Unlike inert objects, organisms and their cells have the ability to initiate activity by themselves and thus change their properties or states even in the absence of an external cause. This crucial difference led us to search for principles suitable for the study organisms. We propose that cells follow the default state of proliferation with variation and motility, a principle of biological inertia. This means that in the presence of sufficient nutrients, cells will express their default state. We also propose (...) a principle of variation that addresses two central features of organisms, variation and historicity. To address interdependence between parts, we use a third principle, the principle of organization, more specifically, the notion of the closure of constraints. Within this theoretical framework, constraints are specific theoretical entities defined by their relative stability with respect to the processes they constrain. Constraints are mutually dependent in an organized system and act on the default state.Here we discuss the application and articulation of these principles for mathematical modeling of morphogenesis in a specific case, that of mammary ductal morphogenesis, with an emphasis on the default state. Our model has both a biological component, the cells, and a physical component, the matrix that contains collagen fibers. Cells are agents that move and proliferate unless constrained; they exert mechanical forces that act (i) on collagen fibers and (ii) on other cells. As fibers are organized, they constrain the cells’ ability to move and to proliferate. This model exhibits a circularity that can be interpreted in terms of the closure of constraints. Implementing our mathematical model shows that constraints to the default state are sufficient to explain the formation of mammary epithelial structures. Finally, the success of this modeling effort suggests a stepwise approach whereby additional constraints imposed by the tissue and the organism can be examined in silico and rigorously tested by in vitro and in vivo experiments, in accordance with the organicist perspective we embrace. (shrink)

A geometrical model of the emergence of a primordium at the shoot apex in dicotyledons is proposed. It is based on recent fundamental results on plant morphogenesis, i.e.:- the emergence is preceded by the reorganization of the microtubules of the cortical cytoskeleton, leading to a new orientation of the synthesis of the cell wall microfibrils; - the resulting global stress is related to the general orientation of the cell growth. So the model sums up the continuous interactions linking the microtubules, (...) the microfibrils and the cell growth axis. (shrink)

Pax genes are a family of development control genes that encode nuclear transcription factors. They are characterized by the presence of the paired domain, a conserved amino acid motif with DNA‐binding activity. Originally, paired‐box‐containing genes were detected in Drosophila malenogaster, where they exert multiple functions during embryogenesis. In vertebrates, Pax genes are also involved in embryogenesis. Mutations in four out of nine characterized Pax genes have been associated with either congenital human diseases such as Waardenburg syndrome (PAX3), Aniridia (PAX6), Peter's (...) anomaly (PAX6), renal coloboma syndrome (PAX2), Small eye (Pax6), (Pax21Neu), which all show defects in development. Recently, analysis of spontaneous and transgenic mouse mutants has revealed that vertebrate Pax genes are key regulators during organogenesis of kidney, eye, ear, nose, limb muscles, vertebral column and brain. Like their Drosophila counterparts, vertebrate Pax genes are involved in pattern formation during embryogenesis, possibly by determiing the time and place of organ initiation of morphogenesis. For most tissues, however, the nature of the primary development action of Pax transcription factors remains to be elucidated. One predominant theme is signal transduction during tissue interactions, which may lead to a position‐specific regulation of cell proliferation. (shrink)

© 2015 Elsevier Inc.Postnatal organogenesis occurs in an immune competent environment and is tightly controlled by interplay between positive and negative regulators. Innate immune cells have beneficial roles in postnatal tissue remodeling, but roles for the adaptive immune system are currently unexplored. Here we show that adaptive immune responses participate in the normal postnatal development of a non-lymphoid epithelial tissue. Since the mammary gland is the only organ developing predominantly after birth, we utilized it as a powerful system to (...) study adaptive immune regulation of organogenesis. We found that antigen-mediated interactions between mammary antigen-presenting cells and interferon-γ -producing CD4+ T helper 1 cells participate in MG postnatal organogenesis as negative regulators, locally orchestrating epithelial rearrangement. IFNγ then affects luminal lineage differentiation. This function of adaptive immune responses, regulating normal development, changes the paradigm for studying players of postnatal organogenesis and provides insights into immune surveillance and cancer transformation. Plaks et al. (shrink)

