53-year-old man who died of chloroquine-resistant Plasmodium falciparum malaria was studied by brightfield and polarized light microscopy. FINDINGS: An epibulbar hemorrhage that involved the conjunctiva, episclera, and tendinous insertion of the medial rectus muscle was present. Cytoadherence and rosetting of the parasitized erythrocytes were observed within the partially occluded lumens of small retinal and uveal blood vessels. The birefringence of hemozoin (malarial pigment) within the lumens of small ocular blood vessels and in the hemorrhagic epibulbar area was demonstrated by polarized light. CONCLUSION: Birefringent hemozoinemia in vascular lumens of ocular tissues indicates systemic malarial infestation by any of the four species of malaria. Cytoadherence and rosetting of the parasitized erythrocytes inside ocular capillaries and venules is diagnostic of P. falciparum and is an important cause of ocular hemorrhage.

Animals↗

PubMed1993

Absence of strong heterosis for life span and other life history traits in Caenorhabditis elegans.

We have examined crosses between wild-type strains of Caenorhabditis elegans for heterosis effects on life span and other life history traits. Hermaphrodites of all wild strains had similar life expectancies but males of two strains had shorter life spans than hermaphrodites while males of two other strains lived longer than hermaphrodites. F1 hermaphrodite progeny showed no heterosis while some heterosis for longer life span was detected in F1 males. F1 hybrids of crosses between two widely studied wild-type strains, N2 (var. Bristol) and Berg BO (var. Bergerac), were examined for rate of development, hermaphrodite fertility, and behavior; there was no heterosis for these life history traits. Both controlled variation of temperature and uncontrolled environmental variation affected the length of life of all genotypes. Significant G x E effects on life span were observed in comparisons of N2 and Berg BO hermaphrodites, or N2 hermaphrodites and males, or N2 and a Ts mutant strain (DH26). Nevertheless, within an experiment, environmental variation was minimal and life spans were quite replicable.

Animals↗

PubMed1992

Formation of open and elongating transcription complexes by RNA polymerase III.

The Saccharomyces cerevisiae transcription factors (TF) IIIB and IIIC assemble onto their respective DNA-binding sites on the SUP4 tRNA(Tyr) gene at 0 degrees C. RNA polymerase III specifically associates at 0 degrees C with this TFIIIC-TFIIIB-DNA complex to form a stable "closed" promoter complex in which the DNA surrounding the transcriptional start retains its duplex form. Promoter "opening" is a temperature-dependent and readily reversible process that involves up to 22 unwound base-pairs of DNA, and can be followed by analyzing the hyperreactivity of thymine to KMnO4 oxidation. This promoter opening increases progressively from 10 degrees C to 40 degrees C, with at least two regions within the transcription bubble appearing to melt independently. In contrast, the temperature dependence of forming an initiated transcription complex containing a 17 nucleotide nascent RNA chain displays a sharp transition between 10 degrees C and 15 degrees C. When RNA polymerase initiates transcription under conditions that limit the nascent RNA chain to less than six nucleotides, there is no displacement of the transcription bubble. These transcription complexes are distinguishable from "open" promoter complexes in their maintenance of the transcription bubble at 0 degrees C, and from transcription complexes with more extended (17 nucleotide) RNA chains in their sensitivity to disruption by heparin. In light of recent results by others that demonstrate a requirement for an RNA transcription factor in a Bombyx mori-based in vitro RNA polymerase III transcription system, we have searched for a comparable component in the S. cerevisiae-derived system. We show that if an RNA component is required in the yeast-derived system, it is not susceptible to inactivation by massive amounts of micrococcal nuclease, RNase A, or RNase T1.

Base Sequence↗

PubMed1992

Karyotypic and phenotypic changes during in vitro aging of human endothelial cells.

