Feinstrukturen und Verwandtschaftsbeziehungen der Graptolithen

Pterobranchs and graptolites exhibit essentially the same skeletal structure, namely a primary skeleton composed of regularly stacked bands and a later thickening made up of irregulary arranged, thinner elements. Both parts of the skeleton were most likely secreted via the individuals' cephalic discs. The most notable structural difference between the pterobranchs and graptolites can be seen in the secondary skeletal layers. In the graptolites it is made up of closely packed parallel fibers. The long distal thread (nema) of the planktonic graptolites is constructed and probably also secreted in a manner similar to that in which the skeleton is formed. Some sessile graptolites have more in common with recent pterobranchs than “normal” graptolites. The Crustoidea seem to be particulary well suited as model for the transition from pterobranch to graptolite structure. The minute structures of various pterobranchs and graptolites are depicted here, arranged approximately according to their probable evolution.     

The ultrastructure of the Crustoidea and the evolution of graptolite skeletal tissues

The Crustoidea are important in discussions of graptolite origins, because they represent a morphoecological type intermediate between the Rhabdopleurida and the Dendroidea. TEM and SEM studies of their rhabdosomes provide new data on the structural variation displayed by the graptolite periderm. Since the crustoid fusellar fabric does not differ markedly from the fuseller fabric of other graptolites and is dissimilar to that of pterobranchs, it is supposed that the fundamental graptolite fibril pattern was attained at the crustoid stage of graptolite evolution. The crustoid cortex is made of paracortex (the multiple deposition of sheets separated by an intersheet material in the form of condensed meshwork of fibrous material) and of pseudocortex (the accumulation of sheets and intersheet material devoid of fibrous character). The presence of sporadically genuine cortex is noted. Presumably the mechanisms of cortical fibrilogenesis were attained at the crustoid stage, but only in an incipient and incomplete form. Modes of periderm corticization arc discussed. Sheets, common elements in secondary deposits of pterobranchs and graptolites, arc compared, but some problems still remain unclear. ?Crustoidea, Pterobranchia, phytogeny, ultrastructure, cortex, morphogenesis, homology.     

Middle Cambrian pterobranchs and the Question: What is a graptolite?

The presence of distinct fusellar structure is taken as evidence to include a number of fossils from the Middle Cambrian to the Lower Ordovician of North America and Europe with the Pterobranchia. The dome of the pterobranchs and the prosicula of the planktic graptolites are contrasted and evidence is given for the re‐assignment of a number of well known dendroid graptolites to the pterobranchs. A non‐destructive method is described to reveal fusellar development of delicate hemichordate exoskeletons from shales. Rhabdotubus robustus n. sp. from the Czech Republic and ? Cephalodiscus sp. from the Wheeler Shale of North America are described as new Middle Cambrian pterobranchs.     

Systematics and phylogenetic implications of the haplosclerid stromatoporoid Newellia mira nov. gen.

Wood, Rachel, Reitner, Joachim & West, Ronald R. 1989 01 15: Systematics and phylogenetic implications of the haploslerid stromatoporoid Newellia mira nov. gen. Lethaia, Vol. 22, pp. 85–93. Oslo. ISSN 0024–1164. The presence of spicules in a Palaeozoic stromatoporoid is here confirmed. Parallelopora mira Newell, 1935 from the Upper Carboniferous of the U.S.A. is redescribed as a calcified haplosclerid sponge with a primary siliceous spicule framework of isodictyally arranged styles, sub-tylostyles and strongyles and a secondary calcareous skeleton of stromatoporoid grade and probable aragonitic original mineralogy. P. mira is placed within a new genus Newellia, and family, the Newellidae. This form is postulated to have possessed large amounts of collagenous organic material which enveloped and bound the spicular framework in place. By the draping outline of the calcareous skeleton around the spicule framework and by analogy with the Recent demosponge genus Vaceletia, the calcareous skeleton is suggested to have formed by the direct mineralization of this collagenous template. Newellia mira nov. gen. is further proposed to constitute a member of a new clack of haplosclerid stromatoporoids, together with Euz-Miella erenoensis (Lower Cretaceous); a clade with some similarity to Recent non-calcified forms, e.g. Adocia. Most notably, the presence of different calcareous skeleton mineralogies and possibly microstructures in these two forms suggests the independent development of a calcareous skeleton at different times within this spicule clade. Demosponges appear to have produced calcareous skeletons independently in many different spicule clades. Calcified demosponges are now known from the Hadro-merida (Lower carboniferous; Upper Cretaceous - Recent), Axinellida (Upper Triassic - Lower Cretaceous; Upper Cretaceous; Recent), Poecilosclerida (Recent) as well as the Haplosclerida (Upper Carboniferous - Lower Cretaceous; Recent).□Upper Carboniferous, stromatoporoid, spicules, haplosclerid demosponges, calcareous skeleton biomineralization, demosponge clades, polyphyly.     

