Is Second Harmonic Generation a reliable tool for studying solid-solid phase transition and structural purity?

International audienceThe second harmonic generation (SHG) is a nonlinear optical effect occurring only in noncentrosymmetric space groups. Two photons (at the fundamental angular frequency ω) can interact in a noncentric crystal structure to give a new photon at twice the fundamental frequency (2ω). In previous studies, we demonstrated that the measurement of the intensity of the signal at 2ω (SHG signal) is a very sensitive probe to detect the noncentrosymmetry of crystal arrangements such as conglomerates [1]. This technique was also used, in rare occasions, to follow centrosymmetric to noncentrosymmetric solid-solid phase transitions [2], [3]. Because of the origin of the SHG signal, only centric to noncentric or noncentric to noncentric phase transitions can be investigated via SHG. However, SHG has proved to be highly sensitive even to a slight deviation from centrosymmetric conditions and could be used to detect noncentric nuclei and as a consequence to follow the nucleation of new phases. This could give great information about the order of the transition (as defined by Ehrenfest classification). Indeed, if the transition is of the first-order kind the signal should be discontinuous at the temperature transition but continuous in the case of a second order transition.In this study, we present the results obtained using a device developed to perform SHG measurements versus temperature for the solid-solid phase transition (from centrosymmetric to noncentrosymmetric structures) of several compounds. The case of 3-Hydroxybenzoic Acid is particularly considered. MHBA is an intermediate in the production of germicides, plasticizer and pharmaceuticals and exhibits two polymorphic forms [4] one of which is noncentrosymmetric. Finally, we evaluate the potential of the SHG signal measurements to follow phase transitions by comparison with other usual techniques such as Differential Scanning Calorimetry (DSC), X-Ray Diffraction or Raman Spectroscopy.REFERENCES[1] A. Galland, V.Dupray, B.Berton, S. Morin-Grognet, M. Sanselme, H. Atmani and G.Coquerel, “Spotting Conglomerates by Second Harmonic Generation,” Crystal Growth & Design, vol. 9, no. 6, pp. 2713–2718, Jun. 2009.[2] J. P. Dougherty and S. K. Kurtz, “A second harmonic analyzer for the detection of non- centrosymmetry,” Journal of Applied Crystallography, vol. 9, no. 2, pp. 145–158, Apr. 1976.[3] L. Smilowitz, B. F. Henson, and J. J. Romero, “Intercomparison of Calorimetry, Raman Spectroscopy, and Second Harmonic Generation Applied to Solid−Solid Phase Transitions,” The Journal of Physical Chemistry A, vol. 113, no. 35, pp. 9650–9657, Sep. 2009. [4] F. L. Nordström and Å. C. Rasmuson, “Polymorphism and thermodynamics of m- hydroxybenzoic acid,” European Journal of Pharmaceutical Sciences, vol. 28, no. 5, pp. 377– 384, Aug. 2006

In situ X-ray for monitoring crystallization in solution : In-situX®

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Relevance of Second Harmonic Generation Microscopy (SHG-M) in Material Sciences

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Second harmonic generation: applications in phase diagram investigations

International audienceThe influence of water (in its gaseous state) on the stability of crystallized organic compounds was investigated. Through two examples of solid/vapour equilibria, several behaviours were highlighted (stoichiometric or non stoichiometric hydrates, hydration/dehydration mechanisms, stability domains of multi-hydrates as a function of relative humidity). Phase diagrams (as a function of partial water pressure) and stability diagrams have been proposed for each example. This study illustrates that solid/vapour equilibrium knowledge is a crucial step during the complete characterization of solid organic compounds

An individual based computational model of intestinal crypt fission and its application to predicting unrestrictive growth of the intestinal epithelium.

Intestinal crypt fission is a homeostatic phenomenon, observable in healthy adult mucosa, but which also plays a pathological role as the main mode of growth of some intestinal polyps. Building on our previous individual based model for the small intestinal crypt and on in vitro cultured intestinal organoids, we here model crypt fission as a budding process based on fluid mechanics at the individual cell level and extrapolated predictions for growth of the intestinal epithelium. Budding was always observed in regions of organoids with abundant Paneth cells. Our data support a model in which buds are biomechanically initiated by single stem cells surrounded by Paneth cells which exhibit greater resistance to viscoelastic deformation, a hypothesis supported by atomic force measurements of single cells. Time intervals between consecutive budding events, as simulated by the model and observed in vitro, were 2.84 and 2.62 days, respectively. Predicted cell dynamics was unaffected within the original crypt which retained its full capability of providing cells to the epithelium throughout fission. Mitotic pressure in simulated primary crypts forced upward migration of buds, which simultaneously grew into new protruding crypts at a rate equal to 1.03 days-1 in simulations and 0.99 days-1 in cultured organoids. Simulated crypts reached their final size in 4.6 days, and required 40 6.2 days to migrate to the top of the primary crypt. The growth of the secondary crypt is independent of its migration along the original crypt. Assuming unrestricted crypt fission and multiple budding events, a maximal growth rate of the intestinal epithelium of 0.10 days-1 43 is predicted and thus approximately 22 days are required for a 10-fold increase of polyp size. These predictions are in agreement with the time reported to develop macroscopic adenomas in mice after loss of Apc in intestinal stem cells

A human organoid model of aggressive hepatoblastoma for disease modeling and drug testing

