Spiculogenesis in the siliceous sponge Lubomirskia baicalensis studied with fluorescent staining

A biogenic geodesic dome of the silica skeleton in Phaeodaria

Unique architectures of microbial skeletons are viewed as a model for the architectural design of artificial structural materials. In particular, the specific geometric arrangement of a spherical skeleton 0.5-1.5 mm in diameter of shell-bearing protists, Phaeodaria (Aulosphaera sp.), is remarkably interesting because of its similarity to a geodesic polyhedron, which is a hollow framework with 6-branched nodes that requires minimal building material for maximal strength. A phaeodarian skeleton composed of silica rods 5-10 µm in diameter was characterized as a distorted dome that is based on an icosahedron sectioned with a 7-frequency subdivision. The major difference of the biogenic architecture from the ideal geodesic dome is the coexistence of 7- and 5-branched nodes with the distortion of the frames and the presence of radial spines. From a microscopic perspective, the frames and radial spines were revealed to be hollow tubes having inner fibers and lamellar walls consisting of silica nanoparticles 4-8 nm in diameter with interlayer organic matter. The high degradability of the silica skeleton in seawater after cell mortality is ascribed to the specific nanometric composite structure. The biological architectonics sheds light on the production of environmentally friendly, lightweight structural materials and microdevices.

Insights into the structure and morphogenesis of the giant basal spicule of the glass sponge Monorhaphis chuni

BACKGROUND

A basal spicule of the hexactinellid sponge Monorhaphis chuni may reach up to 3 m in length and 10 mm in diameter, an extreme case of large spicule size. Generally, sponge spicules are of scales from micrometers to centimeters. Due to its large size many researchers have described its structure and properties and have proposed it as a model of hexactinellid spicule development. Thorough examination of new material of this basal spicule has revealed numerous inconsistencies between our observations and earlier descriptions. In this work, we present the results of detailed examinations with transmitted light and epifluorescence microscopy, SEM, solid state NMR analysis, FTIR and X-ray analysis and staining of Monorhaphis chuni basal spicules of different sizes, collected from a number of deep sea locations, to better understand its structure and function.

RESULTS

Three morphologically/structurally different silica layers i.e. plain glassy layer (PG), tuberculate layer (TL) and annular layer (AL), and an axial cylinder (AC) characterize adult spicules. Young, immature spicules display only plain glassy silica layers which dominate the spicule volume. All three layers i.e. PG, TL and AL can substitute for each other along the surface of the spicule, but equally they are superimposed in older parts of the spicules, with AL being the most external and occurring only in the lower part of the spicules and TL being intermediate between AL and PG. The TL, which is composed of several thinner layers, is formed by a progressive folding of its surface but its microstructure is the same as in the PG layer (glassy silica). The AL differs significantly from the PG and TL in being granular and porous in structure. The TL was found to display positive structures (tubercles), not depressions, as earlier suggested. The apparent perforated and non-perforated bands of the AL are an optical artefact. The new layer type that we called the Ripple Mark Layer (RML) was noted, as well as narrow spikes on the AL ridges, both structures not reported earlier. The interface of the TL and AL, where tubercles fit into depressions of the lower surface of the AL, represent tenon and mortise or dovetail joints, making the spicules more stiff/strong and thus less prone to breaking in the lower part. Early stages of the spicule growth are bidirectional, later growth is unidirectional toward the spicule apex. Growth in thickness proceeds by adding new layers. The spicules are composed of well condensed silica, but the outermost AL is characterized by slightly more condensed silica with less water than the rest. Organics permeating the silica are homogeneous and proteinaceous. The external organic net (most probably collagen) enveloping the basal spicule is a structural element that bounds the sponge body together with the spicule, rather than controlling tubercle formation. Growth of various layers may proceed simultaneously in different locations along the spicule and it is sclerosyncytium that controls formation of silica layers. The growth in spicule length is controlled by extension of the top of the axial filament that is not enclosed by silica and is not involved in further silica deposition. No structures that can be related to sclerocytes (as known in Demospongiae) in Monorhaphis were discovered during this study.

