Observations of the missing baryons in the warm-hot intergalactic medium.

It has been known for decades that the observed number of baryons in the local Universe falls about 30-40 per cent short1,2 of the total number of baryons predicted 3 by Big Bang nucleosynthesis, as inferred4,5 from density fluctuations of the cosmic microwave background and seen during the first 2-3 billion years of the Universe in the so-called 'Lyman α forest'6,7 (a dense series of intervening H I Lyman α absorption lines in the optical spectra of background quasars). A theoretical solution to this paradox locates the missing baryons in the hot and tenuous filamentary gas between galaxies, known as the warm-hot intergalactic medium. However, it is difficult to detect them there because the largest by far constituent of this gas-hydrogen-is mostly ionized and therefore almost invisible in far-ultraviolet spectra with typical signal-to-noise ratios8,9. Indeed, despite large observational efforts, only a few marginal claims of detection have been made so far2,10. Here we report observations of two absorbers of highly ionized oxygen (O VII) in the high-signal-to-noise-ratio X-ray spectrum of a quasar at a redshift higher than 0.4. These absorbers show no variability over a two-year timescale and have no associated cold absorption, making the assumption that they originate from the quasar's intrinsic outflow or the host galaxy's interstellar medium implausible. The O VII systems lie in regions characterized by large (four times larger than average 11 ) galaxy overdensities and their number (down to the sensitivity threshold of our data) agrees well with numerical simulation predictions for the long-sought warm-hot intergalactic medium. We conclude that the missing baryons have been found.

Protein phosphatase 2A plays a role in hydrogen peroxide-induced disruption of tight junctions in Caco-2 cell monolayers.

Evidence indicates that PP2A (protein phosphatase 2A) interacts with epithelial tight junctions and negatively regulates the integrity of the tight junction. In the present study, the role of PP2A in the hydrogen peroxide-induced disruption of the tight junction was examined in Caco-2 cell monolayers. Hydrogen peroxide-induced decrease in electrical resistance and increase in inulin permeability was associated with the dephosphorylation of occludin on threonine residues. The hydrogen peroxide-induced decrease in electrical resistance, increase in inulin permeability and redistribution of occludin and ZO (zonula occludens)-1 from the intercellular junctions were significantly attenuated by selective inhibitors of PP2A (okadaic acid and fostriecin) and by knockdown of PP2A-Calpha (the catalytic subunit of PP2A). The PP2A-Calpha protein and PP2A activity were co-immunoprecipitated with occludin, and this co-immunoprecipitation was rapidly increased by hydrogen peroxide. Hydrogen peroxideinduced increase in co-immunoprecipitation of PP2A-Calpha with occludin was prevented by PP2, a Src kinase inhibitor. GST (glutathione transferase)-pull down assays using recombinant GST-Occludin-C (C-terminal tail of occludin) and the purified PP2A showed that PP2A binds to the C-terminal domain of occludin; Src-induced tyrosine phosphorylation of GST-Occludin-C enhanced this binding. The present study shows that hydrogen peroxide increases the association of PP2A with occludin by a Src kinase-dependent mechanism, and that PP2A activity is involved in hydrogen peroxide-induced disruption of tight junctions in Caco-2 cell monolayers.

Diet-gene interactions in estrogen-induced mammary carcinogenesis in the ACI rat.

It is well accepted that hormonal, dietary and genetic factors each influence breast cancer risk. However, the underlying mechanisms and the extent to which these factors interact are largely unknown. We have demonstrated that the female ACI rat exhibits a unique genetically conferred propensity to develop mammary cancers when treated with physiological levels of 17beta-estradiol (E2). More recently, we have mapped to rat chromosome 5 a strong genetic modifier of susceptibility to E2-induced mammary cancers, termed estrogen-induced mammary cancer 1 (Emca1), and have identified potential Emca1 candidate genes. Because estrogens have been inextricably linked to the genesis of breast cancer in humans, the ACI rat model has the potential to reveal novel physiologically relevant insights into how the contributory actions of E2 are modified by specific dietary factors. In the present study, we have examined the ability of a 40% restriction of dietary energy consumption to inhibit E2-induced mammary carcinogenesis. The hypothesis tested was that energy restriction will inhibit mammary carcinogenesis even when circulating E2 remains elevated through administration of exogenous hormone. The data presented herein strongly suggest that energy restriction inhibits E2-induced mammary carcinogenesis in the ACI rat at least partly by retarding progression of atypical hyperplastic foci to carcinoma.