Developmental biology of pterobranch hemichordates: history and perspectives

Hemichordates, like echinoderms and chordates, are deuterostomes, and study of their developmental biology could shed light on chordate origins. To date, molecular developmental studies in hemichordates have been confined to the enteropneusts or acorn worms. Here, we introduce the developmental biology of the other group of hemichordate, the pterobranchs. Pterobranchs generally live in cold, deep waters; this has hampered studies of this group. However, about 40 years ago, the colonial pterobranchs Rhabdopleura compacta and R. normani were discovered from shallow water, which has facilitated their study. Using Rhabdopleura compacta from south-west England, we have initiated molecular developmental studies in pterobranchs. Here, we outline methods for collecting adults, larvae, and embryos and demonstrate culturing of larvae under laboratory conditions. Given that the larval and adult forms differ from enteropneusts, we suggest that molecular developmental studies of pterobranchs may offer new insights into chordate origins.     

Skeletal formation in the modern but ultraconservative chaetetid spongeSpirastrella (Acanthochaetetes) wellsi (demospongiae,porifera)

Summary The modern hadromerid coralline spongeSpirastrella (Acanthochaetetes) wellsi exhibits a unique secondary high-Mg calcite (>19 mol % MgCO₃) basal skeleton. The basal skeleton is constructed of bundles of elongated crystals more or less tangentially orientated. The initial formation of these crystals is controlled by soluble highly acidic aspartic and glutamic-rich (40%) macromolecules. The skeletal mineralization occurs in four different loci: in the top of the calicles, at the tabulae, on collagenous anchor fibres, and within closed spaces between the tabulae. The clicle walls are formed on the uppermost top of the basal skeleton as a continuous process. Based on long term stainings with Ca²⁺-chelating fluorochroms (calcein, chlorotetracyclines) the growth rate of this sponge is extremely low with ca. 50–100μm/a. The skeletal formation takes places outside the sponge, within a narrow zone (300–500 nm) between the basopinacoderm and the mature basal skeleton. The sponge produces thread-like folded templates (‘spaghetti fibres’) of 0,5–2 μm size, the shape controlling insoluble organic matrix. These templates become mineralized in a first step as MgCO₃, then are stretched. A soluble organic matrix is also secreted, and remains are included inside the mineralized skeleton. This organic matrix consists of in a complex mixture containing small very acidic proteins (5, 13, 31 KD; 40% Asp and Glu and therefore most probably Ca²⁺-binding) and high molecular weight glycoproteins among several other organic compounds. The mature crystals are high-Mg calcites. During calcification large cells with large reserve granules (LCG) are always present in a tight connection with the basopinacoderm. These cells form also the collagenous anchor fibres. Primary tabulae are formed by a non-collagenous organic sheet. Calcification happens only when LCG cells are enriched on the organic sheet. Randomly oriented high-Mg calcite crystals are growing on the collagenous anchor fibres. The same type of the mineralization is observed within the spaces of the tabulae. This particular case of mineralization is controlled by decaying sponge tissue (ammonification). The δ¹³C values are in equilibrium with the ambient sea water and vary between +3.2 and +2.8 ‰. The mode of mineralization of the basal skeleton can be described as biologically induced resp. matrix mediated.     

