Search PubMed⌕ Search

Biomedical subjects

R K Johnson

Publications and source records attributed to R K Johnson.

At least 91 records · Page 5Linked to original sources
PubMed1996

Effect of selection for size of testes in boars on semen and testis traits.

The objective of this study was to evaluate the effects of selection for increased size of testes on semen and testis characteristics. Boars from a line selected for increased size of testes at 150 d of age (TS, n = 25) and a randomly selected control line (C, n = 18) were used. Semen was collected three times per week for 3 wk (TRT1) then daily for 3 wk (TRT2) beginning when boar age averaged 276 d. It was followed by a 4-wk period of one collection per week and then the TRT1-TRT2 sequence was repeated. After 64 collections, boars were castrated and testes were evaluated for sperm numbers. Volume of semen, percentage of motile sperm cells, and percentage of abnormal cells in the semen did not differ (P > .05) between lines. Concentration of sperm cells in the semen was greater for TS boars at TRT 1 (35.0 million cells/mL, P < .10) and TRT 2 (29.5 million cells/mL, P < .01). Number of sperm cells per ejaculate was greater for TS boars (6.1 and 4.3 billion cells for TRT 1 and TRT 2, respectively; P < .05). Percentage of abnormal cells was less (P < .05) for boars at the younger ages. Concentration of sperm cells was 16 to 18 million cells/mL semen greater (P < .05) at the older ages. Significant differences in the shapes of the response curves with increasing collection number across lines and ages were found. These differences were small and not considered to be important. Line differences in testicular and epididymal sperm numbers and in daily sperm production were consistent with differences in semen traits. Repeatabilities of semen traits were between .16 and .74. Selection for increased size of testes can be used to improve the reproductive capacity of boars used for artificial insemination.

Aging↗
PubMed1996

Comparison of circulating concentrations of reproductive hormones in boars of lines selected for size of testes or number of ovulations and embryonal survival to concentrations in respective control lines.

The objectives of this study were to determine whether circulating concentrations of genadotropins and gonadal hormones of boars were altered as a result of selection of pigs for size of testes or for embryonal survival and(or) number of ovulations. Included in Exp. 1 and 2 were boars with the greatest estimated paired weight of testes (TS) and boars from a control (C) line. Concentrations of FSH were similar (P > .10) in boars from the TS and C lines. In Exp. 3, 4, and 5, circulating concentrations of FSH and 17 beta-estradiol (E2) were evaluated in neonates, during pubertal development, and in mature boars of lines selected for an index of number of ovulations and embryonal survival (I), and data were compared to those for boars from a respective C line. Concentrations of E2 were not different in boars from the I line and those from the C line during the early neonatal period but were greater (P < .05) in boars of the C line than in those from the I line during pubertal development. Concentrations of FSH were greater (P < .05) in mature boars from the I line than in those from the C line. In summary, selection for size of testes did not influence circulating concentrations of FSH in mature boars. The secretory pattern of E2 in boars before puberty changed as a result of selection for embryonal survival and number of ovulations in females of the I line, and the different patterns of circulating E2 early in life may result in enhanced circulating concentrations of FSH in adult boars of the I line compared with boars of the C line.

Animals↗
PubMed1996

The association between parental smoking and the diet quality of low-income children.