Susceptibility to estrogen-induced mammary cancer segregates as an incompletely dominant phenotype in reciprocal crosses between the ACI and Copenhagen rat strains.

Estrogens have been inextricably linked to the etiology of breast cancer. We have demonstrated that the female ACI rat exhibits a unique propensity to develop mammary cancers when treated continuously with physiological levels of 17 beta-estradiol (E2). The E2-induced mammary cancers are estrogen dependent and exhibit genomic instability. In contrast, the genetically related Copenhagen (COP) rat strain is relatively resistant to E2-induced mammary cancers. In this study we evaluated susceptibility to E2-induced mammary cancers in first filial (F(1)), second filial (F(2)), and backcross (BC) progeny generated from reciprocal intercrosses between the ACI and COP strains. F(1) progeny resembled the parental ACI strain with respect to incidence of E2-induced mammary cancers. However, latency was significantly prolonged in the F(1) populations. These data indicate that susceptibility behaves as an incompletely dominant phenotype in these crosses. Analysis of phenotypes exhibited by the F(1), F(2), and BC populations suggests that mammary cancer susceptibility is modified by one or two genetic loci in the reciprocal intercrosses between the ACI and COP strains. Susceptibility to E2-induced mammary cancers did not correlate with E2-induced pituitary growth in the genetically diverse F(2) and BC populations, suggesting that the genetic bases for susceptibility to E2-induced mammary cancers differ from those for E2-induced lactotroph hyperplasia.

Resolving the structure of ionized helium in the intergalactic medium with the far ultraviolet spectroscopic explorer.

The neutral hydrogen (H I) and ionized helium (He II) absorption in the spectra of quasars are unique probes of structure in the early universe. We present Far-Ultraviolet Spectroscopic Explorer observations of the line of sight to the quasar HE2347-4342 in the 1000 to 1187 angstrom band at a resolving power of 15,000. We resolve the He II Lyman alpha (Lyalpha) absorption as a discrete forest of absorption lines in the redshift range 2.3 to 2.7. About 50 percent of these features have H I counterparts with column densities N(H I) > 10(12.3) per square centimeter that account for most of the observed opacity in He II Lyalpha. The He II to H I column density ratio ranges from 1 to >1000, with an average of approximately 80. Ratios of <100 are consistent with photoionization of the absorbing gas by a hard ionizing spectrum resulting from the integrated light of quasars, but ratios of >100 in many locations indicate additional contributions from starburst galaxies or heavily filtered quasar radiation. The presence of He II Lyalpha absorbers with no H I counterparts indicates that structure is present even in low-density regions, consistent with theoretical predictions of structure formation through gravitational instability.

The effect of frequency on the visual perception of relative phase and phase variability of two oscillating objects.

Relative phase has been studied extensively as a measure of interlimb coordination. Only two relative phases, namely 0 degrees and 180 degrees, are stably produced at the preferred frequency (approximately 1 Hz). When frequency is increased, movement at 180 degrees becomes unstable and relative phase typically switches to 0 degrees, which remains stable at higher frequencies. The current study was designed to investigate the perception of relative phase and of phase variability. Observers viewed two circles moving rhythmically in a computer display. Mean phases varied from 0 degrees to 180 degrees in 30 degrees steps. Phase variability at each mean phase varied from 0 degrees to 5 degrees, 10 degrees, and 15 degrees phase standard deviation (SD). Frequency of oscillation was either 0.75 Hz or 1.25 Hz. One group of ten observers judged mean relative phase. Another group judged phase variability. As predicted, increase in frequency yielded an increase in perceived phase variability at 180 degrees mean phase and other mean phases, but not at 0 degrees mean phase. In contrast, increase in actual phase variability affected judgments of 0 degrees mean phase most strongly. A second control experiment showed that the frequency effects were not produced by changes in display durations or frames per cycle of oscillation. The results are consistent with those in studies of interlimb coordination and indicate that understanding of interlimb coordination requires further investigation of phase perception.

