Avian eggshell biomineralization: an update on its structure, mineralogy and protein tool kit

The avian eggshell is a natural protective envelope that relies on the phenomenon of biomineralization for its formation. The shell is made of calcium carbonate in the form of calcite, which contains hundreds of proteins that interact with the mineral phase controlling its formation and structural organization, and thus determine the mechanical properties of the mature biomaterial. We describe its mineralogy, structure and the regulatory interactions that integrate the mineral and organic constituents. We underline recent evidence for vesicular transfer of amorphous calcium carbonate (ACC), as a new pathway to ensure the active and continuous supply of the ions necessary for shell mineralization. Currently more than 900 proteins and thousands of upregulated transcripts have been identified during chicken eggshell formation. Bioinformatic predictions address their functionality during the biomineralization process. In addition, we describe matrix protein quantification to understand their role during the key spatially- and temporally- regulated events of shell mineralization. Finally, we propose an updated scheme with a global scenario encompassing the mechanisms of avian eggshell mineralization. With this large dataset at hand, it should now be possible to determine specific motifs, domains or proteins and peptide sequences that perform a critical function during avian eggshell biomineralization. The integration of this insight with genomic data (non-synonymous single nucleotide polymorphisms) and precise phenotyping (shell biomechanical parameters) on pure selected lines will lead to consistently better-quality eggshell characteristics for improved food safety. This information will also address the question of how the evolutionary-optimized chicken eggshell matrix proteins affect and regulate calcium carbonate mineralization as a good example of biomimetic and bio-inspired material design.

The morphostructure of Oxalis incarnata bulbs

The morphostructure of the bulbs of Oxalis incarnata in the conditions of dormancy and the plant’s growth and development are described. The plants were grown in two irrigation modes: 1) with regular irrigation during the year, and 2) with limited irrigation in March-October and without irrigation in November-February. The bulbs were analyzed by way of consequent detaching of the scales. Investigated bulbs always had four fleshy scales, while the number of coriaceous and membranous scales varied. Coriaceous scales, together with two fleshy outer scales, make a protective envelope of the bulb.The overground shoot of O. incarnata, just like in other species of the genus, demonstrates monopodial growth and can produce up to five levels of lateral branches. Elongated parts of overground shoots serve for new territories’ useful occupation, while shortened parts produce new particles. Resting buds (bulbils) of three types were observed in O. incarnata: underground axillary buds, overground axillary gemmae, and terminal gemma. Our investigations showed polyvariance both of organogenesis of the resting buds and ontogenesis of plants in general, depending on irrigation regimes. In the case of limited irrigation, the plants of O. incarnata shed the leaves and can produce terminal gemma. While in the case of regular irrigation during the year, they remain evergreen and form gemmae exclusively in the leaves’ axils. We did not observe the formation of terminal gemmae in the case if axillary gemmae were present.The root system of O. incarnata has a complex structure. It consists of two crowns of the filamentary roots, contractile roots, and additional adventitious roots located along the underground part of the shoot during its growth. Such structure of the root system probably ensures better absorption of the water.

Moonlighting Proteins at the Candidal Cell Surface

The cell wall in Candida albicans is not only a tight protective envelope but also a point of contact with the human host that provides a dynamic response to the constantly changing environment in infection niches. Particularly important roles are attributed to proteins exposed at the fungal cell surface. These include proteins that are stably and covalently bound to the cell wall or cell membrane and those that are more loosely attached. Interestingly in this regard, numerous loosely attached proteins belong to the class of “moonlighting proteins” that are originally intracellular and that perform essentially different functions in addition to their primary housekeeping roles. These proteins also demonstrate unpredicted interactions with non-canonical partners at an a priori unexpected extracellular location, achieved via non-classical secretion routes. Acting both individually and collectively, the moonlighting proteins contribute to candidal virulence and pathogenicity through their involvement in mechanisms critical for successful host colonization and infection, such as the adhesion to host cells, interactions with plasma homeostatic proteolytic cascades, responses to stress conditions and molecular mimicry. The documented knowledge of the roles of these proteins in C. albicans pathogenicity has utility for assisting the design of new therapeutic, diagnostic and preventive strategies against candidiasis.

Form and function of F-actin during biomineralization revealed from live experiments on foraminifera

Although the emergence of complex biomineralized forms has been investigated for over a century, still little is known on how single cells control morphology of skeletal structures, such as frustules, shells, spicules, or scales. We have run experiments on the shell formation in foraminifera, unicellular, mainly marine organisms that can build shells by successive additions of chambers. We used live imaging to discover that all stages of chamber/shell formation are controlled by dedicated actin-driven pseudopodial structures. Successive reorganization of an F-actin meshwork, associated with microtubular structures, is actively involved in formation of protective envelope, followed by dynamic scaffolding of chamber morphology. Then lamellar dynamic templates create a confined space and control mineralization separated from seawater. These observations exclude extracellular calcification assumed in selected foraminiferal clades, and instead suggest a semiintracellular biomineralization pattern known from other unicellular calcifying and silicifying organisms. These results give a challenging prospect to decipher the vital effect on geochemical proxies applied to paleoceanographic reconstructions. They have further implications for understanding multiscale complexity of biomineralization and show a prospect for material science applications.

Biophysics of the structure and function of porins

Gram-negative bacteria such asEscherichia coli(E. coli) andSalmonella typhimurium(S. typhimurium) have two layers of membranes in the cellular envelope – the cytoplasmic membrane and the outer membrane (Fig. I). Between these membranes is a periplasmic space in which there is a peptidoglycan layer that provides the cells with mechanical rigidity. In this periplasmic space, there are also a variety of hydrolases and binding proteins. The composition of the outer membrane is somewhat unusual. This membrane bilayer is asymmetric, having an inner (periplasmic) leaflet composed of phospholipids and an outer (extracellular) leaflet formed by lipopolysaccharide (LPS). Unlike phospholipids having two acyl chains, LPS has six or seven saturated fatty acid chains (see reviews, Lugtenberg & Van Alphen, 1983; Nikaido & Vaara, 1985; Nakae, 1986). The head groups of LPS have a strong affinity for divalent cations such as Ca2+, and given a sufficient concentration of these ions the outer membrane can form quite a formidable permeability barrier through this head group/salt bridge network (Nikaido & Vaara, 1985). The function of the outer membrane is to serve as a protective envelope against hostile environments such as those in the intestinal tract of animals where harmful and toxic substances - for example, bile salts and various enzymes - are often found. The outer membrane itself would be impermeable to most hydrophilic solutes were it not for the presence of membrane channels. The presence of a large number of pore-forming proteins provides both specific and nonspecific diffusion pathways across the outer membrane for solutes such as nutrients and waste products to diffuse into or out of the cell.

Simple Graphical Solutions of Spherical Triangles

A Device known as the Simplified Astro Platten (S.A.P.) is presently being marketed by the Bucks. Gear and Engineering Co. Ltd., of Middle Lane, Mount Pleasant, Aylesbury. It consists of a large rectangular plastic sheet some 29 in. by 16 in. on which are engraved two graduated semicircles with parallel diameters separated by a space of 2 inches. This sheet, on which pencil lines may be drawn and which can easily be cleaned when the lines are no longer required, is housed in a stiff plastic protective envelope. A mimeographed booklet of instructions includes examples and answers, for practice. There is no indication of the principles on which the device is based but the idea is certainly not new.