Hepatoblastoma is the most common childhood liver cancer. Although survival has improved significantly over the past few decades, there remains a group of children with aggressive disease who do not respond to current treatment regimens. There is a critical need for novel models to study aggressive hepatoblastoma as research to find new treatments is hampered by the small number of laboratory models of the disease. Organoids have emerged as robust models for many diseases, including cancer. We have generated and characterized a novel organoid model of aggressive hepatoblastoma directly from freshly resected patient tumors as a proof of concept for this approach. Hepatoblastoma tumor organoids recapitulate the key elements of patient tumors, including tumor architecture, mutational profile, gene expression patterns, and features of Wnt/β-catenin signaling that are hallmarks of hepatoblastoma pathophysiology. Tumor organoids were successfully used alongside non-tumor liver organoids from the same patient to perform a drug screen using twelve candidate compounds. One drug, JQ1, demonstrated increased destruction of liver organoids from hepatoblastoma tumor tissue relative to organoids from the adjacent non-tumor liver. Our findings suggest that hepatoblastoma organoids could be used for a variety of applications and have the potential to improve treatment options for the subset of hepatoblastoma patients who do not respond to existing treatments

EZH2-mediated epigenetic repression of DNA repair in promoting breast tumor initiating cells

Members of the Polycomb-group (PcG) family of proteins, including EZH2 (enhancer of zeste homolog 2), are involved in establishing epigenetic silencing of developmental genes in adult and embryonic stem cells, and their deregulation has been implicated in cancer. In a recent report, EZH2-mediated epigenetic repression of DNA damage repair in breast tumor initiating cells (BTICs) was identified as a mechanism that could promote expansion of BTICs, and may contribute to cancer progression

Quantifying the effect of forest age in annual net forest carbon balance

Forests dominate carbon (C) exchanges between the terrestrial biosphere and the atmosphere on land. In the long term, the net carbon flux between forests and the atmosphere has been significantly impacted by changes in forest cover area and structure due to ecological disturbances and management activities. Current empirical approaches for estimating net ecosystem productivity (NEP) rarely consider forest age as a predictor, which represents variation in physiological processes that can respond differently to environmental drivers, and regrowth following disturbance. Here, we conduct an observational synthesis to empirically determine to what extent climate, soil properties, nitrogen deposition, forest age and management influence the spatial and interannual variability of forest NEP across 126 forest eddy-covariance flux sites worldwide. The empirical models explained up to 62% and 71% of spatio-temporal and across-site variability of annual NEP, respectively. An investigation of model structures revealed that forest age was a dominant factor of NEP spatio-temporal variability in both space and time at the global scale as compared to abiotic factors, such as nutrient availability, soil characteristics and climate. These findings emphasize the importance of forest age in quantifying spatio-temporal variation in NEP using empirical approaches

SARS-CoV-2 infection and replication in human gastric organoids

COVID-19 typically manifests as a respiratory illness, but several clinical reports have described gastrointestinal symptoms. This is particularly true in children in whom gastrointestinal symptoms are frequent and viral shedding outlasts viral clearance from the respiratory system. These observations raise the question of whether the virus can replicate within the stomach. Here we generate gastric organoids from fetal, pediatric, and adult biopsies as in vitro models of SARS-CoV-2 infection. To facilitate infection, we induce reverse polarity in the gastric organoids. We find that the pediatric and late fetal gastric organoids are susceptible to infection with SARS-CoV-2, while viral replication is significantly lower in undifferentiated organoids of early fetal and adult origin. We demonstrate that adult gastric organoids are more susceptible to infection following differentiation. We perform transcriptomic analysis to reveal a moderate innate antiviral response and a lack of differentially expressed genes belonging to the interferon family. Collectively, we show that the virus can efficiently infect the gastric epithelium, suggesting that the stomach might have an active role in fecal-oral SARS-CoV-2 transmission.Several clinical reports have described gastrointestinal symptoms for COVID-19, though whether the virus can replicate within the stomach remains unclear. Here the authors generate gastric organoids from human biopsies and show that the virus can efficiently infect gastric epithelium, suggesting that the stomach might have an active role in fecal-oral transmission

Abnormal Wnt and PI3Kinase Signaling in the Malformed Intestine of lama5 Deficient Mice

Laminins are major constituents of basement membranes and are essential for tissue homeostasis. Laminin-511 is highly expressed in the intestine and its absence causes severe malformation of the intestine and embryonic lethality. To understand the mechanistic role of laminin-511 in tissue homeostasis, we used RNA profiling of embryonic intestinal tissue of lama5 knockout mice and identified a lama5 specific gene expression signature. By combining cell culture experiments with mediated knockdown approaches, we provide a mechanistic link between laminin α5 gene deficiency and the physiological phenotype. We show that laminin α5 plays a crucial role in both epithelial and mesenchymal cell behavior by inhibiting Wnt and activating PI3K signaling. We conclude that conflicting signals are elicited in the absence of lama5, which alter cell adhesion, migration as well as epithelial and muscle differentiation. Conversely, adhesion to laminin-511 may serve as a potent regulator of known interconnected PI3K/Akt and Wnt signaling pathways. Thus deregulated adhesion to laminin-511 may be instrumental in diseases such as human pathologies of the gut where laminin-511 is abnormally expressed as it is shown here