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S C I E N T I F I C H I G H L I G H T S
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PRINCIPAL PUBLICATION AND AUTHORS
Amorphous-to-crystal transition in the layer-by-layer growth of bivalve shell prisms, J. Duboisset (a), P. Ferrand (a), A. Baroni (a), T.A. Grünewald (a), H. Dicko (a), O. Grauby (b), J. Vidal-Dupiol (c), D. Saulnier (d), G. Le Moullac (d), M. Rosenthal (e), M. Burghammer (e), J. Nouet (f), C. Chevallard (g), A. Baronnet (b), V. Chamard (a), Acta Biomater. 142, 194-207 (2022); https:/doi.org/10.1016/j.actbio.2022.01.024 (a) Aix-Marseille Univ, CNRS, Centrale Marseille, Institut Fresnel, Marseille (France) (b) Aix-Marseille Univ, CNRS, CINaM, Marseille (France) (c) IHPE, Univ. Montpellier, CNRS, Ifremer, Univ. Perpignan Via Domitia, Montpellier (France) (d) Ifremer, Environnement Insulaire Océanien (EIO), Vairao (French Polynesia) (e) ESRF (f) GEOPS, Univ. Paris-Sud, CNRS, Université Paris-Saclay, Orsay (France) (g) NIMBE, CEA, CNRS, Université Paris-Saclay, Gif-sur-Yvette (France)
 S. Weiner et al., Science 309, 1027-1028 (2005).  J. Duboisset et al., J. Struct. Biol., in press (2022).  A. Baroni et al., Phys. Rev. Appl. 13, 054028-1-7 (2020).  F. Mastropietro et al., Nat. Mater. 16, 946 (2017).
Ageing and neurodegeneration: from organ down to cell visualisation and quantification in 3D
The pathophysiology of ageing and neurodegeneration of the brain is increasingly understood. However, treatments remain inadequate and the conditions incurable. By using a virtual X-ray phase-contrast histological method, relying on a multiscale and multimodal approach, it was possible to visualise and quantify in 3D the cellular-to-organ degeneration and the therapeutic effects in an experimental mouse model of Alzheimer s disease.
In western industrial nations, Alzheimer s disease (AD) is the leading cause of neurodegeneration and dementia in humans. Diverse and still ill-understood neurological processes, including toxic protein deposition, synapse loss and microglial infiltration, underpin the development of the disease, generating neuronal death and progressive cognitive decline. At present, while it is possible to slow down the degeneration of the brain cells, the disease remains incurable. An improved visualisation, and thus understanding, of the morphological changes and processes induced by AD and its processes is key for treatment development. Modern imaging tools come short of delivering the volumetric cellular-level visualisations that would be necessary to reliably detect and differentiate individual, subtle protein-based cellular lesions or abnormal age-related
intra-cellular accumulations, especially in the likely crucial pre-symptomatic early phases of AD. A certain clinical AD diagnosis is only reached post-mortem by a histopathological workup of nervous-tissue biopsies, by detecting the presence of the two, hallmark protein- based lesions (amyloid-β and hyper-phosphorylated tau protein). Also, in the preclinical context of post-mortem small-animal imaging, methods capable of providing an unbiased, high-throughput, anatomically-dense, brain-wide 3D screening of neuronal damage are still an elusive goal.
In this study, synchrotron 3D hierarchical imaging for original virtual-histological work [1-5] on dissected small animal brain tissue was applied to examine brain cells and gain new insights into the cellular processes that take place during the course of the disease. X-ray phase- contrast computed tomography (X-PCI-CT) was used for the post-mortem volumetric imaging of mouse brain samples to identify and quantify cellular and subcellular ageing and neurodegeneration in an experimental model of AD (3xTgAD).
Multiscale X-PCI-CT  was performed on mouse half-brain samples embedded in minimal paraffin. 33, 0.73 and 0.33 µm3 effective voxel size CT scans were performed at beamline ID17 and at the TOMCAT beamline at SLS on un-sectioned samples. 0.13 µm3 voxel nanoholotomography (XNH) scans  were performed at beamline ID16A on ~ 2 x 2 x 4 mm3 tissue biopsies
Based on these, a temporal biomineralisation cycle was proposed (Figure 67). It starts with the production of an amorphous precursor layer, which further crystallises with a transition front progressing radially from the unit centre, while the organics are expelled towards the prism edge. Simultaneously, along the shell thickness, the growth occurs following a layer-by-layer mode.
These findings open biomimetic perspectives for the design of refined crystalline materials. They present a significant step forward in the understanding of the biomineralisation process, as it provides a clear spatial link between the organics, amorphous and crystalline compounds, and likely their respective evolution over time. With ESRF-EBS, the in-vivo follow up of biomineralisation is in reach.