The rise and decline in Salmonella enterica serovar Enteritidis outbreaks attributed to egg-containing foods in the United States, 1973-2009.

Salmonella enterica causes an estimated 1 million domestically acquired foodborne illnesses annually. Salmonella enterica serovar Enteritidis (SE) is among the top three serovars of reported cases of Salmonella. We examined trends in SE foodborne outbreaks from 1973 to 2009 using Joinpoint and Poisson regression. The annual number of SE outbreaks increased sharply in the 1970s and 1980s but declined significantly after 1990. Over the study period, SE outbreaks were most frequently attributed to foods containing eggs. The average rate of SE outbreaks attributed to egg-containing foods reported by states began to decline significantly after 1990, and the proportion of SE outbreaks attributed to egg-containing foods began declining after 1997. Our results suggest that interventions initiated in the 1990s to decrease SE contamination of shell eggs may have been integral to preventing SE outbreaks.

Role of hydrophobic amino acid clusters in the transactivation activity of the human glucocorticoid receptor.

We have performed a mutagenesis analysis of the 58-amino-acid tau1-core peptide, which represents the core transactivation activity of the tau1 transactivation domain from the glucocorticoid receptor. Mutants with altered activity were identified by phenotypic screening in the yeast Saccharomyces cerevisiae. Most mutants with reduced activity had substitutions of hydrophobic amino acids. Most single-substitution mutants with reduced activity were localized near the N terminus of the tau1-core within a segment that has been shown previously to have a propensity for alpha-helix conformation, suggesting that this helical region is of predominant importance. The particular importance of hydrophobic residues within this region was confirmed by comparing the activities of alanine substitutions of the hydrophobic residues in this and two other helical regions. The hydrophobic residues were shown to be important for the transactivation activity of both the isolated tau1-core and the intact glucocorticoid receptor in mammalian cells. Rare mutations in helical regions I and II gave rise to increased transcriptional activation activity. These mutations increase the hydrophobicity of hydrophobic patches on each of these helices, suggesting a relationship between the hydrophobicity of the patches and transactivation activity. However, certain nonhydrophobic residues are also important for activity. Interestingly, helical region I partially matches a consensus motif found in the retinoic acid receptor, VP16, and several other activator proteins.

myc boxes, which are conserved in myc family proteins, are signals for protein degradation via the proteasome.

Cellular levels of the rapidly degraded c-myc protein play an important role in determining the proliferation status of cells. Increased levels of c-myc are frequently associated with rapidly proliferating tumor cells. We show here that myc boxes I and II, found in the N termini of all members of the myc protein family, function to direct the degradation of the c-myc protein. Both myc boxes I and II contain sufficient information to independently direct the degradation of otherwise stably expressed proteins to which they are fused. At least part of the myc box-directed degradation occurs via the proteasome. The mechanism of myc box-directed degradation appears to be conserved between yeast and mammalian cells. Our results suggest that the myc boxes may play an important role in regulating the level and activity of the c-myc protein.

Recruitment of the SWI-SNF chromatin remodeling complex as a mechanism of gene activation by the glucocorticoid receptor tau1 activation domain.

The SWI-SNF complex has been shown to alter nucleosome conformation in an ATP-dependent manner, leading to increased accessibility of nucleosomal DNA to transcription factors. In this study, we show that the SWI-SNF complex can potentiate the activity of the glucocorticoid receptor (GR) through the N-terminal transactivation domain, tau1, in both yeast and mammalian cells. GR-tau1 can directly interact with purified SWI-SNF complex, and mutations in tau1 that affect the transactivation activity in vivo also directly affect tau1 interaction with SWI-SNF. Furthermore, the SWI-SNF complex can stimulate tau1-driven transcription from chromatin templates in vitro. Taken together, these results support a model in which the GR can directly recruit the SWI-SNF complex to target promoters during glucocorticoid-dependent gene activation. We also provide evidence that the SWI-SNF and SAGA complexes represent independent pathways of tau1-mediated activation but play overlapping roles that are able to compensate for one another under some conditions.

Role of the Ada adaptor complex in gene activation by the glucocorticoid receptor.

We have shown that the Ada adaptor complex is important for the gene activation capacity of the glucocorticoid receptor in yeast. The recently isolated human Ada2 protein also increases the potency of the receptor protein in mammalian cells. The Ada pathway is of key significance for the tau1 core transactivation domain (tau1c) of the receptor, which requires Ada for activity in vivo and in vitro. Ada2 can be precipitated from nuclear extracts by a glutathione S-transferase-tau1 fusion protein coupled to agarose beads, and a direct interaction between Ada2 and tau1c can be shown by using purified proteins. This interaction is strongly reduced by a mutation in tau1c that reduces transactivation activity. Mutations affecting the Ada complex do not reverse transcriptional squelching by the tau1 domain, as they do for the VP16 transactivation domain, and thus these powerful acidic activators differ in at least some important aspects of gene activation. Mutations that reduce the activity of the tau1c domain in wild-type yeast strains cause similar reductions in ada mutants that contain little or no Ada activity. Thus, gene activation mechanisms, in addition to the Ada pathway, are involved in the activity of the tau1c domain.

