Understanding aging and how it affects an organism's lifespan is a fundamental problem in biology. A hallmark of aging is stem cell senescence, the decline of functionality, and number of somatic stem cells, resulting in an impaired regenerative capacity and reduced tissue function. In addition, aging is characterized by profound remodeling of the immune system and a quantitative decline of adequate immune responses, a phenomenon referred to as immune‐senescence. Yet, what is causing stem cell and immune‐senescence? This review discusses experimental (...) studies of potentially immortal Hydra which have made contributions to answering this question. Hydra transcription factor FoxO has been shown to modulate both stem cell proliferation and innate immunity, lending strong support to a role of FoxO as critical rate‐of‐aging regulator from Hydra to human. Constructing a model of how FoxO responds to diverse environmental factors provides a framework for how stem cell factors might contribute to aging. (shrink)

Hydra are remarkable because they are immortal. Much of immortality can be ascribed to the asexual mode of reproduction by budding, which requires a tissue consisting of stem cells with continuous self‐renewal capacity. Emerging novel technologies and the availability of genomic resources enable for the first time to analyse these cells in vivo. Stem cell differentiation in Hydra is governed through the coordinated actions of conserved signaling pathways. Studies of stem cells in Hydra, therefore, promise critical insights of general relevance (...) into stem cell biology including cellular senescence, lineage programming and reprogramming, the role of extrinsic signals in fate determination and tissue homeostasis, and the evolutionary origin of these cells. With these new facts as a backdrop, this review traces the history of studying stem cells in Hydra and offers a view of what the future may hold. (shrink)

Current work in experimental biology revolves around a handful of animal species. Studying only a few organisms limits science to the answers that those organisms can provide. Nature has given us an overwhelming diversity of animals to study, and recent technological advances have greatly accelerated the ability to generate genetic and genomic tools to develop model organisms for research on host–microbe interactions. With the help of such models the authors therefore hope to construct a more complete picture of the mechanisms (...) that underlie crucial interactions in a given metaorganism (entity consisting of a eukaryotic host with all its associated microbial partners). As reviewed here, new knowledge of the diversity of host–microbe interactions found across the animal kingdom will provide new insights into how animals develop, evolve, and succumb to the disease. (shrink)

Peptides serve as important signalling molecules in development and differentiation in the simple metazoan Hydra. A systematic approach (The Hydra Peptide Project) has revealed that Hydra contains several hundreds of peptide signalling molecules, some of which are neuropeptides and others emanate from epithelial cells. These peptides control biological processes as diverse as muscle contraction, neuron differentiation, and the positional value gradient. Signal peptides cause changes in cell behaviour by controlling target genes such as matrix metalloproteases. The abundance of peptides in (...) Hydra raises the question of whether, in early metazoan evolution, cell–cell communication was based mainly on these small molecules rather than on the growth‐factor‐like cytokines that control differentiation and development in higher animals. BioEssays 23:420–427, 2001. © 2001 John Wiley & Sons, Inc. (shrink)

Ecological developmental biology (eco‐devo) explores the mechanistic relationships between the processes of individual development and environmental factors. Recent studies imply that some of these relationships have deep evolutionary origins, and may even pre‐date the divergences of the simplest extant animals, including cnidarians and sponges. Development of these early diverging metazoans is often sensitive to environmental factors, and these interactions occur in the context of conserved signaling pathways and mechanisms of tissue homeostasis whose detailed molecular logic remain elusive. Efficient methods for (...) transgenesis in cnidarians together with the ease of experimental manipulation in cnidarians and sponges make them ideal models for understanding causal relationships between environmental factors and developmental mechanisms. Here, we identify major questions at the interface between animal evolution and development and outline a road map for research aimed at identifying the mechanisms that link environmental factors to developmental mechanisms in early diverging metazoans.Also watch the Video Abstract. (shrink)

Cover Photograph: Transgenic Hydra provide insights of general relevance into stem cell biology. The image shows a mass culture of transgenic Hydra expressing EGFP in all of their ectodermal epithelial cells. See article by Thomas C. G. Bosch pp. 478–486.

