Evolution of Axis Specification Mechanisms in Jawed Vertebrates: Insights from a Chondrichthyan

The genetic mechanisms that control the establishment of early polarities and their link with embryonic axis specification and patterning seem to substantially diverge across vertebrates. In amphibians and teleosts, the establishment of an early dorso-ventral polarity determines both the site of axis formation and its rostro-caudal orientation. In contrast, amniotes retain a considerable plasticity for their site of axis formation until blastula stages and rely on signals secreted by extraembryonic tissues, which have no clear equivalents in the former, for the establishment of their rostro-caudal pattern. The rationale for these differences remains unknown. Through detailed expression analyses of key development genes in a chondrichthyan, the dogfish Scyliorhinus canicula, we have reconstructed the ancestral pattern of axis specification in jawed vertebrates. We show that the dogfish displays compelling similarities with amniotes at blastula and early gastrula stages, including the presence of clear homologs of the hypoblast and extraembryonic ectoderm. In the ancestral state, these territories are specified at opposite poles of an early axis of bilateral symmetry, homologous to the dorso-ventral axis of amphibians or teleosts, and aligned with the later forming embryonic axis, from head to tail. Comparisons with amniotes suggest that a dorsal expansion of extraembryonic ectoderm, resulting in an apparently radial symmetry at late blastula stages, has taken place in their lineage. The synthesis of these results with those of functional analyses in model organisms supports an evolutionary link between the dorso-ventral polarity of amphibians and teleosts and the embryonic-extraembryonic organisation of amniotes. It leads to a general model of axis specification in gnathostomes, which provides a comparative framework for a reassessment of conservations both among vertebrates and with more distant metazoans

Molecular Characterization of the Gastrula in the Turtle Emys orbicularis: An Evolutionary Perspective on Gastrulation

Due to the presence of a blastopore as in amphibians, the turtle has been suggested to exemplify a transition form from an amphibian- to an avian-type gastrulation pattern. In order to test this hypothesis and gain insight into the emergence of the unique characteristics of amniotes during gastrulation, we have performed the first molecular characterization of the gastrula in a reptile, the turtle Emys orbicularis. The study of Brachyury, Lim1, Otx2 and Otx5 expression patterns points to a highly conserved dynamic of expression with amniote model organisms and makes it possible to identify the site of mesoderm internalization, which is a long-standing issue in reptiles. Analysis of Brachyury expression also highlights the presence of two distinct phases, less easily recognizable in model organisms and respectively characterized by an early ring-shaped and a later bilateral symmetrical territory. Systematic comparisons with tetrapod model organisms lead to new insights into the relationships of the blastopore/blastoporal plate system shared by all reptiles, with the blastopore of amphibians and the primitive streak of birds and mammals. The biphasic Brachyury expression pattern is also consistent with recent models of emergence of bilateral symmetry, which raises the question of its evolutionary significance

Molecular Characterization of the Gastrula in the Turtle Emys orbicularis: An Evolutionary Perspective on Gastrulation

Due to the presence of a blastopore as in amphibians, the turtle has been suggested to exemplify a transition form from an amphibian- to an avian-type gastrulation pattern. In order to test this hypothesis and gain insight into the emergence of the unique characteristics of amniotes during gastrulation, we have performed the first molecular characterization of the gastrula in a reptile, the turtle Emys orbicularis. The study of Brachyury, Lim1, Otx2 and Otx5 expression patterns points to a highly conserved dynamic of expression with amniote model organisms and makes it possible to identify the site of mesoderm internalization, which is a long-standing issue in reptiles. Analysis of Brachyury expression also highlights the presence of two distinct phases, less easily recognizable in model organisms and respectively characterized by an early ring-shaped and a later bilateral symmetrical territory. Systematic comparisons with tetrapod model organisms lead to new insights into the relationships of the blastopore/blastoporal plate system shared by all reptiles, with the blastopore of amphibians and the primitive streak of birds and mammals. The biphasic Brachyury expression pattern is also consistent with recent models of emergence of bilateral symmetry, which raises the question of its evolutionary significance

