Espins and the actin cytoskeleton of hair cell stereocilia and sensory cell microvilli

The espins are novel actin-bundling proteins that are produced in multiple isoforms from a single gene. They are present at high concentration in the parallel actin bundle of hair cell stereocilia and are the target of deafness mutations in mice and humans. Espins are also enriched in the microvilli of taste receptor cells, solitary chemoreceptor cells, vomeronasal sensory neurons and Merkel cells, suggesting that espins play important roles in the microvillar projections of vertebrate sensory cells. Espins are potent actin-bundling proteins that are not inhibited by Ca2+. In cells, they efficiently elongate parallel actin bundles and, thereby, help determine the steadystate length of microvilli and stereocilia. Espins bind actin monomer via their WH2 domain and can assemble actin bundles in cells. Certain espin isoforms can also bind phosphatidylinositol 4,5-bisphosphate, profilins or SH3 proteins. These biological activities distinguish espins from other actin-bundling proteins and may make them well-suited to sensory cells.

Microsatellite DNA and isozyme variability in a west African population of Anopheles gambiae

Microsatellites are defined as tracts of tandemly repeated short DNA sequences. Polymorphisms in this class of DNA are currently being used to generate a genetic map of the mosquito Anopheles gambiae. In the present study we explore the potential of microsatellites as a tool for studying the genetic structure of natural populations of this malaria vector. Genetic polymorphism at twenty enzyme coding gene loci and eleven microsatellite DNA loci was surveyed in a population of An. gambiae from Mali, West Africa. All of the microsatellite loci surveyed were polymorphic, as compared to 40% of the isozyme loci. The mean heterozygosity for the isozyme loci was only 0.097 (+/- 0.0035), but for the microsatellite loci it was 0.732 (+/- 0.060). The pattern of variability was very different between isozymes and microsatellites. Typically, at an isozyme locus a single allele occurred at a frequency > or = 0.75, whereas at microsatellite loci the most common allele had a frequency < 0.50. We conclude that microsatellites provide a rich source of genetic polymorphisms for the study of the population genetics of An. gambiae and are in many ways superior to isozymes for this purpose. We discuss the potential for utilizing genetically mapped microsatellite loci to explore the effect of chromosomal inversions on the distribution of genetic polymorphisms in An. gambiae.

Crosstalk between miR-34a and Notch Signaling Promotes Differentiation in Apical Papilla Stem Cells (SCAPs)

Stem cells from the apical papilla (SCAPs) are important for the formation and regeneration of root dentin. Here, we examined the expression of Notch signaling components in SCAPs and investigated crosstalk between microRNA miR-34aand Notch signaling during cell differentiation. We found that human SCAPs express NOTCH2, NOTCH3, JAG2, DLL3, and HES1, and we tested the relationship between Notch signaling and both cell differentiation and miR-34a expression. NOTCH activation in SCAPs inhibited cell differentiation and up-regulated the expression of miR-34a, whereas miR-34a inhibited Notch signaling in SCAPs by directly targeting the 3'UTR of NOTCH2 and HES1 mRNA and suppressing the expression of NOTCH2, N2ICD, and HES1. DSPP, RUNX2, OSX, and OCN expression was consequently up-regulated. Thus, Notch signaling in human SCAPs plays a vital role in maintenance of these cells. miR-34a interacts with Notch signaling and promotes both odontogenic and osteogenic differentiation of SCAPs.

Hec1p, an evolutionarily conserved coiled-coil protein, modulates chromosome segregation through interaction with SMC proteins