Organogenesis and metamorphosis require the intricate orchestration of multiple types of cellular interactions and signaling pathways. Glutamate (Glu) is an excitatory extracellular signaling molecule in the nervous system, while Ca2+ is a major intracellular signaling molecule. The first Glu receptors to be cloned are Ca2+‐permeable receptors in mammalian brains. Although recent studies have focused on Glu signaling in synaptic mechanisms of the mammalian central nervous system, it is unclear how this signaling functions in development. Our recent article demonstrated that (...) Ca2+‐permeable AMPA‐type Glu receptors (GluAs) are essential for formation of a photosensitive organ, development of some neurons, and metamorphosis, including tail absorption and body axis rotation, in ascidian embryos. Based on findings in these embryos and mammalian brains, we formed several hypotheses regarding the evolution of GluAs, the non‐synaptic function of Glu, the origin of GluA‐positive neurons, and the neuronal network that controls metamorphosis in ascidians. (shrink)

This open access book assesses the prospects of (re)adopting organization as a pivotal concept in biology. It shows how organization can nourish biological thinking and practice, by reconnecting with the idea of biology as the science of organized systems. The book provides a comprehensive state-of-the-art picture of the characterizations and uses of the concept of organization in both biological science and philosophy of biology. It also deals with a variety of themes – including evolution, organogenesis, heredity, cognition and ecology (...) – with respect to which the concept of organization can guide the elaboration of original models and new experimental protocols. It will be of interest to biologists and scholars working in philosophy of science alike. (shrink)

The somatic mutation theory has been the prevailing paradigm in cancer research for the last 50 years. Its premises are: (1) cancer is derived from a single somatic cell that has accumulated multiple DNA mutations, (2) the default state of cell proliferation in metazoa is quiescence, and (3) cancer is a disease of cell proliferation caused by mutations in genes that control proliferation and the cell cycle. From this compelling simplicity, an increasingly complicated picture has emerged as more than 100 (...) oncogenes and 30 tumor suppressor genes have been identified. To accommodate this complexity, additional ad hoc explanations have been postulated. After a critical review of the data gathered from this perspective, an alternative research program has been proposed. It is based on the tissue organization field theory, the premises of which are that carcinogenesis represents a problem of tissue organization, comparable to organogenesis, and that proliferation is the default state of all cells. The merits of these competing theories are evaluated herein. BioEssays 26:1097–1107, 2004. © 2004 Wiley Periodicals, Inc. (shrink)

Both paleobiology and investigations of ‘major evolutionary transitions’ are intimately concerned with the macroevolutionary shape of life. It is surprising, then, how little studies of major transitions are informed by paleontological perspectives and. I argue that this disconnect is partially justified because paleobiological investigation is typically ‘phenomena-led’, while investigations of major transitions are ‘theory-led’. The distinction turns on evidential relevance: in the former case, evidence is relevant in virtue of its relationship to some phenomena or hypotheses concerning those phenomena; in (...) the latter, evidence is relevant in virtue of providing insights into, or tests of, an abstract body of theory. Because paleobiological data is by-and-large irrelevant to the theory which underwrites the traditional conception of major transitions, it is of limited use to that research program. I suggest that although the traditional conception of major transitions is neither ad-hoc or problematically incomplete, its promise of providing unificatory explanations of the transitions is unlikely to be kept. Further, examining paleobiological investigations of mass extinctions and organogenesis, I further argue that whether or not transitions in paleobiology count as ‘major’ turns on how we conceive of major transitions ; although major transitions potentially have a unified theoretical basis, recent developments suggest that investigations are becoming increasingly phenomena-led; adopting phenomena-led investigations maximizes the evidence available to paleobiologists. (shrink)

