The pursuit of stability in halide perovskites: the monovalent cation and the key for surface and bulk self-healing.

We find significant differences between degradation and healing at the surface or in the bulk for each of the different APbBr3 single crystals (A = CH3NH3+, methylammonium (MA); HC(NH2)2+, formamidinium (FA); and cesium, Cs+). Using 1- and 2-photon microscopy and photobleaching we conclude that kinetics dominate the surface and thermodynamics the bulk stability. Fluorescence-lifetime imaging microscopy, as well as results from several other methods, relate the (damaged) state of the halide perovskite (HaP) after photobleaching to its modified optical and electronic properties. The A cation type strongly influences both the kinetics and the thermodynamics of recovery and degradation: FA heals best the bulk material with faster self-healing; Cs+ protects the surface best, being the least volatile of the A cations and possibly through O-passivation; MA passivates defects via methylamine from photo-dissociation, which binds to Pb2+. DFT simulations provide insight into the passivating role of MA, and also indicate the importance of the Br3- defect as well as predicts its stability. The occurrence and rate of self-healing are suggested to explain the low effective defect density in the HaPs and through this, their excellent performance. These results rationalize the use of mixed A-cation materials for optimizing both solar cell stability and overall performance of HaP-based devices, and provide a basis for designing new HaP variants.

CARDIOVASCULAR COMPLICATIONS OF ACROMEGALY.

Acromegaly is associated with increased mortality and decreased life expectancy. Cardiovascular disease is the principal cause of premature mortality in patients with acromegaly, accounting for about 60% of deaths. GH and/or IGF-I exert direct cardiac effects: enhance cardiac contractility, stimulate cardiomyocyte growth, influence calcium influx in cardiomyocytes. Cardiac remodelling is influenced by hypertension and insulin resistance. Among cardiovascular risk factors arterial hypertension, reported in 35% of patients with acromegaly, ranks among most important negative prognostic factors for mortality. Hypertension plays significant role in the development of cardiac hypertrophy, especially in older acromegalic patients and diastolic blood pressure is best predictive factor for cardiac hypertrophy. Therefore, early and aggressive hypertension treatment is essential for prognosis in acromegaly. Other important risk factors are: valvular defects, arrhythmias, endothelial dysfunction, heart failure, lipid abnormalities and coronary artery disease. Numerous studies suggest that patients with acromegaly are under threat of arrhythmias, especially those with structural heart abnormalities. Congestive heart failure as end-stage acromegalic cardiomyopathy occurs usually in older patients, with long-term uncontrolled disease and other cardiovascular and metabolic complications. Relation between acromegaly and coronary artery disease is controversial as it seems to be connected rather with classical cardiovascular risk factors than GH and IGF-1 overexpresion.

Enzymatically driven transport: a kinetic theory for nuclear export.

Nuclear import and export are often considered inverse processes whereby transport receptors ferry protein cargo through the nuclear pore. In contrast to import, where the reversible binding of receptor to nuclear RanGTP leads to a balanced bidirectional exchange, termination of export by physiologically irreversible hydrolysis of the Ran-bound GTP leads to unidirectional transport. We present a concise mathematical model that predicts protein distributions and kinetic rates for receptor-mediated nuclear export, which further exhibit an unexpected pseudolinear relation one to the other. Predictions of the model are verified with permeabilized and live cell measurements.

A simple kinetic model with explicit predictions for nuclear transport.

Molecular exchange between the cell nucleus and cytoplasm is one of the most fundamental features of eukaryotic cell biology. The nuclear pores act as a conduit of this transport, both for cargo that crosses the pore autonomously as well as that whose translocation requires an intermediary receptor. The major class of such receptors is regulated by the small GTPase Ran, via whose interaction the nucleo-cytoplasmic transport system functions as a selective molecular pump. We propose a simple analytical model for transport that includes both translocation and receptor binding kinetics. The model is suitable for steady-state kinetics such as fluorescence recovery after photobleaching. Time constants appear as a combination of parameters whose effects on measured kinetics are not separable. Competitive cargo binding to receptors and large cytoplasmic volume buffer the transport properties of any particular cargo. Specific limits to the solutions provide a qualitative insight and interpretation of nuclear transport in the cellular context. Most significantly, we find that under realistic conditions receptor binding, rather than permeability of the nuclear pores, may be rate-limiting for nucleo-cytoplasmic exchange.