Distortions in definite distance and shape perception as measured by reaching without and with haptic feedback.

Psychophysical studies reveal distortions in perception of distance and shape. Are reaches calibrated to eliminate distortions? Participants reached to the front, side, or back of a target sphere. In Experiment 1, feedforward reaches yielded distortion and outward drift. In Experiment 2, haptic feedback corrected distortions and instability. In Experiment 3, feedforward reaches with only haptic experience of targets replicated the shape distortions but drifted inward. This showed that outward drift in Experiment 1 was visually driven. In Experiment 4, visually guided reaches were accurate when participants used binocular vision but when they used monocular vision, reaches were distorted. Haptic feedback corrected inaccuracy and instability of distance but did not correct monocular shape distortions. Dynamic binocular vision is representative and accurate and merits further study.

Enhancement of human immunodeficiency virus type 1-specific CD4 and CD8 T cell responses in chronically infected persons after temporary treatment interruption.

Immunologic and virologic outcomes of treatment interruption were compared for 5 chronically human immunodeficiency virus (HIV)-infected persons who have maintained antiretroviral therapy-mediated virus suppression, as compared with 5 untreated controls. After a median interruption of 55 days of therapy accompanied by rebound of virus, reinitiated therapy in 4 of 5 subjects resulted in suppression of 98.86% of plasma virus load by 21-33 days and no significant decrease in CD4 T cell percentage from baseline. Increased T helper responses against HIV-1 p24 antigen (P=. 014) and interferon-gamma-secreting CD8 T cell responses against HIV-1 Env (P=.004) were present during interruption of therapy and after reinitiation of treatment. The remaining subject whose treatment was interrupted did not resume treatment and continued to have a low virus load (<1080 HIV-1 RNA copies/mL) and persistent antiviral cell-mediated responses. In summary, cellular immunity against autologous HIV-1 has the potential to be acutely augmented in association with temporary treatment interruption in chronically infected persons.

Rat strain-specific actions of 17beta-estradiol in the mammary gland: correlation between estrogen-induced lobuloalveolar hyperplasia and susceptibility to estrogen-induced mammary cancers.

The genetically related ACI and Copenhagen (COP) rat strains display diametrically opposed susceptibilities to mammary cancer development when treated chronically with 17beta-estradiol (E2). Here, we compare the actions of E2 on cell proliferation and lobuloalveolar development in the mammary glands of female ACI and COP rats. After 12 wk of E2 treatment, the mammary glands of ACI rats exhibited a significantly greater proliferative response to E2, compared with COP rats, as evidenced by quantification of S phase fraction and development of lobuloalveolar hyperplasia. Focal regions of atypical epithelial hyperplasia were observed in ACI, but not COP, rats. These strain differences were not because of differences in circulating E2, progesterone or, prolactin. Two-thirds of the induced mammary cancers in ACI rats exhibited aneuploidy. The E2-induced mammary cancers regressed when hormone treatment was discontinued, indicating that they were estrogen-dependent. Progesterone receptor was expressed by the great majority of epithelial cells within the E2-induced atypical hyperplastic foci and the mammary carcinomas, suggesting a link between these lesions. These data demonstrate a correlation between E2 action in the induction of mammary cell proliferation and atypical epithelial hyperplasia and genetically conferred susceptibility to E2-induced mammary cancers.

DES action in the thymus: inhibition of cell proliferation and genetic variation.

Many tissues, including the thymus, represent direct targets of estrogen action. In contrast to many estrogen responsive tissues, the thymus undergoes a profound atrophy in response to elevated levels of estrogens. The mechanism of estrogen-induced atrophy in the thymus is unknown; however, it appears not to involve massive thymocyte apoptosis. Here, we demonstrate that the estrogen diethylstilbestrol (DES) inhibits cell proliferation within the thymic cortex, the primary site of thymocyte proliferation. Unlike glucocorticoid action, the effect of DES on thymocyte proliferation does not appear to be mediated by direct down regulation of cyclin D3. We also demonstrate for the first time that rat strains vary in their sensitivity to DES-induced thymic atrophy. This sensitivity correlates with the ability of DES to inhibit cell proliferation in the thymus. These data suggest that genetic factors may regulate estrogen action within this tissue by affecting estrogen responsive pathways that control cell proliferation.