Karyotypic and phenotypic changes were found in human adult endothelial cells (EC) during aging in vitro. A trisomy of chromosome 11 was found in 11 out of 12 EC cultures examined, derived from 9 cell lines from 8 donors. The incidence of this trisomy in some cell lines increased over time from 0% to as much as 100% near the end of their in vitro life span. A number of oncogenes and other important genes are on chromosome 11. These genes might play a role in the changes observed. An increase in the percentage of polyploid cells was also found near the end of the in vitro life span in 6 lines. The cellular levels of two gene products characteristic of the EC, von Willebrand factor (vWF) or Factor VIII, and angiotensin converting enzyme (ACE) were also monitored. vWf was studied in 2 lines and was decreased in both with serial passage. ACE decreased in three out of the four lines examined. These chromosomal and phenotypic changes which occur with increasing age in vitro make the endothelial cell a suitable model to study in vitro culture-related changes, senescence, cardiovascular disease, and tumorigenesis.

Adult↗

PubMed1992

Mapping quantitative trait loci for behavioral traits in the mouse.

After many years of studying various behavioral characters in the mouse, it is clear that most are heritable and are specified by complexes of genes or quantitative trait loci (QTLs). In order to attain a more complete understanding of the genetic causes of individual differences in behavior, the mechanism of action of these QTLs must be elucidated. The most straightforward approach to determining the mechanism of action of a particular QTL is to identify and molecularly clone the gene; this can be done by positional cloning, which depends on precise knowledge of the genetic map position. As the genetic data base for the mouse genome continues to develop, such strategies will become increasingly easy to perform. Here we suggest a multistage strategy for QTL mapping using recombinant-inbred strains of mice: (1) characterize genomic DNA from parental strains originally used to generate the RI strains; (2) characterize the RI strains for a quantitative character and for DNA markers that differ in the parental strains; and (3) assess the quantitative character in F2 mice derived from crosses between the parental strains, then determine the genotypes of extreme F2 mice for markers that account for at least 5% of the additive genetic variance. Data from these F2 crosses can be used to test hypotheses from the analysis of RI strains, i.e., that a QTL maps to a particular region. Using data from the mouse genome data base, this strategy should allow the molecular identification of the gene based on a candidate-gene approach. We illustrate the approach with examples from our work in mapping QTLs specifying neural sensitivity to the anesthetic effects of ethanol.

Alcoholism↗

PubMed1992

The search for the genetic basis of aging: the identification of gerontogenes in the nematode Caenorhabditis elegans.

Study of C. elegans has provided much information for gerontologists. The influence of the genome on life span is clearly observable, and at least one gerontogene, age-1, has been defined. Data relating to important evolutionary questions has emerged and will continue to be used in testing current hypotheses. We are using an approach unbiased by theoretical constraints to delineate aging processes simultaneously at the molecular and organismal levels. Much remains to be discovered before fundamental questions posed in this article are answered to a satisfactory degree. The immediate agenda is the identification and isolation of gerontogenes which influence life span in invertebrate models. This work is well in hand and will lead to the unraveling of specific life-span-determining processes. At this point we may be able to predict whether analogous processes also limit life in mammals. If we are fortunate and aging processes exhibit evolutionary conservation, many exciting possibilities await. Molecular tools provided by the invertebrate system can then be used to isolate homologous mammalian gerontogenes that could be subsequently utilized in highly targeted attempts to intervene in mammalian aging. This offers the most direct strategy for identifying life-span prolongation genes in humans.

Aging↗

PubMed1992

Genetic influences on oestrous cyclicity in mice: evidence that cycle length and frequency are differentially regulated.