Generation of Animals is one of Aristotle's most mature, sophisticated, and carefully crafted scientific writings. His overall goal is to provide a comprehensive and systematic account of how animals reproduce, including a study of their reproductive organs, what we would call fertilization, embryogenesis, and organogenesis. In this book, international experts present thirteen original essays providing a philosophically and historically informed introduction to this important work. They shed light on the unity and structure of the Generation of Animals, the main (...) theses that Aristotle defends in the work, and the method of inquiry he adopts. They also open up new avenues of exploration of this difficult and still largely unexplored work. The volume will be essential for scholars and students of ancient philosophy as well as of the history and philosophy of science. (shrink)

Colonial ascidians offer opportunities to investigate how developmental events are integrated to generate the animal form, since they can develop similar individuals (oozooids from eggs, blastozooids from pluripotent somatic cells) through very different reproductive processes, i.e. embryogenesis and blastogenesis. Moreover, thanks to their key phylogenetic position, they can help in the understanding of the molecular mechanisms of morphogenesis and their evolution in chordates. We review organogenesis of the ascidian neural complex comparing embryos and buds in terms of topology, developmental (...) mechanisms and terminology. We propose a new interpretation of bud territories, and reconsider nervous system development based on recent results suggesting that ascidians have vertebrate placodal and neural‐crest‐like cells. Comparing embryonic and blastogenic development in Botryllus schlosseri, we propose that the bud has territories with a placodal potentiality, suggesting that chordate ancestors possessed neurogenic placodes, and that the genetic pathways regulating neurogenic placode formation were co‐opted for new developmental processes, such as blastogenesis. BioEssays 28: 902–912, 2006. © 2006 Wiley periodicals, Inc. (shrink)

A wide range of anatomical features are shared by all vertebrates, but absent in our closest invertebrate relatives. The origin of vertebrate embryogenesis must have involved the evolution of new regulatory pathways to control the development of new features, but how did this occur? Mutations affecting regulatory genes, including those containing homeobox sequences, may have been important: for example, perhaps gene duplications allowed recruitment of genes to new roles. Here I ask whether comparative data on the genomic organization and expression (...) patterns of homeobox genes support this hypothesis. I propose a model in which duplications of particular homeobox genes, followed by the acquisition of gene‐specific secondary expression domains, allowed the evolution of the neural crest, extensive organogenesis and craniofacial morphogenesis. Specific details of the model are amenable to testing by extension of this comparative approach to molecular embryology. (shrink)

Recently, there has been a growing interest, both within theoretical biology and the philosophy of biology, in the possibility and desirability of a theory of development. Among the many issues raised within this debate, the questions of the spatial and temporal boundaries of development have received particular attention. In this article, noting that so far the discussion has mostly centered on the processes of morphogenesis and organogenesis, we argue that an important missing element in the equation, namely the development (...) of language and cognition in general, may play an important role in settling the issue of temporal boundaries. After examining the idea that the development of language, cognition, and action are bona fide biological processes, we explore the consequences for a general theory of development of taking them into consideration. (shrink)

Cells can transit between a range of stable epithelial and mesenchymal states and this has allowed the evolution of complex body forms. Epithelial to mesenchymal transition (EMT) and its reverse, mesenchymal to epithelial transition (MET), occur sequentially in development and organogenesis. EMT often accompanies transitions between stem‐like cells and their more differentiated progeny, as occurs at gastrulation, although the relevance of this had not been clarified. New findings from the cancer and cell reprogramming fields suggest that EMT and MET (...) can act as essential portals to stem cell character. Here, we review these findings in the broader context of EMT and MET with emphasis on stem cell biology. Using the heart as an example, we also explore the potential role of EMT/MET in organ regeneration. Understanding EMT and MET at a network level will give us new tools to probe stem cell character and enhance tissue repair. (shrink)

