Almost all mineralized tissues contain proteins that are unusually acidic. As they are also often intimately associated with the mineral phase, they are thought to fulfill important functions in ...controlling mineral formation. Relatively little is known about these important proteins, because their acidic nature causes technical difficulties during purification and characterization procedures. Much effort has been made to overcome these problems, particularly in the study of mollusk-shell formation. To date about 16 proteins from mollusk-shell organic matrices have been sequenced, but only two are unusually rich in aspartic and glutamic acids. Here we screened a cDNA library made from the mRNA of the shell-forming cells of a bivalve, Atrina rigida, using probes for short Asp-containing repeat sequences, and identified ten different proteins. Using more specific probes designed from one subgroup of conserved sequences, we obtained the full sequences of a family of seven aspartic acid-rich proteins, which we named “Asprich”; a subfamily of the unusually acidic shell-matrix proteins. Polyclonal antibodies raised against a synthetic peptide of the conserved acidic1 domain of these proteins reacted specifically with the matrix components of the calcitic prismatic layer, but not with those of the aragonitic nacreous layer. Thus the Asprich proteins are constituents of the prismatic layer shell matrix. We can identify different domains within these sequences, including a signal peptide characteristic of proteins destined for extracellular secretion, a conserved domain rich in aspartic acid that contains a sequence very similar to the calcium-binding domain of Calsequestrin, and another domain rich in aspartic acid, that varies between the seven sequences. We also identified a domain with DEAD repeats that may have Mg-binding capabilities. Although we do not know, as yet, the function of these proteins, their generally conserved sequences do indicate that they might well fulfill basic functions in shell formation.
Cancellous bone is an intricate network of interconnected trabeculae, to which analysis of network topology can be applied. The inter-trabecular angle (ITA) analysis—an analysis of network ...topological parameters and regularity of network-forming nodes—was previously carried out on human proximal femora and showed that trabecular bone follows two main principles: sparsity of the network connectedness (prevalence of nodes with low connectivity in the network) and maximal space spanning (angular offset of connected elements is maximal for their number and approximates the values of geometrically symmetric shapes). These observations suggest that 3D organization of trabecular bone, irrespective of size and shape of individual elements, reflects a tradeoff between minimal metabolic cost of maintenance and maximal network stability under conditions of multidirectional loading. In this study, we validate the ITA application using additional 3D structures (cork and 3D-printed metal lattices), analyze the ITA parameters in porcine proximal femora and mandibles, and carry out a spatial analysis of the most common node type in the porcine mandibular condyle. The validation shows that the ITA application reliably detects designed or evolved topological parameters. The ITA parameters of porcine trabecular bones are similar to those of human bones. We demonstrate functional adaptation in the pig mandibular condyle by showing that the planar nodes with three edges are preferentially aligned in relation to the muscle forces that are applied to the condyle. We conclude that the ITA topological parameters are remarkably conserved, but locally do adapt to applied stresses.
Many mineralizing organisms selectively form either calcite or aragonite, two polymorphs of calcium carbonate with very similar crystalline structures. Understanding how these organisms achieve this ...control has represented a major challenge in the field of biomineralization. Macromolecules extracted from the aragonitic shell layers of some mollusks induced aragonite formation in vitro when preadsorbed on a substrate of β-chitin and silk fibroin. Macromolecules from calcitic shell layers induced mainly calcite formation under the same conditions. The results suggest that these macromolecules are responsible for the precipitation of either aragonite or calcite in vivo.
Phytolith assemblages are analysed in an ethnographic agro-pastoral community in Northern Greece. A new method for analyzing the data, combined with the concentrations of phytoliths per gram ...sediment, helps to differentiate diverse uses of space in the village. The Phytolith Difference Index (PDI) contrasts the phytolith assemblages in sediment samples from the region around the village least affected by human activities with those in the village and its immediate surroundings. The PDI reveals that many of the samples are dominated by the input of the stalks of the domestic cereal, rye, which is used for food, animal fodder and roof thatching. The PDI also differentiates between dung from mules or donkeys with dung from free ranging cows and goats. Activity areas analysed include storage areas, stabling areas, animal enclosures, floors from living areas that were repeatedly swept, hearths and open areas between structures. The combined use of the PDI, together with phytolith concentrations and phytolith morphotype analyses, may prove to be useful for deciphering activity areas in archaeological sites of not only agro-pastoralists, but also pastoralists and hunter–gatherers.
