Ultrasonic subwavelength phase conjugated mirror with a layer of bubbles.

A single layer of gas bubbles in a yield-stress fluid is experimentally shown to behave as a phase-conjugated (PC) mirror with a thickness 250 times smaller than the wavelength (0.14mm-diameter bubbles for phase-conjugation at 40kHz). A high amplitude pump wave at frequency 80kHz interacts with a lower amplitude probe wave centered at 40kHz. A PC-reflection coefficient of 0.15 is obtained for a 50kPa pump. A perturbative second-order theory is shown to quantitatively describe the experimental observations.

Novel neuronal proteolipid protein isoforms encoded by the human myelin proteolipid protein 1 gene.

The human myelin proteolipid protein 1 gene (hPLP1), which encodes the major structural myelin proteins of the central nervous system (CNS), is classically described as expressed in the oligodendrocytes, the CNS myelinating cells. We identified two new exons in the intron 1 of the hPLP1 gene that lead to the expression of additional mRNA and protein isoforms mainly expressed in neurons instead of oligodendrocytes. Those novel neuronal PLP isoforms are detected as soon as human fetal development and their concomitant expression is specific of the human species. As classical PLP proteins, the novel protein isoforms seem to be addressed to the plasma membrane. These results suggest for the first time that PLP may have functions in humans not only in oligodendrocytes but also in neurons and could be implicated in axono-glial communication. Moreover, this neuronal expression of the hPLP1 gene might explain the neuronal dysfunctions in patients carrying hPLP1 gene mutations.

[Mouse models of K-ras-initiated oncogenesis]. / Apport des modèles animaux pour l'étude du rôle de K-ras dans l'oncogenèse.

Activating mutations of the oncogene K-ras are found in one third of all human cancers. Much of our knowledge on K-ras signal transduction and its influence on tumor initiation and progression come from in vitro studies with cell lines. However, mouse models of human cancer allow a much more faithful recapitulation of the human disease, and the in vivo perspective is crucial for our understanding of neoplasia. In recent years, several new murine models for K-ras-induced tumorigenesis have been described. They allow new insights into the specific role that oncogenic K-ras proteins play in different solid tumors, and they permit the molecular dissection of the pathways that are initiated by somatic mutations in subsets of cells. Key advances have been made by the use of tissue-specific and inducible control of expression, which is achieved by the Cre/loxP technology or the tetracycline system. From these sophisticated models, a common picture emerges: the effects of K-ras on tumor initiation depend strongly on the cellular context, and different tissues vary in their susceptibility to K-ras transformation.

Acoustoelasticity in soft solids: assessment of the nonlinear shear modulus with the acoustic radiation force.

The assessment of viscoelastic properties of soft tissues is enjoying a growing interest in the field of medical imaging as pathologies are often correlated with a local change of stiffness. To date, advanced techniques in that field have been concentrating on the estimation of the second order elastic modulus (mu). In this paper, the nonlinear behavior of quasi-incompressible soft solids is investigated using the supersonic shear imaging technique based on the remote generation of polarized plane shear waves in tissues induced by the acoustic radiation force. Applying a theoretical approach of the strain energy in soft solid [Hamilton et al., J. Acoust. Soc. Am. 116, 41-44 (2004)], it is shown that the well-known acoustoelasticity experiment allowing the recovery of higher order elastic moduli can be greatly simplified. Experimentally, it requires measurements of the local speed of polarized plane shear waves in a statically and uniaxially stressed isotropic medium. These shear wave speed estimates are obtained by imaging the shear wave propagation in soft media with an ultrafast echographic scanner. In this situation, the uniaxial static stress induces anisotropy due to the nonlinear effects and results in a change of shear wave speed. Then the third order elastic modulus (A) is measured in agar-gelatin-based phantoms and polyvinyl alcohol based phantoms.

Golli-MBP copy number analysis by FISH, QMPSF and MAPH in 195 patients with hypomyelinating leukodystrophies.