This article is concerned with the problem of the relation between the genetic information contained in the DNA and the emergence of visible structure in multicellular animals. The answer is sought in a reappraisal of the data of experimental embryology, considering molecular, cellular and organismal aspects. The presence of specific molecules only confers a tissue identity on the cells when their concentration exceeds the threshold of differentiation. When this condition is not fulfilled the activity of the genes that code for (...) the specific molecules in question only confers on them a histogenetic potency, i.e. the capacity to form the corresponding tissue in further development (or to transdifferentiate to that tissue). The progressive restriction of histogenetic potencies during development reflects the irreversible repression of more and more genes. The establishment of a given tissue identity under the influence of an inducing tissue (or a morphogenetic hormone) is only possible when the cells have acquired the competence to respond. Tissue differentiation proceeds progressively during development thanks to the cytoplasmic memory that cells retain collectively (or sometimes individually) of the items of information successively registered by their ancestors cells. The increasing complexity of visible structure emerging during development results only from the progression of tissue differentiation. This involves continual exchange of information among the cells and leads to (1) cell displacements and rearrangements, particularly during organogenesis and (2) extreme diversification of cell individualities within tissues, particularly during postembryonic growth. A mutation (just as a teratogenic factor) evokes an anomaly that is localized in both space and time because it alters a certain aspect of cell behaviour (particularly cell surface adhesiveness or mitotic activity) at the time when this is involved in the establishment of a particular structural trait. Neither the organization of the adult nor the modalities of development are encoded in the DNA. The automatic concatenation of cell interactions in the embryo and the structural amplification it entails is conditioned by the specific biochemical composition of the cytoplasm of the egg and by the heterogeneous distribution of its inclusions. (shrink)

The tenascins are a growing family of extracellular matrix proteins of typical multidomain structure. The prototype to be discovered was tenascin‐C. It shows a highly regulated expression pattern during embryonic development and is often transiently associated with morphogenetic tissue interactions during organogenesis. In the adult organism reexpression of tenascin‐C occurs in tumors and many other pathological conditions. Tenascin‐C expression can be regulated by many different growth factors and hormones. Furthermore, mechanical strain exerted by fibroblasts seems to induce the expression (...) of tenascin‐C. This could represent a mechanism of translating mechanical forces into protein patterns, a step of potential relevance in the organization of embryogenesis. Tenascin‐C as well as tenascin‐R are believed to counteract the cell adhesion and spreading activity of fibronectin, thereby facilitating cell movement. (shrink)

The advent of cinema brought with it a different kind of image montage, to which Warburg’s iconological project was strangely oblivious. Are we meant to believe, then, that the cinema does not produce icons? Is iconology destined to be only a science of classical culture, or can it also evolve to integrate into its own study new forms of kinematic art? We would like to ask the question of organogenesis of iconology here, that is to say, the invention of (...) an iconological science for temporal objects by means of appropriate instruments for this new medium. The instrument is both conceived as a means of acting upon the real, and as a means of activating noetic capacities. The aim of our study will be to first outline the iconographic and iconological consequences stemming from animation and flux that have governed images since the birth of cinema, precipitating a crisis in classical iconology. Secondly, through the analysis of the noetic function of animated GIFs (Graphics Interchange Format) in digital streams, we will introduce the notion of ‘temporal gesture’ – as a tertiarized retentional technology, which can be reused for imagining an iconology of temporal suspension and insistence. This will be presented in the third part of this work to reflect on an iconological device for temporal objects by the grammatization and the engramming of ‘temporal gesture’, as an art of delay and repetition. This thinking will be based on the video artwork produced in collaboration with Gregory Dassié titled Iconologie pour objet temporel. (shrink)

This research is conducted by the Intellectual Property and Policy Research Group at the W. Maurice Young Centre for Applied Ethics at the University of British Columbia. It is part of the GE3LS component of the Genome Canada Project "Dissecting Gene Expression Networks in Mammalian Organogenesis," MORGEN, which is located principally at the British Columbia Cancer Agency, Vancouver, British Columbia, Canada. The project is involved in upstream, basic genomic research. Part of this work includes the characterization of gene regulatory (...) mechanisms governing organogenesis with a special focus on the heart, liver and pancreas. This paper serves as an introduction to both the MORGEN case study and the role of alternative mechanisms, such as open source. We discuss interim research results as they relate to our broader study of the relationship between open science, commercialization and technology transfer offices. The role of technology transfer offices is central to our analysis and is viewed as a key factor in implementing Genome Canada policies and principles associated with IP and commercialization. (shrink)