Estrogen-induced pituitary tumor development in the ACI rat not inhibited by dietary energy restriction.

We have demonstrated that a 40% restriction of dietary energy consumption virtually abolishes the development of prolactin (PRL)-producing pituitary tumors in Fischer 344 (F344) rats treated chronically with estrogen, apparently by inhibiting the ability of estrogen to enhance survival within a rapidly proliferating lactotroph population. The purpose of the study reported here was to determine whether energy restriction exerts a similar antitumorigenic action in another rat strain, August x Copenhagen-Irish (ACI), in which PRL-producing pituitary tumors develop in response to estrogen treatment. Ovariectomized female ACI rats were either allowed to consume a control diet ad libitum or were fed a modified diet that restricted energy consumption by 40% relative to the amount of energy consumed by animals fed the control diet. We also examined the ability of 17beta-estradiol (E2) administered for 20 wk via subcutaneous Silastic implants to induce development of PRL-producing pituitary tumors. Treatment with E2 increased pituitary weight as well as the pituitary weight-to-body weight ratio and induced gross hyperprolactinemia to the same extent in ACI rats fed either the control or the energy-restricted diet. Moreover, dietary energy restriction did not affect the ability of E2 to induce pituitary cell proliferation or inhibit apoptosis, as evidenced by quantification of two surrogate markers. These data provide compelling evidence that a 40% restriction of energy consumption does not inhibit the ability of E2 to induce pituitary tumor development in the ACI rat. In conjunction with our published studies of the F344 rat strain, the data presented herein indicate that the inhibitory effects of dietary energy restriction on estrogen-induced pituitary tumor development are rat-strain specific and suggest that sensitivity to specific antitumorigenic actions of energy restriction is strongly affected by genetic background.

Genetic bases of estrogen-induced pituitary growth in an intercross between the ACI and Copenhagen rat strains: dominant mendelian inheritance of the ACI phenotype.

Estrogens stimulate cell proliferation in a variety of tissues and are widely believed to be contributing factors in the etiology of certain cancer types in humans. The molecular mechanisms through which estrogens regulate cell proliferation are currently unknown. Estrogens stimulate proliferation of the PRL-producing lactotroph of the rat anterior pituitary gland and induce development of PRL-producing pituitary tumors in several inbred rat strains. Therefore, the lactotroph provides a well defined model for identifying the mechanisms through which estrogens regulate cell proliferation and/or survival. Data from our laboratory and others indicate that the relative sensitivity to the pituitary growth-promoting actions of estrogens is highly strain specific. This allows genetics-based approaches to be used to address the molecular mechanisms through which estrogens stimulate lactotroph proliferation and induce pituitary tumor development. In the present study we have examined the ability of diethylstilbestrol (DES) to induce pituitary growth in the genetically related AxC-Irish (ACI) and Copenhagen (COP) strains and their derived F1, F2, and backcross progeny. The data presented herein indicate that the anterior pituitary gland of the ACI strain displays approximately a 2-fold greater growth response to administered DES than does the pituitary gland of the COP strain. The average pituitary weight in male ACI rats was increased from 9.2 +/- 0.2 mg (mean +/- SD in untreated rats to 63.7 +/- 12.6 mg in rats treated with DES for 12 weeks, whereas in male COP rats, DES increased pituitary weight from 12.7 +/- 0.9 to 38.1 +/- 8.2 mg. The ACI phenotype was inherited in the F1, F2, and backcross progeny of an ACI x COP intercross as a dominant genetic trait, and the approximately 30 mg of additional pituitary growth displayed by the DES-treated ACI rat, relative to that of the treated COP rat, appeared to result from the actions of a single locus. Moreover, in F1 progeny from an ACI x Brown Norway intercross, the ACI phenotype was inherited as a dominant or incompletely dominant genetic trait. These data, when compared with findings of previous studies using the Fischer 344 rat strain, provide the first indication that distinct genetic pathways contribute to regulation of estrogen-induced pituitary growth and induction of PRL-producing pituitary tumors in the ACI and F344 rat strains.