Histone acetyltransferase complexes can mediate transcriptional activation by the major glucocorticoid receptor activation domain.

Previous studies have shown that the Ada adapter proteins are important for glucocorticoid receptor (GR)-mediated gene activation in yeast. The N-terminal transactivation domain of GR, tau1, is dependent upon Ada2, Ada3, and Gcn5 for transactivation in vitro and in vivo. Using in vitro techniques, we demonstrate that the GR-tau1 interacts directly with the native Ada containing histone acetyltransferase (HAT) complex SAGA but not the related Ada complex. Mutations in tau1 that reduce tau1 transactivation activity in vivo lead to a reduced binding of tau1 to the SAGA complex and conversely, mutations increasing the transactivation activity of tau1 lead to an increased binding of tau1 to SAGA. In addition, the Ada-independent NuA4 HAT complex also interacts with tau1. GAL4-tau1-driven transcription from chromatin templates is stimulated by SAGA and NuA4 in an acetyl coenzyme A-dependent manner. Low-activity tau1 mutants reduce SAGA- and NuA4-stimulated transcription while high-activity tau1 mutants increase transcriptional activation, specifically from chromatin templates. Our results demonstrate that the targeting of native HAT complexes by the GR-tau1 activation domain mediates transcriptional stimulation from chromatin templates.

Direct interaction of the tau 1 transactivation domain of the human glucocorticoid receptor with the basal transcriptional machinery.

We have used a yeast (Saccharomyces cerevisiae) cell free transcription system to study protein-protein interactions involving the tau 1 transactivation domain of the human glucocorticoid receptor that are important for transcriptional transactivation by the receptor. Purified tau 1 specifically inhibited transcription from a basal promoter derived from the CYC1 gene and from the adenovirus 2 major late core promoter in a concentration-dependent manner. This inhibition or squelching was correlated with the transactivation activity of tau 1. Recombinant yeast TATA-binding protein (yTFIID), although active in vitro, did not specifically reverse the inhibitory effect of tau 1. In addition, no specific interaction between tau 1 and yTFIID could be shown in vitro by affinity chromatography. Taken together, these results indicate that the tau 1 transactivation domain of the human glucocorticoid receptor interacts directly with the general transcriptional apparatus through some target protein(s) that is distinct from the TATA-binding factor. Furthermore, this assay can be used to identify interacting factors, since after phosphocellulose chromatography of a whole-cell yeast extract, a fraction that contained an activity which selectively counteracted the squelching effect of tau 1 was found.

Involvement of the transcription factor IID protein complex in gene activation by the N-terminal transactivation domain of the glucocorticoid receptor in vitro.

HeLa cell nuclear extracts were used to study the mechanism of activation of RNA polymerase II-mediated transcription by the N-terminal transactivation domain (tau1) of the glucocorticoid receptor in vitro. When fused to the Gal4 DNA-binding domain, the tau1 domain activated transcription approximately 9-fold in HeLa nuclear extracts. Using heat treatment to inactivate transcription factor IID (TFIID) in the extract, it was shown that the addition of purified TFIID complex, but not the TATA-binding protein alone, was sufficient to restore this level of activation. The tau1 domain was shown to interact directly with the TFIID complex. This interaction was markedly reduced by a mutation in the tau1 domain that reduces its activity. Furthermore, the interaction was specific for the TFIID complex, since no interaction was seen with TFIIIB, an analogous protein complex involved in RNA polymerase III transcription. The tau1 domain was further shown to interact with the TATA-binding protein subunit of the TFIID complex. These results suggest a mechanism by which the GR tau1 domain might contribute to gene activation by recruitment of the TFIID complex to target promoters.

Identification of single amino acid substitutions of Cys-736 that affect the steroid-binding affinity and specificity of the glucocorticoid receptor using phenotypic screening in yeast.