The inherited disorders of CNS myelin formation represent a heterogeneous group of leukodystrophies. The proteolipoprotein (PLP1) gene has been implicated in two X-linked forms, Pelizaeus-Merzbacher disease (PMD) and spastic paraplegia type 2, and the gap junction protein alpha12 (GJA12) gene in a recessive form of PMD. The myelin basic protein (MBP) gene, which encodes the second most abundant CNS myelin protein after PLP1, presents rearrangements in hypomyelinating murine mutants and is always included in the minimal region deleted in 18q- patients with an abnormal hypomyelination pattern on cerebral MRI. In this study, we looked at the genomic copy number at the Golli-MBP locus in 195 patients with cerebral MRI suggesting a myelin defect, who do not have PLP1 mutation. Although preliminary results obtained by FISH suggested the duplication of Golli-MBP in 3 out of 10 patients, no abnormal gene quantification was found using Quantitative Multiplex PCR of Short Fluorescent fragments (QMPSF), Multiplex Amplifiable Probe Hybridization (MAPH), or another FISH protocol using directly-labelled probes. Pitfalls and interest in these different techniques to detect duplication events are emphasised. Finally, the study of this large cohort of patients suggests that Golli-MBP deletion or duplication is rarely involved in inherited defects of myelin formation.

DNA microarray analysis of gene expression profiles in deep endometriosis using laser capture microdissection.

Endometriosis, a common gynecological disorder that causes infertility and pelvic pain, is defined as the presence of endometrial glands and stroma within extra-uterine sites. However, despite extensive studies its etiology and pathogenesis are not completely understood. Differentially expressed genes were investigated in epithelial and stromal cells from deep endometriosis and matched eutopic endometrium using cDNA microarrays and laser capture microdissection. Validation of results of several up- and down-regulated genes was performed by quantitative real-time RT-PCR. Our data showed that platelet-derived growth factor receptor alpha (PDGFRA), protein kinase C beta1 (PKC beta1) and janus kinase 1 (JAK1) were upregulated, and Sprouty2 and mitogen-activated protein kinase kinase 7 (MKK7) were downregulated in endometriosis stromal cells, suggesting the involvement of the RAS/RAF/MAPK signaling pathway through PDGFRA in endometriosis pathophysiology. In addition, two potential negative regulators of aromatase expression, chicken ovalbumin upstream promoter transcription factor 2 (COUP-TF2) and prostaglandin E2 receptor subtype EP3 (PGE2EP3), were downregulated in endometriosis epithelial cells, which might result in increased local production of estrogen in endometriosis epithelial cells. Furthermore, three potential candidate genes that might be involved in endometriosis related pain were identified: tyrosine kinase receptor B (TRkB) in endometriosis epithelial cells, and serotonin transporter (5HTT) and mu opioid receptor (MOR) in endometriosis stromal cells were all upregulated. One of the candidate genes, MOR, may be involved in a defective immune system in endometriosis. This study has provided new insights into endometriosis pathophysiology.

DNA methylation patterns in hereditary human cancers mimic sporadic tumorigenesis.

Cancer cells have aberrant patterns of DNA methylation including hypermethylation of gene promoter CpG islands and global demethylation of the genome. Genes that cause familial cancer, as well as other genes, can be silenced by promoter hypermethylation in sporadic tumors, but the methylation of these genes in tumors from kindreds with inherited cancer syndromes has not been well characterized. Here, we examine CpG island methylation of 10 genes (hMLH1, BRCA1, APC, LKB1, CDH1, p16(INK4a), p14(ARF), MGMT, GSTP1 and RARbeta2) and 5-methylcytosine DNA content, in inherited (n = 342) and non-inherited (n = 215) breast and colorectal cancers. Our results show that singly retained alleles of germline mutated genes are never hypermethylated in inherited tumors. However, this epigenetic change is a frequent second "hit", associated with the wild-type copy of these genes in inherited tumors where both alleles are retained. Global hypomethylation was similar between sporadic and hereditary cases, but distinct differences existed in patterns of methylation at non-familial genes. This study demonstrates that hereditary cancers "mimic" the DNA methylation patterns present in the sporadic tumors.

[Molecular abnormalities in epithelial ovarian tumors: present and future]. / Les anomalies moléculaires des tumeurs epithéliales ovariennes: actualités et perspectives.

