Crusade for iron: iron uptake in unicellular eukaryotes and its significance for virulence

The effective acquisition of iron is a pre-requisite for survival of all organisms, especially parasites that have a high iron requirement. In mammals, iron homeostasis is meticulously regulated; extracellular free iron is essentially unavailable and host iron availability has a crucial role in the host-pathogen relationship. Therefore, pathogens use specialized and effective mechanisms to acquire iron. In this review, we summarize the iron-uptake systems in eukaryotic unicellular organisms with particular focus on the pathogenic species: Candida albicans, Tritrichomonas foetus, Trypanosoma brucei and Leishmania spp. We describe the diversity of their iron-uptake mechanisms and highlight the importance of the process for virulence.     

γCOP Is Required for Apical Protein Secretion and Epithelial Morphogenesis in Drosophila melanogaster

Background

There is increasing evidence that tissue-specific modifications of basic cellular functions play an important role in development and disease. To identify the functions of COPI coatomer-mediated membrane trafficking in Drosophila development, we were aiming to create loss-of-function mutations in the γCOP gene, which encodes a subunit of the COPI coatomer complex.

Principal Findings

We found that γCOP is essential for the viability of the Drosophila embryo. In the absence of zygotic γCOP activity, embryos die late in embryogenesis and display pronounced defects in morphogenesis of the embryonic epidermis and of tracheal tubes. The coordinated cell rearrangements and cell shape changes during tracheal tube morphogenesis critically depend on apical secretion of certain proteins. Investigation of tracheal morphogenesis in γCOP loss-of-function mutants revealed that several key proteins required for tracheal morphogenesis are not properly secreted into the apical lumen. As a consequence, γCOP mutants show defects in cell rearrangements during branch elongation, in tube dilation, as well as in tube fusion. We present genetic evidence that a specific subset of the tracheal defects in γCOP mutants is due to the reduced secretion of the Zona Pellucida protein Piopio. Thus, we identified a critical target protein of COPI-dependent secretion in epithelial tube morphogenesis.

Conclusions/Significance

These studies highlight the role of COPI coatomer-mediated vesicle trafficking in both general and tissue-specific secretion in a multicellular organism. Although COPI coatomer is generally required for protein secretion, we show that the phenotypic effect of γCOP mutations is surprisingly specific. Importantly, we attribute a distinct aspect of the γCOP phenotype to the effect on a specific key target protein.     

Phylogenetic classification of transporters and other membrane proteins from Saccharomyces cerevisiae

On the basis of functional and phylogenetic criteria, we have identified a total of 229 subfamilies and 111 singletons predicted to carry out transport or other membrane functions in Saccharomyces cerevisiae. We have extended the Transporter Classification (TC) and created a Membrane Classification (MC) for non-transporter membrane proteins. Using the preliminary phylogenetic digits X, Y, Z (for new families, subfamilies, and clusters, respectively), we allocated a five-digit number to 850 proteins predicted to contain more than two transmembrane domains. Compared with a previous TC of the yeast genome, we classified an additional set of 538 membrane proteins (transporters and non-transporters) and identified 111 novel phylogenetic subfamilies. Electronic Publication     

Metabolic Tumour Burden Measured by 18F-FDG PET/CT Predicts Malignant Transformation in Patients with Neurofibromatosis Type-1

Background

To investigate the diagnostic and prognostic performances of ¹⁸F-FDG PET/CT measures of metabolic tumour burden in patients with neurofibromatosis type-1 (NF1), suspect of malignant transformation.

Methods

This retrospective study included 49 patients (15–60 years old, 30 women) with a diagnosis of NF1, followed in our Reference Centre for Rare Neuromuscular Diseases, who presented clinical signs of tumour progression (pain, neurological deficit, tumour growth). Quantitative metabolic parameters were measured on 149 tumoral targets, using semi-automatic software and the best cut off values to predict transformation was assessed by Receiver Operating Characteristics (ROC) analysis. Prognostic value of PET/CT metabolic parameters was assessed by Kaplan-Meier estimates of overall survival.

