In some recent papers (G. ‘t Hooft and others), it has been argued that quantum mechanics can arise from classical cellular automata. Nonetheless, G. Shpenkov has proved that the classical wave equation makes it possible to derive a periodic table of elements, which is very close to Mendeleyev’s one, and describe also other phenomena related to the structure of molecules. Hence the classical wave equation complements Schrödinger’s equation, which implies the appearance of a cellular automaton molecular model starting (...) from classical wave equation. The other studies show that the microworld is constituted as a tessellation of primary topological balls. The tessellattice becomes the origin of a submicrospic mechanics in which a quantum system is subdivided to two subsystems: the particle and its inerton cloud, which appears due to the interaction of the moving particle with oncoming cells of the tessellattice. The particle and its inerton cloud periodically change the momentum and hence move like a wave. The new approach allows us to correlate the Klein-Gordon equation with the deformation coat that is formed in the tessellatice around the particle. The submicroscopic approach shows that the source of any type of wave movements including the Klein-Gordon, Schrödinger, and classical wave equations is hidden in the tessellattice and its basic exciations – inertons, carriers of mass and inert properies of matter. We also discuss possible correspondence with Konrad Zuse’s calculating space. (shrink)

Cellular automata (henceforth: CA) are discrete, abstract computational systems that have proved useful both as general models of complexity and as more specific representations of non-linear dynamics in a variety of scientific fields. Firstly, CA are (typically) spatially and temporally discrete: they are composed of a finite or denumerable set of homogeneous, simple units, the atoms or cells. At each time unit, the cells instantiate one of a finite set of states. They evolve in parallel at discrete time steps, (...) following state update functions or dynamical transition rules: the update of a cell state obtains by taking into account the states of cells in its local neighborhood (there are, therefore, no actions at a distance). Secondly, CA are abstract, as they can be specified in purely mathematical terms and implemented in physical structures. Thirdly, CA are computational systems: they can compute functions and solve algorithmic problems. Despite functioning in a different way from traditional, Turing machine-like devices, CA with suitable rules can emulate a universal Turing machine, and therefore compute, given Turing's Thesis, anything computable.... (shrink)

Cells live in dynamic environments that necessitate perpetual adaptation. Since cells have limited resources to monitor external inputs, they are required to maximize the information content of perceived signals. This challenge is not unique to microscopic life: Animals use senses to perceive inputs and adequately respond. Research showed that sensory‐perception is actively shaped by learning and expectation allowing internal cognitive models to “fill in the blanks” in face of limited information. We propose that cells employ analogous strategies and use internal (...) models shaped through the long process of evolutionary adaptation. Given this perspective, we postulate that cells are prone to “misperceptions,” analogous to visual illusions, leading them to incorrectly decode patterns of inputs that lie outside of their evolutionary experience. Mapping cellular misperception can serve as a fundamental approach for dissecting regulatory networks and could be harnessed to modulate cell behavior, a potentially new avenue for therapy. (shrink)

Recall that for any Boolean algebra (BA) A, the cellularity of A is c(A) = sup{|X| : X is a pairwise-disjoint subset of A}. A pseudo-tree is a partially ordered set (T, ≤) such that for every t in T, the set {r ∊ T : r ≤ t} is a linear order. The pseudo-tree algebra on T, denoted Treealg(T), is the subalgebra of ℘(T) generated by the cones {r ∊ T : r ≥ t}, for t in T. We (...) characterize the cellularity of pseudo-tree algebras in terms of cardinal functions on the underlying pseudo-trees. For T a pseudo-tree, c(Treealg(T)) is the maximum of four cardinals c\sbT, ι\sbT, φ\sbT, and μ\sbT : roughly, c\sbT measures the "tallness" of the pseudo-tree T; ι\sbT the "breadth"; φ\sbT the number of "finite branchings"; and μ\sbT the number of places where T "does not branch." We give examples to demonstrate that all four of these cardinals are needed. (shrink)

Depression might be associated with accelerated cellular aging. However, does this result in an irreversible state or is the body able to slow down or recover from such a process? Telomeres are DNA‐protein complexes that protect the ends of chromosomes and generally shorten with age; and therefore index cellular aging. The majority of studies indicate that persons with depression have shorter leukocyte telomeres than similarly aged non‐depressed persons, which may contribute to the observed unfavorable somatic health outcomes in (...) the depressed population. Some small‐scale preliminary studies raise the possibility that behavioral or pharmacological interventions may either slow down or else reverse this accelerated telomere shortening, possibly through increasing the activity of the telomere‐lengthening enzyme telomerase. This paper covers the current state of evidence in the relationship between depression and the telomere‐telomerase system and debates whether depression‐related cellular aging should be considered a reversible process or permanent damage. (shrink)

