Fine Structure of the Tentacles of Phoronis australis Haswell (Phoronida,Lophophorata)

The epidermis of the tentacles of Phoronis australis consists of six cell types: supporting cells, choanocyte-like sensory cells, both types monociliated, secretory A-cells with a mucous secretion, and three kinds of B-cells with mucoprotein secretions. On cross-sections of the tentacle, one can distinguish four faces: the frontal one, heavily ciliated and located between the two frontolateral rows of sensory cells, the lateral and the abfrontal ones. The orientation of the basal structures of the cilia is related to the direction of their beat. The basiepidermal nervous system is grouped mainly at the frontal and abfrontal faces. The basement membrane is thickest on the frontal face and consists of circular collagen fibrils near the epidermis and longitudinal ones near the peritoneum. All peritoneal cells surrounding the mesocoel are provided with smooth longitudinal myofibrils, and isolated axons are situated between these cells and the basement membrane. The wall of the single blood capillary in each tentacle consists of epitheliomuscular cells with circular myofilaments, lying on a thin internal basal lamina; there is no endothelium.     

Réflexions critiques sur l'écologieet la systématique des Lingules actuelles et fossiles

New topics on ecology and systematics of recent and fossil Lingulids lead to an obvious revision of our knowledges on this zoological group. At first, the recent species need systematics and taxonomy on the bases of new described specific criteria (as, morphology of deltidial areas, muscle disposition); the results are briefly indicated. But, in fossil species, disorder and disparity of used characteristics are emphasized.The general conceiving on ecology of Lingulids are reviewed and discussed, especially on bathymetry and salinity; sediment and oxygenation conditions; taphocoenosis and lingulid «communities. On recent species, all these points are also studied, especially some ecological requirements (salinity, bathymetry, grain size), and mechanism of burrowing ability, burrow living positions in the sediments, as shell preservations after death and fossilization, to facilitate the paleobiotope interpretations. Recent animals are euryhalin, surviving at salinities from about 13 to 42‰; they could be considered as well adapted to waters with strong salinity fluctuations. They show preference to fine sand bottoms (lowest particle size about 40–60 μm). Their bathymetric distribution occurs between 0 and about 500 m (Lingula especially between 5–50 m; Glottidia 15–70 m). The isotherms 8–10°C seem to restrict their geographical and bathymetric distribution.Therefore, some post-palaeozoic lingulid bedsare studied or redescribed on the bases of the above discussed characteristics, and new interpretations on the environmental situation are given (Trias of Vosges Mountains; Oligocene from Japan; Eocene of London Basin). More caution must be used in study of fossil Lingulids that are not especially animals living in infralittoral bottoms with low salinity and deficient oxygenation, as generally accepted.     

Étude des variations du nombre et de la répartition des muscles longitudinaux chez Phoronis psammophila Cori

In 21 samples, staggered over 18 months, 1725 composite muscle formulae have been established for Phoronis psammophila Cori. The study of variations of the number and distribution of longitudinal muscle bundles demonstrates the increase of the muscle number (3 or 4) with the age of the animals. This increase is displayed with difficulty because of the interactions of many phenomena, especially reproduction and so statistical tests have not indicated significance. The general and especially mean formulae of different samples do not indicate the increase of the number of muscle bundles with time, as proposed by Emig.     

Evidence of lophophore diversity in early Cambrian brachiopoda

The lophophore, an essential organ of the Brachiopoda, has been used widely in evolutionary and advanced phylogenetic studies, but is hitherto unknown in the fossil record. Here, the extraordinarily well-preserved lophophores of two inarticulated brachiopods Lingulella chengjiangensis and Heliomedusa orienta, from the Lower Cambrian Chengjiang fauna (Yunnan, China) are described. These primitive lophophores, respectively, trocholophous and schizolophous, have some key characters that may be plesiomorphies inherited by their recent descendants. This discovery provides direct evidence regarding the taxonomy, ecosystems and early evolution of inarticulated brachiopods.     

Structural and functional importance of first-shell metal ligands in the binuclear manganese cluster of arginase I

Arginase is a binuclear manganese metalloenzyme that hydrolyzes l-arginine to form l-ornithine and urea. The three-dimensional structures of D128E, D128N, D232A, D232C, D234E, H101N, and H101E arginases I have been determined by X-ray crystallographic methods to elucidate the roles of the first-shell metal ligands in the stability and catalytic activity of the enzyme. This work represents the first structure-based dissection of the binuclear manganese cluster using site-directed mutagenesis and X-ray crystallography. Substitution of the metal ligands compromises the catalytic activity of the enzyme, either by the loss or disruption of the metal cluster or the nucleophilic metal-bridging hydroxide ion. However, the substitution of the metal ligands or the reduction of Mn(2+)(A) or Mn(2+)(B) occupancy does not compromise enzyme-substrate affinity as reflected by K(M), which remains relatively invariant across this series of arginase variants. This implicates a nonmetal binding site for substrate l-arginine in the precatalytic Michaelis complex, as proposed based on analysis of the native enzyme structure (Kanyo, Z. F., Scolnick, L. R., Ash, D. E., and Christianson, D. W. (1996) Nature 383, 554-557).     

Measuring and analyzing tissue specificity of human genes and protein complexes

Proteins and their interactions are essential for the survival of each human cell. Knowledge of their tissue occurrence is important for understanding biological processes. Therefore, we analyzed microarray and high-throughput RNA-sequencing data to identify tissue-specific and universally expressed genes. Gene expression data were used to investigate the presence of proteins, protein interactions and protein complexes in different tissues. Our comparison shows that the detection of tissue-specific genes and proteins strongly depends on the applied measurement technique. We found that microarrays are less sensitive for low expressed genes than high-throughput sequencing. Functional analyses based on microarray data are thus biased towards high expressed genes. This also means that previous biological findings based on microarrays might have to be re-examined using high-throughput sequencing results.     

Epibionts on the lingulate brachiopod Diandongia from the Early Cambrian Chengjiang Lagerst?tte,South China

The classic Chengjiang Lagerstätte (Lower Cambrian, Atdabanian stage: Yu''anshan Formation) Yunnan, southwestern China, has yielded, besides the exceptional and often controversial soft-bodied fossils, a fauna of primitive/early lingulid brachiopods. Diandongia pista (Rong 1974) is one of the commonest and most strongly mineralized of the phosphatic brachiopods from the Lagerstätte. The shells of this species have been found to commonly serve as a basibiont host. Epibionts comprise the coeval brachiopod Longtancunella chengjiangensis and the cone-shaped cnidarian-related Archotuba conoidalis, as well as rounded smaller-sized epizoans (lesser than 2 mm). A principle morphological analysis demonstrates that the ovoid and rounded organisms that often occur along the commissure of D. pista resemble small juvenile or immature brachiopods. Epibiont-bearing shells of D. pista with soft-tissue preservation demonstrate that the host brachiopods were overgrown while alive, and provide an argument for D. pista having a semi-infaunal life style with only the slim pedicle embedded in sediment. The epibiotic association sheds direct light on the ecology of Cambrian brachiopods in soft-substrate marine environments. The Chengjiang fossils demonstrate that the Early Cambrian brachiopods, as compared with recent lingulids, occupied different and a wider spectrum of ecological niches and tiers of space.