Détection fortuite d’une synovite villonodulaire extra-articulaire du muscle psoas en tomographie par émission de positons au 18F-fluorodésoxyglucose

Pigmented villonodular synovitis (PVNS) is a benign but locally aggressive disorder, which commonly involves large joints. This article reports a rare case of an extra-articular PVNS located within the left psoas muscle. This lesion has been accidentally discovered during a follow-up FDG PET/CT. The patient was asymptomatic and did not undergo any surgery. This article reports that FDG PET/CT could be helpful for monitoring PVNS.     

Characterization of CD200 Ectodomain Shedding

We have previously reported the existence of a soluble form of CD200 (sCD200) in human plasma, and found sCD200 to be elevated in the plasma of Chronic Lymphocytic Leukemia (CLL) patients. CLL cells release CD200 at a constitutive level, which could be attenuated partially by ADAM28 silencing. In this study, we further explored mechanisms of CD200 shedding beyond that of ADAM28, and performed biochemical analysis of sCD200 using materials derived from purified CLL cells and Hek293 cells stably transfected with CD200, and antibodies generated specifically against either the extracellular or cytoplasmic regions of CD200. CD200 shedding was enhanced by PMA stimulation, and the loss of cell surface CD200 could be monitored as a reduction in CD200 cell surface expression by flow cytometry, in parallel with an increase in the detection of sCD200 in the supernatant. Western blot analyses and functional studies using CD200R1 expressing Hek293 cells showed that the shed CD200 detected in CLL and Hek293-hCD200 supernatants lacked the cytoplasmic domain of CD200 but retained the functional extracellular domain required for binding to, and phosphorylation of, CD200R. These data confirms that a functionally active CD200 extracellular moiety can be cleaved from the surface of CD200 expressing cells following ectodomain shedding.     

Plant Parasitic Oomycetes Such as Phytophthora Species Contain Genes Derived from Three Eukaryotic Lineages

