Bone is the most widespread mineralized tissue in vertebrates and its formation is orchestrated by specialized cells – the osteoblasts. Crystalline carbonated hydroxyapatite, an inorganic calcium ...phosphate mineral, constitutes a substantial fraction of mature bone tissue. Yet key aspects of the mineral formation mechanism, transport pathways and deposition in the extracellular matrix remain unidentified. Using cryo-electron microscopy on native frozen-hydrated tissues we show that during mineralization of developing mouse calvaria and long bones, bone-lining cells concentrate membrane-bound mineral granules within intracellular vesicles. Elemental analysis and electron diffraction show that the intracellular mineral granules consist of disordered calcium phosphate, a highly metastable phase and a potential precursor of carbonated hydroxyapatite. The intracellular mineral contains considerably less calcium than expected for synthetic amorphous calcium phosphate, suggesting the presence of a cellular mechanism by which phosphate entities are first formed and thereafter gradually sequester calcium within the vesicles. We thus demonstrate that in vivo osteoblasts actively produce disordered mineral packets within intracellular vesicles for mineralization of the extracellular developing bone tissue. The use of a highly disordered precursor mineral phase that later crystallizes within an extracellular matrix is a strategy employed in the formation of fish fin bones and by various invertebrate phyla. This therefore appears to be a widespread strategy used by many animal phyla, including vertebrates.
Fish have evolved biogenic multilayer reflectors composed of stacks of intracellular anhydrous guanine crystals separated by cytoplasm, to produce the silvery luster of their skin and scales. Here we ...compare two different variants of the Japanese Koi fish; one of them with enhanced reflectivity. Our aim is to determine how biology modulates reflectivity, and from this to obtain a mechanistic understanding of the structure and properties governing the intensity of silver reflectance. We measured the reflectance of individual scales with a custom-made microscope, and then for each individual scale we characterized the structure of the guanine crystal/cytoplasm layers using high-resolution cryo-SEM. The measured reflectance and the structural-geometrical parameters were used to calculate the reflectance of each scale, and the results were compared to the experimental measurements. We show that enhanced reflectivity is obtained with the same basic guanine crystal/cytoplasm stacks, but the structural arrangement between the stack, inside the stacks, and relative to the scale surface is varied when reflectivity is enhanced. Finally, we propose a model that incorporates the basic building block parameters, the crystal orientation inside the tissue, and the resulting reflectance and explains the mechanistic basis for reflectance enhancement.
As one of the most abundant materials in the world, calcium carbonate, CaCO
, is the main constituent of the skeletons and shells of various marine organisms. It is used in the cement industry and ...plays a crucial role in the global carbon cycle and formation of sedimentary rocks. For more than a century, only three polymorphs of pure CaCO
-calcite, aragonite, and vaterite-were known to exist at ambient conditions, as well as two hydrated crystal phases, monohydrocalcite (CaCO
·1H
O) and ikaite (CaCO
·6H
O). While investigating the role of magnesium ions in crystallization pathways of amorphous calcium carbonate, we unexpectedly discovered an unknown crystalline phase, hemihydrate CaCO
·½H
O, with monoclinic structure. This discovery may have important implications in biomineralization, geology, and industrial processes based on hydration of CaCO
.
•The provisional ossification zone of the mouse growth plate is a complex of hypertrophic chondrocytes, bone trabeculae and blood vessel extremities.•Membrane-bound mineral-containing vesicles are ...present in the blood serum, and mineral particles without membranes are associated with blood vessel walls.•Intracellular mineral particles are observed in cells associated with bone formation, but not in the cells associated with mineralized cartilage.•There are open continuous pathways between some blood vessel extremities and the hypertrophic cell matrix where mineralized cartilage forms.•We postulate that the mineral for cartilage and bone is derived from the blood vessels in the metaphysis.
Endochondral ossification in the growth plate of long bones involves cartilage mineralization, bone formation and the budding vasculature. Many of these processes take place in a complex and dynamic zone, the provisional ossification zone, of the growth plate. Here we investigate aspects of mineralization in 2D and 3D in the provisional ossification zone at different length scales using samples preserved under cryogenic or fully hydrated conditions. We use confocal light microscopy, cryo-SEM and micro-CT in the phase contrast mode. We show in 9 week old BALB/c mice the presence of vesicles containing mineral particles in the blood serum, as well as mineral particles without membranes integrated with the blood vessel walls. We also observe labeled mineral particles within cells associated with bone formation, but not in the hypertrophic cartilage cells that are involved with cartilage mineralization. High resolution micro-CT images of fresh hydrated tibiae, show that there are open continuous pathways between the blood vessel extremities and the hypertrophic chondrocyte zone. As the blood vessel extremities, the mineralizing cartilage and the forming bone are all closely associated within this narrow zone, we raise the possibility that in addition to ion transport, mineral necessary for both cartilage and bone formation is also transported through the vasculature.