Graphical AbstractCIFAR's Humans & the Microbiome program is a multidisciplinary group of biological, clinical, and social scientists who explore the links between microbiome biology and sociocultural, historical, evolutionary, and environmental aspects of human existence that may impact the microbiome or be impacted by it. In this focus issue, members of the program focus on topics ranging from decoding the link between nutrition, the microbiome and human developmental, metabolic, and immune health and aging, to understanding past changes in the environment and (...) microbiome. The image depicts a population of bacteria (green) in association with the epithelia tissues (magenta and blue), perhaps the most common type of symbiosis in humans and other animals. Image contribution: Tara Essock-Burns. DOI: 10.1002/bies.201900130. (shrink)

Cells in the basal metazoan phylum Cnidaria are characterized by remarkable plasticity in their differentiation capacity. The mechanism controlling asymmetric cell divisions is not understood in cnidarians or in any other animal group. PIWI proteins recently have been shown to be involved in maintaining the self‐renewal capacity of stem cells in organisms as diverse as ciliates, flies, worms and mammals. Seipel et al.1 find that, in the cnidarian Podocoryne carnea, the Piwi homolog Cniwi is transcriptionally upregulated when the polyp generates (...) buds, which will develop into medusae. Since transdifferentiation of striated muscle cells to smooth muscle cells also activated Cniwi expression, Cniwi appears to play a crucial role in differentiation events. The discovery should facilitate elucidation of the poorly understood factors that control asymmetric cell divisions at the beginning of animal evolution. BioEssays 26:929–931, 2004. © 2004 Wiley Periodicals, Inc. (shrink)

While largely studied because of their harmful effects on human health, there is growing appreciation that bacteria are important partners for invertebrates and vertebrates, including man. Epithelia in metazoans do not only select their microbiota; a coevolved consortium of microbes enables both invertebrates and vertebrates to expand the range of diet supply, to shape the complex immune system and to control pathogenic bacteria. Microbes in zebrafish and mice regulate gut epithelial homeostasis. In a squid, microbes control the development of the (...) symbiotic light organ. These discoveries point to a key role for bacteria in any metazoan existence, and imply that beneficial bacteria‐host interactions should be considered an integral part of development and evolution. (shrink)

Here we evaluate our current understanding of the function of the nervous system in Hydra, a non‐bilaterian animal which is among the first metazoans that contain neurons. We highlight growing evidence that the nervous system, with its rich repertoire of neuropeptides, is involved in controlling resident beneficial microbes. We also review observations that indicate that microbes affect the animal's behavior by directly interfering with neuronal receptors. These findings provide new insight into the original role of the nervous system, and suggest (...) that it emerged to orchestrate multiple functions including host‐microbiome interactions. The excitement of future research in the Hydra model now relies on uncovering the common rules and principles that govern the interaction between neurons and microbes and the extent to which such laws might apply to other and more complex organisms. (shrink)

The conference explored an extraordinary diversity of aging strategies in organisms ranging from short‐lived species to “immortal” animals and plants. Research on the biological processes of aging is at the brink of a revolution with respect to our understanding of its underlying mechanisms as well as our ability to prevent and cure a wide variety of age‐related pathologies.

Humans’ indigenous microbes strongly influence organ functions in an age‐ and diet‐dependent manner, adding an important dimension to aging biology that remains poorly understood. Although age‐related differences in the gut microbiota composition correlate with age‐related loss of organ function and diseases, including inflammation and frailty, variation exists among the elderly, especially centenarians and people living in areas of extreme longevity. Studies using short‐lived as well as nonsenescent model organisms provide surprising functional insights into factors affecting aging and implicate attenuating effects (...) of microbes as well as a crucial role for certain transcription factors like forkhead box O. The unexpected beneficial effects of microbes on aged animals imply an even more complex interplay between the gut microbiome and the host. The microbiome constitutes the major interface between humans and the environment, is influenced by biosocial stressors and behaviors, and mediates effects on health and aging processes, while being moderated by sex and developmental stages. (shrink)