Ovarian cancer is the fourth most common cancer in women. Its pronostic is dreadful and, in spite of numerous studies, the steps of ovarian carcinogenesis are unclear. Histologically, three sub-types of ovarian tumors (benign, borderline and invasive) are distinguished, suggesting the existence of a continuum. However, as each sub-type presents its own biologic characteristics, the hypothesis of the progression of a pre-neoplastic precursor (benign or borderline tumor) into an invasive tumor is still open to discussion. Numerous molecular biological studies have been conducted on ovarian tumors, with the aims of identifying their molecular abnormalities and better understanding the process of ovarian carcinogenesis. Synthesis of the published data (concerning oncogene amplification and/or surexpression, loss of heterozygosity, tumor suppressor gene inactivation, microsatellite instability) shows that there are numerous abnormalities, confirming the heterogeneity and the complexity of these tumors. Hence, it remains very difficult to draw a scheme of ovarian carcinogenesis. Nevertheless, in a near future the new technology of laser microdissection may improve the quality of the results and the study of early ovarian lesions. Indeed, with this technique, it becomes possible to isolate well-defined and homogeneous cell populations and to study small or architecturally complex (surface lesions) tumors. In the next years, the results obtained may allow the identification of early events of the ovarian carcinogenesis and the development of diagnostic and therapeutic tools.

Characterization of catalase and superoxide dismutase in Staphylococcus carnosus 833 strain.

AIMS: Staphylococcus carnosus, used as starter culture in fermented meat products, decreases the level of volatiles arising from lipid oxidation. To analyse its antioxidant capacities, catalase and superoxide dismutase (SOD) were characterized. METHODS AND RESULTS: Catalase and SOD activities were measured with spectrophotometric methods and visualized on non-denaturing polyacrylamide gels. The corresponding sod gene was identified by PCR. Southern hybridizations and enzymatic analyses showed that there was a single catalase and a single SOD in Staph. carnosus 833 strain. The gene encoding the Staph. carnosus SOD was found to encode a protein closely related to SOD requiring manganese. Catalase and SOD levels increased in mid-log phase. Only catalase was induced by oxygen, nitrate or nitrite while glucose induced neither enzyme. Metal ion limitation increased catalase and decreased SOD activities. CONCLUSION: Staph. carnosus synthesizes both enzymes in conditions encountered in sausage manufacturing. These results could explain the antioxidant properties of Staph. carnosus starter culture. SIGNIFICANCE AND IMPACT OF THE STUDY: The knowledge of the antioxidant properties of Staphylococci will allow a more rational use of these starters in meat fermented products.

Characterization of the single superoxide dismutase of Staphylococcus xylosus.

Staphylococcus xylosus is a facultative anaerobic bacterium used as a starter culture for fermented meat products. In an attempt to analyze the antioxidant capacities of this organism, the superoxide dismutase (SOD) was characterized. S. xylosus contains a single cytoplasmic SOD, which was not inhibited by H2O2. The SOD activity in crude extracts was completely lost upon metal depletion, but it could be recovered by manganese and very weakly by iron. It is therefore suggested that the S. xylosus SOD is a manganese-preferring enzyme. The corresponding gene, sod, was isolated from a genomic library of S. xylosus DNA and complemented the growth defect of an Escherichia coli SOD-deficient mutant. As deduced from the nucleotide sequence, sod encodes a protein of 199 amino acids with a molecular mass of 22.5 kDa. Two transcriptional start sites 25 and 120 bp upstream of the sod start codon were identified. A terminator-like structure downstream of the gene suggested a monocistronic sod mRNA. Regulation of sod expression was studied using fusions of the sod promoters to a genomic promoterless beta-galactosidase gene. The sod expression was not affected by manganese and increased slightly with paraquat. It was induced during stationary phase in a complex medium but not in a chemically defined medium. To investigate the physiological role of SOD, a mutant devoid of SOD activity was constructed. Growth experiments showed that sod is not essential for aerobic growth in complex medium. However, in chemically defined medium without leucine, isoleucine, and valine, the sod mutant hardly grew, in contrast to the wild-type strain. In addition, the mutant was sensitive to hyperbaric oxygen and to paraquat. Therefore, sod plays an important role in the protection of S. xylosus from oxidative stress.

Roles of superoxide dismutase and catalase of Staphylococcus xylosus in the inhibition of linoleic acid oxidation.

