Signaling across the synapse: a role for Wnt and Dishevelled in presynaptic assembly and neurotransmitter release

Proper dialogue between presynaptic neurons and their targets is essential for correct synaptic assembly and function. At central synapses, Wnt proteins function as retrograde signals to regulate axon remodeling and the accumulation of presynaptic proteins. Loss of Wnt7a function leads to defects in the localization of presynaptic markers and in the morphology of the presynaptic axons. We show that loss of function of Dishevelled-1 (Dvl1) mimics and enhances the Wnt7a phenotype in the cerebellum. Although active zones appear normal, electrophysiological recordings in cerebellar slices from Wnt7a/Dvl1 double mutant mice reveal a defect in neurotransmitter release at mossy fiber-granule cell synapses. Deficiency in Dvl1 decreases, whereas exposure to Wnt increases, synaptic vesicle recycling in mossy fibers. Dvl increases the number of Bassoon clusters, and like other components of the Wnt pathway, it localizes to synaptic sites. These findings demonstrate that Wnts signal across the synapse on Dvl-expressing presynaptic terminals to regulate synaptic assembly and suggest a potential novel function for Wnts in neurotransmitter release.     

Novel anti-repression mechanism of H-NS proteins by a phage protein

H-NS family proteins, bacterial xenogeneic silencers, play central roles in genome organization and in the regulation of foreign genes. It is thought that gene repression is directly dependent on the DNA binding modes of H-NS family proteins. These proteins form lateral protofilaments along DNA. Under specific environmental conditions they switch to bridging two DNA duplexes. This switching is a direct effect of environmental conditions on electrostatic interactions between the oppositely charged DNA binding and N-terminal domains of H-NS proteins. The Pseudomonas lytic phage LUZ24 encodes the protein gp4, which modulates the DNA binding and function of the H-NS family protein MvaT of Pseudomonas aeruginosa. However, the mechanism by which gp4 affects MvaT activity remains elusive. In this study, we show that gp4 specifically interferes with the formation and stability of the bridged MvaT–DNA complex. Structural investigations suggest that gp4 acts as an ‘electrostatic zipper’ between the oppositely charged domains of MvaT protomers, and stabilizes a structure resembling their ‘half-open’ conformation, resulting in relief of gene silencing and adverse effects on P. aeruginosa growth. The ability to control H-NS conformation and thereby its impact on global gene regulation and growth might open new avenues to fight Pseudomonas multidrug resistance.     

Limites de la scintigraphie osseuse dans le suivi des métastases osseuses du carcinome mammaire : étude du centre tunisien

Bone metastases, a relatively frequent complication of breast carcinoma, are more and more associated with better survival. This in part through a specific detection and monitoring. In Sousse (Tunisia), bone scan is the exam most frequently performed for monitoring bone metastases, which is also the only functional exam available until December 2011. We studied the place of bone scan in the monitoring of these bone metastases. We followed 115 patients between 2000 and 2004 with a follow-up of 7 to 11 years. We used Measurable Criteria Disease response of Anderson (MDA) scintigraphic criteria. Complete remission was rare. Partial remission rate decreased gradually over time. Partial remission rate was 22.6% at the first evaluation and became equal to 10% at the fourth assessment. Stability is a false reassuring category since among the 27 cases judged to be stable after the first evaluation, only nine continued to be stable at the fourth evaluation and one at the sixth. In conclusion, bone scan is reliable only in cases of complete or partial remission. For other stages bone scintigraphy had many limitations since this examination informs about the osteoblastic reaction around metastases and not the tumour itself. ¹⁸F-FDG-PET/CT (¹⁸Fluoro-deoxy-glucose) indeed shows the metastasis metabolism itself, so is better positioned to evaluate the therapeutic response.     

Continued colonization of the human genome by mitochondrial DNA

Integration of mitochondrial DNA fragments into nuclear chromosomes (giving rise to nuclear DNA sequences of mitochondrial origin, or NUMTs) is an ongoing process that shapes nuclear genomes. In yeast this process depends on double-strand-break repair. Since NUMTs lack amplification and specific integration mechanisms, they represent the prototype of exogenous insertions in the nucleus. From sequence analysis of the genome of Homo sapiens, followed by sampling humans from different ethnic backgrounds, and chimpanzees, we have identified 27 NUMTs that are specific to humans and must have colonized human chromosomes in the last 4–6 million years. Thus, we measured the fixation rate of NUMTs in the human genome. Six such NUMTs show insertion polymorphism and provide a useful set of DNA markers for human population genetics. We also found that during recent human evolution, Chromosomes 18 and Y have been more susceptible to colonization by NUMTs. Surprisingly, 23 out of 27 human-specific NUMTs are inserted in known or predicted genes, mainly in introns. Some individuals carry a NUMT insertion in a tumor-suppressor gene and in a putative angiogenesis inhibitor. Therefore in humans, but not in yeast, NUMT integrations preferentially target coding or regulatory sequences. This is indeed the case for novel insertions associated with human diseases and those driven by environmental insults. We thus propose a mutagenic phenomenon that may be responsible for a variety of genetic diseases in humans and suggest that genetic or environmental factors that increase the frequency of chromosome breaks provide the impetus for the continued colonization of the human genome by mitochondrial DNA.     