Results

Lesions were histologically documented in 40 patients: a sarcomatous transformation was found in 16, a dysplastic neurofibroma (NF) in 7, and a benign NF in 17; in the remaining 9 patients, a minimal follow-up of 12 mo (median 59 mo) confirmed the absence of transformation. The optimal cut off values for detection of malignant transformation were, in decreasing order of area under the ROC curves, a tumour-to-liver (T/L) ratio >2.5, SUV_max > 4.5, total lesion glycolysis (TLG) > 377, total metabolic tumour volume (TMTV) > 88 cm³, and heterogeneity index (HI_suv) > 1.69. The best prognostic marker was the TLG: the 4-y estimates of survival were 97% [95% CI, 90% - 100%] in patients with TLG ≤ 377 vs. 27% [95% CI, 5% - 49%] in patients with TLG > 377 (P < 0.0001; χ² 27.85; hazard ratio 13.27 [95% CI, 3.72–47.35]). T/L ratio, SUV_max and TMTV demonstrated slightly lower performance to predict survival, with χ² ranging 14.41–19.12. The HI_suv index was not predictive of survival.

Conclusion

Our study demonstrates that TLG and TMTV, as PET/CT measures of metabolic tumour burden, may be used clinically to identify sarcomatous transformation in patients with NF1 and predict overall survival, with a higher specificity for the TLG. Conventional measures such as the SUV_max, and T/L ratio also demonstrate high prognostic value.     

Phylogenetic Analysis of Thecosomata Blainville, 1824 (Holoplanktonic Opisthobranchia) Using Morphological and Molecular Data

Thecosomata is a marine zooplankton group, which played an important role in the carbonate cycle in oceans due to their shell composition. So far, there is important discrepancy between the previous morphological-based taxonomies, and subsequently the evolutionary history of Thecosomata. In this study, the remarkable planktonic sampling of TARA Oceans expedition associated with a set of various other missions allowed us to assess the phylogenetic relationships of Thecosomata using morphological and molecular data (28 S and COI genes). The two gene trees showed incongruities (e.g. Hyalocylis, Cavolinia), and high congruence between morphological and 28S trees (e.g. monophyly of Euthecosomata). The monophyly of straight shell species led us to reviving the Orthoconcha, and the split of Limacinidae led us to the revival of Embolus inflata replacing Limacina inflata. The results also jeopardized the Euthecosomata families that are based on plesiomorphic character state as in the case for Creseidae which was not a monophyletic group. Divergence times were also estimated, and suggested that the evolutionary history of Thecosomata was characterized by four major diversifying events. By bringing the knowledge of palaeontology, we propose a new evolutionary scenario for which macro-evolution implying morphological innovations were rhythmed by climatic changes and associated species turn-over that spread from the Eocene to Miocene, and were shaped principally by predation and shell buoyancy.     

Smooth Pursuit Eye Movements in Children with Strabismus and in Children with Vergence Deficits

Purpose

The objective of our study was to examine horizontal smooth pursuit performance in strabismic children and in children with vergence deficits, and to compare these data with those recorded in a group of control age-matched children.

Methods

Binocular eye movements were recorded by video-oculography in ten strabismic children (mean age: 9.8±0.8) and seven children with vergence deficits (mean age: 10.8±0.6). Data were compared to that of age-matched control children (mean age: 9.8±0.8 years).

Results

Catch-up saccades amplitude in strabismic children and in children with vergence deficits were significantly higher than in control age-matched children. Moreover, in strabismic children the amplitude of catch-up saccades was significantly higher in rightward than in leftward direction. The number of catch-up saccades was also significantly higher in rightward than in leftward direction. The gain value of pursuits in rightward direction was significantly higher in the right eye than in the left one; for the right eye, the gain value was significantly higher in rightward than in leftward direction. Binocular coordination of pursuit was better in control age-matched children than in children with vergence deficits and than in strabismic children.

Conclusions

Binocular coordination of pursuit is abnormal in children with vergence deficits and worse in strabismic children. Binocular vision plays an important role in improving binocular coordination of pursuit.     