The image-forming mirror in the eye of the scallop Palmer, Benjamin A.; Taylor, Gavin J.; Brumfeld, Vlad ...
Science (American Association for the Advancement of Science),
12/2017, Letnik:
358, Številka:
6367
Journal Article
Recenzirano
Scallops possess a visual system comprising up to 200 eyes, each containing a concave mirror rather than a lens to focus light. The hierarchical organization of the multilayered mirror is controlled ...for image formation, from the component guanine crystals at the nanoscale to the complex three-dimensional morphology at the millimeter level. The layered structure of the mirror is tuned to reflect the wavelengths of light penetrating the scallop’s habitat and is tiled with a mosaic of square guanine crystals, which reduces optical aberrations. The mirror forms images on a double-layered retina used for separately imaging the peripheral and central fields of view. The tiled, off-axis mirror of the scallop eye bears a striking resemblance to the segmented mirrors of reflecting telescopes.
Sea urchin larvae have an endoskeleton consisting of two calcitic spicules. We reconstructed various stages of the formation pathway of calcium carbonate from calcium ions in sea water to mineral ...deposition and integration into the forming spicules. Monitoring calcium uptake with the fluorescent dye calcein shows that calcium ions first penetrate the embryo and later are deposited intracellularly. Surprisingly, calcium carbonate deposits are distributed widely all over the embryo, including in the primary mesenchyme cells and in the surface epithelial cells. Using cryo-SEM, we show that the intracellular calcium carbonate deposits are contained in vesicles of diameter 0.5–1.5 μm. Using the newly developed airSEM, which allows direct correlation between fluorescence and energy dispersive spectroscopy, we confirmed the presence of solid calcium carbonate in the vesicles. This mineral phase appears as aggregates of 20–30-nm nanospheres, consistent with amorphous calcium carbonate. The aggregates finally are introduced into the spicule compartment, where they integrate into the growing spicule.
An ugly duckling grows into a swan: Many organisms grow their crystalline mineral phases through the secondary nucleation of nanospheres made of an amorphous precursor phase. Stable amorphous calcium ...carbonate biominerals were used to induce a similar transformation in vitro. The amorphous nanospheres underwent a solid‐phase transformation that resulted in highly ordered calcite crystals composed of aggregated particles (see SEM image).
Light‐induced tunable photonic systems are rare in nature, and generally beyond the state‐of‐the‐art in artificial systems. Sapphirinid male copepods produce some of the most spectacular colors in ...nature. The male coloration, used for communication purposes, is structural and is produced from ordered layers of guanine crystals separated by cytoplasm. It is generally accepted that the colors of the males are related to their location in the epipelagic zone. By combining correlative reflectance and cryoelectron microscopy image analyses, together with optical time lapse recording and transfer matrix modeling, it is shown that male sapphirinids have the remarkable ability to change their reflectance spectrum in response to changes in the light conditions. It is also shown that this color change is achieved by a change in the thickness of the cytoplasm layers that separate the guanine crystals. This change is reversible, and is both intensity and wavelength dependent. This capability provides the male with the ability to efficiently reflect light under certain conditions, while remaining transparent and hence camouflaged under other conditions. These copepods can thus provide inspiration for producing synthetic tunable photonic arrays.
Male sapphirinids have the remarkable ability to change their reflectance spectrum in response to changes in the light conditions. This change is reversible, and is both intensity and wavelength dependent.
The skeletons of adult echinoderms comprise large single crystals of calcite with smooth convoluted fenestrated morphologies, raising many questions about how they form. By using water etching, ...infrared spectroscopy, electron diffraction, and environmental scanning electron microscopy, we show that sea urchin spine regeneration proceeds via the initial deposition of amorphous calcium carbonate. Because most echinoderms produce the same type of skeletal material, they probably all use this same mechanism. Deposition of transient amorphous phases as a strategy for producing single crystals with complex morphology may have interesting implications for the development of sophisticated materials.
The continuously forming fin bony rays of zebrafish represent a simple bone model system in which mineralization is temporally and spatially resolved. The mineralized collagen fibrils of the fin ...bones are identical in structure to those found in all known bone materials. We study the continuous mineralization process within the tissue by using synchrotron microbeam x-ray diffraction and small-angle scattering, combined with cryo-scanning electron microscopy. The former provides information on the mineral phase and the mineral particles size and shape, whereas the latter allows high-resolution imaging of native hydrated tissues. The integration of the two techniques demonstrates that new mineral is delivered and deposited as packages of amorphous calcium phosphate nanospheres, which transform into platelets of crystalline apatite within the collagen matrix.
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