[Social inequalities in health and public health: from research to policies]. / Inégalités sociales de santé et santé publique: des recherches aux politiques.

This paper analyses the main results and prospects concerning research and studies about social inequalities in health in France. Research orientations, which may contribute usefully to defining health and social policies in this field and favour their development are then proposed. Health policy content and implementation placing high priority on the problem of social inequalities in health are discussed.

A new dimension in retrograde flow: centripetal movement of engulfed particles.

Centripetal motion of surface-adherent particles is a classic experimental system for studying surface dynamics on a eukaryotic cell. To investigate bead migration over the entire cell surface, we have developed an experimental assay using multinuclear giant fibroblasts, which provide expanded length scales and an unambiguous frame of reference. Beads coated by adhesion ligands concanavalin A or fibronectin are placed in specific locations on the cell using optical tweezers, and their subsequent motion is tracked over time. The adhesion, as well as velocity and directionality of their movement, expose distinct regions of the cytoplasm and membrane. Beads placed on the peripheral lamella initiate centripetal motion, whereas beads placed on the central part of the cell attach to a stationary cortex and do not move. Careful examination by complementary three-dimensional methods shows that the motion of a bead placed on the cell periphery takes place after engulfment into the cytoplasm, whereas stationary beads, placed near the cell center, are not engulfed. These results demonstrate that centripetal motion of adhering particles may occur inside as well as outside the cell. Inhibition of actomyosin activity is used to explore requirements for engulfment and aspects of the bead movement. Centripetal movement of adherent particles seems to depend on mechanisms distinct from those driving overall cell contractility.

Kinetics and mechanism of DNA uptake into the cell nucleus.

Gene transfer to eukaryotic cells requires the uptake of exogenous DNA into the cell nucleus. Except during mitosis, molecular access to the nuclear interior is limited to passage through the nuclear pores. Here we demonstrate the nuclear uptake of extended linear DNA molecules by a combination of fluorescence microscopy and single-molecule manipulation techniques, using the latter to follow uptake kinetics of individual molecules in real time. The assays were carried out on nuclei reconstituted in vitro from extracts of Xenopus eggs, which provide both a complete complement of biochemical factors involved in nuclear protein import, and unobstructed access to the nuclear pores. We find that uptake of DNA is independent of ATP or GTP hydrolysis, but is blocked by wheat germ agglutinin. The kinetics are much slower than would be expected from hydrodynamic considerations. A fit of the data to a simple model suggests femto-Newton forces and a large friction relevant to the uptake process.

p120 catenin affects cell motility via modulation of activity of Rho-family GTPases: a link between cell-cell contact formation and regulation of cell locomotion.