M & L Jaargang 7/1

GeneriekJuul Slembrouck, Paul Stryckers, Piet Gillard en Herman Van den Bossche Het Boekenbergpark in Deurne (Antwerpen). [The Boekenberg park at Deurne (Antwerp).]Meer dan ooit is deze uit 1911 daterende, tot de verbeelding sprekende omschrijving van het Boekenbergpark in Deurne op zijn plaats.Nu een aangepast beheer en een wandelbrochure actief aanzetten tot passieve recreatie, gaat Herman Van den Bossche, ruim vijf jaar nà M&L 1/6, over tot een stand van zaken.Marjan Buyle Een middeleeuws stripverhaal. De conservering van een 15de-eeuwse kruisdraging in de Antwerpse kathedraal. [A medieval cartoon. The conservation of a 15th-century Bearing-of-the-Cross in the Antwerp Our Ladys cathedral.]Geen zinnig mens kan heden nog het uitermate artificiële ontkennen van onze hagelwitte middeleeuwse kathedralen.Flard na flard, helaas nog steeds te vaak bij toeval, hertekent zich intussen een rijkelijke, originele binnendecoratie.In de Antwerpse Onze-Lieve-Vrouwekathedraal ondervond Marjan Buyle aldus andermaal hoe verrassend het ene kruis een ander kan verbergen.E. Roekens, L. Leysen, R. Van Grieken en E. Keppens Verwering van historische gebouwen door luchtverontreiniging. De Sint-Romboutskathedraal in Mechelen. [Chemical weathering of historic buildings by air pollution. The Saint-Rombouts cathedral at Mechelen.]Het gegeven noch de resultaten zijn geheel nieuw te noemen. De effect-analyse van luchtpollutie op historische gebouwen, in opdracht van het Ministerie van de Vlaamse Gemeenschap uitgevoerd door E. Roekens, L. Leysen, R. Van Grieken (U.I.A.) en E. Keppens (V.U.B.), is in haar toepassing op de Mechelse Sint-Romboutskathedraal nochtans voldoende beangstigend voor enige extra aandacht.Jos Martens, Sieg Vlaeminck en Louis Coolen Het Capucijnenklooster te Sint-Truiden. Een maatschappelijke toekomst voor een religieus verleden. [The monastery of the Capuchins at St. Truiden. A social future for a relgious past.]Verlaten door de oorspronkelijke kloosterlingen, na wisselend gebruik bestemd voor afbraak, beschermd als monument Een routine-gegeven.Maar hoe krijg je nu een herbestemmingsproject voor een dergelijk complex ensemble bijvoorbeeld voor het O.C.M.W. van Sint-Truiden effectief van de grond?Met andere woorden: wàt met de gebundelde inspanningen van Jos Martens, Sieg Vlaeminck en Louis Coolen?SummaryM&L Foto-reportag

Imprecise system reliability using the survival signature

The survival signature has been introduced to simplify quantification of reliability of systems which consist of components of different types, with multiple components of at least one of these types. The survival signature generalizes the system signature, which has attracted much interest in the theoretical reliability literature but has limited practical value as it can only be used for systems with a single type of components. The key property for uncertainty quantification of the survival signature, in line with the signature, is full separation of aspects of the system structure and failure times of the system components. This is particularly useful for statistical inference on the system reliability based on component failure times.\u3cbr/\u3eThis paper provides a brief overview of the survival signature and its use for statistical inference for system reliability. We show the application of generalized Bayesian methods and nonparametric predictive inference, both these inference methods use imprecise probabilities to quantify uncertainty, where imprecision reflects the amount of information available. The paper ends with a discussion of related research challenges

Bayesian nonparametric system reliability using sets of priors

An imprecise Bayesian nonparametric approach to system reliability with multiple types of components is developed. This allows modelling partial or imperfect prior knowledge on component failure distributions in a flexible way through bounds on the functioning probability. Given component level test data these bounds are propagated to bounds on the posterior predictive distribution for the functioning probability of a new system containing components exchangeable with those used in testing. The method further enables identification of prior–data conflict at the system level based on component level test data. New results on first-order stochastic dominance for the Beta-Binomial distribution make the technique computationally tractable. Our methodological contributions can be immediately used in applications by reliability practitioners as we provide easy to use software tools.\u3cbr/\u3

Reliability analysis of general phased mission systems with a new survival signature

It is often difficult for a phased mission system (PMS) to be highly reliable, because this entails achieving high reliability in every phase of operation. Consequently, reliability analysis of such systems is of critical importance. However, efficient and interpretable analysis of PMSs enabling general component lifetime distributions, arbitrary structures, and the possibility that components skip phases has been an open problem. In this paper, we show that the survival signature can be used for reliability analysis of PMSs with similar types of component in each phase, providing an alternative to the existing limited approaches in the literature. We then develop new methodology addressing the full range of challenges above. The new method retains the attractive survival signature property of separating the system structure from the component lifetime distributions, simplifying computation, insight into, and inference for system reliability