Comparative analysis of acoel embryonic development

Acoels are bilaterally symmetric aquatic worms, that lack a through gut and have a single body opening to their digestive syncytium. Although they were initially placed within spiralians, because of their morphological affinities with turbellarians, acoels, together with nemertodermatids and Xenoturbella (Xenacoelomorpha), are now placed as sister group of all the remaining bilaterians (Nephrozoa = Protostomia + Deuterostomia), based on several molecular studies. This phylogenetic position gives acoels a critical role for our understanding of bilaterian evolution. Acoels show a stereotypic cleavage pattern, called duet cleavage, and also, they possess a regulative development, meaning that their embryos have the ability to adapt to perturbations of the normal development, such as the deletion of one or more blastomeres at different developmental stages. Although several studies described acoel cleavage pattern, a comprehensive study on their embryonic development, also uncovering the molecular patterning of developmental genes, is missing. Thus, to have a better understanding of the evolution of developmental traits, I analysed and compared the early embryogenesis of two acoels species, Isodiametra pulchra and Convolutriloba macropyga, focusing on the fate of the early blastomeres, on their ability to regulate (or not) cell ablations, and on the expression pattern of several developmental genes during the early cleavages. In the first part of this thesis, I provide a comprehensive study on the embryonic development of the acoel I. pulchra. The detailed fate map of the early blastomeres showed how they contribute to the germ layer derivatives and to the bilateral ground plan of these animals, while the immunostaining after the ablation of specific blastomeres showed the extent to which regulation occurs in these embryos. These data revealed similarities with the embryonic development of another acoel species Neochildia fusca, showing a general conservation of cell fates between the two acoel species, but also highlighted that the regulative potential is restricted to specific embryonic stages in the species I. pulchra. In the second part of the thesis, I analysed the spatial and temporal expression of 17 developmental genes, during the early development of the acoel C. macropyga. The expression of several ectodermal markers (dlx, emx, gata1/2/3, otx, pax2/5/8, six3/6, and nk2.1) in the micromere lineages revealed the ectodermal identity of the early micromeres, while the expression of the endomesodermal markers (gata4/5/6, fox A and foxF) in the macromere lineages revealed the endomesodermal identity of the early macromeres. The characterised molecular fates of the early blastomeres vi are consistent with the acoel fate map and provide the first early expression analysis of regulatory genes in an acoel species. This thesis expands the knowledge on the embryonic development of acoels, combining classical embryological studies, such as the fate map analyses and the perturbation experiments, with modern molecular approaches, such as whole mount in situ hybridization (WMISH)