The microbiome of human hair follicles (HFs) has emerged as an important player in different HF and skin pathologies, yet awaits in‐depth exploration. This raises questions regarding the tightly linked interactions between host environment, nutrient dependency of host‐associated microbes, microbial metabolism, microbe‐microbe interactions and host immunity. The use of simple model systems facilitates addressing generally important questions and testing overarching, therapeutically relevant principles that likely transcend obvious interspecies differences. Here, we evaluate the potential of the freshwater polyp Hydra, to dissect (...) fundamental principles of microbiome regulation by the host, that is the human HF. In particular, we focus on therapeutically targetable host‐microbiome interactions, such as nutrient dependency, microbial interactions and host defence. Offering a new lens into the study of HF – microbiota interactions, we argue that general principles of how Hydra manages its microbiota can inform the development of novel, microbiome‐targeting therapeutic interventions in human skin disease. (shrink)

Meet the Metaorganism is a web‐based learning app that combines three fundamental biological concepts (coevolution, community dynamics, and immune system) with latest scientific findings using the metaorganism as a central case study. In a transdisciplinary team of scientists, information designers, programmers, science communicators, and educators, we conceptualized and developed the app according to the latest didactic and scientific findings and aimed at setting new standards in visual design, digital knowledge transfer, and online education. A content management system allows continuous integration (...) of new findings, which enables us to expand the app with the dynamics of the research field. Students can thus gain a close insight and connection to current research, and at the same time learn that knowledge is not static but grows dynamically. Especially in the realm of the easily accessible metaorganism research, visualization plays an essential role to keep complex processes understandable and memorable. Meet the Metaorganism is freely available online and can be accessed here: www.metaorganism.app. (shrink)

The evidence compiled in the target article demonstrates that the assumptions of cultural group selection theory are often met, and it is therefore a useful framework for generating plausible hypotheses. However, more can be said about how we can test the predictions of CGS hypotheses against competing explanations using historical, archaeological, and anthropological data.

Das Netz der Kultur bildet eine kommunikative Medialität, in der sich Freiheitsspielräume des menschlichen Lebens eröffnen.

Thomas Reid saw the three subjects of logic, rhetoric, and the fine arts as closely cohering aspects of one endeavor that he called the culture of the mind. This was a topic on which Reid lectured for many years in Glasgow, and this volume presents as near a reconstruction of these lectures as is now possible. Though virtually unknown today, this material in fact relates closely to Reid's published works and in particular to the late Essays on the Intellectual (...) Powers of Man and Essays on the Active Powers of Man. When composing these works, Reid drew primarily on his lectures on "pneumatology," which presented a theory of the mental powers, broadly conceived. These lectures were basic to the course on the culture of the mind that explained the cultivation of the mental powers. Although the Essays also included some elements from the material on the culture of the mind, the bulk of the latter was left in manuscript form, and Alexander Broadie's edition restores this important extension of Reid's overall work. In addition, this volume continues the attractive combination of manuscript material and published work, in this case Reid's important and well-known essay on Aristotle's logic. This text was corrupted in earlier editions of Reid's works and is now restored to the state in which Reid left it. This volume underscores Reid's great and growing significance, viewed both as a historical figure and as a philosopher. At the same time, it is of great interdisciplinary importance. While the material emerges directly from the core of Reid's philosophy, as now understood, it will appeal widely to people in literary, cultural, historical, and communications studies. In this regard, the present volume is a true fruit of the Scottish Enlightenment. (shrink)

This paper explores structuralism as a way to model theories from scientific practice. As a case study I analyzed a theory about the dynamics of the basal ganglia, a part of the brain that is involved in Parkinson's disease. After introducing the case study I explore how to structurally represent qualitative assumptions about disease, intervention and dynamical systems in general. I further explicate the structure of the basal ganglia theory in detail, how it explains Parkinson's disease and how it implies (...) treatments. I close with a consideration of how a structuralist representation could be useful in practice to explore and develop theories with the aid of a computer. (shrink)