hsHec1p, a Homo sapiens coiled-coil-enriched protein, plays an important role in M-phase progression in mammalian cells. A Saccharomyces cerevisiae protein, identical to Tid3p/Ndc80p and here designated scHec1p, has similarities in structure and biological function to hsHec1p. Budding yeast cells deleted in the scHEC1/NDC80 allele are not viable, but this lethal phenotype can be rescued by hsHEC1 under control of the endogenous scHEC1 promoter. At the nonpermissive temperature, significant mitotic delay, chromosomal missegregation, and decreased viability were observed in yeast cells with temperature-sensitive (ts) alleles of hsHEC1. In the hshec1-113 ts mutant, we found a single-point mutation changing Trp395 to a stop codon, which resulted in the expression of a C-terminally truncated 45-kDa protein. The binding of this mutated protein, hshec1-113p, to five identified hsHec1p-associated proteins was unchanged, while its binding to human SMC1 protein and yeast Smc1p was ts. Hec1p also interacts with Smc2p, and the binding of the mutated hshec1-113p to Smc2p was not ts. Overexpression of either hsHEC1 or scHEC1 suppressed the lethal phenotype of smc1-2 and smc2-6 at nonpermissive temperatures, suggesting that the interactions between Hec1p and Smc1p and -2p are biologically significant. These results suggest that Hec1 proteins play a critical role in modulating chromosomal segregation, in part, through their interactions with SMC proteins.

Alveolar macrophage TNF-alpha release and BAL cell phenotypes in sarcoidosis

The aim of this study was to investigate the relationship between release of tumor necrosis factor-alpha (TNF-alpha) by alveolar macrophages (AM) and the phenotypic characteristics of bronchoalveolar lavage (BAL) cells in sarcoidosis. We studied the spontaneous release of TNF-alpha by AM in vitro and the phenotypic characteristics of freshly recovered BAL T-cells and AM in 31 individuals (13 with active sarcoidosis, nine with inactive sarcoidosis, and nine normal controls). TNF-alpha was measured by enzyme-linked immunosorbent assay (ELISA) in supernatants from unstimulated AM after 24 h culture. Phenotypic markers of BAL cells were determined by an immunocytochemical assay. AM of patients with active sarcoidosis released more TNF-alpha (1,355 +/- 133 pg/ml/ 10(6) AM/24 h) than those of the inactive group (651 +/- 142 pg/ml/10(6) AM/24 h) or the normal controls (425 +/- 121 pg/ml/10(6) AM/24 h), with p < 0.001 for both comparisons. The amount of TNF-alpha released correlated positively with the percentage expression of CD4 (r = 0.72) and CD25 (r = 0.70) by lymphocytes, and of CD14 (r = 0.63), VLA-4 (r = 0.59), FRD1 (r = 0.67) and 27E10 (r = 0.67) by AM, with p < 0.001 for all correlations. In conclusion, this relationship suggests that these antigens may be considered as cellular activation markers, and that some of these AM antigens may indirectly characterize the AM phenotype that is capable of producing TNF-alpha.

A chemometric study of chromatograms of tea extracts by correlation optimization warping in conjunction with PCA, support vector machines and random forest data modeling

A reverse phase high performance liquid chromatography (HPLC) separation was established for profiling water soluble compounds in extracts from tea. Whole chromatograms were pre-processed by techniques including baseline correction, binning and normalisation. In addition, peak alignment by correction of retention time shifts was performed using correlation optimization warping (COW) producing a correlation score of 0.96. To extract the chemically relevant information from the data, a variety of chemometric approaches were employed. Principle component analysis (PCA) was used to group the tea samples according to their chromatographic differences. Three principal components (PCs) described 78% of the total variance after peak alignment (64% before) and analysis of the score and loading plots provided insight into the main chemical differences between the samples. Finally, PCA, support vector machines (SVMs) and random forest (RF) machine learning methods were evaluated comparatively on their ability to predict unknown tea samples using models constructed from a predetermined training set. The best predictions of identity were obtained by using RF.