Evidence that the collagen in the culture medium of Chinese hamster lung cells contains components related at the primary structural level to the alpha1(V) collagen chain

The collagenous protein synthesized by cultured Chinese hamster lung (CHL) cells and present in the culture medium has been isolated after limited pepsin digestion and differential salt precipitation. Molecular size analysis of this material indicates that the CHL cell medium collagen contains chains which exhibit an apparent molecular mass of approximately 85,000 Da. When chromatographed on CM-cellulose under denaturing conditions, the reduced and alkylated CHL cell medium collagen chains elute slightly after the human alpha1(I) chain but well before the pepsin-derived alpha1(V) chain, which is the constituent chain present in the CHL cell cellular matrix collagen. Analysis of the peptides derived by CNBr cleavage of the CHL medium collagen chains by chromatography on CM-cellulose reveals, however, that these chains contain peptides which correspond both in size and in chemical properties to those derived from the alpha1(V) collagen chain, but clearly lack two peptides (alpha1(V)-CB4 and alpha1(V)-CB5) which are normally present in pepsin-derived alpha1(V) chains. Furthermore, analysis of the CHL cell culture medium collagenous material obtained without pepsin digestion indicates the presence of collagenous chains that exhibit after reduction a molecular mass of approximately 160,000 Da, which is smaller than the proposed size of the pro alpha1(V) collagen chain. These results demonstrate that the collagenous protein present in the culture medium of CHL cells is directly related at the primary structural level to the alpha1(V) collagen chain, and it is postulated that this material represents the large fragment derived from a collagenase cleavage of the [pro alpha1(V)]3 molecules present in the cell layer. Furthermore, these results and previous reports indicate that the only identifiable genetic type of procollagen chain synthesized by this cloned cell line in culture corresponds to the pro alpha1(V) chain.     

The origins of graptolites and other pterobranchs: a journey from ‘Polyzoa’

The graptolites, known only from fossils, have been convincingly allied to the pterobranch hemichordates, a group of tiny, mostly colonial marine invertebrates bearing feeding arms. The phylogenetic position of pterobranchs has been subject to debate and revision for over a century. Their colonial lifestyle and feeding arms were originally seen as evidence placing them among the bryozoans, until later and more careful anatomical studies revealed more characters in common with acorn worms. Pterobranchs and acorn worms are now grouped as the phylum Hemichordata. For many decades, it was thought that pterobranchs were closer to the ancestral form of hemichordates, particularly because ‘lophophorate’ invertebrates also possess feeding arms, notably the phoronids and bryozoans, as do crinoid echinoderms. This traditional view has been challenged by recent molecular evidence. First, there is strong molecular evidence to indicate that lophophorates are very distant from hemichordates and echinoderms, in a different major branch of the animal phylogenetic tree. Therefore, similarities between the feeding structures must be due to convergent evolution. Second, there is strong evidence that hemichordates and echinoderms form a clade (Ambulacraria) within the deuterostomes, rather than hemichordates being closer to chordates. Third, there is weaker evidence that pterobranchs may be derived from acorn worms, and hence that the vermiform body plan may be ancestral within hemichordates. This suggestion warrants further testing. Here we review the evidence for these conclusions, highlight strengths and weaknesses in the data and analyses, and consider the implications for the origins of pterobranchs and graptolites.     