OBJECTIVE: To assess the association between parental smoking and the diet quality of children residing in low-income housholds in the United States. MTHODS: Data from 515 low-income children (less than or equal to 185% of the poverty line), ages 2 to 17, who participated in the 1989 and 1990 United States Department of Agriculture Continuing Survey of Food Intakes of Individuals were examined. Diet quality was assessed by examining the average daily amount of nutrients consumed per 1000 kcal for protein, fiber, and 14 essential vitamins and minerals as well as total energy, percent of energy from total fat and saturated fat, and cholesterol and sodium intakes using the 3-day average of one 24-hour recall and 2 days of diet records. Parental smoking was categorized as four levels (nonsmoker; 1 to 10, 11 to 20, and more than 20) on the basis of the average number of cigarettes smoked per day by the sample child's parents. Analysis of covariance examined differences in the children's nutrient intake among the four smoking categories while controling for race, mother's age and occupation, child age, and sex. RESULTS: Low-income children with parents who smoked (n = 235) were more likely to be white (P <.001), had younger mothers (P <.05) and were more likely to have mothers employed in blue-collar occupations (P <.001) than children whose parents were nonsmokers (N = 280). Children whose parents smoked more than 20 cigarettes per day had a higher level of energy from saturated fat, and children whose parents smoked 11 to 20 cigarettes per day had the highest cholesterol intakes in comparison with the rest of the sample. Parental smoking was also related to total fiber intake per 1000 kcal, with children of smokers having lower fiber intakes than children of nonsmokers. CONCLUSIONS: On average, low-income children of smokers had a poorer diet quality than low-income children of nonsmokers, thus increasing their future risk of chronic disease.

Adolescent↗
PubMed1995

Sperm production in boars after nine generations of selection for increased weight of testis.

Body, testis, and epididymis weights were recorded and homogenization-resistant sperm nuclei were counted to determine daily sperm production and the number of sperm stored within the cauda epididymis (CAUDASP) in 145 boars of a control line (C) and 128 boars of a line selected for increased predicted weight of testis (TS) at 150 d of age. Random samples of boars were evaluated at five ages between 70 and 450 d in Generation 8 and 15 ages between 70 and 296 d in Generation 9. Data were analyzed using an animal model that included the fixed effect of line and the linear, quadratic, and cubic effects of age. Variance components were estimated using a DFREML algorithm. Boars of the TS and C line did not differ in body weight (P > .05) in Generation 8. In Generation 9, boars of line TS were heavier between 118 and 198 d of age (P < .001); thereafter, body weights of the lines were similar (P > .05). The increase in organ weights for the testes and epididymides between 70 and 160 d of age were greater (P < .01) for boars of line TS in each generation, and differences between the lines in testis weights established around puberty were maintained at 450 d of age. Daily sperm production and CAUDASP increased more rapidly at younger ages and plateaued at greater values (P < .05) in boars of line TS. At ages less than 200 d, boars of line TS produced more sperm per gram of parenchyma than control boars.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗
PubMed1995

Growth of testes and testicular morphology after eight generations of selection for increased predicted weight of testes at 150 days of age in boars.

Weights of testes and epididymides, body weight, and morphometric measurements of testicular tissue of 75 boars of a line selected for eight generations for predicted weight of testes at 150 d of age and 75 boars of a randomly selected control line were used to evaluate the effects of selection on testicular development at 70, 100, 130, 160, and 450 d of age (n = 15 boars per line per age). Body weights for boars of the select and control line did not differ (P < .05) and the shape of the body growth curve was similar for both lines. Boars of the select line had larger testes than control boars at each age (P < .05), but there was a significant line x age interaction. The percentage increase of the select line mean over the control mean for weight of testes was 37% at 70 d, a maximum of 120% at 100 d, and 25% at 450 d. The percentage of the testes made up of seminiferous tubules differed between lines (P < .01). Lines had similar means of approximately 28% at 70 d and 71% at 450 d, but the mean for the select line was larger between 100 and 160 d of age; the greatest difference was 11.6% (control = 43.7, select = 55.3%) at 100 d. After 70 d of age, select-line boars had a greater percentage of seminiferous tubules with lumens that contained elongated spermatids (P < .10).(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗
PubMed1994

The yeast FKS1 gene encodes a novel membrane protein, mutations in which confer FK506 and cyclosporin A hypersensitivity and calcineurin-dependent growth.