Fungi and the oomycetes include several groups of plant pathogenic microbes. Although these two eukaryotic groups are unrelated they have a number of phenotypic similarities suggested to have evolved convergently. We have recently shown that gene transfer events have occurred from fungi to the oomycetes. These gene transfer events appear to be only one part of a complex and chimeric ancestry for the oomycete genome, which has also received genes from a red algal endosymbiont.Key Words: horizontal gene transfer, osmotrophy, phototrophy, biotrophy, endosymbiosis, fungi, Magnaporthe griseaAs genomic sampling increases, a persistent pattern of horizontal gene transfer (HGT) between microbial lineages is becoming evident.^1,2 So far, patterns of horizontal gene transfer have been identified in four main forms: (A) gene transfer between prokaryote lineages, such that a large proportion of many prokaryote genomes are likely to be chimeric,^3,4 (B) gene transfer from the prokaryote progenitors of the mitochondrion and the plastid organelles to a host eukaryote nuclear genome (e.g., refs. ^5–7), (C) gene transfer from prokaryote genomes to eukaryote microbes, often involving phagocytic eukaryotes and microbes that share similar habitats⁸ and (D) gene transfer from a eukaryotic endosymbiont to their host eukaryotic genomes.^9,10 This fourth form of gene transfer includes secondary and tertiary endosymbiotic events and has so far provided our best examples of eukaryote-to-eukaryote gene transfer.^11,12 Secondary and tertiary endosymbiotic events are typified by the engulfment of a photosynthetic eukaryote by another eukaryote followed by the reduction of the consumed photosynthetic eukaryote and transfer of genes from the endosymbiont to the host nuclei with some retargeting of the transferred gene products back to the remnant organelle.^9,10Gene transfer events can be identified using phylogenetic analysis when an individual gene tree topology contradicts a known species relationship. HGT can only be seriously considered, however, if the gene phylogeny shows that the putative HGT is nested within a donor clade with strong bootstrap support.² Endosymbiosis typically leads to multiple cases of nuclear-encoded genes demonstrating endosymbiotic ancestry, with the candidate genes grouping within a clade representing the lineage that gave rise to the progenitor of the endosymbiont.⁵ There have been multiple cases of both secondary and tertiary endosymbiosis within the eukaryotes, making the evolutionary reconstruction of phototrophy in the eukaryotes highly complex.⁹ Secondary and tertiary endosymbiotic remnant organelles are often identified by the presence of three or more membranes surrounding the organelle body.¹⁰ However, secondary endosymbiotic events have led to a range of different combinations of cell apparatus, from the total loss of the endosymbiont-derived organelle^13,14 to the maintenance of the organelle compartment¹⁰ and the possession of a remnant nucleus as a nucleomorph.¹⁵The oomycetes include the plant pathogenic Phytophthora spp. and are heterokonts (sometimes called Stramenopiles).¹⁶ The heterokonts also encompass numerous groups of photosynthetic algae (e.g., Bolidomonas, Diatoms, Xanthophyceae, Phaeophyceae and Chrysophyceae) and are proposed to be derived from an ancestrally photosynthetic cell that obtained its plastid by engulfment of a red alga.¹⁶ Cytological studies of the oomycetes have so far failed to identify a relic plastid organelle but the recent publication of the Phytophthora sojae and Phytophthora ramorum genomes identified 855 genes putatively originating from the genome of a photosynthetic microbe consistent with a phototrophic ancestry for the oomycetes.¹³Phytophthora plant pathogens include the causal agents of sudden oak death (P. ramorum), potato blight (P. infestans) and, P. sojae which causes serious root and stem rot of soybean plants. Initially, P. infestans was identified as a fungal pathogen and the causal agent of the great 1845 Irish potato famine by Rev. Miles J. Berkeley,¹⁷ due to life cycle similarities and an apparently homologous mode of plant infection to ascomycete plant pathogens. It was only with the use of molecular phylogenetic methods starting with small subunit rDNA analysis¹⁶ followed by multiple concatenated gene phylogenies¹⁸ that the oomycetes were demonstrated to group within the heterokont radiation. With the apparent phylogenetic origins of the oomycetes pinpointed it left the apparent similarities in pathogenic mechanism and infective lifecycle between the filamentous ascomycetes and the oomycetes a mysterious case of convergent evolution.¹⁹During the evolutionary analyses of the predicted proteome of the filamentous plant pathogenic ascomycete Magnaporthe grisea²⁰ we detected a series of unexpected similarities in the genomes of plant pathogenic ascomycetes and the oomycete genomes.¹³ We followed up this observation by further investigation using phylogenetic methods combined with comparative genomic analysis, which revealed a series of HGT events. We subjected our datasets to a range of tests: (A) to test that the level of support for the tree topology seen was robust given random resampling of the sequence alignments used to reconstruct the gene phylogenies; (B) to ensure that the possibility that similar topologies with the oomycete/filamentous ascomycete relationship removed could be rejected at the 0.05 confidence level and; (C) to test for alternative patterns of gene evolution including hidden paralogy (duplication with differential patterns of gene loss) were unlikely. Four of the datasets tested in this way held up to our scrutiny and were thus proposed as fungi-to-oomycete horizontal gene transfers.²¹ The predicted function of three of the four genes (CodB, a purine permease, AraJ, a sugar transporter and a PcaH an extracellular dioxygenase) could conceivably be useful for an osmotrophic microbe living in a plant associated habitat (biotrophy), suggesting that these HGT events could in-part explain the convergently evolved similarities in osmotrophy and filamentous growth habit seen in the oomycetes and fungi. Our analyses also suggested that three of these HGTs originated from a genome closely related to the last common ancestor of the Magnaporthe and Aspergillus evolutionary branches. Although the specific branching position of the transferred lineage could not be pinpointed in the fourth analysis, the same point of origin could not however be excluded. This suggests that the four HGTs we identified could be derived from the same source, a phenomenon similar in pattern (if not involving the same lineages) to that seen for phylogenetic tree topologies used to investigate the endosymbiotic events discussed above. Although these analyses do not shed any light on the circumstances in which these transfers occurred, it is possible that an intimate association between a fungus and a heterokont has led to genetic exchange and demonstrates that eukaryote-to-eukaryote gene transfers are not just associated with the acquisition of phototrophy by secondary/tertiary endosymbiosis.Our published study was conducted using only published genome sequences as a seed for comparative genomic analyses.²¹ However, with the very recent publication of two Phytophthora genomes¹³ it is possible that further analyses will identify additional candidate Phytophthora-Fungi HGT events when they are carried out. These tests may determine how pervasive the pattern of HGT is within the oomycetes.The oomycetes have been classified within the phylum Pseudofungi¹⁶ which comprises a number of microbial lineages with phenotypic similarities to true fungi, including hyphae-like structures and osmotrophy. Originally, the term Pseudofungi was used to group together ‘water-moulds’ possessing mastigonemes (tubular tri-partite hairs) on one flagellum. Currently the phylum Pseudofungi comprises the biotrophic oomycetes including parasites of plants and brown algae, the phagotrophic Developayella and the biotrophic hyphochytrids, including the diatom ectoparasite Pirsonia.¹⁶ It will be interesting to ascertain at what point within the diversification of the Pseudofungi the HGTs that are identified²¹ became fixed and how the acquisition of these phenotypes relates to the evolution of Pseudofungi phenotypes within the heterokonts. Independent of the specific ancestry of the gene transfer events within the Pseudofungi it is clear that P. sojae and P. ramorum have chimeric genomes, originating from three separate eukaryotic lineages, the ancestral heterokont nuclear genome, the red algal endosymbiont and at least four genes of fungal ancestry donated to an oomycete nuclear genome.     