I. THE HIGH STRAIN RATE RESPONSE OF HOLLOW SPHERE STEEL FOAM; II. THE DYNAMIC RESPONSE OF AN AMERICAN ELM TREE

PART I Hollow-sphere (HS) steel foam is a relatively new material whose cellular morphology and material properties qualify it as a metallic foam. This is an innovative foam-like material that exhibits high stiffness paired with low relative densities. Technological advancements in the past few decades have enabled the manufacturing of this material by a sintering process and, as a result, research has begun to accelerate as a multi-school collaboration effort for this particular work. Even though commercialization has been a challenge for metallic foams, it is imperative that researchers continue to prove and promote the advantages of metallic foams despite the current challenges posed by commercialization. One of the most promising characteristics of metallic foams is their energy absorption capacity. This work explores hollow-sphere steel foam’s ability to absorb energy at high strain rates under a dynamic impact load and builds upon an earlier work of quasi-static compression loading. Since most research in this field has been attributed to aluminum open-cell foams, the objective of this work seeks to build upon and apply existing methods to cultivate new research material for hollow-sphere steel foam. The premise of this work began with experimental research analyzing stress-strain relationships of a mass impacting samples of HS steel foam with different kinetic energies. As a result, material properties were extracted and quantified such as elastic modulus, yield stress, and energy absorption, among others. These properties set the foundation for the next set of research; finite element analysis whose objective is to develop a functional material model that could be used for a later application in structural engineering, such as a blast or crash impact. PART II The second part of this thesis applies structural engineering mechanics to a complex arboricultural project. A particular American elm (Ulmus americana L.) tree is the focus of analysis due to its usage for tree climbing competitions. Structurally, this work is relevant to structural engineering by involving finite element analysis of a branch of this American elm tree. This particular work has the objective of understanding how a particular American elm branch behaves structurally under a variety of dynamic loads with different input parameters. Before any of the analyses can be implemented, the definite geometry of the tree has to be measured and material properties have to be calculated. Field experimental data are imperative for this project so that the idealized model can represent the real system as best as possible. Following the data acquisition and modeling of the tree, loads that were either measured or calculated are applied. These loads can be idealized as an impulse load and a cyclic load, with variability imposed within each of them. It is within this variability of the parameters within the loads that the purpose of this work arises. By applying extreme loads upon this tree branch, critical points along the branch can be identified by calculating maximum bending and axial stresses. These stresses indicate not only the critical points along the primary branch but in addition, they indicate the magnitude and severity of these potential stresses, which can be compared directly with the mechanical properties of the wood in the branch. The final intent of this work is to contribute to the knowledge of how a particular branch behaves dynamically in order to better equip tree climbers, academics, and professionals by integrating structural mechanics and arboriculture

América en la escena operística

El argumento del primer encuentro cultural entre europeos y americanos fue terreno fértil para ejercitar dos representaciones diferentes del extranjero. Para los compositores europeos América fue parangón y pretexto tanto para sublimar al otro desde el iluminismo que escamoteaba su diversidad, como desde la visión exotizante que hacía del extraño ocasión de pintoresquismos. Ambas perspectivas resultaron ser muy afines a las que en el siglo XIX preocuparon a compositores sudamericanos. Cuando estos trataron de elaborar por fin un repertorio lírico propio, no hicieron otra cosa que recorrer otra vez más uno de aquellos dos senderos que la ópera de los italianos ya había trazado, es decir, o bien la entonación del mito, de la leyenda, de la proclamación de un regreso al campo en cuanto lugar arcádico y libre de la corrupción urbana o, en cambio, la exaltación de la historia.The subject of the first cultural contacts between Europe and America was a pretext to demonstrate two different representations of the foreign. For those European composers influenced by Illuminist ideas, America was a way to exalt the other, overlooking his diversity, but to other musicians, America was an exotic and picturesque subject. Both perspectives were alike to those conceived by Latin-American composers in Nineteenth Century. When they tried to elaborate a national operatic repertoire, they also walked through those ways: the myth, the legend, the return to an archaic paradise free of urban corruption or, instead, glorifying the History

Use of animal models to understand titin physiology and pathology

In recent years, increasing attention has been paid to titin (TTN) and its mutations. Heterozygous TTN truncating variants (TTNtv) increase the risk of a cardiomyopathy. At the same time, TTNtv and few missense variants have been identified in patients with mainly recessive skeletal muscle diseases. The pathogenic mechanisms underlying titin-related diseases are still partly unknown. Similarly, the titin mechanical and functional role in the muscle contraction are far from being exhaustively clarified. In the last few years, several animal models carrying variants in the titin gene have been developed and characterized to study the structural and mechanical properties of specific titin domains or to mimic patients' mutations. This review describes the main animal models so far characterized, including eight mice models and three fish models (Medaka and Zebrafish) and discusses the useful insights provided by a thorough characterization of the cell-, tissue- and organism-phenotypes in these models.Peer reviewe

Ensayos no destructivos aplicados a la caracterización de estructuras y materiales de construcción