Modulation of estrogen action in the rat pituitary and mammary glands by dietary energy consumption.

We are investigating the mechanisms through which estrogens induce development of prolactin (PRL)-producing pituitary tumors and mammary carcinomas in rats and how these mechanisms are affected by dietary energy consumption. The hypothesis under examination is that dietary energy restriction inhibits tumorigenesis in estrogen-responsive tissues by altering cellular responsiveness to estrogenic hormones. In the Fischer 344 (F344) rat strain, a 40% restriction of energy consumption virtually abolishes development of estrogen-induced pituitary tumors. Inhibition of pituitary tumorigenesis in the F344 strain by energy restriction results from modulation of estrogen regulation of cell survival, not cell proliferation. In contrast, energy restriction has no inhibitory effect on estrogen-induced pituitary tumor development in the ACI rat strain. However, energy restriction markedly inhibits induction of mammary carcinomas in female ACI rats treated with 17beta-estradiol. Data presented herein indicate that dietary energy restriction modulates the responsiveness of specific cell populations to estrogenic hormones and thereby inhibits estrogen-induced tumorigenesis in a manner specific to both rat strain and tissue.

Estrogen action in the regulation of cell proliferation, cell survival, and tumorigenesis in the rat anterior pituitary gland.

Estrogens act as important regulators of cell proliferation, cell survival, and differentiation in a variety of organ systems and tissues and have been implicated in the etiology of a variety of malignant cancers and benign tumors. The anterior pituitary gland of the rat provides an excellent model for the study of estrogen action in the regulation of cell proliferation and survival. Estrogens stimulate proliferation of the prolactin (PRL)-producing lactotroph and enhance lactotroph survival. Through these actions on lactotroph proliferation and survival, estrogens induce or contribute to the development of PRL-producing pituitary tumors in several rat strains. Data from our laboratory and others indicate that estrogen-induced pituitary growth is rat strain specific and segregates as a quantitative genetic trait in crosses between different rat strains. The purpose of this review is to summarize current knowledge pertaining to estrogen action in the regulation of cell proliferation, cell survival, and tumorigenesis in the anterior pituitary gland of the rat species, Rattus norvegicus, and to illustrate the advantages of the rat pituitary gland as a model for elucidating the mechanisms through which estrogens regulate these processes.

Identification in the rat prolactin gene of sequences homologous to the distal promoter of the human prolactin gene.

The goal of the present study was to test the hypothesis that a second, more distal, promoter exists upstream from the rat prolactin (PRL) gene (rPrl) that is homologous to that identified upstream from the human prolactin gene (hPrl). The nucleotide sequence of the rat genome extending from 7.4 to 2.5 kb upstream from the proximal rPrl promoter was determined, revealing significant sequence homology to the hPrl distal promoter and its 5'-flanking domain. Using reverse transcription-polymerase chain reaction, novel rPrl transcripts that originate upstream from the proximal rPrl promoter were detected in rat uterus, spleen, pons medulla, anterior pituitary and the GH4C1 pituitary tumor cell line. Further characterization of these novel 5'-extended rPrl transcripts from GH4C1 cells indicated that they were full length, polyadenylated and properly spliced. However, data from primer extension (5'-RACE) experiments strongly suggested that the 5'-extended rPrl transcripts originate, not at the distal promoter-like motif, but at scattered sites located 60-153 bp upstream from the proximal promoter. Therefore, it appears improbable that the rat sequences homologous to the hPrl distal promoter comprise a functional promoter.

Dietary energy restriction abolishes development of prolactin-producing pituitary tumors in Fischer 344 rats treated with 17beta-estradiol.