Molecular modeling of vimentin filament assembly

Intermediate-filament forming proteins are known to form rod-shaped dimers that are calculated to be 45 nm in length. Molecular modeling indicates that the dimerization is promoted by interchain hydrophobic interactions between sections of α helix β and helix. Further aggregation involves the formation of tetramers in which two dimers are anti-parallel and staggered to two characteristic degrees of overlap. Modeling indicated that the degrees of stagger are dictated by the association of sections of α helix in 4-chain bundles, in which hydrophobic side chains are sequestered from contact with water. The staggered arrangement of two dimers produces a tetramer having sections of 2-chain rod in which hydrophobic side chains are exposed to water. Extension of the tetramer to form protofilaments may be driven by associations with the 2-chain regions that reduce aqueous exposure of the hydrophobic side chains. Exposure of hydrophobic groups may be reduced by the 2-chain regions folding back upon themselves so that the entire tetramer becomes a 4-chain conformation. This prediction is in line with electron microscope data showing that mixtures of the lower oligomers contain rods of uniform thickness ranging upwards from 45 nm in a series having incremental increases in length. Data from previous chemical crosslinking studies support this model and also the idea that the completed intermediate filaments each consist of seven 4-chain protofilaments. Proteins 26:472–478 © 1996 Wiley-Liss, Inc.     

Persistent infection of human oligodendrocytic and neuroglial cell lines by human coronavirus 229E

Human coronaviruses (HuCV) cause common colds. Previous reports suggest that these infectious agents may be neurotropic in humans, as they are for some mammals. With the long-term aim of providing experimental evidence for the neurotropism of HuCV and the establishment of persistent infections in the nervous system, we have evaluated the susceptibility of various human neural cell lines to acute and persistent infection by HuCV-229E. Viral antigen, infectious virus progeny and viral RNA were monitored during both acute and persistent infections. The astrocytoma cell lines U-87 MG, U-373 MG, and GL-15, as well as neuroblastoma SK-N-SH, neuroglioma H4, and oligodendrocytic MO3.13 cell lines, were all susceptible to an acute infection by HuCV-229E. The CHME-5 immortalized fetal microglial cell line was not susceptible to infection by this virus. The MO3.13 and H4 cell lines also sustained a persistent viral infection, as monitored by detection of viral antigen and infectious virus progeny. Sequencing of the S1 gene from viral RNA after approximately 130 days of infection showed two point mutations, suggesting amino acid changes during persistent infection of MO3.13 cells but none for H4 cells. Thus, persistent in vitro infection did not generate important changes in the S1 portion of the viral spike protein, which was shown for murine coronaviruses to bear hypervariable domains and to interact with cellular receptor. These results are consistent with the potential persistence of HuCV-229E in cells of the human nervous system, such as oligodendrocytes and possibly neurons, and the virus's apparent genomic stability.     

The EGF-CFC protein one-eyed pinhead is essential for nodal signaling

The zebrafish EGF-CFC gene one-eyed pinhead (oep) is required zygotically for the formation of the ventral neuroectoderm, endoderm, and prechordal plate. Here we report that embryos lacking both maternal and zygotic Oep activity are defective in germ layer formation, organizer development, and the positioning of the anterior-posterior axis. An identical phenotype is displayed by double mutants for the nodal-related genes squint and cyclops. Mutations in oep eliminate the response to Squint and Cyclops overexpression but are suppressed by expression of Activin and activated forms of the type I receptor ActRIB and Smad2. Expression of the murine EGF-CFC gene cripto rescues oep mutants. These results suggest a conserved role for EGF-CFC proteins as essential extracellular cofactors for Nodal signaling during vertebrate development.