Shifts in Microbial Community Composition Following Surface Application of Dredged River Sediments

Sediment input to the Illinois River has drastically decreased river depth and reduced habitats for aquatic organisms. Dredging is being used to remove sediment from the Illinois River, and the dredged sediment is being applied to the surface of a brownfield site in Chicago with the goal of revegetating the site. In order to determine the effects of this drastic habitat change on sediment microbial communities, we examined sediment physical, chemical, and microbial characteristics at the time of sediment application to the soil surface as well as 1 and 2 years after application. Microbial community biomass was determined by measurement of lipid phosphate. Microbial community composition was assessed using phospholipid fatty acid (PLFA) analysis, terminal restriction fragment length polymorphism (T-RFLP) analysis of 16S rRNA genes, and clone library sequencing of 16S rRNA genes. Results indicated that the moisture content, organic carbon, and total nitrogen content of the sediment all decreased over time. Total microbial biomass did not change over the course of the study, but there were significant changes in the composition of the microbial communities. PLFA analysis revealed relative increases in fungi, actinomycetes, and Gram positive bacteria. T-RFLP analysis indicated a significant shift in bacterial community composition within 1 year of application, and clone library analysis revealed relative increases in Proteobacteria, Gemmatimonadetes, and Bacteriodetes and relative decreases in Acidobacteria, Spirochaetes, and Planctomycetes. These results provide insight into microbial community shifts following land application of dredged sediment.     

Late cytoplasmic maturation of the small ribosomal subunit requires RIO proteins in Saccharomyces cerevisiae

Numerous nonribosomal trans-acting factors involved in pre-rRNA processing have been characterized, but few of them are specifically required for the last cytoplasmic steps of 18S rRNA maturation. We have recently demonstrated that Rrp10p/Rio1p is such a factor. By BLAST analysis, we identified the product of a previously uncharacterized essential gene, YNL207W/RIO2, called Rio2p, that shares 43% sequence similarity with Rrp10p/Rio1p. Rio2p homologues were identified throughout the Archaea and metazoan species. We show that Rio2p is a cytoplasmic-nuclear protein and that its depletion blocks 18S rRNA production, leading to 20S pre-rRNA accumulation. In situ hybridization reveals that in Rio2p-depleted cells, 20S pre-rRNA localizes in the cytoplasm, demonstrating that its accumulation is not due to an export defect. We also show that both Rio1p and Rio2p accumulate in the nucleus of crm1-1 cells at the nonpermissive temperature. Nuclear as well as cytoplasmic Rio2p and Rio1p cosediment with pre-40S particles. These results strongly suggest that Rio2p and Rrp10p/Rio1p are shuttling proteins which associate with pre-40S particles in the nucleus and they are not necessary for export of the pre-40S complexes but are absolutely required for the cytoplasmic maturation of 20S pre-rRNA at site D, leading to mature 40S ribosomal subunits.     

Transcriptional regulation of ATP-binding cassette transporter A1 expression by a novel signaling pathway

ATP-binding cassette transporter A1 (ABCA1) is a membrane-bound protein that regulates the efflux of cholesterol derived from internalized lipoproteins. Using a mouse macrophage cell line, this report studied the impact of low-density lipoproteins (LDL) on ABCA1 expression and the signaling pathway responsible for lipoprotein-induced ABCA1 expression. Our data demonstrated that treatment of macrophages with LDL increased ABCA1 mRNA and protein levels 4.3- and 3.5-fold, respectively. LDL also induced an ～2-fold increase in macrophage surface expression of ABCA1 and a 14-fold-increase in apolipoprotein AI-mediated cholesterol efflux. In addition, LDL significantly increased the level of phosphorylated specificity protein 1 (Sp1) and the amount of Sp1 bound to the ABCA1 promoter without alteration in total Sp1 protein level. Mutation of the Sp1 binding site in the ABCA1 promoter and inhibition of Sp1 DNA binding with mithramycin A suppressed the ABCA1 promoter activity and reduced the ABCA1 expression level induced by LDL. LDL treatment also elevated protein kinase C-ζ (PKC-ζ) phosphorylation and induced PKC-ζ binding with Sp1. Inhibition of PKC-ζ with kinase inhibitors or overexpression of kinase-dead PKC-ζ attenuated Sp1 phosphorylation and ABCA1 expression induced by LDL. These results demonstrate for the first time that activation of the PKCζ-Sp1 signaling cascade is a mechanism for regulation of LDL-induced ABCA1 expression.