The molecular basis for contact inhibition of cell locomotion is still largely unknown. Cadherins, the major receptors mediating cell-cell adhesion, associate in the cytoplasm with armadillo family proteins, including beta- and gamma-catenin and p120 catenin (p120ctn). E-cadherin-mediated contact formation was shown to inhibit cellular motility. We examine whether p120ctn may have a role in this regulation. We show here that overexpression of p120ctn in fibroblasts and epithelial cells induces pronounced changes in cell shape, motility and adhesion to the extracellular matrix. p120ctn-transfected cells display increased filopodial/lamellipodial activity, decreased contractility and focal adhesion formation, and augmented migratory ability. These effects of p120ctn are mediated by small GTPases of the Rho family. Direct assessment of the activity of these GTPases in cells expressing a 5-fold higher level of p120ctn as compared to non-transfected control cells revealed significant augmentation of Cdc42 and Rac activity. Moreover, co-transfection of p120ctn with dominant-negative Cdc42 and Rac, or constitutively active Rho suppressed morphological effects of p120ctn. Confocal immunofluorescence visualization of the distribution of endogenous p120ctn in dense cultures showed that formation of cadherin-mediated cell-cell contacts is accompanied by sequestering of p120ctn to the junction regions. In sparse cultures p120ctn is distributed over the cytoplasm. Co-transfection with an excess of E-cadherin leads to sequestration of exogenous p120ctn to cell-cell junctions or to small cadherin-containing vesicles, and abolishes p120ctn effects on cell morphology. Thus, p120ctn may couple the formation and disruption of cadherin-mediated contacts with regulation of cell motility by triggering pathway(s) affecting Rho family GTPases.

Automatic differentiation of melanoma from melanocytic nevi with multispectral digital dermoscopy: a feasibility study.

BACKGROUND: Differentiation of melanoma from melanocytic nevi is difficult even for skin cancer specialists. This motivates interest in computer-assisted analysis of lesion images. OBJECTIVE: Our purpose was to offer fully automatic differentiation of melanoma from dysplastic and other melanocytic nevi through multispectral digital dermoscopy. METHOD: At 4 clinical centers, images were taken of pigmented lesions suspected of being melanoma before biopsy. Ten gray-level (MelaFind) images of each lesion were acquired, each in a different portion of the visible and near-infrared spectrum. The images of 63 melanomas (33 invasive, 30 in situ) and 183 melanocytic nevi (of which 111 were dysplastic) were processed automatically through a computer expert system to separate melanomas from nevi. The expert system used either a linear or a nonlinear classifier. The "gold standard" for training and testing these classifiers was concordant diagnosis by two dermatopathologists. RESULTS: On resubstitution, 100% sensitivity was achieved at 85% specificity with a 13-parameter linear classifier and 100%/73% with a 12-parameter nonlinear classifier. Under leave-one-out cross-validation, the linear classifier gave 100%/84% (sensitivity/specificity), whereas the nonlinear classifier gave 95%/68%. Infrared image features were significant, as were features based on wavelet analysis. CONCLUSION: Automatic differentiation of invasive and in situ melanomas from melanocytic nevi is feasible, through multispectral digital dermoscopy.

Doublecortin mutations cluster in evolutionarily conserved functional domains.

Mutations in the X-linked gene doublecortin ( DCX ) result in lissencephaly in males or subcortical laminar heterotopia ('double cortex') in females. Various types of mutation were identified and the sequence differences included nonsense, splice site and missense mutations throughout the gene. Recently, we and others have demonstrated that DCX interacts and stabilizes microtubules. Here, we performed a detailed sequence analysis of DCX and DCX-like proteins from various organisms and defined an evolutionarily conserved Doublecortin (DC) domain. The domain typically appears in the N-terminus of proteins and consists of two tandemly repeated 80 amino acid regions. In the large majority of patients, missense mutations in DCX fall within the conserved regions. We hypothesized that these repeats may be important for microtubule binding. We expressed DCX or DCLK (KIAA0369) repeats in vitro and in vivo. Our results suggest that the first repeat binds tubulin but not microtubules and enhances microtubule polymerization. To study the functional consequences of DCX mutations, we overexpressed seven of the reported mutations in COS7 cells and examined their effect on the microtubule cytoskeleton. The results demonstrate that some of the mutations disrupt microtubules. The most severe effect was observed with a tyrosine to histidine mutation at amino acid 125 (Y125H). Produced as a recombinant protein, this mutation disrupts microtubules in vitro at high molar concentration. The positions of the different mutations are discussed according to the evolutionarily defined DC-repeat motif. The results from this study emphasize the importance of DCX-microtubule interaction during normal and abnormal brain development.

