Assessing the Diversity and Specificity of Two Freshwater Viral Communities through Metagenomics

Transitions between saline and fresh waters have been shown to be infrequent for microorganisms. Based on host-specific interactions, the presence of specific clades among hosts suggests the existence of freshwater-specific viral clades. Yet, little is known about the composition and diversity of the temperate freshwater viral communities, and even if freshwater lakes and marine waters harbor distinct clades for particular viral sub-families, this distinction remains to be demonstrated on a community scale

Évolution et diversité des structures minéralisées chez les sélaciens : approche paléo-développementale

Chondrichthyans exhibit a number of interesting features which make them valuable organisms to investigate from an evo-devo perspective. However, due to their cartilaginous skeleton, isolated teeth are usually the only available fossil material to reconstruct their evolutionary history. Their teeth are covered by enameloid, a hypermineralized tissue whose microstructure has proven a useful taxonomic tool to differentiate between modern forms (neoselachians) and their extinct relatives. However it is poorly known in several groups, thus casting doubts on the validity of such characters.In this work, I first describe the enameloid microstructure of batoids based on an extensive sampling of both their extant and extinct diversity. I highlight unexpected diversity in the microstructural organization of enameloid which was thought to be very stable in neoselachians. The developmental basis for this diversity was then investigated in two extant chondrichthyan models through classic histological techniques and in situ hybridization. The results highlight differences in their enameloid organic matrix, as well as important differences with enameloid formation in osteichthyans, casting doubts on the homology of the two tissues. Finally I investigate skeletogenesis in the lesser spotted catshark from both a morphological and molecular perspective. Using X-Ray microtomography and in situ hybridization, I highlight both the mineralization sequence of the cartilaginous skeleton and the molecular context in which it calcifies over the course of embryonic development. I find that skeletal calcification in chondrichthyans appears to be much more versatile than in osteichthyans.Les chondrichthyens sont caractérisés par des particularités anatomiques uniques, ce qui, combiné à leur position phylogénétique, en fait un groupe particulièrement attrayant en biologie de l’évolution. Compte tenu de leur squelette cartilagineux, leur registre fossile est principalement constitué de dents isolées, dont la microstructure des tissus est utilisée depuis longtemps dans un contexte taxonomique. Celle-ci permet en effet de différencier les chondrichthyens modernes (néosélaciens) des groupes éteints dans le registre fossile. La microstructure dentaire de nombreux d’entre eux demeure toutefois peu connue, notamment celle des batoïdes, pourtant le groupe de chondrichthyen le plus diversifié à l’heure actuelle.La première partie de ce travail porte sur une description approfondie de la microstructure dentaire des batoïdes, basée sur un large échantillonnage de formes fossiles et actuelles. Ces observations ont permis de décrire une diversité microstructurale importante et inattendue compte tenu de la stabilité évolutive de ces tissus chez les requins. Cette variation est ensuite abordée à travers une approche histologique et transcriptionelle du développement dentaire de formes actuelles. Les résultats obtenus suggèrent la convergence de ces tissus avec l’émailloïde présent chez certains ostéichthyens. La troisième partie de ce travail porte sur la calcification du squelette cartilagineux au cours du développement embryonnaire, dans un contexte morphologique et moléculaire. Les modalités de calcification des pièces squelettiques apparaissent ainsi beaucoup plus versatiles chez les chondrichthyens que chez les ostéichthyens

Evolution and diversity of mineralized structures in selachians : a palaeontological and developmental approach