FK506 and cyclosporin A (CsA) are potent immunosuppressive agents that display antifungal activity. They act by blocking a Ca(2+)-dependent signal transduction pathway leading to interleukin-2 transcription. Each drug forms a complex with its cognate cytosolic immunophilin receptor (i.e., FKBP12-FK506 and cyclophilin-CsA) which acts to inhibit the Ca2+/calmodulin-dependent protein phosphatase 2B, or calcineurin (CN). We and others have defined the Saccharomyces cerevisiae FKS1 gene by recessive mutations resulting in 100-1000-fold hypersensitivity to FK506 and CsA (as compared to wild type), but which do not affect sensitivity to a variety of other antifungal drugs. The fks1 mutant also exhibits a slow-growth phenotype that can be partially alleviated by exogenously added Ca2+ [Parent et al., J. Gen. Microbiol. 139 (1993) 2973-2984]. We have cloned FKS1 by complementation of the drug-hypersensitive phenotype. It contains a long open reading frame encoding a novel 1876-amino-acid (215 kDa) protein which shows no similarity to CN or to other protein phosphatases. The FKS1 protein is predicted to contain 10 to 12 transmembrane domains with a structure resembling integral membrane transporter proteins. Genomic disruption experiments indicate that FKS1 encodes a nonessential function; fks1::LEU2 cells exhibit the same growth and recessive drug-hypersensitive phenotypes observed in the original fks1 mutants. Furthermore, the fks1::LEU2 allele is synthetically lethal in combination with disruptions of both of the nonessential genes encoding the alternative forms of the catalytic A subunit of CN (CNA1 and CNA2). These data suggest that FKS1 provides a unique cellular function which, when absent, increases FK506 and CsA sensitivity by making the CNs (or a CN-dependent function) essential.

Amino Acid Sequence↗
PubMed1994

Interaction between FKBP12-rapamycin and TOR involves a conserved serine residue.

The yeast TOR1 and TOR2 proteins were previously discovered as putative targets of the immunosuppressive drug rapamycin. Although their cellular function is unknown, they are predicted to be at least 215 kDa in size and possess a C-terminal phosphatidylinositol (PI) kinase-related domain. We previously identified a conserved Ser residue, within the PI kinase-related domain of both yeast TOR proteins (Ser1972 in TOR1; Ser1975 in TOR2), as being the site of missense mutations conferring dominant rapamycin resistance. The Ser1972/1975 residue of yeast TOR is conserved in mammalian TOR homologs. One possibility is that this residue is critical for a direct interaction between TOR and the FKBP12-rapamycin complex. There is very recent biochemical evidence for an interaction between mammalian TOR and FKBP12-rapamycin (Brown, E. J., Albers, M. W., Shin, T. B., Ichikawa, K., Keith, C. T., Lane, W. S., and Schreiber, S. L. (1994) Nature 369, 756-758; Sabatini, D. M., Erdjument-Bromage, H., Lui, M., Tempst, P., and Snyder, S. H. (1994) Cell 78, 35-43). Using the yeast two-hybrid system, we now have obtained genetic proof of a physical interaction between FKBP12-rapamycin and TOR and have demonstrated that this interaction requires the conserved Ser residue. We have found that a small fragment of wild-type yeast TOR2 spanning Ser1975 is capable of interacting with human FKBP12 in the presence of rapamycin, whereas an Arg1975 mutant fails to interact. This effect is dependent upon rapamycin and is antagonized by FK506.

Amino Acid Sequence↗
PubMed1994

Yeast TOR (DRR) proteins: amino-acid sequence alignment and identification of structural motifs.

The yeast TOR1 (DRR1) and TOR2 (DRR2) proteins are putative targets of the immunosuppressive drug rapamycin (Rm), defined by dominant drug-resistance mutations. They share a large C-terminal domain that exhibits sequence similarity to the 110-kDa subunit of phosphatidylinositol (PI) 3-kinases. In this report, we present an amino acid (aa) sequence alignment of TOR1 (DRR1) and TOR2 (DRR2) and identify conserved and nonconserved motifs within the N-terminal domain that are indicative of possible nuclear localization. We also show that the mutations responsible for Rm resistance in four independent drr2dom alleles alter the identical aa (Ser1975-->Arg) previously identified in drr1dom mutants (Ser1972-->Arg or Asn). Models for TOR (DRR) protein function are discussed.

Alleles↗
PubMed1994

Kinetic and mutational analysis of human immunodeficiency virus type 1 reverse transcriptase inhibition by inophyllums, a novel class of non-nucleoside inhibitors.