In this study a yeast-screening system has been developed for the isolation of rarely occurring change-of-function missense mutations in defined protein segments that have potential to give more information about the function of mutated residues. Mutagenesis of cysteine-736 was chosen for this initial study because it has been shown previously, by photoaffinity labeling, to lie in close proximity to the bound hormone molecule. After randomization of residue 736 by oligonucleotide-directed mutagenesis, two functional substitutions with serine (C736S) and threonine (C736T) were found. These were further analyzed using transactivation assays in both yeast and mammalian cells and by steroid-binding assays using wild type and mutant proteins expressed in mammalian cells. The C736S protein showed reduced sensitivity to all hormones tested in transactivation assays and a reduced affinity of hormone binding. A correspondence between sensitivity to hormones in transactivation assays and hormone-binding affinity was also observed for the C736T protein. However, in this case the sensitivity to the synthetic hormone triamcinolone acetonide was higher than that for wild type whereas the sensitivity to endogenous hormones was somewhat lower. To test the efficacy of the yeast-screening system in relation to the two informative mutations identified, all 20 alternative substitutions at position 736 were constructed and analyzed. In addition to Ser and Thr, which resulted in change of function, alanine was the only other substitution that resulted in significant activity. The activity of this mutant was indistinguishable from wild type in yeast. Thus we conclude that very conservative substitutions of cysteine-736 (C736A, C736S, and C736T) cause variable effects on hormone binding that distinguish between different glucocorticoid steroid hormones.

High level expression of the major transactivation domain of the human glucocorticoid receptor in yeast cells inhibits endogenous gene expression and cell growth.

A number of alternative mechanisms by which the DNA-bound glucocorticoid receptor transactivates gene expression have been suggested. The fact that the glucocorticoid and other steroid hormone receptors function in yeast suggests that at least one of these mechanisms has been conserved throughout evolution. Here we show that overexpression of one of the glucocorticoid receptor transactivation domains (tau 1) in yeast causes a reduction in expression of a yeast reporter gene, followed by a severe reduction in the growth rate of the yeast cells. This is analogous to the phenomenon of squelching, first described for the GAL4 protein, and suggests that the tau 1 domain of the glucocorticoid receptor functions by contacting limiting transcription factors needed for efficient gene activity. A similar level of squelching was seen after removal of the up-stream activation sequences from the yeast reporter gene, suggesting that the squelching interactions were with transcription factors needed for the activity of a basal promoter.

Cholera toxin B-gold, a retrograde tracer that can be used in light and electron microscopic immunocytochemical studies.

The purpose of this study was to test whether a new retrograde tracer, the B subunit of cholera toxin conjugated to colloidal gold particles (CTB-gold), was taken up and transported by neurons in the central nervous system of the rat. Retrograde transport of CTB-gold was assessed from axon terminals, from damaged nerve fibers, and from axons of passage. For light microscopy, CTB-gold was visualized by silver intensification; for electron microscopy, sections were silver-intensified with or without subsequent gold toning. Retrogradely transported CTB-gold was detected in neurons after survival times of 12 hours to 42 days and appeared as black punctate deposits in perikarya and proximal dendrites at the light microscope level. Ultrastructurally, the deposits were usually associated with lysosomes. Injections of CTB-gold into the caudal ventrolateral medulla or into the lateral horn of the spinal cord gave small well-defined injection sites and resulted in retrograde labelling in medullary neurons in the same locations as similarly placed injections of wheat germ agglutinin-horseradish peroxidase. When injected into the superior cervical ganglion, CTB-gold was transported to nerve cell bodies in the spinal cord, but application of CTB-gold to the cut cervical sympathetic trunk did not label neurons in the spinal cord. Injection of CTB-gold into the nodose ganglion retrogradely labelled neurons in the dorsal motor nucleus of the vagus and the nucleus ambiguus. CTB-gold was not transported anterogradely from injections sites within the medulla. Nerve fibers and cell bodies containing neuropeptides, monoamines, or neurotransmitter-synthesizing enzymes were readily immunostained after silver intensification of retrogradely transported CTB-gold. Immunoreactivity for neuropeptides and enzymes was also demonstrated ultrastructurally after silver intensification and gold toning. These results show that CTB-gold is retrogradely transported from nerve terminals and fibers of passage but not from damaged axons. CTB-gold gives well-localized injection sites and persists in neurons for weeks. Transported CTB-gold is easily visualized and its detection is compatible with light and electron microscopic immunocytochemistry. These properties make CTB-gold a valuable tool for studying the connectivity and neurochemistry of pathways in the central nervous system.

Structure and function of the glucocorticoid receptor.