Molecular requirements for the effect of neuregulin on cell spreading, motility and colony organization.

Neuregulin can trigger morphogenetic signals in cells both in vivo and in culture through the activation of receptors from the ErbB family. We have ectopically expressed various ErbB-receptors in 32D myeloid cells lacking endogenous ErbB-proteins, and in CHO cells, which express only ErbB-2. We show here that activation of ErbB-3/ErbB-2 heterodimeric receptors triggers PI3-kinase-dependent lamellipodia formation and spreading, while individual ErbB-receptor homodimers as well as ErbB-3/ErbB-1 heterodimers are much less effective. CHO cells expressing ErB-3/ErbB-2 together with N-cadherin, an adhesion receptor, form epithelioid colonies. Neuregulin activates cell motility leading to transition of these colonies into ring-shaped multicellular arrays, similar to those induced by neuregulin in epithelial cells of different types (Chausovsky et al., 1998). This process requires both PI3-kinase and MAP kinase kinase activity and depends on coordinated changes in the actin- and microtubule-based cytoskeleton. Transactivation of ErbB-2 is not sufficient for the activation of cell motility and ring formation, and the C-terminal domain of ErbB-3 bearing the docking sites for the p85 subunit of PI3-kinase is essential for these morphogenetic effects. Thus, ErbB-3 in conjunction with ErbB-2 mediates, via its C-terminal domain, cytoskeletal and adhesion alterations which activate cell spreading and motility, leading to the formation of complex structures such as multicellular rings. Oncogene (2000) 19, 878 - 888.

Disruption of microtubules in living cells by tyrphostin AG-1714.

Tyrphostin AG-1714 and several related molecules with the general structure of nitro-benzene malononitrile (BMN) disrupt microtubules in a large variety of cultured cells. This process can be inhibited by the stabilization of microtubules with taxol or by pretreatment of the cells with pervanadate, which inhibits tyrosine phosphatases and increases the overall levels of phosphotyrosine in cells. Unlike other microtubule-disrupting drugs such as nocodazole or colchicine, tyrphostin AG-1714 does not interfere with microtubule polymerization or stability in vitro, suggesting that the effect of this tyrphostin on microtubules is indirect. These results imply an involvement of protein tyrosine phosphorylation in the regulation of overall microtubule dynamics. Tyrphostins of AG-1714 type could thus be powerful tools for the identification of such microtubule regulatory pathways.

Enhanced diffusion in active intracellular transport.

We show that within a living eukaryotic cell, mean square displacement of an engulfed microsphere shows enhanced diffusion scaling as t(3/2) at short times, with a clear crossover to subdiffusive or ordinary diffusion scaling at longer times. The motion, observed nearby the nucleus, is due to interactions with microtubule-associated motor proteins rather than thermal Brownian motion. We propose that time-dependent friction introduced by the intracellular polymer networks leads to sub-ballistic motion, analogous to subdiffusion observed in passive networks of semiflexible biopolymers.

Precision of automatic measurements of pigmented skin lesion parameters with a MelaFind(TM) multispectral digital dermoscope.

The purpose of this study was to assess the precision of automatic computerized measurement of parameters that may be useful in the differentiation of malignant melanoma from benign pigmented skin lesions, and also to determine the feasibility of quantitative monitoring of skin lesions over time. Ten independent sequences of images were acquired with a MelaFind multispectral digital dermoscope for each of 12 benign or malignant pigmented skin lesions. The sequences of images were processed automatically to provide 10 independent measurements of the various parameters for each lesion. Parameters included lesion area, greatest 'diameter', perimeter, reflectance and asymmetry. The precision of each parameter determination was computed from the mean and standard deviation of the 10 measurements of that parameter. The relative errors in determining the lesion area, 'diameter' and perimeter were found to be 6%, 3% and 4%, respectively. Other lesion parameters that are used in differentiating melanomas from benign skin lesions were also analysed as a function of wavelength. In the blue band (about 430 nm) the relative error was about 7% for the mean lesion reflectance and about 7% for the asymmetry parameter. These results demonstrate the feasibility of using MelaFind for objective quantitative monitoring of changes in pigmented skin lesions over time. As suggested by some studies, such information is useful in the early detection of malignant melanoma. The results show that parameters obtained automatically from MelaFind images are sufficiently precise to allow pertinent parameters to be used to classify pigmented skin lesions.