Collagen of slow twitch and fast twitch muscle fibres in different types of rat skeletal muscle

The appearance of collagen around individual fast twitch (FT) and slow twitch (ST) muscle fibres was investigated in skeletal muscles with different contractile properties using endurance trained and untrained rats as experimental animals. The collagenous connective tissue was analyzed by measuring hydroxyproline biochemically and by staining collagenous material histochemically in M. soleus (MS), M. rectus femoris (MRF), and M. gastrocnemius (MG). The concentration of hydroxyproline in the ST fibres dissected from MS (2.72 +/- 0.35 micrograms X mg-1 d.w.) was significantly higher than that of the FT fibres dissected from MRF (1.52 +/- 0.33 micrograms X mg-1 d.w.). Similarly, the concentration of hydroxyproline was higher in ST (2.54 +/- 0.51 micrograms X mg-1 d.w.) than in FT fibres (1.60 +/- 0.43 micrograms X mg-1 d.w.), when the fibres were dissected from the same muscle, MG. Histochemical staining of collagenous material agreed with the biochemical evidence that MS and the slow twitch area of MG are more collagenous than MRF and the fast twitch area of MG both at the level of perimysium and endomysium. The variables were not affected by endurance training. When discussing the role of collagen in the function of skeletal muscle it is suggested that the different functional demands of different skeletal muscles are also reflected in the structure of intramuscular connective tissue, even at the level of endomysial collagen. It is supposed that the known differences in the elastic properties of fast tetanic muscle compared to slow tonic muscle as, e.g., the higher compliance of fast muscle could at least partly be explained in terms of the amount, type, and structure of intramuscular collagen.     

An early Cambrian hemichordate zooid

Hemichordates are known as fossils from at least the earliest mid-Cambrian Period (ca. 510 Ma) and are well represented in the fossil record by the graptolithinid pterobranchs ("graptolites"), which include the most abundantly preserved component of Paleozoic macroplankton. However, records of the soft tissues of fossil hemichordates are exceedingly rare and lack clear anatomical details. Galeaplumosus abilus gen. et sp. nov. from the lower Cambrian of China, an exceptionally preserved fossil with soft parts, represents by far the best-preserved, the earliest, and the largest hemichordate zooid from the fossil record; it provides new insight into the evolution of the group. The fossil is assigned to the pterobranch hemichordates on the basis of its morphological similarity to extant representatives. It has a zooidal tube (coenecium) with banding throughout comparable to that in the extant pterobranchs and a zooid with paired annulated arms bearing paired rows of annulated tentacles; it also displays a putative contractile stalk. G. abilus demonstrates stasis in pterobranch morphology, mode of coenecium construction, and probable feeding mechanism over 525 million years.     

Arterial basement-membrane-like material isolated and characterized from rabbit aortic myomedial cells in culture.

Arterial basement-membrane-like material was isolated from rabbit aortic myomedial cell cultures by sonication and differential centrifugation. Isolated basement-membrane-like material was shown to be free of both cellular and matrix contaminants, on the basis of determinations of DNA, RNA, cholesterol, phosphorus and (Na+ + K+)-activated ATPase, combined with electron microscopy. Amino acid analyses showed that arterial basement-membrane-like material was composed of predominantly non-collagenous amino acids. Evaluated by sodium dodecyl sulphate/polyacrylamide-gel electrophoresis, reduced basement-membrane-like material comprised six major and about 30 minor components in the Mr range 10 000-600 000. One of the major peptides (Mr 225 000) was disulphide-linked. Periodic acid-Schiff staining of gels indicated that most high-molecular-weight components were glycoproteins. Two-dimensional gel electrophoresis resolved reduced basement-membrane-like material into more than 100 components, with pI from 5 to 7. The disulphide-linked Mr-225 000 peptide appeared heterogeneous, with pI of 5.6-6.0, and was considered to represent fibronectin. All major peptides were of non-collagenous nature, on the basis of their susceptibility to pepsin and resistance to collagenase. Purified myomedial basement-membrane-like material contained collagenous peptides, as indicated by the presence of hydroxyproline and hydroxylysine. Sodium dodecyl sulphate/polyacrylamide-gel electrophoresis of pepsin-treated and reduced basement-membrane-like material revealed five high-molecular-weight collagenous components appearing in the Mr range 105 000-375 000 relative to type I collagen standards.     