Les chondrichthyens sont caractérisés par des particularités anatomiques uniques, ce qui, combiné à leur position phylogénétique, en fait un groupe particulièrement attrayant en biologie de l’évolution. Compte tenu de leur squelette cartilagineux, leur registre fossile est principalement constitué de dents isolées, dont la microstructure des tissus est utilisée depuis longtemps dans un contexte taxonomique. Celle-ci permet en effet de différencier les chondrichthyens modernes (néosélaciens) des groupes éteints dans le registre fossile. La microstructure dentaire de nombreux d’entre eux demeure toutefois peu connue, notamment celle des batoïdes, pourtant le groupe de chondrichthyen le plus diversifié à l’heure actuelle.La première partie de ce travail porte sur une description approfondie de la microstructure dentaire des batoïdes, basée sur un large échantillonnage de formes fossiles et actuelles. Ces observations ont permis de décrire une diversité microstructurale importante et inattendue compte tenu de la stabilité évolutive de ces tissus chez les requins. Cette variation est ensuite abordée à travers une approche histologique et transcriptionelle du développement dentaire de formes actuelles. Les résultats obtenus suggèrent la convergence de ces tissus avec l’émailloïde présent chez certains ostéichthyens. La troisième partie de ce travail porte sur la calcification du squelette cartilagineux au cours du développement embryonnaire, dans un contexte morphologique et moléculaire. Les modalités de calcification des pièces squelettiques apparaissent ainsi beaucoup plus versatiles chez les chondrichthyens que chez les ostéichthyens.Chondrichthyans exhibit a number of interesting features which make them valuable organisms to investigate from an evo-devo perspective. However, due to their cartilaginous skeleton, isolated teeth are usually the only available fossil material to reconstruct their evolutionary history. Their teeth are covered by enameloid, a hypermineralized tissue whose microstructure has proven a useful taxonomic tool to differentiate between modern forms (neoselachians) and their extinct relatives. However it is poorly known in several groups, thus casting doubts on the validity of such characters.In this work, I first describe the enameloid microstructure of batoids based on an extensive sampling of both their extant and extinct diversity. I highlight unexpected diversity in the microstructural organization of enameloid which was thought to be very stable in neoselachians. The developmental basis for this diversity was then investigated in two extant chondrichthyan models through classic histological techniques and in situ hybridization. The results highlight differences in their enameloid organic matrix, as well as important differences with enameloid formation in osteichthyans, casting doubts on the homology of the two tissues. Finally I investigate skeletogenesis in the lesser spotted catshark from both a morphological and molecular perspective. Using X-Ray microtomography and in situ hybridization, I highlight both the mineralization sequence of the cartilaginous skeleton and the molecular context in which it calcifies over the course of embryonic development. I find that skeletal calcification in chondrichthyans appears to be much more versatile than in osteichthyans

Evolution of Dental Tissues and Paleobiology in Selachians

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Skeletogenesis during the late embryonic development of the catshark Scyliorhinus canicula (Chondrichthyes; Neoselachii)

International audienceCurrent knowledge on the skeletogenesis of Chondrichthyes is scarce compared with their extant sister group, the bony fishes. Most of the previously described developmental tables in Chondrichthyes have focused on embryonic external morphology only. Due to its small body size and relative simplicity to raise eggs in laboratory conditions, the small-spotted catshark Scyliorhinus canicula has emerged as a reference species to describe developmental mechanisms in the Chondrichthyes lineage. Here we investigate the dynamic of mineralization in a set of six embryonic specimens using X-ray microtomography and describe the developing units of both the dermal skeleton (teeth and dermal scales) and endoskeleton (vertebral axis). This preliminary data on skeletogenesis in the catshark sets the first bases to a more complete investigation of the skeletal developmental in Chondrichthyes. It should provide comparison points with data known in osteichthyans and could thus be used in the broader context of gnathostome skeletal evolution

Figure 1 in Chondrichthyan tooth enameloid: past, present, and future

Figure 1. Schematic organization of a typical selachimorph tooth illustrating the various tissues composing the enameloid cover.Published as part of <i>Enault, Sébastien, Guinot, Guillaume, Koot, Martha B. & Cuny, Gilles, 2015, Chondrichthyan tooth enameloid: past, present, and future, pp. 549-570 in Zoological Journal of the Linnean Society 174 (3)</i> on page 555, DOI: 10.1111/zoj.12244, <a href="http://zenodo.org/record/10106794">http://zenodo.org/record/10106794</a&gt

Figure 5. Batomorphii enameloid. A, B in Chondrichthyan tooth enameloid: past, present, and future