Caldesmon inhibits nonmuscle cell contractility and interferes with the formation of focal adhesions.

Caldesmon is known to inhibit the ATPase activity of actomyosin in a Ca(2+)-calmodulin-regulated manner. Although a nonmuscle isoform of caldesmon is widely expressed, its functional role has not yet been elucidated. We studied the effects of nonmuscle caldesmon on cellular contractility, actin cytoskeletal organization, and the formation of focal adhesions in fibroblasts. Transient transfection of nonmuscle caldesmon prevents myosin II-dependent cell contractility and induces a decrease in the number and size of tyrosine-phosphorylated focal adhesions. Expression of caldesmon interferes with Rho A-V14-mediated formation of focal adhesions and stress fibers as well as with formation of focal adhesions induced by microtubule disruption. This inhibitory effect depends on the actin- and myosin-binding regions of caldesmon, because a truncated variant lacking both of these regions is inactive. The effects of caldesmon are blocked by the ionophore A23187, thapsigargin, and membrane depolarization, presumably because of the ability of Ca(2+)-calmodulin or Ca(2+)-S100 proteins to antagonize the inhibitory function of caldesmon on actomyosin contraction. These results indicate a role for nonmuscle caldesmon in the physiological regulation of actomyosin contractility and adhesion-dependent signaling and further demonstrate the involvement of contractility in focal adhesion formation.

Doublecortin, a stabilizer of microtubules.

X-linked lissencephaly is a severe brain malformation affecting males. Recently it has been demonstrated that the doublecortin gene is implicated in this disorder. In order to study the function of Doublecortin, we analyzed the protein upon transfection of COS cells. Doublecortin was found to bind to the microtubule cytoskeleton. In vitro assays (using biochemical methods, DIC microscopy and electron microscopy) demonstrate that Doublecortin binds microtubules directly, stabilizes them and causes bundling. In vivo assays also show that Doublecortin stabilizes microtubules and causes bundling. Doublecortin is a basic protein with an iso-electric point of 10, typical of microtubule-binding proteins. However, its sequence contains no known microtubule-binding domain(s). The results obtained in this study with Doublecortin and our previous work on another lissencephaly gene ( LIS1 ) emphasize the central role of regulation of microtubule dynamics and stability during neuronal morphogenesis.

Microtubule involvement in regulating cell contractility and adhesion-dependent signalling: a possible mechanism for polarization of cell motility.

The dynamic shape of an isolated cell results from an interplay between protrusion, adhesion and contraction activities. These are most closely associated with the actin cytoskeleton. In many cell types, microtubules have been shown to be involved in the development of morphological polarity required for directional migration. This suggests a role for the microtubule system in regulating both the actin cytoskeleton and the formation of cell-substrate adhesions. The most prominent role of microtubules in the cell is in transport of vesicles and organelles. Disruption of the microtubules, on the other hand, leads to a significant increase in actomyosin-driven contractility. This suggests the involvement of microtubules in the control of forces produced by the cell against the points at which it contacts the substrate or extracellular matrix. We show that microtubule disruption also activates an adhesion-dependent signal transduction cascade and promotes the formation of focal adhesions and associated actin microfilament bundles. Using overexpression of caldesmon, a regulatory protein which inhibits the interaction between actin and myosin, we show that these effects of microtubule disruption depend on the activation of contractility. Formation of focal adhesions induced by the small GTPase Rho is also blocked by the caldesmon inhibition of contractility. We infer that there is a step in the adhesion-dependent signalling pathway that requires mechanical tension applied to cell-substrate contacts. Although the experimental data are based on complete microtubule disruption, we suggest that a similar effect occurs locally following depolymerization of individual microtubules. We speculate that the interplay among microtubule dynamics, actomyosin contractility and adhesion-dependent signalling can produce a mechanism for the determination of cell polarity and direction of migration. In essence, microtubule depolymerization would create a local increase in contractile force, testing and promoting the maturation of nearby cell-substrate adhesions.