Ultrastructural and cytochemical studies of the fate of unsecreted collagen precursors after administration of colchicine to mice

The administration of colchicine disrupts the normal organization of the Golgi complex and blocks the secretion of collagen precursors in periodontal ligament fibroblasts of the mouse. The fate of the unsecreted collagen precursors contained in Golgi-derived saccules and newly formed dense bodies was followed by electron microscopy. A progressive condensation of saccule content along with phase separation of electron-dense and electron-lucent material was observed. Fusion of saccules with dense secretory bodies gave rise to larger inclusions (zebra bodies; ZB) filled with a combination of electron-dense and electron-lucent material. In some ZB, these materials appeared to polymerize into fibrillar units. The fibrillar units stained with silver methenamine like normal collagenous fibrils. These results suggest that unsecreted collagen precursors accumulate in vesicular compartments within which partial polymerization can occur. This finding may explain some reports of intracellular collagenous fibrils in fibroblasts of pathologically altered connective tissues.     

The comparative morphology of the photophores of the squid Pyroteuthis margaritifera (Cephalopoda: Enoploteuthidae)

Pyroteuthis margaritifera has morphologically distinctive photophores on the tentacles, eyeball and in the mantle cavity. The photogenic tissue in each photophore is identical, has a blue-green fluorescence and luminesces on treatment with dilute hydrogen peroxide. The photocytes frequently contain organized fibrillar material akin to that in the photocytes of certain other cephalopods. Several different types of blood vessel are present among the photocytes, including some, apparently restricted to the photophores, with a microvillous endothelium. Haemocyanin is present not only within identifiable blood vessels but also in some intercellular spaces.
On the basis of their characteristic optical systems the photophores can be separated into three types: (1) tentacular; (2) ocular and anal; (3) branchial and median abdominal. The tentacular photophores have collagenous reflector and light guide systems and the median ones are double organs. The ocular and anal organs do not have collagenous optical structures but an elaborate variety of reflective iridosomes. Those in the aperture of the photophores appear to act as interference filters. The branchial and abdominal organs have iridosomes as the major reflective tissue but collagenous fibrils function as light guides in the aperture of these organs and their emission is diffuse rather than collimated.     

Ultrastructural studies of regenerating spines of the sea urchin Strongylocentrotus purpuratus I. Cell types without spherules

The fine structure of regenerating tips of spines of the sea urchin Strongylocentrotus purpuratus was investigated. Each conical tip consisted of an inner dermis, which deposits and contains the calcite skeleton, and an external layer of epidermis. Although cell types termed spherulecytes containing large, intracellular membrane bound spherules were also present in spine tissues, only epidermal and dermal cell types lacking such spherules are described in this paper. The epidermis was composed largely of free cells representing several functional types. Over the apical portion of the tip these cells occurred in groups, while proximally they were distributed within longitudinal grooves present along the periphery of the spine from the base to the tip. The terminal portions of apical processes extending from some of the epidermal cells formed a thin, contiguous outer layer consisting of small individual islands of cytoplasm bearing microvilli. Adjacent islands were connected around the periphery by a junctional complex extending roughly 200 Å in depth in which the opposing plasma membranes were separated by a narrow gap about 145 Å in width bridged by amorphous material. Other epidermal cells were closely associated with the basal lamina, which was 900 Å in thickness and delineated the dermoepidermal junction; some of these cells appeared to synthesize the lamina, while others may be sensory nerve cells. The dermis at the spine tip also consisted of several functional types of free cells; the most interesting of these was the calcoblast, which deposits the skeleton. Calcoblasts extended a thin, cytoplasmic skeletal sheath which surrounded the tips and adjacent proximal portions of each of the longitudinally oriented microspines comprising the regenerating skeleton, and distally, formed a conical extracellular channel ahead of the mineralizing tip. The intimate relationship between calcoblasts and the growing mineral surface strongly suggests that these cells directly control both the kinetics of mineral deposition and morphogenesis of the skeleton. Other cell types in the dermis were precalcoblasts and phagocytes. Precalcoblasts may function as fibroblasts and are possible precursors of calcoblasts. Closely associated with the basal lamina at the dermoepidermal junction were extracellular unbanded anchoring fibrils 150 Å to 200 Å in diameter. Scattered proximally among dermal cells were other extracellular fibrils, presumably collagenous, about 300 Å in diameter with a banding periodicity of 210 Å.     