Douleurs thoraciques et scintigraphie myocardique : à propos de 171 cas

Study aimTo find a correlation between epidemiological factors, risk factors and history and the results of myocardial scintigraphy according to the type of pain and discuss the role of scintigraphy in the diagnosis and therapeutic care.Patients and methodsOur study is retrospective, on 171 patients with typical chest pain (TCP) or atypical (ACP), addressed for myocardial scintigraphy.ResultsFemale predominance was clear. Average age was 59 years. Frequency of risk factors: smoking, diabetes, hypertension, hyperlipidemia, history of heart disease and hypothyroidism was respectively 21.6%, 39.8%, 73.7%, 25.1%, 11.1% and 6.4%. ACP was found in 57.9% of patients, it was more common among women (59.8%). Scintigraphy was abnormal in 36.8% of patients. Scintigraphy was normal in 59.7% of patients with TCP. In the case of ACP, scintigraphy was normal in 65.7%. This difference is not significant. All patients having abnormal scintigraphy had abnormal coronary angiography with a statistically significant correlation. Normal scintigraphy was more frequent (83.3%) in young patients ( < 40 years) and more common in women (67%) than men (55.9%). The sensitivity of scintigraphy is 100%. Its specificity is 66.6%. Its PPV of 57.1%. Its VPN is 100%.ConclusionMyocardial scintigraphy can help clinicians to identify the etiologic diagnosis and assess the prognosis of chest pain.     

Correcting for the effects of natural abundance in stable isotope resolved metabolomics experiments involving ultra-high resolution mass spectrometry

Background  

Stable isotope tracing with ultra-high resolution Fourier transform-ion cyclotron resonance-mass spectrometry (FT-ICR-MS) can provide simultaneous determination of hundreds to thousands of metabolite isotopologue species without the need for chromatographic separation. Therefore, this experimental metabolomics methodology may allow the tracing of metabolic pathways starting from stable-isotope-enriched precursors, which can improve our mechanistic understanding of cellular metabolism. However, contributions to the observed intensities arising from the stable isotope's natural abundance must be subtracted (deisotoped) from the raw isotopologue peaks before interpretation. Previously posed deisotoping problems are sidestepped due to the isotopic resolution and identification of individual isotopologue peaks. This peak resolution and identification come from the very high mass resolution and accuracy of FT-ICR-MS and present an analytically solvable deisotoping problem, even in the context of stable-isotope enrichment.     

Two novel gene orders and the role of light-strand replication in rearrangement of the vertebrate mitochondrial genome

Two novel mitochondrial gene arrangements are identified in an agamid lizard and a ranid frog. Statistical tests incorporating phylogeny indicate a link between novel vertebrate mitochondrial gene orders and movement of the origin of light-strand replication. A mechanism involving errors in light-strand replication and tandem duplication of genes is proposed for rearrangement of vertebrate mitochondrial genes. A second mechanism involving small direct repeats also is identified. These mechanisms implicate gene order as a reliable phylogenetic character. Shifts in gene order define major lineages without evidence of parallelism or reversal. The loss of the origin of light-strand replication from its typical vertebrate position evolves in parallel and, therefore, is a less reliable phylogenetic character. Gene junctions also evolve in parallel. Sequencing across multigenic regions, in particular transfer RNA genes, should be a major focus of future systematic studies to locate novel gene orders and to provide a better understanding of the evolution of the vertebrate mitochondrial genome.      

Contribution of β-globin cluster polymorphisms to raise fetal hemoglobin levels in normal adults

Hereditary persistence of fetal hemoglobin (HPFH) is a group of genetically heterogeneous conditions characterized by continued expression of fetal hemoglobin (HbF) in adulthood. HPFH may be due not only to point mutations or large deletions in different regions of the cluster β globin, but also to variations in several polymorphic sequences in this cluster. The objective of this work was to evaluate effects of polymorphic markers within cluster β globin on HbF expression. For the purpose, we have explored in this first study of Tunisian HPFH four polymorphic regions of β globin cluster in 68 healthy adults (34 subjects with high levels of HbF and 34 with normal HbF levels). Our results showed that the increase of HbF levels is associated with the −158 Gγ C → T polymorphism, the TG₁₈CG₂CACG, TC TG₉AG TG₂CG₂ and TG₁₁CG₄ configurations in the second intron of Gγ gene and the −540 β (AT)₆T₉ and (AT)₇T₈ repeated sequences. Among the 34 subjects with raised levels of HbF, approximately 97% carried one or more of these six markers. This study suggests that there is a significant association between certain polymorphic configurations of the β globin cluster and the increase of HbF levels in healthy individuals.