Activation of human neutrophils by Mycobacterium tuberculosis H37Ra involves phospholipase C gamma 2, Shc adapter protein, and p38 mitogen-activated protein kinase

Recent studies have shown that human neutrophils play a significant protective role in mycobacteria infection. When encountered with mycobacteria, neutrophils exhibit the typical early bactericidal responses including phagocytosis and generation of reactive oxygen intermediates (ROI), but the underlying mechanisms are largely unknown. The present study shows that stimulation of neutrophils with an attenuated strain of Mycobacterium tuberculosis H37Ra (Mtb) led to a tyrosine kinase-dependent ROI production in these cells. Stimulation with Mtb induces a rapid and transient tyrosine phosphorylation of several proteins, one of which was identified as phospholipase C gamma 2 (PLC gamma 2). Several tyrosine-phosphorylated proteins were associated with the PLC gamma 2 precipitates from Mtb-stimulated neutrophils, of which pp46 was characterized as the Shc adapter protein. A role for PLC gamma 2-Shc association in the generation of ROI is supported by the observations that stimulation with Mtb causes the activation of p38 mitogen-activated protein kinase (MAPK), a downstream target of the Shc/Ras signaling cascade, and that the effect of genistein on ROI production coincided with its ability to inhibit both PLC gamma 2-Shc association and p38 MAPK activation. Moreover, pretreatment of neutrophils with a PLC inhibitor markedly suppresses the Mtb-stimulated ROI production as well as p38 MAPK activation in these cells. Taken together, these results indicate that stimulation of neutrophils with Mtb triggers the tyrosine phosphorylation of PLC gamma 2 and its association with Shc, and that such association is critical for the Mtb-stimulated ROI production through activating p38 MAPK.

The circadian clock in oral health and diseases

Most physiological processes in mammals display circadian rhythms that are driven by the endogenous circadian clock. This clock is comprised of a central component located in the hypothalamic suprachiasmatic nucleus and subordinate clocks in peripheral tissues. Circadian rhythms sustain 24-hour oscillations of a large number of master genes controlling the correct timing and synchronization of diverse physiological and metabolic processes within our bodies. This complex regulatory network provides an important communication link between our brain and several peripheral organs and tissues. At the molecular level, circadian oscillations of gene expression are regulated by a family of transcription factors called "clock genes". Dysregulation of clock gene expression results in diverse human pathological conditions, including autoimmune diseases and cancer. There is increasing evidence that the circadian clock affects tooth development, salivary gland and oral epithelium homeostasis, and saliva production. This review summarizes current knowledge of the roles of clock genes in the formation and maintenance of oral tissues, and discusses potential links between "oral clocks" and diseases such as head and neck cancer and Sjögren's syndrome.

Seasonal variation of cerebral hemorrhage in 236 consecutive cases in Brussels

BACKGROUND AND PURPOSE

Seasonal variation in the incidence of cerebral hemorrhage has been previously demonstrated. In this study, we sought to identify the climatological data best correlated with this seasonal variation.

METHODS

In a retrospectively studied sequential series of 236 patients with nontraumatic cerebral hemorrhage observed in Brussels over a period of 8 years, we cumulatively grouped the dates of stroke occurrence into a single calendar year.

RESULTS

We found marked seasonal variation in incidence, with the highest value (23%) observed in November-December and the lowest (10%) in July-August. Seasonal variations in incidence of cerebral hemorrhage were shown to be correlated not only with the inverse of ambient temperature, but also with the inverse of hours of sunshine and with ambient humidity. We found no difference between hypertensive and normotensive patients.

CONCLUSIONS

Our study fails to bear out the hypothesis that the higher incidence of cerebral hemorrhage in late autumn and winter is due to the influence of low ambient temperature on blood pressure.

Endobronchial biopsy and bronchoalveolar lavage in stable lung transplant recipients and chronic rejection

We have obtained endobronchial biopsies (EBB), bronchoalveolar lavage (BAL), and transbronchial biopsies (TBB) in 17 stable lung transplant recipients (sLTR), 8 subjects with physiologic evidence of chronic rejection (BOS), and 9 normal subjects. A striking finding was the marked neutrophilia in BAL samples from patients with BOS, in the carefully screened absence of infection. A statistically higher neutrophil count was also present in the sLTR group relative to the normal group. Median BAL neutrophil count in BOS was 100 x 10(3)/ml, range 13-1,661 10(3)/ml (p < 0.001 relative to normal subjects and sLTR). Median BAL neutrophil count in sLTR was 7 x 10(3)/ml, range 1-81 10(3)/ml (p < 0.01 relative to normal subjects). Normal subjects had a median BAL neutrophil count of 3 x 10(3)/ml, range 1-7 10(3)/ml. There was evidence of a predominance of CD8 lymphocytes in BAL from sLTR and BOS with a lower CD4/CD8 ratio in both compared to normal subjects (p < 0.05). EBB mononuclear cell counts, class II major histocompatibility complex expression, and T-cell activation markers were normal in BOS, in contrast to the sLTR group. Our data may be consistent with BOS, representing a relative resolution of an active mononuclear cell chronic inflammation, perhaps at the expense of airway fibrosis. The relevance of the BAL neutrophilia and its role in BOS pathogenesis need further longitudinal investigation.