Collagenous constituents of amniotic fluid.

The amniotic fluid (AF) was fractionated by dialysis, gel filtration and SDS/PAGE, and submitted to the assay of collagenous constituents. The collagenous character of peptides and proteins of amniotic fluid was confirmed by hydroxyproline (Hyp) assay and treatment with bacterial collagenase followed by electrophoresis and gel filtration of the digestion products. It was found that AF contains collagen degradation products but the classical method of Hyp determination described by Woessner (Arch. Biochem. Biophys., 1961, 93, 440-447) gives overestimated values due to the interference with other AF components. Fractionation of AF on Sephadex G-100 column allowed to remove the interfering material and to estimate the actual Hyp content which equals to approx. 6.2 microg/ml. About 70% of Hyp was found in low molecular dialyzable products and the rest (about 30%) appears to be a constituent of nondialyzable collagenous polypeptides of the molecular mass of about 7.9-26.3 kDa. It is suggested that such collagenous polypeptides may be the products of proteolytic conversion of collagen precursor (procollagen) into the monomeric form of this protein. No high molecular forms of collagen, corresponding to alpha-subunits, were found.     

Substrate recognition by the collagen-binding domain of Clostridium histolyticum class I collagenase

Clostridium histolyticum type I collagenase (ColG) has a segmental structure, S1+S2+S3a+S3b. S3a and S3b bound to insoluble collagen, but S2 did not, thus indicating that S3 forms a collagen-binding domain (CBD). Because S3a+S3b showed the most efficient binding to substrate, cooperative binding by both domains was suggested for the enzyme. Monomeric (S3b) and tandem (S3a+S3b) CBDs bound to atelocollagen, which contains only the collagenous region. However, they did not bind to telopeptides immobilized on Sepharose beads. These results suggested that the binding site(s) for the CBD is(are) present in the collagenous region. The CBD bound to immobilized collagenous peptides, (Pro-Hyp-Gly)(n) and (Pro-Pro-Gly)(n), only when n is large enough to allow the peptides to have a triple-helical conformation. They did not bind to various peptides with similar amino acid sequences or to gelatin, which lacks a triple-helical conformation. The CBD did not bind to immobilized Glc-Gal disaccharide, which is attached to the side chains of hydroxylysine residues in the collagenous region. These observations suggested that the CBD specifically recognizes the triple-helical conformation made by three polypeptide chains in the collagenous region.     

Ultrastructural analysis of collagen fibers in the conductive and working myocardium of the sinoatrial region of the human heart

Qualitative and quantitative electron microscopic analysis of collagenous fibers has been performed in the sinusal node (SN) and perinodal working myocardium of the right atrium (RA) in the hearts of 22 men, died at the age of 23-63 years. Five of them died from alcoholic cardiomyopathy, 8--from coronary cardiac disease and 9--from noncardiac causes and craniocerebral trauma (group of comparison). In 21 cases seven types of ultrastructural changes of the collagenous fibers have been revealed in the SN (changes in the form, size and degree of their osmiophilia). As a whole the volumetric density of the collagenous fibers in the selection makes 24.4 +/- 1.6% from the volume of the SN conductive myocardium and 5.7 +/- 0.8% from the volume of the RA perinodal working myocardium. Content of the collagenous fibers in the SN does not depend on the death cause, age of the dead or on degree of the cardiac hypertrophy. Content of the collagenous fibers in the RA is 2.2 times higher at a sudden coronary death, than in the group of comparison. With age in the RA the volumetric density of the collagenous fibers increases by 1.9 times, and with rise in the cardiac mass, it increases by 2.2 times. The data obtained are discussed in order to understand the role of the collagenous fibers in functioning of the sinoauricular area both normal and at the cardiac pathology.     

