Genes that exert their function when they are introduced into a foreign genetic background pose many questions to our current understanding of the forces and mechanisms that promote either the maintenance or divergence of gene functions over evolutionary time. The melanoma inducing Xmrk oncogene of the Southern platyfish (Xiphophorus maculatus) is a stable constituent of the genome of this species. It displays its tumorigenic function, however, almost exclusively only after inter‐populational or, even more severely, interspecific hybridization events. The Xiphophorus hybrid (...) melanoma system has gained attention in biomedical research as a genetic model for studying tumor formation. From an evolutionary perspective, a prominent question is: how could this gene persist over millions of years? An attractive hypothesis is that Xmrk, acting as a detrimental gene in a hybrid genome, could be a speciation gene that shields the gene pool of its species from mixing with other closely related sympatric species. In this article, I briefly review our current knowledge of the molecular genetics and biochemical functions of the Xmrk gene and discuss aspects of its evolutionary history and presence with respect to this idea. While Xmrk as a potentially injurious oncogene has clearly survived for millions of years, its role as a speciation gene has to be questioned. BioEssays 30:822–832, 2008. © 2008 Wiley Periodicals, Inc. (shrink)

Graphical AbstractThe origins of asexuality in plants as well as animals have long puzzled researchers. In article 2000111, Diego Hojsgaard and Manfred Schartl integrate old ideas with recent molecular and genomic data and provide a single mechanistic model for this phenomenon. They highlight two usually overlooked conditions to understand the molecular nature of clonal organisms to explain asexuals' developmental diversity and biologically vague cases such as automixis and polyploidy.

Cancer is one of the most frequent fatal human diseases. It is a genetic disease, and molecular analysis of the genes involved revealed that they belong to several distinct classes of molecules, one of which is the receptor tyrosine kinases. Neoplastic transformation is regarded as the result of a multistep process and, in most cases, it is hard to evaluate what the initial events in tumor formation are. What makes it difficult to approach this question is the paucity of animal (...) models for tumorigenesis allowing investigation of the mechanisms leading to uncontrolled cell proliferation. Melanoma formation in Xiphophorus is one of these model systems. Here, overexpression and activation of a receptor tyrosine kinase causes neoplastic transformation of pigment cells. Xiphophorus provides all the advantages of a well‐characterised genetic system. In addition, some crucial components of the transformation pathway have been identified at the molecular level. As a vertebrate, Xiphophorus might serve as a model system to aid understanding, in more general terms, of the mechanisms of tumorigenesis in human diseases. (shrink)

The unusual occurrence and developmental diversity of asexual eukaryotes remain a puzzle. De novo formation of a functioning asexual genome requires a unique assembly of sets of genes or gene states to disrupt cellular mechanisms of meiosis and gametogenesis, and to affect discrete components of sexuality and produce clonal or hemiclonal offspring. We highlight two usually overlooked but essential conditions to understand the molecular nature of clonal organisms, that is, a nonrecombinant genomic assemblage retaining modifiers of the sexual program, and (...) a complementation between altered reproductive components. These subtle conditions are the basis for physiologically viable and genetically balanced transitions between generations. Genomic and developmental evidence from asexual animals and plants indicates the lack of complementation of molecular changes in the sexual reproductive program is likely the main cause of asexuals' rarity, and can provide an explanatory frame for the developmental diversity and lability of developmental patterns in some asexuals as well as for the discordant time to extinction estimations. (shrink)

The paper outlines the analysis of certain question types in the Commitment Space framework, as presented in Krifka (2015). The two basic ideas are: Assertions and most questions involve commitments of speaker and addressee to the truth of a proposition, and questions consist in restricting the continuation of the conversation to answers to the question. The main focus is on breadth, not depth and the detailed comparison with alternative approaches, and on semantic modelling, not on the syntactic and prosodic realizations. (...) Topics are polar questions and their bias, alternative questions, constituent questions, high negation in questions, declarative questions, root vs. embedded questions, and deliberative questions. (shrink)

Este artículo intenta identificar los acuerdos y desacuerdos entre Benjamin Constant y Alexis de Tocqueville en torno a la pregunta de cómo fundar un orden político respetuoso de las libertades y que, al mismo tiempo, asuma y proyecte la ruptura revolucionaria. En otras palabras, cómo articular orden, libertad y política. nuestra tesis es que la diferencia en el modo de aproximarse a la cuestión encuentra su origen en diversas concepciones de la historia. Para los efectos de evaluar los procesos históricos, (...) Constant nunca abandona del todo ciertas intuiciones progresistas. Tocqueville, por su parte, se mantiene siempre a distancia de las distintas versiones de la filosofía de la historia. Para ilustrar el argumento, nuestro trabajo se divide en cuatro partes. En la primera, exponemos la relación entre ambos autores y su concepción del movimiento histórico. Luego, examinamos cómo entiende cada uno de ellos el concepto de perfectibilidad, siempre a la luz de la primera diferencia. En la tercera parte, exploramos la noción de anacronismo empleada por Constant, y las críticas —más o menos implícitas— de Tocqueville a esa idea. Por último, analizaremos las distintas concepciones de política que se deducen de cada uno de los sistemas. (shrink)

The contribution tackles the analytical and hermeneutic problem, implied in today's notion of the 17-century “Scientific Revolution”, which comes to the front in trying to come to grips with the notion of European science, its discovery in Antiquity and its history in Middle Ages and Modern Age. We shall try to argue that, in its core, this revolution implies a notional revolution. The contribution investigates the function the of notions of “theory”, “doctrine” and “system”, which are constitutive for the formation (...) of science, each in itself being correlative to a specific type of scientific units attributed to the classical-Greek , Christian-Mediaeval , and modern notion of science . Pondering on the topic of these notions and their shifts in the Modern Age is the key towards a new understanding of the history of science, extending beyond the borders of the existing conceptions as based on natural sciences. (shrink)

Präsenz und Distanz: von diesem Verhältnis handelt die Phänomenologie, wenn sie sich, behutsam beschreibend, der Lebenswelt und dem Zeitbewußtsein zuwendet. Lebensweltliches Leben ist unmittelbare Anschauung am Anfang des Übergangs zu begrifflichem Denken und symbolischen Repräsentanten, ist ursprüngliche Einheit und beginnendes Auseinander von subjektivem Erlebnis und objektiver Realität. All unsere Erlebnisse aber kommen und gehen in der Zeit des Bewußtseins. Sie ist die Form eines Fließens, in dem uns der Augenblick der Gegenwart erst nachträglich faßbar wird; er erweist sich als der (...) immer schon vergangene Anfang einer Nah-Erinnerung, die beides zugleich ist: Noch-Gegenwart und Schon-Vergangenheit: Präsenz gibt es erst im Abstand von ihr. - Mit dem, was unser bewußtes Leben zuunterst trägt und zuinnerst hält, befassen sich die Beschreibungen und Interpretationen dieses Buches: mit dem lebensweltlichen Grund und der zeitlichen Form. (shrink)