The ability of two or more cells to unite to form a new syncytial cell has been utilized in metazoans throughout evolution to form many complex organs, such as muscles, bones and placentae. This requires migration, recognition and adhesion between cells together with fusion of their plasma membranes and rearrangement of their cytoplasmic contents. Until recently, understanding of the mechanisms of cell fusion was restricted to fusion between enveloped viruses and their target cells. The identification of new factors that take (...) part in developmental cell fusion in C. elegans opens the way to understanding how cells fuse and what the functions of this process are. In this review, we describe current knowledge on the mechanisms and putative roles of developmental cell fusion in C. elegans and how cell fusion is regulated, together with other intercellular processes to promote organogenesis. BioEssays 25:672–682, 2003. © 2003 Wiley Periodicals, Inc. (shrink)

The correct positioning of organs during embryonic development requires multiple cues. The Xenopus cement gland is a mucus‐secreting epithelium that is a simple model for organogenesis, allowing detailed analysis of this complex process. The cement gland forms at a conserved anterior position, where embryonic ectoderm and endoderm touch. In all deuterostomes, this region will form the stomodeum (primitive mouth) and, in some aquatic larva, will also form a cement gland. In recent years, a model has been put forward suggesting (...) that an intermediate level of BMP signaling in the ectoderm leads to cement gland formation. We propose an alternative model whereby, during gastrulation, the cement gland (CG) is positioned by the overlap of three domains, corresponding to anterodorsal identity (AD), ventrolateral identity (VL), and ectodermal outer layer identity (EO), defining the equation (AD + VL + EO = CG). Anterodorsal identity requires a contribution by the transcription factor Otx2 while ventrolateral identity requires the BMP4 signaling pathway. These postional cues are integrated to activate cement gland differentiation. This integration appears to require intermediate steps, including expression of pitx genes, and members of the ATF/CREB and Ets transcription factor families. BioEssays 25:717–726, 2003. © 2003 Wiley Periodicals, Inc. (shrink)

Because of its elegant simplicity, the Arabidopsis root has become a model for studying plant organogenesis. In this review we focus on recent results indicating the importance of signaling in root development. A role for positional information in root cell specification has been demonstrated by ablation analyses. Through mutational analysis, genes have been identified that play a role in radial pattern formation. The embryonic phenotypes of these mutants raised the possibility that division patterns in post‐embryonic roots are dependent on (...) signaling that originates during embryonic development. Analysis of expression of the SCARECROW gene indicates that it may play a role in this ‘top‐down’ signaling process. Characterization of root epidermis development has led to the identification of negative regulators of root‐hair formation. These appear to set up a prepattern which is reinforced by signaling by plant hormones. (shrink)

Formation of branching epithelial trees from unbranched precursors is a common process in animal organogenesis. In humans, for example, this process gives rise to the airways of the lungs, the urine‐collecting ducts of the kidneys and the excretory epithelia of the mammary, prostate and salivary glands. Branching in these different organs, and in different animal classes and phyla, is morphologically similar enough to suggest that they might use a conserved developmental programme, while being dissimilar enough not to make it (...) obviously certain that they do. In this article, I review recent discoveries about the molecular regulation of branching morphogenesis in the best‐studied systems, and present evidence for and against the idea of there being a highly conserved mechanism. Overall, I come to the tentative conclusion that key mechanisms are highly conserved, at least within vertebrates, but acknowledge that more work needs to be done before the case is proved beyond reasonable doubt. BioEssays 24:937–948, 2002. © 2002 Wiley Periodicals, Inc. (shrink)