Wavelet representations for monitoring changes in teeth imaged with digital imaging fiber-optic transillumination.

Digital imaging fiber-optic transillumination (DI-FOTI) is a novel method to detect and monitor dental caries, using light, a charge-coupled device (CCD) camera, and computer-controlled image acquisition. The advantages of DIFOTI over radiography include: no ionizing radiation, no film, real-time diagnosis, and higher sensitivity in detection of early lesions not apparent to X-ray, as demonstrated in vitro. Here, we present a method of processing DIFOTI images, acquired at different times, for monitoring changes. Of central importance to this application is pattern matching of image frames that is invariant to translation and rotation of a tooth, relative to the field of view of the imaging camera, and that is robust to changes in illumination source intensity. Our method employs: 1) wavelet modulus maxima representations for segmentation of teeth images; 2) first and second moments of gray level representations of DIFOTI images in the spatial domain, to estimate tooth location and orientation; and 3) multiresolution wavelet magnitude representations for quantitative monitoring. Even with illumination source intensity variation, it is demonstrated in vitro that such wavelet representations can facilitate detection of simulated clinical changes in light transmission that cannot be detected in the spatial domain.

Assessment of dental caries with Digital Imaging Fiber-Optic TransIllumination (DIFOTI): in vitro study.

This paper describes Digital Imaging Fiber-Optic TransIllumination (DIFOTI-TM), a new method for the reliable detection of dental caries. Images of teeth obtained through visible-light, fiber-optic transillumination (FOTI) are acquired with a digital CCD camera, and sent to a computer for analysis with dedicated algorithms. The algorithms were developed to facilitate the location and diagnosis of carious lesions by the operator in real time, and provide quantitative characterization for monitoring of the lesions. The DIFOTI method has been tested by imaging teeth in vitro. The results suggest the superior sensitivity of DIFOTI for detection of approximal, occlusal and smooth-surface caries vis-à-vis radiological imaging.

Reduction of microtubule catastrophe events by LIS1, platelet-activating factor acetylhydrolase subunit.

Forming the structure of the human brain involves extensive neuronal migration, a process dependent on cytoskeletal rearrangement. Neuronal migration is believed to be disrupted in patients exhibiting the developmental brain malformation lissencephaly. Previous studies have shown that LIS1, the defective gene found in patients with lissencephaly, is a subunit of the platelet-activating factor acetylhydrolase. Our results indicated that LIS1 has an additional function. By interacting with tubulin it suppresses microtubule dynamics. We detected LIS1 interaction with microtubules by immunostaining and co-assembly. LIS1-tubulin interactions were assayed by co-immunoprecipitation and by surface plasmon resonance changes. Microtubule dynamic measurements in vitro indicated that physiological concentrations of LIS1 indeed reduced microtubule catastrophe events, thereby resulting in a net increase in the maximum length of the microtubules. Furthermore, the LIS1 protein concentration in the brain, measured by quantitative Western blots, is high and is approximately one-fifth of the concentration of brain tubulin. Our new findings show that LIS1 is a protein exhibiting several cellular interactions, and the interaction with the cytoskeleton may prove to be the mode of transducing a signal generated by platelet-activating factor. We postulate that the LIS1-cytoskeletal interaction is important for neuronal migration, a process that is defective in lissencephaly patients.