Helicobacter pylori sero-prevalence in asthma

Asthma is a very common respiratory disease which is characterized by the presence of cytokine-mediated airway inflammation leading to smooth muscle contraction, oedema and progressive airway damage in some cases. In light of our recent finding of an increased sero-prevalence of Helicobacter pylori in bronchiectasis, we have determined serum levels of H. pylori-specific IgG in asthmatic and control subjects. Altogether 90 consecutive asthmatic [mean age +/- SD 42.6+/-16 years and 52 female (F)] and 97 healthy control subjects (mean age +/- SD 43.2+/-13.3 years and 51 female (F); P = 0.78 and 0.39 respectively) were recruited prospectively. H. pylori sero-prevalence was not significantly different between asthmatic and control subjects (P>0.05). Serum H. pylori IgG levels did not correlate with FEV1 % predicted, FVC % predicted or duration of asthma (P>0.05). Similar to the results of previously published sero-epidemiological studies, there was a weak correlation between serum H. pylori IgG with increasing age (r = 0.43, P = 0.004). Despite the sero-epidemiological association of H. pylori infection with many inflammatory conditions, our data showed no such association for middle age asthmatic patients with mild intermittent asthma in our locality.

Activation of chromosomal DNA replication in Saccharomyces cerevisiae by acidic transcriptional activation domains

A large body of evidence from viral systems has established that transcription factors play an important and direct role in activating viral DNA replication. Among the transcriptional activation domains that can stimulate viral DNA replication are acidic domains such as those derived from herpes simplex virus VP16 and the tumor suppressor p53. Here we show that acidic activation domains can also activate a cellular origin of replication in a chromosomal context. When tethered to the yeast ARS1 (autonomously replicating sequence 1) origin of replication, both VP16 and p53 activation domains can enhance origin function. In addition, the C-terminal acidic region of the yeast transcription factor ABF1, which normally activates the ARS1 origin, is sufficient for activating ARS1 function when tethered to the origin. Mutations at residues Trp-53 and Phe-54 of a 20-residue (41 to 60) activation region of p53 abolish the activation of both replication and transcription, suggesting that the same structural determinants may be employed to activate both processes in yeast. Furthermore, using a two-dimensional gel electrophoresis method, we demonstrate that the GAL4-p53 chimeric activator can activate initiation of chromosomal replication from an origin inserted at the native ARS1 locus. These findings strongly suggest functional conservation of the mechanisms used by the acidic activation domains to activate viral DNA replication in mammalian cells and chromosomal replication in yeast.

Lymphocyte subsets in bronchoalveolar lavage fluid of children without bronchopulmonary disease

Bronchoalveolar lavage (BAL) is increasingly used in the pediatric age group. However, normal values for BAL fluid (BALF) constituents are lacking. As part of an investigation to define reference values in children, we studied lymphocyte surface markers of BALF in 28 children 3 to 16 yr of age without bronchopulmonary disease. All of them were undergoing elective surgery for nonpulmonary illnesses. BAL was performed under general anaesthesia with tracheal intubation. A flexible bronchoscope (Pentax 3.5 or 4.9 mm) was wedged into the middle lobe or into one of its segments, and 3 x 1 ml/kg body weight normal saline warmed to body temperature were instilled and immediately withdrawn. The first sample was studied separately; subsequent samples were pooled for analysis. Studies on lymphocyte surface markers were performed on the pooled sample only. The distribution of B-cells, pan T-cells, and CD57 positive cells was within the range reported for adult subjects. However, CD4/CD8 ratios were lower than in adults (0.7 +/- 0.4, mean +/- SD). This decrease in the CD4/CD8 ratio was caused by an increase in CD8 cells. Comparative analysis of blood and BALF lymphocytes in a subgroup of children showed that CD4/CD8 ratios in blood were within the normal range reported for this age group and significantly higher when compared with BALF. The lower CD4/CD8 ratios in normal children have to be considered in the interpretation of BALF in children with pulmonary diseases.