Apical cells are universally present in lower plants and their description has been mostly viewed morphologically as single-celled meristems. This study attempts to demonstrate that the roles of apical cells and more generally of meristems collectively are (a) often the proliferative source of all cells in a plant, (b) sometimes a formative centre in histogenesis and organogenesis and (c) always a regulatory site. As a proliferative centre it occurs as a series of apical cells through a mitotic lineage by (...) unequal divisions which includes a rotational pattern to form cells distributed according to the symmetry of its organ. As a formative centre it determines leaf arrangement in mosses and leafy liverworts as well as the root cap and gametophyte cushion in ferns. It appears initially to determine the type of organ and later the organ determines the type of apical cells within. As a regulatory centre it activates distal secondary cells to proliferate as well as inhibiting neighbouring cells from becoming apical cells to preserve the identity of an organ during its development.Based on these three roles by which apical cells can be recognized an argument can be drafted that seed plants may have apical cells, although morphologically indistinguishable from other cells, singularly or in batteries instead of possessing the traditionally described multicellular meristems. (shrink)

Scientific description of Nature is here based on geometry, number and energy. Geometry and number are the two only forms of our mind by which we describe Nature. Energy is here considered as the ultimate entity, which in physics is defined by the help of six propreties. The author holds that for an adequate description of physical Nature seven propreties of energy are required and eight are necessary in biology adding the holistic tendencies. On this basis an attempt is made (...) to show that holism is a scientific theory. As we can only perceive geometry and number, holistic propreties as such cannot be dealt with, we can only study the underlying physico-chemical manifestation. There are three holistic principles: 1) Interaction of parts leads to neocreation of propreties; this interaction can only be energetic. 2) The propreties of the whole are not potentially contained in the propreties of the parts. 3) The whole is more than the sum of its parts. Close interaction means fields of force and organisation, which implies that holism is organismic. The second principle is a safeguard against all unwarranted extrapolation. The whole and its parts only have additive propreties in common. Thus it is impossible to derive a macroscopic deterministic world from a microscopic undeterministic world because determinism is additive. The third principle is opposed to all attempts to describe holisation on a logical or mathematical basis. There is holisation in time and holisation in space and the latter can be subdivided into three groups according to their type of wholeness. Energy acts on energy and not on wholeness. All energetic interference with the basis has a holistic repercussion. The question of the egg and epigenetic organogenesis are also discussed from a holistic point of view.Naturbeschreibung ist hier auf Geometrie, Zahl und Energie begründet. Geometrie und Zahlenmässigkeit sind die einzigen Formen unseres Geistes durch die wir die Natur beschreiben. Energie, hier als Grundstein der Welt betrachtet, wird in der Physik durch sechs Eigenschaften definiert; zur vollständigen Beschreibung der physischen Welt seien aber sieben notwendig, während in der Biologie acht Eigenschaften nötig sind, indem Ganzheitsschöpfung als achte zählt. Auf dieser Basis wird gezeigt, dass der Holismus eine wissenschaftliche Theorie ist. Da wir nur Geometrie und Zahlenmässigkeit in der Natur erfassen, so können die holistischen Eigenschaften nicht direkt als solche betrachtet werden, sondern immer nur die ihnen zu Grunde liegenden physiko-chemischen Erscheinungen. Es gibt drei holistische Prinzipien: 1) Gegenseitige Beeinflussung führt zu Ganzheitseigenschaften. Beeinflussung kann nur energetisch sein. 2) Die Eigenschaften der Ganzheit sind nicht potential in den Eigenschaften der Teile enthalten. 3) Das Ganze ist mehr als die Summe seiner Teile. Gegenseitige Beeinflussung bedingt Kraftfelder und diese wieder Organisation. und so ist denn der Holismus seinem Wesen nach organismisch. Das zweite Prinzip legt Verwahrung gegen unstatthafte Extrapolation ein. Das Ganze und seine Teile haben nur additive Eigenschaften im gemein. Es ist also unmöglich eine deterministische makroskopische Welt von einer undeterministischen mikrophysischen abzuleiten weil Determinismus additiv ist. Das dritte Prinzip verwehrt sich gegen alle Anwendung von Logik und Mathematik zur Erklärung oder Beschreibung von Holisation . Es gibt Holisation 1) in der Zeit, 2) im Raum. Im Raum unterscheiden sich die Holisationen nach dem Wirkungskreis der Kraftfelder oder durch Abwesenheit solcher. Dies ist eine neue Aufteilung der Welt nach dem Wesen der Ganzheit. Die Einwirkung der Energie auf die Ganzheit ist mikrophysisch. Energie wirkt auf Energie und nicht auf die Ganzheit als solche. Jede energetische Einwirkung besitzt jedoch eine holistische Auswirkung. Das Problem der Eizelle und der epigenetischer Entwicklung wird auch besprochen. (shrink)