CONCLUSIONS

Our studies resulted in a new insight into the structure and growth of the basal Monorhaphis spicules that contradicts earlier results, and permitted us to propose a new model of this spicule's formation. Due to its unique structure, associated with its function, the basal spicule of Monorhaphis chuni cannot serve as a general model of growth for all hexactinellid spicules.

Cultivation of fractionated cells from a bioactive-alkaloid-bearing marine sponge Axinella sp

Sponges are among the most primitive multicellular organisms and well-known as a major source of marine natural products. Cultivation of sponge cells has long been an attractive topic due to the prominent evolutionary and cytological significance of sponges and as a potential approach to supply sponge-derived compounds. Sponge cell culture is carried out through culturing organized cell aggregates called 'primmorphs.' Most research culturing sponge cells has used unfractionated cells to develop primmorphs. In the current study, a tropical marine sponge Axinella sp., which contains the bioactive alkaloids, debromohymenialdisine (DBH), and hymenialdisine (HD), was used to obtain fractionated cells and the corresponding primmorphs. These alkaloids, DBH and HD, reportedly show pharmacological activities for treating osteoarthritis and Alzheimer's disease. Three different cell fractions were obtained, including enriched spherulous cells, large mesohyl cells, and small epithelial cells. These cell fractions were cultivated separately, forming aggregates that later developed into different kinds of primmorphs. The three kinds of primmorphs obtained were compared as regards to appearance, morphogenesis, and cellular composition. Additionally, the amount of alkaloid in the primmorphs-culture system was examined over a 30-d culturing period. During the culturing of enriched spherulous cells and developed primmorphs, the total amount of alkaloid declined notably. In addition, the speculation of alkaloid secretion and some phenomena that occurred during cell culturing are discussed.

Adhesion of freshwater sponge cells mediated by carbohydrate-carbohydrate interactions requires low environmental calcium

Marine ancestors of freshwater sponges had to undergo a series of physiological adaptations to colonize harsh and heterogeneous limnic environments. Besides reduced salinity, river-lake systems also have calcium concentrations far lower than seawater. Cell adhesion in sponges is mediated by calcium-dependent multivalent self-interactions of sulfated polysaccharide components of membrane-bound proteoglycans named aggregation factors. Cells of marine sponges require seawater average calcium concentration (10 mM) to sustain adhesion promoted by aggregation factors. We demonstrate here that the freshwater sponge Spongilla alba can thrive in a calcium-poor aquatic environment and that their cells are able to aggregate and form primmorphs with calcium concentrations 40-fold lower than that required by marine sponges cells. We also find that their gemmules need calcium and other micronutrients to hatch and generate new sponges. The sulfated polysaccharide purified from S. alba has sulfate content and molecular size notably lower than those from marine sponges. Nuclear magnetic resonance analyses indicated that it is composed of a central backbone of non- and 2-sulfated α- and β-glucose units decorated with branches of α-glucose. Assessments with atomic force microscopy/single-molecule force spectroscopy show that S. alba glucan requires 10-fold less calcium than sulfated polysaccharides from marine sponges to self-interact efficiently. Such an ability to retain multicellular morphology with low environmental calcium must have been a crucial evolutionary step for freshwater sponges to successfully colonize inland waters.