Espin gene (ESPN) mutations associated with autosomal dominant hearing loss cause defects in microvillar elongation or organisation

BACKGROUND

Espins are actin bundling proteins present in hair cell stereocilia. A recessive mutation in the espin gene (Espn) has been detected in the jerker mouse and causes deafness, vestibular dysfunction, and hair cell degeneration. More recently mutations in the human espin gene (ESPN) have been described in two families affected by autosomal recessive hearing loss and vestibular areflexia.

OBJECTIVE

To report the identification of four additional ESPN mutations (S719R, D744N, R774Q, and delK848) in patients affected by autosomal dominant hearing loss without vestibular involvement.

RESULTS

To determine whether the mutated ESPN alleles affected the biological activity of the corresponding espin proteins in vivo, their ability to target and elongate the parallel actin bundles of brush border microvilli was investigated in transfected LLC-PK1-CL4 epithelial cells. For three mutated alleles clear abnormalities in microvillar length or distribution were obtained.

CONCLUSIONS

The results further strengthen the causative role of the espin gene in non-syndromic hearing loss and add new insights into espin structure and function.

Denervation Resulting in Dento-Alveolar Ankylosis Associated with Decreased Malassez Epithelium

Inferior alveolar nerve denervation causes appreciable decreases in the distribution of epithelial rests of Malassez. To explore roles of the Malassez epithelium, we attempted to evaluate possible changes in dento-alveolar tissues surrounding this epithelium by experimental denervation. We found that denervation led to dento-alveolar ankylosis with a decrease in the width of the periodontal spaces. Interestingly, with regeneration of the Malassez epithelium 10 weeks after the denervation, the periodontal space width showed a correspondingly significant increase. These findings suggest that the Malassez epithelium may be involved in the maintenance of periodontal space and that sensory innervation might be indirectly associated with it. In addition, it is of interest that denervation activated root resorption of the coronal root surface and that the consequently resorbed lacunae were repaired by cellular cementum. It is suggested that Malassez epithelium may negatively regulate root resorption and induce acellular cementum formation.

Active MR guidance of interventional devices with target-navigation

This project incorporated a novel inductive coupling structure of three micro coils into an invasive device tip to determine both its tip position and orientation. Moreover, with the introduction of a new target-navigation technique the MR scan plane was defined automatically by the invasive device orientation and target tissue location. A time domain multiplexing technique was applied for simultaneous MR imaging and device tracking. Using these techniques, the acquired MR images always showed both the invasive device and its target tissue. Thus, roadmap images and their potential misregistration errors were avoided. A graphical user interface (GUI) was also designed to assist interventional physicians in monitoring and guiding the insertion of the interventional device. Ex vivo phantom and in vivo animal experiments were performed to test this new technique. The methods developed in this project provide a new active technique for interventional device guidance using MRI. Magn Reson Med 44:56-65, 2000.