Reduction in energy consumption is known to inhibit development of a variety of spontaneous, carcinogen-induced, and hormone-dependent cancers, but the mechanism or mechanisms by which this occurs remain unknown. We hypothesize that energy consumption may modulate development of estrogen-dependent neoplasms by altering the manner in which target cells respond to estrogens. To test this hypothesis, ovariectomized female Fischer 344 rats were fed diets that allowed consumption of different amounts of energy, and the ability of 17beta-estradiol (E2), administered for 10 wk from subcutaneous Silastic implants, to promote development of prolactin-producing pituitary tumors was examined. A 40% restriction of energy consumption virtually abolished the ability of E2 to promote development of pituitary tumors and associated hyperprolactinemia. A 25% restriction of energy consumption appeared to slightly inhibit E2-induced pituitary growth and hyperprolactinemia, but the observed degree of inhibition was not statistically significant. Interestingly, dietary energy restriction did not inhibit induction by E2 of pituitary cell proliferation and lactotroph hyperplasia. Furthermore, E2 treatment inhibited expression of testosterone-repressed prostate message-2 mRNA, a cellular marker of apoptosis, and this inhibitory effect of E2 was blocked by 40% energy restriction. These data suggest that dietary energy restriction virtually abolished E2-induced development of prolactin-producing pituitary tumors, not by blocking the ability of E2 to induce cell proliferation but rather by blocking the ability of E2 to enhance cell survival. This study and the accompanying paper provide the first indication that dietary energy consumption may modulate estrogen action at the level of the target cell.

Estrogen induction of prolactin-producing pituitary tumors in the Fischer 344 rat: modulation by dietary-energy but not protein consumption.

Our laboratory is examining the hypothesis that diet may modulate the ability of estrogens to regulate cell proliferation and survival, either of which could affect development of neoplasms in estrogen-responsive tissues. In this study, we examined whether the amount of energy and protein consumed in the diet modulates the ability of the synthetic estrogen diethylstilbestrol (DES) to induce development of prolactin-producing pituitary tumors in two strains of rat, Fischer 344 (F344) and Holtzman, that differ in their propensity to develop pituitary tumors when treated with estrogens. Male F344 rats treated with DES for 8 wk developed pituitary tumors (defined as grossly enlarged pituitary masses that displayed diffuse lactotroph hyperplasia but lacked adenomatous foci). In contrast, male Holtzman rats displayed only a modest increase in pituitary weight in response to DES. Energy consumption but not protein consumption modulated DES-induced pituitary tumorigenesis in the male F344 rat. Relative to that observed in untreated animals, pituitary weights in F344 rats treated with DES increased 11.2- and 9.2-fold in animals fed either the control diet or an equicaloric high-protein diet, respectively, but only 3.5-fold in animals fed an energy-restricted diet. In contrast, neither the amount of energy nor protein consumed in the diet affected the modest pituitary growth response of male Holtzman rats to administered DES. Energy restriction had no apparent effect on pituitary cell proliferation, either basal or DES stimulated, in these rat strains. We concluded that dietary energy restriction inhibits the ability of administered DES to induce pituitary tumor development in the F344 rat by acting at a step after induction of pituitary cell proliferation.

Dietary lignin, and insoluble fiber, enhance uterine cancer but did not influence mammary cancer induced by N-methyl-N-nitrosourea in rats.

Previous investigations suggested potential breast cancer-preventive properties of dietary fiber from cabbage. The purpose of the present investigation was to determine whether lignin, a component of cabbage fiber, would protect against mammary carcinogenesis by N-methyl-N-nitrosourea (MNU) in Sprague-Dawley rats. A six-week study was conducted using diets containing 0.5-5% dietary wood lignin (a readily available, purified source). These diets were well tolerated by the rats, and a carcinogenesis study using 5 mg MNU/100 g body wt i.v. at 50 days of age was conducted, with the 2.5% lignin diet fed from 6 through 8 weeks of age followed by 5% lignin diet until 20 weeks after MNU. Dietary lignin and MNU treatment increased food consumption (p < 0.05), and body weight was slightly reduced at 10 and 20 weeks after MNU in the MNU-5% lignin diet group (p < 0.05). Serum estradiol was not altered by dietary lignin or MNU treatment, but uterine weights were highest in the MNU-control diet group 4 and 12 weeks after MNU. Expression of creatine kinase B, and estrogen-responsive gene, was lower in eh uteri of the MNU-lignin diet group than in other groups at 20 weeks. Mammary carcinogenesis was not altered by dietary lignin. However, uterine endometrial adenocarcinoma was observed only in the MNU-lignin diet group (4 carcinomas/40 effective rats) (p < 0.05).