The Regenerative Capacity of the Zebrafish Caudal Fin Is Not Affected by Repeated Amputations

Background: The zebrafish has the capacity to regenerate many tissues and organs. The caudal fin is one of the most convenient tissues to approach experimentally due to its accessibility, simple structure and fast regeneration. In this work we investigate how the regenerative capacity is affected by recurrent fin amputations and by experimental manipulations that block regeneration. Methodology/Principal Findings: We show that consecutive repeated amputations of zebrafish caudal fin do not reduce its regeneration capacity and do not compromise any of the successive regeneration steps: wound healing, blastema formation and regenerative outgrowth. Interfering with Wnt/ß-catenin signalling using heat-shock-mediated overexpression of Dickkopf1 completely blocks fin regeneration. Notably, if these fins were re-amputated at the non-inhibitory temperature, the regenerated caudal fin reached the original length, even after several rounds of consecutive Wnt/ß-catenin signalling inhibition and re-amputation. Conclusions/Significance: We show that the caudal fin has an almost unlimited capacity to regenerate. Even after inhibition of regeneration caused by the loss of Wnt/ß-catenin signalling, a new amputation resets the regeneration capacity within the caudal fin, suggesting that blastema formation does not depend on a pool of stem/progenitor cells that require Wnt/ßcateni

Thermodynamics and Instabilities of a Strongly Coupled Anisotropic Plasma

We extend our analysis of a IIB supergravity solution dual to a spatially anisotropic finite-temperature N=4 super Yang-Mills plasma. The solution is static, possesses an anisotropic horizon, and is completely regular. The full geometry can be viewed as a renormalization group flow from an AdS geometry in the ultraviolet to a Lifshitz-like geometry in the infrared. The anisotropy can be equivalently understood as resulting from a position-dependent theta-term or from a non-zero number density of dissolved D7-branes. The holographic stress tensor is conserved and anisotropic. The presence of a conformal anomaly plays an important role in the thermodynamics. The phase diagram exhibits homogeneous and inhomogeneous (i.e. mixed) phases. In some regions the homogeneous phase displays instabilities reminiscent of those of weakly coupled plasmas. We comment on similarities with QCD at finite baryon density and with the phenomenon of cavitation.Comment: 62 pages, 13 figures; v2: typos fixed, added reference

QCD and strongly coupled gauge theories : challenges and perspectives

We highlight the progress, current status, and open challenges of QCD-driven physics, in theory and in experiment. We discuss how the strong interaction is intimately connected to a broad sweep of physical problems, in settings ranging from astrophysics and cosmology to strongly coupled, complex systems in particle and condensed-matter physics, as well as to searches for physics beyond the Standard Model. We also discuss how success in describing the strong interaction impacts other fields, and, in turn, how such subjects can impact studies of the strong interaction. In the course of the work we offer a perspective on the many research streams which flow into and out of QCD, as well as a vision for future developments.Peer reviewe

Model selection in rheology: Providing a practical framework, surveying the field, and assessing the uses and limitations of BIC

The selection of which model or models to use when studying a complex fluid is of constant relevance in rheology, though often too little attention is paid to framing this problem of selection such as to yield consistent, credible, and meaningful results. In this thesis I provide a novel framework for identifying the purpose of rheological models along with background on model selection techniques and criteria, assess the state of and need for model selection in rheological literature, and perform several case studies investigating how model selection techniques may be applied in rheology and note their advantages and limitations. While there remains no single, straightforward technique for selecting a model in all cases, the rheological literature so rarely acknowledges this crucial step in analysis and often fails to sufficiently report methodology relating to model fits, let alone selection, that even preliminary consideration of this problem and the application of simple criteria such as the Bayesian Information Criterion (BIC) may add significant value and validity to these analyses. There remains even greater opportunity in the application of more sophisticated methods such as the calculation of Bayes Factors and the formulation of priors for rheological models. The background, review, case studies, and examples presented in this thesis provide a jumping-off point for an ongoing discussion regarding the place of these theories and techniques in rheology while offering clear examples of their use and conclusions that may be drawn from them

Model selection in rheology: Providing a practical framework, surveying the field, and assessing the uses and limitations of BIC

The selection of which model or models to use when studying a complex fluid is of constant relevance in rheology, though often too little attention is paid to framing this problem of selection such as to yield consistent, credible, and meaningful results. In this thesis I provide a novel framework for identifying the purpose of rheological models along with background on model selection techniques and criteria, assess the state of and need for model selection in rheological literature, and perform several case studies investigating how model selection techniques may be applied in rheology and note their advantages and limitations. While there remains no single, straightforward technique for selecting a model in all cases, the rheological literature so rarely acknowledges this crucial step in analysis and often fails to sufficiently report methodology relating to model fits, let alone selection, that even preliminary consideration of this problem and the application of simple criteria such as the Bayesian Information Criterion (BIC) may add significant value and validity to these analyses. There remains even greater opportunity in the application of more sophisticated methods such as the calculation of Bayes Factors and the formulation of priors for rheological models. The background, review, case studies, and examples presented in this thesis provide a jumping-off point for an ongoing discussion regarding the place of these theories and techniques in rheology while offering clear examples of their use and conclusions that may be drawn from them

Analysis of morphogenetic potential of caudal spinal cord in Triturus carnifex adults (Urodele amphibians) subjected to repeated tail amputations.

The present research was aimed at testing whether the extraordinary morphogenetic and histogenetic potential exhibited in the regenerating new tail remains constant even after repeated amputation or whether it changes as a result of the mechanisms responsible for the regenerative process. Particular attention was focused on regeneration of the spinal cord and ganglia. For this purpose, tail regeneration in adult specimens of Triturus carnifex subjected to repeated amputation (up to 7 times) was compared with that of control animals subjected to a single amputation. Results show that although it slowed down the morphogenetic and differentiative phase, repeated amputation did not significantly alter either the morphogenetic or the histogenetic potential of the ependymal layer of the regenerating spinal cord. The latter result leads to hypothesized that the cells of the ependymal layer of the stump, which are responsible for the formation of the apical ampulla and the ependymal tubule inside the regenerative blastema, do not derive from undifferentiated reserve elements triggered after tail amputation but rather from differentiated ependymal elements that dedifferentiate after the trauma and re-acquire embryonic potential. If this regeneration were actually to take place at the expense of the reserve elements, the continual regenerative processes induced by the repeated amputation would lead to the increasing depletion of these elements and a consequent reduction in regenerative capacity