The evolutionarily conserved Notch signaling pathway regulates a broad spectrum of cell fate decisions and differentiation processes during fetal and postnatal life. It is involved in embryonic organogenesis as well as in the maintenance of homeostasis of self‐renewing systems. In this article, we review the role of Notch signaling in the hematopoietic system with particular emphasis on lymphocyte development and highlight the similarities in Notch function between Drosophila and mammalian differentiation processes. Recent studies indicating that aberrant NOTCH signaling is (...) frequently linked to the induction of T leukemia in humans will also be discussed. BioEssays 27:1117–1128, 2005. © 2005 Wiley Periodicals, Inc. (shrink)

Higher plant shoot meristems are multicellular structures that are the site of postembryonic organogenesis. Analysis of chimeric plants has indicated that cells in different regions of the meristem can interact with each other so that their activities are coordinated during developmental processes. Correlations have not been demonstrated between events at a molecular level and the interactions observed at a phenotypic level in chimeras. Two recent papers(1,2) address this problem by reporting that expression of the floricaula gene in one region (...) of chimeric snapdragon meristems is sufficient to promote the transition from inflorescence to floral development and to induce the expression of the downstream organ identity genes deficiens and plena throughout the meristem. (shrink)

Numerous liver specific genes are transcriptionally activated by the binding to their promoter or enhancer of Hepatic Nuclear Factor 1 (HNF1). HNF1 contains a variant homeo‐domain and binds to DNA as either a homod‐imer or a heterodimer with the vHNF1 protein. Surprisingly, HNF1 is not restricted to hepatocytes but is expressed in epithelial cells of several endoderm derived organs and in mesoderm derived kidney tubules. Hence, HNF1 alone can not account for the differentiated state of the hepatic cells. In fact, (...) several other liver‐enriched transcription factors have been cloned. The hepatic phenotype could result from the combinatorial. expression of these regulators. Possible involvement of these trans‐acting factors in liver organogenesis and hepatic differentiation is discussed. (shrink)

The recent publications reported in 2022 reveal the possibility of obtaining mouse embryos without the need for egg or sperm. These ‘artificial embryos’ can recapitulate some stages of development ex utero – from neurulation to organogenesis – without implantation. Synthetic mouse embryos might serve as a valuable model to gain further insights into early developmental stages. Indeed, it is expected for these models to be replicated by employing human cells. This promising research raises ethical issues and expands the horizon (...) of ethics in regard to the development of the human embryo. From this point of view, we state some of the new open venues for bioethical research. (shrink)

Large‐scale patterns of correlated growth in development are partially driven by competition for metabolic and informational resources. It is argued that competition between organs for limited resources is an important mesoscale morphogenetic mechanism that produces fitness‐enhancing correlated growth. At the genetic level, the growth of individual characters appears independent, or “modular,” because patterns of expression and transcription are often highly localized, mutations have trait‐specific effects, and gene complexes can be co‐opted as a unit to produce novel traits. However, body parts (...) are known to interact over the course of ontogeny, and these reciprocal exchanges can be an important determinant of developmental outcomes. Genetic mechanisms underlie cell and tissue behaviors that allow organs to communicate with one another, but they also create evolutionarily adaptive competitive dynamics that are driven by physiological and biophysical processes. Advances in the understanding of competitive and closely related coordinative interactions across scales will complement existing research programs that emphasize the role of cellular mechanisms in morphogenesis. Study of the large‐scale order produced by competitive dynamics promises to facilitate advances in basic evolutionary and developmental biology, as well as applied research in fields such as bioengineering and regenerative medicine that aim to regulate patterning outcomes. (shrink)