Unlike eggs and diatoms, most single cells in nature do not have structured shells to provide extensive protection. It is a challenge to artificially confer shell structures on living cells to improve their inherent properties and functions. We discuss four different types of cellular shellizations: man‐made hydrogels, sol‐gels, polyelectrolytes, and mineral shells. We also explore potential applications, such as cell storage, protection, delivery, and therapy. We suggest that shellization could provide another means to regulate and functionalize cells. Specifically, the (...) integration of living cells and non‐living functional shells may be developed as a novel strategy to create “super” or intelligent cells. Unlike biological approaches, this material‐based bio‐interface regulation is inexpensive, effective, and convenient, opening up a novel avenue for cell‐based technologies and practices. (shrink)

This book presents the deterministic view of quantum mechanics developed by Nobel Laureate Gerard 't Hooft. Dissatisfied with the uncomfortable gaps in the way conventional quantum mechanics meshes with the classical world, 't Hooft has revived the old hidden variable ideas, but now in a much more systematic way than usual. In this, quantum mechanics is viewed as a tool rather than a theory. The book presents examples of models that are classical in essence, but can be analysed by the (...) use of quantum techniques, and argues that even the Standard Model, together with gravitational interactions, might be viewed as a quantum mechanical approach to analysing a system that could be classical at its core. He shows how this approach, even though it is based on hidden variables, can be plausibly reconciled with Bell's theorem, and how the usual objections voiced against the idea of 'superdeterminism' can be overcome, at least in principle. This framework elegantly explains - and automatically cures - the problems of the wave function collapse and the measurement problem. Even the existence of an "arrow of time" can perhaps be explained in a more elegant way than usual. As well as reviewing the author's earlier work in the field, the book also contains many new observations and calculations. It provides stimulating reading for all physicists working on the foundations of quantum theory. (shrink)

We exhibit a bridge between the theory of cellular categories, used in algebraic topology and homological algebra, and the model-theoretic notion of stable independence. Roughly speaking, we show that the combinatorial cellular categories (those where, in a precise sense, the cellular morphisms are generated by a set) are exactly those that give rise to stable independence notions. We give two applications: on the one hand, we show that the abstract elementary classes of roots of Ext studied by (...) Baldwin–Eklof–Trlifaj are stable and tame. On the other hand, we give a simpler proof (in a special case) that combinatorial categories are closed under 2-limits, a theorem of Makkai and Rosický. (shrink)

The target article on cellular mechanisms of long-term depression appears to have been well received by most authors of the relevant commentaries. This may be due to the fact that this review aimed to give a general account of the topic, rather than just describe previous work of the present author. The present response accordingly only raises questions of major interest for future research.

It has been known for long time that the cosmic sound wave was there since the early epoch of the Universe. Signatures of its existence are abound. However, such a sound wave model of cosmology is rarely developed fully into a complete framework. This paper can be considered as our second attempt towards such a complete description of the Universe based on soliton wave solution of cosmological KdV equation. Then we advance further this KdV equation by virtue of Cellular (...) Automaton method to solve the PDEs. We submit wholeheartedly Robert Kurucz’s hypothesis that Big Bang should be replaced with a finite cellular automaton universe with no expansion. Nonetheless, we are fully aware that our model is far from being complete, but it appears the proposed cellular automaton model of the Universe is very close in spirit to what Konrad Zuse envisaged long time ago. It is our hope that the new proposed method can be verified with observation data. But we admit that our model is still in its infancy, more researches are needed to fill all the missing details. (shrink)

Ranging from miniaturized biological robots to organoids, multi-cellular engineered living systems (M-CELS) pose complex ethical and societal challenges. Some of these challenges, such as how to best distribute risks and benefits, are likely to arise in the development of any new technology. Other challenges arise specifically because of the particular characteristics of M-CELS. For example, as an engineered living system becomes increasingly complex, it may provoke societal debate about its moral considerability, perhaps necessitating protection from harm or recognition of (...) positive moral and legal rights, particularly if derived from cells of human origin. The use of emergence-based principles in M-CELS development may also create unique challenges, making the technology difficult to fully control or predict in the laboratory as well as in applied medical or environmental settings. In response to these challenges, we argue that the M-CELS community has an obligation to systematically address the ethical and societal aspects of research and to seek input from and accountability to a broad range of stakeholders and publics. As a newly developing field, M-CELS has a significant opportunity to integrate ethically responsible norms and standards into its research and development practices from the start. With the aim of seizing this opportunity, we identify two general kinds of salient ethical issues arising from M-CELS research, and then present a set of commitments to and strategies for addressing these issues. If adopted, these commitments and strategies would help define M-CELS as not only an innovative field, but also as a model for responsible research and engineering. (shrink)