Stimulation of eukaryotic flap endonuclease-1 activities by proliferating cell nuclear antigen (PCNA) is independent of its in vitro interaction via a consensus PCNA binding region

Interaction between human flap endonuclease-1 (hFEN-1) and proliferating cell nuclear antigen (PCNA) represents a good model for interactions between multiple functional proteins involved in DNA metabolic pathways. A region of 9 conserved amino acid residues (residues Gln-337 through Lys-345) in the C terminus of human FEN-1 (hFEN-1) was shown to be responsible for the interaction with PCNA. Our current study indicates that 4 amino acid residues in hFEN-1 (Leu-340, Asp-341, Phe-343, and Phe-344) are critical for human PCNA (hPCNA) interaction. A conserved PCNA interaction motif in various proteins from assorted species has been defined as Q(1)X(2)X(3)(L/I)(4)X(5)X(6)F(7)(F/Y)(8), although our results fail to implicate Q(1) (Gln-337 in hFEN-1) as a crucial residue. Surprisingly, all hFEN-1 mutants, including L340A, D341A, F343A, and F344A, retained hPCNA-mediated stimulation of both exo- and flap endonuclease activities. Furthermore, our in vitro assay showed that hPCNA failed to bind to the scRad27 (yeast homolog of FEN-1) nuclease. However, its nuclease activities were significantly enhanced in the presence of hPCNA. Four additional Saccharomyces cerevisiae scRad27 mutants, including multiple alanine mutants and a deletion mutant of the entire PCNA binding region, were constructed to confirm this result. All of these mutants retained PCNA-driven nuclease activity stimulation. We therefore conclude that stimulation of eukaryotic hFEN-1 nuclease activities by PCNA is independent of its in vitro interaction via the PCNA binding region.

Clinicopathological concordance of dementia diagnoses by community versus tertiary care clinicians

Subjects enrolled in the Autopsy Program at the University of Southern California Alzheimer's Disease Research Center may receive clinical diagnoses from primary care providers in the community or from specialists in neurology. We reviewed the autopsy concordance rates for 463 subjects for diagnoses made by both groups of clinicians. Seventy-seven percent of the sample met neuropathological criteria for Alzheimer's disease (AD). The overall diagnostic accuracy for this sample was 81 percent. Neurologists assessed 200 of the subjects (43 percent). The diagnostic accuracy for any clinical diagnosis among the non-neurologists was 84 percent, and 78 percent (p = 0.07) among neurologists. For AD, non-neurologists had a diagnostic concordance rate of 91 percent and neurologists 87 percent. Where neuropathological AD was missed, non-neurologists had failed to detect any cognitive impairment; neurologists had diagnosed Parkinson's disease (PD) and amyotrophic lateral sclerosis (ALS). Erroneous clinical diagnoses of AD missed dementia with Lewy bodies (DLB) or AD concurrent with Parkinson's disease (PD). Our findings identify specific foci for improving clinical diagnosis of dementia among all physicians managing dementia.

Differential reactivity of brain microvascular endothelial cells to TNF reflects the genetic susceptibility to cerebral malaria

Upon infection with Plasmodium berghei ANKA (PbA), various inbred strains of mice exhibit different susceptibility to the development of cerebral malaria (CM). Tumor necrosis factor-alpha (TNF) and interferon-gamma (IFN-gamma) have been shown to be crucial mediators in the pathogenesis of this neurovascular complication. Brain microvascular endothelial cells (MVEC) represent an important target of both cytokines. In the present study, we show that brain MVEC purified from CM-susceptible (CM-S) CBA/J mice and CM-resistant (CM-R) BALB/c mice exhibit a different sensitivity to TNF. CBA/J brain MVEC displayed a higher capacity to produce IL-6 and to up-regulate intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) in response to TNF than BALB/c brain MVEC. In contrast, no difference was found in the induction of E-selectin after TNF challenge. CM-S brain MVEC were also significantly more sensitive to TNF-induced lysis. This differential reactivity to TNF was further substantiated by comparing TNF receptor expression on CM-S and CM-R brain MVEC. Although the constitutive expression of TNF receptors was comparable on cells from the two origins, TNF induced an up-regulation of both p55 and p75 TNF receptors in CM-S, but not in CM-R brain MVEC. A similar regulation was found at the level of TNF receptor mRNA, but not for receptor shedding. Although a protein kinase C inhibitor blocked the response to TNF in both the brain MVEC, an inhibitor of protein kinase A selectively abolished the response to TNF in CM-R, but not CM-S brain MVEC, suggesting a differential protein kinase involvement in TNF-induced activation of CM-S and CM-R brain MVEC. These results indicate that brain MVEC purified from CM-S and CM-R mice exhibit distinctive sensitivity to TNF This difference may be partly due to a differential regulation of TNF receptors and via distinct protein kinase pathways.