Studies in C57BL/6J, DBA/2J and C3H/HeJ mice and in two F1 hybrid strains (B6D2F1 and B6C3HF1) 2-5 months old revealed marked genotypic differences among inbred strains. C57 mice had three times as many regular (3-6 days) cycles as DBA and C3H mice, due largely to fewer pseudopregnant-like (7-14 day) cycles. C57 had longer regular cycles than DBA and C3H mice. Although the frequencies of regular cycles of DBA and C3H mice were similar, the cycles of C3H mice were shorter than those of DBA mice. The results indicated that the genetic determinants of the frequency of regular cycles differ from those specifying cycle length. Frequency of regular cycles of F1 hybrids was either intermediate between the parent strains (B6D2F1) or similar to the C57 strain (B6C3HF1), suggesting that regular cycle frequency shows additive genetic variation in the former crosses, but mostly dominant variance in the latter background. Regular cycles were either shorter than in both parent strains (B6D2F1) or similar to one of them (B6C3HF1), indicating heterosis and dominance for genes specifying short cycles. Although the lack of reciprocal crosses meant that maternal effects and possible genomic imprinting effects could not be assessed, these results reveal marked genetic influences on cycle length and frequency and suggest that some of the genes specifying these two traits differ.

Animals↗

PubMed1991

Two essential components of the Saccharomyces cerevisiae transcription factor TFIIIB: transcription and DNA-binding properties.

RNA polymerase III transcription factor TFIIIB from Saccharomyces cerevisiae contains at least two polypeptides, with apparent masses of 90 and 70 kDa, that were previously identified by photocrosslinking to DNA. It is shown here that TFIIIB can be chromatographically separated into two components, each of which is required for efficient tRNA gene transcription. DNA-protein photocrosslinking experiments show these two components separately contain the 90- and 70-kDa TFIIIB-specific polypeptides. The 70-kDa component forms a heparin-sensitive complex with transcription factor TFIIIC and DNA, stabilizes TFIIIC interaction with the tRNA gene promoter elements, and protects against DNase I digestion in the 3' portion of the upstream DNA sequence that is occupied by TFIIIB. The 90-kDa component of TFIIIB, which only detectably interacts with the TFIIIC-DNA complex when the 70-kDa component is also present, generates the complete DNase I protection pattern of TFIIIB and bestows heparin-insensitivity on the TFIIIB-DNA complex. The resolution of TFIIIB into two functional components further defines the probable steps and interactions involved in the formation of stable transcription complexes.

Chromatography, Ion Exchange↗

PubMed1991

Caenorhabditis elegans: a model system for space biology studies.

The utility of the nematode Caenorhabditis elegans in studies spanning aspects of development, aging, and radiobiology is reviewed. These topics are interrelated via cellular and DNA repair processes especially in the context of oxidative stress and free-radical metabolism. The relevance of these research topics to problems in space biology is discussed and properties of the space environment are outlined. Exposure to the space-flight environment can induce rapid changes in living systems that are similar to changes occurring during aging; manipulation of these environmental parameters may represent an experimental strategy for studies of development and senscence. The current and future opportunities for such space-flight experimentation are presented.

Aging↗

PubMed1991

Genetic specification of life span and self-fertility in recombinant-inbred strains of Caenorhabditis elegans.

The genetic basis of life-span and age-specific fertility has been analysed using recombinant-inbred strains of the nematode Caenorhabditis elegans. Estimates of narrow-sense heritability range from 0.05 to 0.36 for life span and from 0.36 to 0.49 for total self-fertility. Positive phenotypic and genetic correlations for life span and total fertility were also observed, although in most cases the correlations were not significant. In general, age-specific hermaphrodite fertility was positively correlated with fertility on contiguous days but was negatively correlated with fertility on more distant days. We estimate that a minimum of two to three genes specify each of these traits in this genetic background. Three single-gene markers were used to generate strain distribution patterns, and two of these were found to be linked with loci that specify life span and/or fertility. We also saw evidence for a significant environmental component affecting self-fertility.

Animals↗

PubMed1990

Increased life-span of age-1 mutants in Caenorhabditis elegans and lower Gompertz rate of aging.