Inophyllums are novel non-nucleoside inhibitors of human immunodeficiency virus (HIV) type 1 reverse transcriptase identified through an enzyme screening program and isolated from the plant Calophyllum inophyllum. The kinetics of reverse transcriptase inhibition by inophyllum B were characterized using recombinant purified enzyme, a heteropolymeric RNA template, and a scintillation proximity assay. Preincubation of inhibitor with the enzyme-template-primer complex for 11 min was required for maximal inhibition of reverse transcriptase to occur, suggesting that inophyllum B had a slow on-rate and that template-primer must bind to reverse transcriptase prior to inhibitor binding. Inhibition of reverse transcriptase by inophyllums was shown to be reversible. When thymidine triphosphate was the variable substrate, inophyllum B inhibited reverse transcriptase noncompetitively with a Ki of 42 nM. Enzyme inhibition with respect to template-primer was uncompetitive with a Ki of 26 nM. Reverse transcriptase enzymes containing point mutations in which tyrosine 181 was changed to either cysteine or isoleucine exhibited marginal resistance to inophyllums but were resistant to (+)-(5S)-4,5,6,7-tetrahydro-9-chloro-5-methyl-6- (3-methyl-2-butenyl)-imidazo[4,5,1-j,k][1,4]benzodiazepin-2-(1H)-t hione (TIBO R82913). A mutant enzyme in which tyrosine 188 was changed to leucine was cross-resistant to both inophyllum B and TIBO R82913, as was HIV type 2 reverse transcriptase. These studies suggest that inophyllum B and TIBO R82913 bind to distinct but overlapping sites. Inhibition of avian myeloblastosis virus reverse transcriptase and Moloney murine leukemia virus reverse transcriptase by inophyllum B was detectible, suggesting that these inhibitors may be more promiscuous than other previously described non-nucleoside inhibitors. Inophyllums were active against HIV type 1 in cell culture with IC50 values of approximately 1.5 microM. These studies imply that the inophyllums have a novel mechanism of interaction with reverse transcriptase and as such could conceivably play a role in combination therapy.

Antiviral Agents↗
PubMed1994

Rapamycin selectively inhibits the growth of childhood rhabdomyosarcoma cells through inhibition of signaling via the type I insulin-like growth factor receptor.

We show that cell lines derived from childhood alveolar rhabdomyosarcoma (RMS) are very sensitive to the growth-inhibitory effects of the immunosuppressive agent rapamycin (RAP), compared to other human cell lines (50% inhibitory concentration range of 0.1-8 ng/ml, compared to 1280 to > 10,000 ng/ml). Our data suggest that the sensitivity of RMS lines is due to RAP inhibition of insulin-like growth factor 1 receptor-mediated signaling, which is essential for continued proliferation of RMS cells. The embryonal RMS line Rh1, which was resistant to RAP in serum-containing medium (50% inhibitory concentration, 4180 ng/ml), was highly sensitive under autocrine conditions of growth, indicating that resistance was due to paracrine signaling pathways insensitive to RAP action. FK506 reversed RAP action in all cell lines, indicating a dependence on complexing with the cytosolic FK506-binding protein for activity.

Carrier Proteins↗
PubMed1994

Catalytic and ligand binding properties of the FK506 binding protein FKBP12: effects of the single amino acid substitution of Tyr82 to Leu.

The binding of FK506 and rapamycin to their cytosolic receptor FKBP12 is an intermediate step in the paths leading to their potent immunosuppressive properties. One of the amino acids defining the hydrophobic binding cleft for the macrocycles is Tyr82, which is thought to form a hydrogen bond with the amide oxygens of the common pipecolyl structural element within the two macrolides. To understand better the influence of this amino acid residue in catalytic activity (cis-trans peptidyl prolyl isomerization) and ligand binding properties, a Tyr82 to Leu site-specific modification of FKBP12 was prepared, purified and characterized. Kinetic experiments have demonstrated that the Tyr82 to Leu modification has a greater effect on catalytic properties than on ligand binding affinities, a result which indicates that these inhibitors may not be binding as true transition-state analogues. In an additional test for cellular function, expression of both wild-type and mutant human FKBP12 in a strain of Saccharomyces cerevisiae rendered resistant to rapamycin by deletion of the gene encoding a cytosolic rapamycin binding protein (RPB1), the yeast homologue of FKBP12, restored wild-type drug sensitivity.