Glucocorticoids cause changes in the expression of target genes via interaction with an intracellular receptor protein, the glucocorticoid receptor. This signal transduction process can be divided into a number of steps, each of which represents a functional facet of the receptor protein. These steps include (i) receptor transformation to an active form resulting from specific interaction with glucocorticoid steroid hormones, (ii) homo-dimerization, (iii) DNA-binding to specific hormone response elements in the genome and (iv) modulation of the expression levels of linked genes. These aspects of glucocorticoid receptor function have been studied using a combination of tertiary structure determination, biochemical assays and a genetic approach using a yeast system to screen for mutant receptors that are altered in function. The results show that contacts involving both the DNA and steroid binding domains are involved in dimerization and high affinity DNA binding. Genetic experiments have illuminated the role of amino acids within the recognition helix of the DNA-binding domain in discriminating between cognate DNA response elements for the glucocorticoid receptor and closely related binding sites for other nuclear receptors. Squelching experiments suggest that the N-terminal transactivation domain of the receptor contacts components of the general transcriptional machinery that appear to be distinct from the TATA binding protein, TFIID, during transactivation of gene expression by the DNA-bound receptor.

Rapid purification of glial cells using immunomagnetic separation.

By purifying glial cells from brain tissue containing a heterogeneous cell population, a number of interactions that define glial cell diversification and function within the central nervous system have been determined. The current methods for purifying glial cells, however, can be time consuming and costly. In the following study we have adapted the technique of immunomagnetic separation to separately enrich 0-2A progenitor cells and astrocytes from the rat central nervous system (CNS). In this procedure, tissue from the CNS was enzymatically dissociated and incubated in a primary antibody specific to a surface antigen found on the target cell type (e.g. A2B5 or RAN-2). The target cells were then immunologically coupled to magnetic beads, which were precoated with a secondary antibody specific to the primary, and then separated out from the heterogeneous cell population using a magnetic field. We found that the immunomagnetic separation procedure, which was completed within 2 h, produced a near pure population of glial cells (> 99%). This was confirmed by the absence of unbound cells in the bead-bound fraction. The identification and viability of bead-bound cells were established by culturing these cells and subsequently examining their morphology and antigenic expression. This study shows that glial cell types can be separated out of brain tissue to near purity using immunomagnetic separation. This simple procedure is reliable, inexpensive, and achieves levels of purity and viability comparable with currently available techniques of immunopanning and fluorescence-activated cell sorting, within a fraction of the time.

Mechanisms of transcription activation by nuclear receptors: studies on the human glucocorticoid receptor tau 1 transactivation domain.

Nuclear receptors are important signalling molecules that directly mediate the effects of hormones, vitamins and xenobiotic compounds at the level of gene expression. Several members of this superfamily of proteins have been implicated in receptor-dependent carcinogenesis. In this review, we summarise how these receptors can function as transcription factors with particular emphasis on the mechanism of transcription activation by the human glucocorticoid receptor tau 1 transactivation domain.

Effect of prostaglandin E2 and its metabolites on lower segment myometrium in vitro.

The spontaneous activity of pregnant human lower segment myometrium has been studied in vitro using strips removed at cesarean section. Contractions were measured isometrically. During the 4-h experiments there was in increase in amplitude and decrease in frequency of contractions in control preparations. Prostaglandin F2 alpha (PGF2 alpha), its metabolites and prostaglandin E2 (PGE2) have been shown to be oxytocic in vivo, but there are no published data on the oxytocic effect of PGE2 metabolites. The effect on contractile activity of adding either PGE2 or one of its initial metabolites (15-keto-PGE2, 13,14-dihydro-15-keto-PGE2 or 13,14-dihydro-PGE2) or prostaglandin A2 (PGA2) to the tissue baths has been tested. No significant or consistent change in contractility was observed after the addition of any of the compounds tested. This probably indicates an inherent difference in the response of different portions of the uterine muscle, and cannot be taken to exclude activity in the intact uterus, particularly since PGE2 is a well-known oxytocic agent in vivo. The difficulty of working with this type of preparation is stressed, since there is wide variation in contractility as well as a constantly changing pattern.

Listen while you work? The attitude of healthcare professionals to music in the operating theatre.

Although the playing of music is commonplace in the operating theatre, there is nothing in the literature examining whether staff feel this is beneficial. Questionnaires were distributed amongst a random selection of staff in practice at a district general hospital: medical staff from a range of surgical specialities, anaesthetists, and all grades of perioperative staff (nurse/operating department practitioners/healthcare assistants) were encouraged to participate. There were 121 health professionals in total working in the operating theatres. The authors compared the responses to each question amongst the respondents, to check for the tendency to correlate. Out of the 52 health professionals who responded, 36 stated that music is played in their theatre either every day, or two to three times a week. Only five respondents felt that this was too often. Fifteen percent of medical staff were of the opinion that the nursing staff controlled the choice of music. Nursing staff were almost evenly split in thinking that nursing staff, surgical staff and the whole theatre team controlled the choice of music. The majority of both nursing and medical staff felt that they enjoyed their work more and performed better when music was played in theatre. The study concluded that the majority of theatre staff found listening to music while they work a positive experience. The potential for music to have a distracting or detrimental effect on a minority of individuals should always be considered.