Staphylococcus xylosus used as starter culture in sausages decreases the level of volatile organic compounds arising from lipid oxidation and so contributes to the aroma by avoiding rancidity. The aim of this study was to characterize the roles of catalase and superoxide dismutase (SOD) in the inhibition of free fatty acid oxidation by comparing antioxidant capacity of the S. xylosus wild-type strain with those of the katA mutant and the sod mutant. Antioxidant capacity was determined by measuring the volatile organic compounds and the conjugated diene hydroperoxides arising from linoleic acid oxidation. The three strains inhibited the oxidation of linoleic acid. However, the katA mutant, and especially the sod mutant, had less antioxidant capacity than the S. xylosus wild-type strain. Thus both catalase and SOD of S. xylosus contributed to the inhibition of lipid oxidation.

Diffraction effects in the parametric interaction of acoustic waves: application to measurements of the nonlinearity parameter B/A in liquids.

This paper deals with diffraction effects related to the determination of nonlinearity parameters B/A in liquids using the parametric interaction. A diffraction model, based on plane wave expansions, is applied to weak nonlinear interactions between two ultrasonic waves propagating in an absorbing medium. A validation of the model has been carried out with an experiment performed using an optical interferometer. A method is proposed to measure nonlinearity parameters with the parametric interaction of two waves with a high frequency ratio. With respect to diffraction effects, the parametric interaction can then be identified with a phase modulation of the high frequency wave. A prototype, using the interaction of a 30-MHz frequency continuous wave with an acoustic pulse of central frequency 2.5 MHz, has been designed. The proposed method is validated by nonlinearity parameters measurements in well-known liquids (water and ethanol). The uncertainty on absolute measurements is discussed, and a relative method is proposed to increase the accuracy. This method enables measurements without any transducer calibration.

Effect of nitrate and incubation conditions on the production of catalase and nitrate reductase by staphylococci.

The objective of this work was to study the production of catalase and nitrate reductase by staphylococci in order to understand their role in lipid oxidation during sausage manufacturing. Catalase and nitrate reductase were measured in resting cells and supernatants of staphylococci grown in different conditions. All staphylococci (except S. warneri) synthetized nitrate reductase. In static condition, the synthesis was maximal during exponential growth phase, whereas in shaking condition, the synthesis was maximal at the beginning of stationary phase. The production of nitrate reductase was increased in presence of nitrate, this effect was particularly important for the two S. carnosus strains which exhibited the highest activity. For all staphylococci, the production of catalase was maximal at the end of the exponential growth phase. The lowest amount of catalase was produced by S. warneri and the highest by S. carnosus. Only S. xylosus 873 and S. saprophyticus 852 released high amounts of catalase in the supernatant growth. Staphylococci produced higher amounts of catalase in shaking conditions. Addition of nitrate in the growth media favoured the synthesis of catalase, with a pronounced effect for S. carnosus. Nitrate also favoured the release of catalase.

Pathology of sporadic breast tumors with LOH at the BRCA1 locus: correlation with histopathological features specific to familial BRCA1 tumors and absence of microsatellite instability.

To investigate the coordinated occurrence of loss of heterozygosity (LOH) at the BRCA1 locus and microsatellite instability (MI) in sporadic breast carcinomas, 56 tumors were analysed for both genetic alterations. The comparison of clinicopathological features with the obtained data revealed that LOH at the BRCA1 locus was significantly correlated with features specific for familial BRCA1 tumors and with absence of hormone receptors. No correlation was found between LOH and MI. These results suggest that sporadic and familial breast tumors, where BRCA1 is altered, could display similar clinicopathological features and that LOH and MI are distinct genetic events in sporadic breast carcinogenesis.

Human identification of letters in mixed-script handwriting: an upper bound on recognition rates.

This paper focuses on a reading task consisting of the identification of letters in mixed-script handwritten words. This task is performed by humans using extended or limited linguistic context. Their performance rate is to give an upper bound on recognition rates of computer programs designed to recognize handwritten letters in mixed-script writing. Many recognition algorithms are being developed in the research community, and there is a need for establishing ways to compare them. As some effort is on its way to give large test sets with standard formats, we propose an algorithm to determine a test set of reduced size that is appropriate for the task to achieve (the type of texts or words to be recognized). Also, with respect to a particular task, we propose a method for finding an upper limit to the letter recognition rate to aim for.