Fiodor Dostoievski rasga el alma humana hasta dejarla herida por el sufrimiento, la culpa y el aislamiento. Y, sin embargo, la derrota no gana la batalla. La escritora sureña estadounidense Carson McCullers escribe sobre la soledad y la miseria del sur de los Estados Unidos con una mirada atenta a los paisajes desolados de la Rusia de Fiodor Dostoievski, no sólo físicos sino esencialmente metafísicos. Esta autora que ya leyó al maestro ruso a los 13 años explora las entrañas humanas (...) desde un terreno rural, desolador, inhóspito y desafortunado, con diferencias raciales, sobreexposición de alcohol y con un concepto de bien moral interno que aparece como una pulsión constante e inagotable. En esta aproximación queremos destacar cómo el misterio del mal, pero también el acto de la voluntad y la incomunicación, son aspectos que unen a ambos autores, especialmente en dos de sus obras maestras, Crimen y Castigo y El corazón es un cazador solitario, respectivamente. (shrink)

Issues of reliability are claiming center-stage in the epistemology of machine learning. This paper unifies different branches in the literature and points to promising research directions, whilst also providing an accessible introduction to key concepts in statistics and machine learning---as far as they are concerned with reliability.

Zu den bedeutendsten Leistungen der Friedensschrift Kants für die Entwicklung der Völkerrechtsidee gehört die Zurückweisung der bisherigen Leitvorstellung eines ius ad bellum. Unmißverständlich formuliert er: „Bei dem Begriffe des Völkerrechts, als eines Rechts zum Kriege, läßt sich eigentlich gar nichts denken“ . Eine internationale Rechtsordnung müsse dem Ziele dauerhafter Friedenssicherung dienen, und in einem Bund freier Völker soll dieser zwischenstaatliche Konsens institutionalisiert werden.

The words quoted above distill the common secular conception of death. If we decline the traditional religious reassurances of an afterlife, or their fuzzy new age equivalents, and instead take the hard-boiled and thoroughly modern materialist view of death, then we likely end up with Gonzalez-Cruzzi. Rejecting visions of reunions with loved ones or of crossing over into the light, we anticipate the opposite: darkness, silence, an engulfing emptiness. But we would be wrong.

Hannah Arendts politischer Theorie liegt eine relationale Ontologie zugrunde, in der Pluralität und singuläre Freiheit in einem wechselseitigen Bedingungsverhältnis stehen. Das politische Zusammenhandeln setzt freie Individuen voraus, die sich im Netzwerk sozialer Beziehungen differenzieren und identifizieren. Freiheit verwirklicht sich als Partizipation an öffentlicher Verständigung, in der die lebensweltliche Begrenztheit der eigenen Perspektive durch die Auseinandersetzung mit anderen Perspektiven überschritten wird. Darin liegt die kommunikative Basis posttraditioneller politischer Gemeinschaft. Politisches Handeln ist Selbstverwirklichung öffentlicher Beziehungsnetze, die sich als Wir-Identitäten begreifen können. Ebensowenig (...) wie die Individuen stehen die Netzwerke in atomistischer Isolation. Die partikularen politischen Bewegungen sind Teil eines globalen Handlungszusammenhangs. Neben die Pluralität als politischer Leitidee stellt Arendt den integrativen Impuls einer globalen Weltverantwortung. Die partikular-kulturellen Kontexte werden im Sinne der kantischen erweiterten Denkungsart auf einen menschheitlich-universalen Handlungskontext bezogen. Der Perspektivenvielfalt steht eine regulative Universalität der Weltverantwortung gegenüber, die der reflektierenden Urteilskraft überantwortet ist. So verbindet Arendt den republikanischen Partikularismus mit kantisch-universellem Weltbürgertum. (shrink)