A mutation in the age-1 gene of the nematode Caenorhabditis elegans has been shown to result in a 65 percent increase in mean life-span and a 110 percent increase in maximum life-span at 25 degrees. One of the hallmarks of organismic aging and senescent processes is an exponential acceleration of age-specific mortality rate with chronological age. This exponential acceleration is under genetic control: age-1 mutant hermaphrodites show a 50 percent slower rate of acceleration of mortality with chronological age than wild-type strains. Mutant males also show a lengthening of life and a slowing of the rate of acceleration of mortality, although age-1 mutant males still have significantly shorter life-spans than do hermaphrodites of the same genotype. The slower rates of acceleration of mortality are recessive characteristics of the age-1 mutant alleles examined.

Aging↗

PubMed1990

Enchondromatosis and hemangioma (Maffucci's syndrome) with orbital involvement.

Maffucci's syndrome is a rare, congenital disease of unknown cause characterized by the development of multiple enchondromas and soft-tissue hemangiomas. We treated a 34-year-old man with Maffucci's syndrome, bilateral proptosis secondary to multiple intraorbital hemangiomas, corneal exposure secondary to a left facial nerve palsy, and multiple intra-abdominal tumors. The skeletal manifestations were not clinically apparent and were only discovered after a careful radiologic survey. Simultaneous bilateral orbital cavernous hemangiomas should alert the physician to the possibility of Maffucci's syndrome.

Adult↗

PubMed1990

Genetic influences on the timing of puberty in mice.

Genetic influences on the timing of three pubertal events--vaginal opening, first vaginal cornification, and onset of cyclicity--were studied in C57BL/6J, DBA/2J, and C3H/HeJ mice and in two F1 hybrid strains (B6D2F1 and B6C3HF1). Marked genotypic differences were found. Among inbred strains, differences in the onset of vaginal opening and first vaginal cornification (C3H less than DBA less than C57) did not parallel those for the onset of cyclicity (C3H much greater than DBA = C57). Compared to parental strains, F1 hybrid strains were intermediate for times of vaginal opening and first vaginal cornification, consistent with the model in which the genetic effects on the timing of these events are additive. By contrast, onset of cyclicity occurred significantly earlier in the F1 hybrids than in their parent strains, indicating heterosis for one or more genes specifying this event. Body weights also differed among the genotypes from weaning onward, but these differences were only partially correlated with the differences in the timing of the pubertal events. Thus, genetic influences other than those affecting body weight contribute to the differential timing of pubertal events in these mouse strains. These results reveal marked genetic variation in the timing of puberty, and indicate that the set of genes specifying the timing of vaginal opening and first vaginal cornification differs from those specifying the onset of cyclicity.

Age Factors↗

PubMed1990

Nutrition and the precontest preparations of a male bodybuilder.

A 27-year-old male bodybuilder was studied during a 30-day precontest period when his goal was to lose fat and retain muscle mass. Weighted dietary intakes were obtained for each day of the study. The subject trained 6 days per week with weights and included an aerobic component on most days. Ergogenic drugs and a diuretic were self-administered. At the contest, the subject placed in the top three for his weight division. The strict diet enabled the subject to lose fat weight predictably in preparation for the contest. However, some weight lost was lean body tissue, suggesting the rate of loss was too fast. Blood chemistry studies revealed abnormalities, including hemoconcentration and alterations in cholesterol metabolism, which could have placed the subject at risk for thromboembolic phenomena because of increased blood viscosity. Those abnormalities could reflect the use of ergogenic drugs. For this subject, bodybuilding included diet, exercise, and drug regimens, which are common among competitive athletes.

Adult↗

PubMed1989

The Caenorhabditis elegans genome contains monomorphic minisatellites and simple sequences.

Many species have been shown to contain tandemly repeated short sequence DNA known as minisatellites and simple sequence motifs. Due to allelic variation in the copy number of the repeat unit these loci are usually highly polymorphic. Here we demonstrate the presence of sequences in the genome of the nematode Caenorhabditis elegans which are homologous to two sets of short sequence DNA. However, when two independent strains were compared no polymorphism for these sequences could be detected.

Animals↗