Abstract Lamellar bone is the most common bone type in humans. The predominant components of individual lamellae are plywood-like arrays of mineralized collagen fibrils aligned in different ...directions. Using a dual-beam electron microscope and the Serial Surface View (SSV) method we previously identified a small, but significantly different layer in rat lamellar bone, namely a disordered layer with collagen fibrils showing little or no preferred orientation. Here we present a 3D structural analysis of 12 SSV volumes (25 complete lamellae) from femora of 3 differently aged human individuals. We identify the ordered and disordered motifs in human bone as in the rat, with several significant differences. The ordered motif shows two major preferred orientations, perpendicular to the long axis of the bone, and aligned within 10–20° of the long axis, as well as fanning arrays. At a higher organizational level, arrays of ordered collagen fibrils are organized into ‘rods’ around 2 to 3 μm in diameter, and the long axes of these ‘rods’ are parallel to the lamellar boundaries. Human bone also contains a disordered component that envelopes the rods and fills in the spaces between them. The disordered motif is especially well-defined between adjacent layers of rods. The disordered motif and its interfibrillar substance stain heavily with osmium tetroxide and Alcian blue indicating the presence of another organic component in addition to collagen. The canalicular network is confined to the disordered material, along with voids and individual collagen fibrils, some of which are also aligned more or less perpendicular to the lamellar boundaries. The organization of the ordered fibril arrays into rods enveloped in the continuous disordered structure was not observed in rat lamellar bone. We thus conclude that human lamellar bone is comprised of two distinct materials, an ordered material and a disordered material, and contains an additional hierarchical level of organization composed of arrays of ordered collagen fibrils, referred to as rods. This new structural information on human lamellar bone will improve our understanding of structure–mechanical function relations, mechanisms of mechano-sensing and the characterizations of bone pathologies.
Shining light on local order: The relations between local crystalline order and peak intensities in the infrared spectra of calcite are explained in terms of different sensitivities to CaO and O⋅⋅⋅O ...distances (see picture) by comparing ab initio phonon spectra for ideal and distorted calcite unit cells with experimental spectra of various biogenic and geological calcites.
Calcium oxalate stone formation occurs under pathological conditions and accounts for more than 80% of all types of kidney stones. In the current study, we show for the first time that calcium ...oxalate stones are formed in the mouse inner ear of a genetic model for hearing loss and vestibular dysfunction in humans. The vestibular system within the inner ear is dependent on extracellular tiny calcium carbonate minerals for proper function. Thousands of these biominerals, known as otoconia, are associated with the utricle and saccule sensory maculae and are vital for mechanical stimulation of the sensory hair cells. We show that a missense mutation within the Slc26a4 gene abolishes the transport activity of its encoded protein, pendrin. As a consequence, dramatic changes in mineral composition, size, and shape occur within the utricle and saccule in a differential manner. Although abnormal giant carbonate minerals reside in the utricle at all ages, in the saccule, a gradual change in mineral composition leads to a formation of calcium oxalate in adult mice. By combining imaging and spectroscopy tools, we determined the profile of mineral composition and morphology at different time points. We propose a novel mechanism for the accumulation and aggregation of oxalate crystals in the inner ear.
It was assumed for a long time that organisms produce minerals directly from a saturated solution. A few exceptions were known, including the well documented mineralized teeth of the chiton. In 1997 ...it was demonstrated that sea urchin larva form their calcitic spicules by first depositing a highly unstable mineral phase called amorphous calcium carbonate. This strategy has since been shown to be used by animals from other phyla and for both aragonite and calcite. Recent evidence shows that vertebrate bone mineral may also be formed via a precursor phase of amorphous calcium carbonate. This strategy thus appears to be widespread. The challenge now is to understand the mechanisms by which these unstable phases are initially formed, how they are temporarily stabilized and how they are destabilized and transform into a crystalline mature product.
Our current understanding of the structures of vertebrate mineralized tissues is largely based on light microscopy/histology and projections of 3D structures onto 2D planes using electron microscopy. ...We know little about the fine details of these structures in 3D at the length scales of their basic building blocks, the inherent variations of structure within a tissue and the cell-extracellular tissue interfaces. This limits progress in understanding tissue formation, relating structure to mechanical and metabolic functions, and obtaining deeper insights into pathologies and the evolution of these tissues. In this perspective we identify and discuss a series of open questions pertaining to collagen containing vertebrate mineralized tissues that can be addressed using appropriate 3D structural determination methods. By so doing we hope to encourage more research into the 3D structures of mineralized vertebrate tissues.
The earliest food producers in Africa were mobile pastoralists who left limited archaeological traces. As a result archaeologists studying the spread of food production in the region have difficulty ...distinguishing early pastoralists from hunter-gatherers with whom they interacted. This geo-ethnoarchaeological study contributes to the resolution of the problem through identification of sediments distinctive of livestock enclosures, and thus of pastoral settlements. Sediments were sampled in and around currently occupied and recently abandoned Maasai livestock enclosures ranging in age between one and 40 years. Twenty to thirty years after site abandonment, there is no visible difference between enclosure and regional sediments. Micromorphological, mineralogical, and phytolith analyses, of enclosure sediments, however, allow differentiation of enclosure from regional sediments. Our results show that a unique undulating microlaminated structure is distinctive of enclosure sediments. Enclosure sediments, especially small stock, also contain a rare mineral, monohydrocalcite (CaCO
3
.
H
2O). In addition, large amounts of opal (SiO
2
.
nH
2O), in the form of phytoliths, are found in enclosure relative to regional sediments. These differences are likely to be preserved in the archaeological record, and this approach will allow better understanding of the spread of pastoralism in Africa and elsewhere.
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