Los materiales de construcción utilizados en edificaciones presentan un comportamiento mecánico que puede variar con las propiedades específicas del material utilizado, con las condiciones de contorno o con el ambiente al que se encuentra sometido. La utilización y desarrollo de técnicas o métodos de caracterización de los diferentes materiales de forma no destructiva posibilita conocer ciertas propiedades físicas y mecánicas sin necesidad de realizar ensayos de rotura. En este sentido, el presente trabajo presenta la implementación de métodos no destructivos y los resultados de aplicaciones a materiales de construcción para el diagnóstico de estructuras. Primero se estudia el comportamiento no lineal dinámico de elementos de hormigón, y sometidos a diferentes estados de carga mediante la respuesta dinámica de elementos de hormigón. Luego se desarrollan el trabajo realizado para le determinación de humedad en materiales de construcción utilizando ondas electromagnéticas, específicamente se plantea la determinación del contenido de humedad en muros fabricados con ladrillos cerámicos, ya sean huecos, como sólidos, y de fabricación artesanal como de fabricación industrial. Finalmente se presenta el estudio que el efecto de diferentes tipos de apoyo en la respuesta dinámica de vigas de madera. Los resultados obtenidos en probetas de hormigón muestran la dependencia de la respuesta dinámica con la carga de compresión, en los valores de frecuencia de resonancia torsional como en los parámetros vinculados a la de amortiguación. Se desarrolló una metodología para la determinación y cuantificación de humedad en mampostería cerámica. Por último se pudo verificar el efecto que diferentes tipos de apoyo tienen en el comportamiento no lineal dinámico de vigas de madera, sin encontrar diferencias significativas entre los apoyos analizados

Tax Policy in Argentina: Between Solvency and Emergency

At the turn of the century, Argentina experienced a serious economic crisis, brought about by the forced abandonment of the monetary convertibility regime and characterized by sharp changes in relative prices and income, as well as by widespread breaches of contracts. This economic crisis proved to be different from previous crises, however, as Argentina managed to recover quickly and significantly. The recovery presents some exceptional features. At few times in Argentina's economic history has Argentina had such external and fiscal surpluses. More importantly, for the purposes of this study, Argentina's tax burden is far higher than ever before. Understanding these historic trends is necessary to our study of the characteristics, strengths, weaknesses and reforms of Argentina's tax system. The second section of this chapter, which serves as an introduction to this study, examines the central features of Argentina's fiscal situation from a historical viewpoint. Next, we present an explanation of the particular institutional characteristics of Argentina's federalism, which is necessary to the study of Argentina's tax system. Lastly, the next section places the Argentine tax system in context, introducing the principal features of taxation in Latin America. The main body of this chapter includes a detailed analysis of the evolution of Argentine tax level and structure, the key stylized characteristics of this structure, and the principal challenges that Argentina continues to face. Finally, readers who are interested in the specific details of the system will find a more exhaustive explanation of the technical characteristics of the tax system in the Appendix

Mitochondrial Dysfunction in Cancer and Neurodegenerative Diseases: Spotlight on Fatty Acid Oxidation and Lipoperoxidation Products

In several human diseases, such as cancer and neurodegenerative diseases, the levels of reactive oxygen species (ROS), produced mainly by mitochondrial oxidative phosphorylation, is increased. In cancer cells, the increase of ROS production has been associated with mtDNA mutations that, in turn, seem to be functional in the alterations of the bioenergetics and the biosynthetic state of cancer cells. Moreover, ROS overproduction can enhance the peroxidation of fatty acids in mitochondrial membranes. In particular, the peroxidation of mitochondrial phospholipid cardiolipin leads to the formation of reactive aldehydes, such as 4-hydroxynonenal (HNE) and malondialdehyde (MDA), which are able to react with proteins and DNA. Covalent modifications of mitochondrial proteins by the products of lipid peroxidation (LPO) in the course of oxidative cell stress are involved in the mitochondrial dysfunctions observed in cancer and neurodegenerative diseases. Such modifications appear to affect negatively mitochondrial integrity and function, in particular energy metabolism, adenosine triphosphate (ATP) production, antioxidant defenses and stress responses. In neurodegenerative diseases, indirect confirmation for the pathogenetic relevance of LPO-dependent modifications of mitochondrial proteins comes from the disease phenotypes associated with their genetic alterations