Population genetics of the potentially invasive African fruit fly species, Ceratitis rosa and Ceratitis fasciventris (Diptera: Tephritidae)

A set of 10 microsatellite markers was used to survey the levels of genetic variability and to analyse the genetic aspects of the population dynamics of two potentially invasive pest fruit fly species, Ceratitis rosa and C. fasciventris, in Africa. The loci were derived from the closely related species, C. capitata. The degree of microsatellite polymorphism in C. rosa and C. fasciventris was extensive and comparable to that of C. capitata. In C. rosa, the evolution of microsatellite polymorphism in its distribution area reflects the colonization history of this species. The mainland populations are more polymorphic than the island populations. Low levels of differentiation were found within the Africa mainland area, while greater levels of differentiation affect the islands. Ceratitis fasciventris is a central-east African species. The microsatellite data over the Uganda/Kenya spatial scale suggest a recent expansion and possibly continuing gene flow within this area. The microsatellite variability data from C. rosa and C. fasciventris, together with those of C. capitata, support the hypothesis of an east African origin of the Ceratitis spp.

WdChs4p, a homolog of chitin synthase 3 in Saccharomyces cerevisiae, alone cannot support growth of Wangiella (Exophiala) dermatitidis at the temperature of infection

By using improved transformation methods for Wangiella dermatitidis, and a cloned fragment of its chitin synthase 4 structural gene (WdCHS4) as a marking sequence, the full-length gene was rescued from the genome of this human pathogenic fungus. The encoded chitin synthase product (WdChs4p) showed high homology with Chs3p of Saccharomyces cerevisiae and other class IV chitin synthases, and Northern blotting showed that WdCHS4 was expressed at constitutive levels under all conditions tested. Reduced chitin content, abnormal yeast clumpiness and budding kinetics, and increased melanin secretion resulted from the disruption of WdCHS4 suggesting that WdChs4p influences cell wall structure, cellular reproduction, and melanin deposition, respectively. However, no significant loss of virulence was detected when the wdchs4Delta strain was tested in an acute mouse model. Using a wdchs1Delta wdchs2Delta wdchs3Delta triple mutant of W. dermatitidis, which grew poorly but adequately at 25 degrees C, we assayed WdChs4p activity in the absence of activities contributed by its three other WdChs proteins. Maximal activity required trypsin activation, suggesting a zymogenic nature. The activity also had a pH optimum of 7.5, was most stimulated by Mg(2+), and was more inhibited by polyoxin D than by nikkomycin Z. Although the WdChs4p activity had a broad temperature optimum between 30 to 45 degrees C in vitro, this activity alone did not support the growth of the wdchs1Delta wdchs2Delta wdchs3Delta triple mutant at 37 degrees C, a temperature commensurate with infection.

Genetic characterization of toxin A-negative, toxin B-positive Clostridium difficile isolates by PCR

Toxin-specific enzyme immunoassays, cytotoxicity assays, and PCR were used to analyze 48 toxin A-negative, toxin B-positive Clostridium difficile isolates from various geographical sites around the world. All the isolates were negative by the TOX-A TEST and positive by the TOX A/B TEST. A deletion of approximately 1.7 kb was found at the 3' end of the toxA gene for all the isolates, similar to the deletion in toxinotype VIII strains (e.g., C. difficile serotype F 1470). Additional PCR analysis indicated that the toxin B encoded by these isolates contains sequence variations downstream of the active site compared to the sequence of reference strain VPI 10463. This variation may extend the glucosylation spectrum to Ras proteins, as observed previously for closely related lethal toxin from Clostridium sordellii and toxin B from toxin A-negative, toxin B-positive strain F 1470. Toxin A-negative, toxin B-positive isolates have recently been associated with disease in humans, and they may be more common than was previously supposed.