Skeleton construction upon local regression of the sponge body

We previously revealed that the mechanism of demosponge skeleton construction is self-organization by multiple rounds of sequential mechanical reactions of player cells. In these reactions, "transport cells" dynamically carry fine skeletal elements (spicules) on epithelia surrounding the inner body space of sponges (basal epithelium (basopinacoderm) and the endodermal epithelium (ENCM)). Once spicules pierce ENCM and apical pinacoderm, subsequently they are cemented to the substratum under the sponge body, or connected to other skeleton-constructing spicules. Thus, the "pierce" step is the key to holding up spicules in the temporary periphery of growing sponges' bodies. Since sponges can regress as well as grow, here we asked how skeleton construction occurs during local regression of the body. We found that prior to local basopinacoderm retraction (and thus body regression), the body became thinner. Some spicules that were originally carried outward stagnated for a while, and were then carried inwards either on ENCM or basopinacoderm. Spicules that were carried inwards on ENCM pierced epithelia after a short transport, and thus became held up at relatively inward positions compared to spicules carried on outwardly extending basopinacoderm. The switch of epithelia on which transport cells migrate efficiently occurred in thinner body spaces where basopinacoderm and ENCM became close to each other. Thus, the mechanisms underlying this phenomenon are rather mechanical: the combination of sequential reactions of skeleton construction and the narrowed body space upon local retraction of basopinacoderm cause spicules to be held up at more-inward positions, which might strengthen the basopinacoderm's attachment to substratum.

Produce, carry/position, and connect: morphogenesis using rigid materials

Animal morphogenesis can be summarized as a reconfiguration of a mass of cells. Although extracellular matrices that include rigid skeletal elements, such as cartilage/bones and exoskeletons, have important roles in morphogenesis, they are also secreted in situ by accumulated cells or epithelial cells. In contrast, recent studies of the skeleton construction of sponges (Porifera) illuminate a conceptually different mechanism of morphogenesis in which cells manipulate rather fine rigid materials (spicules) to form larger structures. Here, two different types of sponge skeleton formation using calcareous spicules or siliceous spicules are compared with regard to the concept of the production of rigid materials and their use in skeletons. The comparison highlights the advantages of their different strategies of forming sponge skeletons.

Modelling the early evolution of extracellular matrix from modern Ctenophores and Sponges

Animals (metazoans) include some of the most complex living organisms on Earth, with regard to their multicellularity, numbers of differentiated cell types, and lifecycles. The metazoan extracellular matrix (ECM) is well-known to have major roles in the development of tissues during embryogenesis and in maintaining homoeostasis throughout life, yet insight into the ECM proteins which may have contributed to the transition from unicellular eukaryotes to multicellular animals remains sparse. Recent phylogenetic studies place either ctenophores or poriferans as the closest modern relatives of the earliest emerging metazoans. Here, we review the literature and representative genomic and transcriptomic databases for evidence of ECM and ECM-affiliated components known to be conserved in bilaterians, that are also present in ctenophores and/or poriferans. Whereas an extensive set of related proteins are identifiable in poriferans, there is a strikingly lack of conservation in ctenophores. From this perspective, much remains to be learnt about the composition of ctenophore mesoglea. The principal ECM-related proteins conserved between ctenophores, poriferans, and bilaterians include collagen IV, laminin-like proteins, thrombospondin superfamily members, integrins, membrane-associated proteoglycans, and tissue transglutaminase. These are candidates for a putative ancestral ECM that may have contributed to the emergence of the metazoans.

Shaping highly regular glass architectures: A lesson from nature

Demospongiae is a class of marine sponges that mineralize skeletal elements, the glass spicules, made of amorphous silica. The spicules exhibit a diversity of highly regular three-dimensional branched morphologies that are a paradigm example of symmetry in biological systems. Current glass shaping technology requires treatment at high temperatures. In this context, the mechanism by which glass architectures are formed by living organisms remains a mystery. We uncover the principles of spicule morphogenesis. During spicule formation, the process of silica deposition is templated by an organic filament. It is composed of enzymatically active proteins arranged in a mesoscopic hexagonal crystal-like structure. In analogy to synthetic inorganic nanocrystals that show high spatial regularity, we demonstrate that the branching of the filament follows specific crystallographic directions of the protein lattice. In correlation with the symmetry of the lattice, filament branching determines the highly regular morphology of the spicules on the macroscale.