Involvement of a Toxoplasma gondii Chromatin Remodeling Complex Ortholog in Developmental Regulation

The asexual cycle of the parasite Toxoplasma gondii has two developmental stages: a rapidly replicating form called a tachyzoite and a slow growing cyst form called a bradyzoite. While the importance of ATP-independent histone modifications for gene regulation in T. gondii have been demonstrated, ATP-dependent chromatin remodeling pathways have not been examined. In this study we characterized C9, an insertional mutant showing reduced expression of bradyzoite differentiation marker BAG1, in cultured human fibroblasts. This mutant contains an insertion in the gene encoding TgRSC8, which is homologous to the Saccharomyces cerevisiae proteins Rsc8p (remodel the structure of chromatin complex subunit 8) and Swi3p (switch/sucrose non-fermentable [SWI/SNF]) of ATP-dependent chromatin-remodeling complexes. In the C9 mutant, TgRSC8 is the downstream open reading frame on a dicistronic transcript. Though protein was expressed from the downstream gene of the dicistron, TgRSC8 levels were decreased in C9 from those of wild-type parasites, as determined by western immunoblot and flow cytometry. As TgRSC8 localized to the parasite nucleus, we postulated a role in gene regulation. Transcript levels of several markers were assessed by quantitative PCR to test this hypothesis. The C9 mutant displayed reduced steady state transcript levels of bradyzoite-induced genes BAG1, LDH2, SUSA1, and ENO1, all of which were significantly increased with addition of TgRSC8 to the mutant. Transcript levels of some bradyzoite markers were unaltered in C9, or unable to be increased by complementation with TgRSC8, indicating multiple pathways control bradyzoite-upregulated genes. Together, these data suggest a role for TgRSC8 in control of bradyzoite-upregulated gene expression. Thus chromatin remodeling, by both ATP-independent and dependent mechanisms, is an important mode of gene regulation during stage differentiation in parasites

Sequence Elements Necessary for Transcriptional Activation of BAD1 in the Yeast Phase of Blastomyces dermatitidis

Blastomyces dermatitidis is a dimorphic fungal pathogen that converts from mycelia or conidia to a host-adapted yeast morphotype upon infection. Conversion to the yeast form is accompanied by the production of the virulence factor BAD1. Yeast-phase-specific expression of BAD1 is transcriptionally regulated, and its promoter shares homology with that of the yeast-phase-specific gene YPS3 of Histoplasma capsulatum. Serial truncations of the BAD1 upstream region were fused to the lacZ reporter to define functional areas in the promoter. Examination of P(BAD1)-lacZ fusions in B. dermatitidis indicated that BAD1 transcription is upregulated in the yeast phase. The 63-nucleotide box A region conserved in the YPS3 upstream region was shown to be an essential component of the minimal BAD1 promoter. A matched P(YPS3)-lacZ construct indicated that this same region was needed for minimal YPS3 promoter activity in B. dermatitidis transformants. Reporter activity in H. capsulatum transformants similarly showed a requirement for box A in the minimal BAD1 promoter. Several putative transcription factor binding sites were identified within box A of BAD1. Replacement of two of these predicted sites within box A—a cAMP responsive element and a Myb binding site—sharply reduced transcriptional activity, indicating that these regions are critical in dictating the yeast-phase-specific expression of this crucial virulence determinant of B. dermatitidis

Agrobacterium tumefaciens Integrates Transfer DNA into Single Chromosomal Sites of Dimorphic Fungi and Yields Homokaryotic Progeny from Multinucleate Yeast

The dimorphic fungi Blastomyces dermatitidis and Histoplasma capsulatum cause systemic mycoses in humans and other animals. Forward genetic approaches to generating and screening mutants for biologically important phenotypes have been underutilized for these pathogens. The plant-transforming bacterium Agrobacterium tumefaciens was tested to determine whether it could transform these fungi and if the fate of transforming DNA was suited for use as an insertional mutagen. Yeast cells from both fungi and germinating conidia from B. dermatitidis were transformed via A. tumefaciens by using hygromycin resistance for selection. Transformation frequencies up to 1 per 100 yeast cells were obtained at high effector-to-target ratios of 3,000:1. B. dermatitidis and H. capsulatum ura5 lines were complemented with transfer DNA vectors expressing URA5 at efficiencies 5 to 10 times greater than those obtained using hygromycin selection. Southern blot analyses indicated that in 80% of transformants the transferred DNA was integrated into chromosomal DNA at single, unique sites in the genome. Progeny of B. dermatitidis transformants unexpectedly showed that a single round of colony growth under hygromycin selection or visible selection of transformants by lacZ expression generated homokaryotic progeny from multinucleate yeast. Theoretical analysis of random organelle sorting suggests that the majority of B. dermatitidis cells would be homokaryons after the ca. 20 generations necessary for colony formation. Taken together, the results demonstrate that A. tumefaciens efficiently transfers DNA into B. dermatitidis and H. capsulatum and has the properties necessary for use as an insertional mutagen in these fungi

Terlipressin in combination with albumin as a therapy for hepatorenal syndrome in patients aged 65 years or older

Introduction and Objectives: Clinical data for older patients with advanced liver disease are limited. This post hoc analysis evaluated the efficacy and safety of terlipressin in patients aged ≥65 years with hepatorenal syndrome using data from 3 Phase III, randomized, placebo-controlled studies(OT-0401, REVERSE, CONFIRM). Patients and Methods: The pooled population of patients aged ≥65 years (terlipressin, n = 54; placebo, n = 36) was evaluated for hepatorenal syndrome reversal—defined as a serum creatinine level ≤1.5 mg/dL (≤132.6 μmol/L) while receiving terlipressin or placebo, without renal replacement therapy, liver transplantation, or death—and the incidence of renal replacement therapy (RRT). Safety analyses included an assessment of adverse events. Results: Hepatorenal syndrome reversal was almost 2-times higher in terlipressin-treated patients compared with patients who received placebo (31.5% vs 16.7%; P = 0.143). Among surviving patients, the need for RRT was significantly reduced in the terlipressin group, with an almost 3-times lower incidence of RRT versus the placebo group (Day 90: 25.0% vs 70.6%; P = 0.005). Among 23 liver-transplant-listed patients, significantly fewer patients in the terlipressin versus placebo group needed RRT by Days 30 and 60 (P = 0.027 each). Fewer patients in the terlipressin group needed RRT post-transplant (P = 0.011). More terlipressin-treated patients who were listed for and received a liver transplant were alive and RRT-free by Day 90. No new safety signals were revealed in the older subpopulation compared with previously published data. Conclusions: Terlipressin therapy may lead to clinical improvements in highly vulnerable patients aged ≥65 years with hepatorenal syndrome. Clinical trial numbers: OT-0401, NCT00089570; REVERSE, NCT01143246; CONFIRM, NCT0277071

Modelling the effects of copper on soil organisms and processes using the free ion approach: towards a multi-species toxicity model

The free ion approach has been previously used to calculate critical limit concentrations for soil metals based on point estimates of toxicity. Here, the approach was applied to dose–response data for copper effects on seven biological endpoints in each of 19 European soils. The approach was applied using the concept of an effective dose, comprising a function of the concentrations of free copper and ‘protective’ major cations, including H+. A significant influence of H+ on the toxicity of Cu2+ was found, while the effects of other cations were inconsistent. The model could be generalised by forcing the effect of H+ and the slope of the dose–response relationship to be equal for all endpoints. This suggests the possibility of a general bioavailability model for copper effects on organisms. Furthermore, the possibility of such a model could be explored for other cationic metals such as nickel, zinc, cadmium and lead