Base Sequence↗
PubMed1994

Characterizing nutrient intakes of adolescents by sociodemographic factors.

PURPOSE: The purpose of this study was to provide a description of the current dietary intake of a large sample of U.S. adolescents and to identify sociodemographic risk factors for nutrient intakes that did not meet recommended levels. METHODS: The 1987-88 USDA Nationwide Food Consumption Survey was used to assess the nutrient intake of 933 adolescents aged 11 to 18 years. Analysis of covariance was used to determine the effect of the following on the nutrient intakes of males and females: household income and size, race, geographic region, degree of urbanization, and head of household status. Subject age was entered as a control variable. RESULTS: Vitamin A, vitamin E, calcium, magnesium, and zinc were the nutrients most often consumed below recommended levels. In addition the females consumed low levels of phosphorus and iron. Percent calories from total fat and saturated fat and mean sodium intakes were above recommended levels for the majority of the sample. Females were more likely to meet cholesterol recommendations than males. Race and region affected the most nutrient intake variables. For the females, living in the south was a significant predictor for low intakes of several essential vitamins and minerals. CONCLUSIONS: On average, the adolescents consumed diets that were low in several essential vitamins and minerals and high in some nutrients related to increased incidence of chronic disease. There were groups of teens who had dietary patterns that placed them at especially high risk, in particular the black and Southern females.

Adolescent↗
PubMed1994

Isolation of bioactive and other oxoaporphine alkaloids from two annonaceous plants, Xylopia aethiopica and Miliusa cf. banacea.

The oxoaporphine alkaloids oxophoebine [1] and liriodenine [2] have been isolated from Xylopia aethiopica (Annonaceae). Both showed selective toxicity against DNA repair and recombination deficient mutants of the yeast Saccharomyces cerevisae. Three related but inactive compounds, oxoglaucine [3], O-methylmoschatoline [4], and lysicamine [5], were also isolated from this plant. Selective toxicity was also observed for 10-methoxyliriodenine (lauterine) [6] and 10-hydroxyliriodenine [7], two oxoaporphine alkaloids isolated from Miliusa cf. banacea (Annonaceae). The structure of 10-hydroxyliriodenine [7], a novel oxoaporphine, was determined by spectroscopic methods and chemical conversion to compound 6. The role of the bioactive oxoaporphine alkaloids as DNA topoisomerase inhibitors is discussed.

Antineoplastic Agents, Phytogenic↗
PubMed1994

Biological activity of some coumarins from Sri Lankan Rutaceae.

Twelve coumarins isolated from plants of the Rutaceae collected in Sri Lanka have been subjected to a mechanism-based anticancer bioassay employing DNA repair-deficient and repair-proficient yeasts. Of these, seselin [10] and xanthyletin [11] were found to be active. Seselin also exhibited moderate cytotoxicity.

Animals↗
PubMed1994

Correlates of over- and underreporting of energy intake in healthy older men and women.

The aim of this study was to determine whether variations in physiological characteristics were predictive of over- or underreporting of energy intake in older men and women. Total energy expenditure was predicted in 81 older men (66 +/- 6 y) and 56 older women (66 +/- 6 y) from a previously developed equation that uses the doubly labeled water method. The degree of over- or underreporting of energy intake was derived by subtracting predicted total daily energy expenditure from self-reported energy intake obtained from a 3-d diet record. Older women underreported energy intake (-2206 kJ/d +/- 1841) to a greater degree than did older men (-1301 kJ/d +/- 1908) (P < or = 0.01). In men, none of the physiological variables were significantly correlated with over- or underreporting of energy intake. Among the women, percent body fat was negatively correlated with underreporting of energy intake (r = -0.42, P = 0.001). Thus, the underreporting of energy intake increased with the amount of adiposity in women.

Adipose Tissue↗