Rate of basement membrane biosynthesis as an index to angiogenesis

A method was developed for assessing collagenous protein biosynthesis from [U-14C]proline in relation to angiogenesis in the chick chorioallantoic membrane (CAM). The rate of collagenous protein biosynthesis both in vitro and in vivo was maximum between days 8 and 11 of chick embryo development. This was the stage of maximum angiogenesis as shown by morphological evaluation of the vascular density. At day 10 the rate of collagenous protein biosynthesis was 11-fold higher than that of day 15, when angiogenesis had reached a plateau. The collagenous protein formed by CAM co-elutes on SDS-agarose chromatography with the collagenous component of [3H]-acetylated-basement membrane (BM) from bovine lens capsule. 8,9-dihydroxy-7-methyl-benzo[b]quinolizinium bromide (GPA1734), which was shown previously to be a specific inhibitor of BM collagen biosynthesis, caused about 80% reduction in collagenous protein synthesis by CAM. These results indicate that most of the collagenous protein synthesized by CAM was BM collagen and this can be used as a biochemical index of angiogenesis.     

Thermomechanical analysis of soft-tissue thermotherapy

Soft-tissue thermotherapy based on sub-ablative heating of collagenous tissues finds wide-spread application in medicine such as tissue welding, thermokeratoplasty, skin resurfacing, elimination of discogenic pain in the spine and treatment of joint instability. In this paper, heat-induced thermomechanical response characteristics of collagenous tissues are quantified by means of in vitro experimentation with a representative model tissue (New Zealand white rabbit patellar tendon). Three distinct heat-induced thermomechanical response regimes (defined by the rate of deformation and the variation of material properties) are identified. Arrhenius damage integral representation of collagenous tissue thermal history is shown to be adequate in establishing the master response curves for quantification of thermomechanical response for modeling purposes. The trade-off between the improved kinematical stability and compromised mechanical stability of the heated collagenous tissue is shown to be the major challenge hindering the success of subablative thermotherapies.     

Biologically controlled mineralization in the hypercalcified sponge Petrobiona massiliana (Calcarea, Calcaronea)

Hypercalcified sponges, endowed with a calcium carbonate basal skeleton in addition to their spicules, form one of the most basal metazoan group engaged in extensive biomineralization. The Mediterranean species Petrobiona massiliana was used to investigate biological controls exerted on the biomineralization of its basal skeleton. Scanning and transmission electron microscopy (SEM, TEM) confirmed that basopinacocytes form a discontinuous layer of flattened cells covering the skeleton and display ultrastructural features attesting intense secretory activity. The production of a highly structured fibrillar organic matrix framework by basopinacocytes toward the growing skeleton was highlighted both by potassium pyroantimonate and ruthenium red protocols, the latter further suggesting the presence of sulfated glycosaminoglycans in the matrix. Furthermore organic material incorporated into the basal skeleton was shown by SEM and TEM at different structural levels while its response to alcian blue and acridine orange staining might suggest a similar acidic and sulfated chemical composition in light microscopy. Potassium pyroantimonate revealed in TEM and energy electron loss spectroscopy (EELS) analysis, heavy linear precipitates 100-300 nm wide containing Ca(2+) and Mg(2+) ions, either along the basal cell membrane of basopinacocytes located toward the decalcified basal skeleton or around decalcified spicules in the mesohyl. Based on the results of the previous mineralogical characterization and the present work, an hypothetical model of biomineralization is proposed for P. massiliana: basopinacocytes would produce an extracellular organic framework that might guide the assemblage of submicronic amorphous Ca- and Mg-bearing grains into higher structural units.