Figure 5. Batomorphii enameloid. A, B, Hypsobatis weileri, transverse section etched 5 s in 10% HCl. A, general view of the thin SCE. B, inner part of the enameloid layer, with crystallites showing a slight preferential orientation normal to the occlusal surface. C, D, Rhombodus binkhorsti, transverse section etched 5 s in 10% HCl. C, general view of the thin SCE. D, detail of the SCE. E, Leidybatis jugosus, transverse section etched 5 s in 10% HCl. SCE forming thick pillars extending far into the dentine layer, with patches of dentine fully enclosed in the enameloid (arrows). F, G, Belemnobatis sp., transverse section etched 5 s in 10% HCl. F, enameloid on the lingual face of the crown. G, detail of the enameloid layer at the level of the transverse crest. H, I, J, Parapalaeobates cf. atlanticus, transverse section etched 5 s in 10% HCl. H, enameloid microstructure showing the RBE. I, detail of the randomly oriented crystallites forming the outer SCE. J, general view of the enameloid at the level of the crown ornamentation. K, L, Ptychotrygon sp., transverse section etched 5 s in 10% HCl. K, detail of the RBE. L, detail of the SCE.Published as part of <i>Enault, Sébastien, Guinot, Guillaume, Koot, Martha B. & Cuny, Gilles, 2015, Chondrichthyan tooth enameloid: past, present, and future, pp. 549-570 in Zoological Journal of the Linnean Society 174 (3)</i> on page 562, DOI: 10.1111/zoj.12244, <a href="http://zenodo.org/record/10106794">http://zenodo.org/record/10106794</a&gt

Figure 4. Selachimorpha enameloid. A, P in Chondrichthyan tooth enameloid: past, present, and future

Figure 4. Selachimorpha enameloid. A, P. pockrandti, radial furrows near the SCE, transverse section etched 5 s in 10% HCl. B, P. jurensis, lingual ornament made of SCE, transverse section etched 5 s in 10% HCl. C, Sphyrna sp., cutting edge showing bundles of the PBE oriented normal to the axis of the cutting edge, transverse section etched 5 s in 10% HCl. D, Squatina sp., cutting edge showing bundles of the PBE oriented normal to the axis of the cutting edge, transverse section etched 5 s in 10% HCl.Published as part of <i>Enault, Sébastien, Guinot, Guillaume, Koot, Martha B. & Cuny, Gilles, 2015, Chondrichthyan tooth enameloid: past, present, and future, pp. 549-570 in Zoological Journal of the Linnean Society 174 (3)</i> on page 560, DOI: 10.1111/zoj.12244, <a href="http://zenodo.org/record/10106794">http://zenodo.org/record/10106794</a&gt

Evolution of dental tissue mineralization: an analysis of the jawed vertebrate SPARC and SPARC-L families

Abstract Background The molecular bases explaining the diversity of dental tissue mineralization across gnathostomes are still poorly understood. Odontodes, such as teeth and body denticles, are serial structures that develop through deployment of a gene regulatory network shared between all gnathostomes. Dentin, the inner odontode mineralized tissue, is produced by odontoblasts and appears well-conserved through evolution. In contrast, the odontode hypermineralized external layer (enamel or enameloid) produced by ameloblasts of epithelial origin, shows extensive structural variations. As EMP (Enamel Matrix Protein) genes are as yet only found in osteichthyans where they play a major role in the mineralization of teeth and others skeletal organs, our understanding of the molecular mechanisms leading to the mineralized odontode matrices in chondrichthyans remains virtually unknown. Results We undertook a phylogenetic analysis of the SPARC/SPARC-L gene family, from which the EMPs are supposed to have arisen, and examined the expression patterns of its members and of major fibrillar collagens in the spotted catshark Scyliorhinus canicula, the thornback ray Raja clavata, and the clawed frog Xenopus tropicalis. Our phylogenetic analyses reveal that the single chondrichthyan SPARC-L gene is co-orthologous to the osteichthyan SPARC-L1 and SPARC-L2 paralogues. In all three species, odontoblasts co-express SPARC and collagens. In contrast, ameloblasts do not strongly express collagen genes but exhibit strikingly similar SPARC-L and EMP expression patterns at their maturation stage, in the examined chondrichthyan and osteichthyan species, respectively. Conclusions A well-conserved odontoblastic collagen/SPARC module across gnathostomes further confirms dentin homology. Members of the SPARC-L clade evolved faster than their SPARC paralogues, both in terms of protein sequence and gene duplication. We uncover an osteichthyan-specific duplication that produced SPARC-L1 (subsequently lost in pipidae frogs) and SPARC-L2 (independently lost in teleosts and tetrapods).Our results suggest the ameloblastic expression of the single chondrichthyan SPARC-L gene at the maturation stage reflects the ancestral gnathostome situation, and provide new evidence in favor of the homology of enamel and enameloids in all gnathostomes