This paper is an introduction into the theory of cellular spaces. From the more general model of nets of abstract cells which are interpreted by finite automata, it is shown how the model of cellular spaces is achieved by specialization. Cellular spaces are extremely homogeneous in function and in geometry. The relation between local and global behavior is regarded as the main topic of the theory. After a formal definition of cellular spaces, it is shown that (...) not all functions of the configuration space are induced by cellular spaces. In addition, the Garden-of-Eden problem is discussed, and a simple self-reproduction property is explained. (shrink)

Skeletal muscle formation is studied in vitro with myogenic cell lines and primary muscle cell cultures, and in vivo with embryos of several species. We review several of the notable advances obtained from studies of cultured cells, including the recognition of myoblast diversity, isolation of the MyoD family of muscle regulatory factors, and identification of promoter elements required for muscle‐specific gene expression. These studies have led to the ideas that myoblast diversity underlies the formation of the multiple types of fast (...) and slow muscle fibers, and that myogenesis is controlled by a combination of ubiquitous and muscle‐specific transcriptional regulators that may be different for each gene. We further review some unexpected results that have been obtained when ideas from work in culture have been tested in developing animals. The studies in vivo point to additional molecular and cellular mechanisms that regulate muscle formation in the animal. (shrink)

The study of cellular senescence and proliferative lifespan is becoming increasingly important because of the promises of autologous cell therapy, the need for model systems for tissue disease and the implication of senescent cell phenotypes in organismal disease states such as sarcopenia, diabetes and various cancers, among others. Here, we explain the concepts of proliferative cellular lifespan and cellular senescence, and we present factors that have been shown to mediate cellular lifespan positively or negatively. We review (...) much recent literature and present potential molecular mechanisms by which lifespan mediation occurs, drawing from the fields of telomere biology, metabolism, NAD+ and sirtuin biology, growth factor signaling and oxygen and antioxidants. We conclude that cellular lifespan and senescence are complex concepts that are governed by multiple independent and interdependent pathways, and that greater understanding of these pathways, their interactions and their convergence upon specific cellular phenotypes may lead to viable therapies for tissue regeneration and treatment of age‐related pathologies, which are caused by or exacerbated by senescent cells in vivo. (shrink)

Central nervous system (CNS)Abbreviations: CNS=central nervous system; PNS=peripheral nervous system; MS=multiple sclerosis; MBP=myelin basic protein; MHC=major histocompatibility complex; EAE=experimental allergic encephalomyelitis; O‐2A=oligodendrocyte‐type 2 astrocyte; GC=galactocerebroside; GFAP=glial fibrillary acidic protein; FGF=fibroblast growth factor; IGF1=insulin‐like growth factor. regeneration is a subject of great interest, particularly in diseases causing a dramatic loss of neurons. However, some CNS diseases do not affect neurons but damage other cells, such as the myelin‐forming cells — called oligodendrocytes — which are also crucial to the harmonious function of (...) the nervous system. Diseases in which oligodendrocytes and myelin are attacked can cause devastating neurological dysfunction which is sometimes followed by recovery and myelin repair or remyelination. The question of the regeneration potential of oligodendrocytes in experimental and human demyelinating diseases such as multiple sclerosis has been debated for a long time. Present evidence suggests that oligodendrocyte precursor cells persist in the adult CNS and that oligodendrocyte regeneration can occur but may be limited by ongoing disease processes. Here we will briefly review recent advances which have broadened our understanding of the cellular and molecular events of CNS remyelination. (shrink)

The occurrence of oscillatory behaviours in living cells can be viewed as a visible consequence of stable, regulatory homeostatic cycles. Therefore, they may be used as experimental windows on the underlying physiological mechanisms. Recent studies show that growing pollen tubes are an excellent biological model for these purposes. They unite experimental simplicity with clear oscillatory patterns of both structural and temporal features, most being measurable during real‐time in live cells. There is evidence that these cellular oscillators involve an integrated (...) input of plasma membrane ion fluxes, and a cytosolic choreography of protons, calcium and, most likely, potassium and chloride. In turn, these can create positive feedback regulation loops that are able to generate and self‐sustain a number of spatial and temporal patterns. Other features, including cell wall assembly and rheology, turgor, and the cytoskeleton, play important roles and are targets or modulators of ion dynamics. Many of these features have similarities with other cell types, notably with apical‐growing cells. Pollen tubes may thus serve as a powerful model for exploring the basis of cell growth and morphogenesis. BioEssays 23:86–94, 2001. © 2001 John Wiley & Sons, Inc. (shrink)

The capacity of cells and organisms to respond to external stimuli and to maintain stability in order to survive decreases progressively during ageing. The mitogenic and stimulatory effects of growth factors, hormones and other agents are reduced significantly during cellular ageing. The sensitivity of ageing cells to toxic agents including antibiotics, phorbol esters, radiations and heat shock increases. This failure of homeostasis during cellular ageing does not appear to be due to any quantitative and qualitative defects in the (...) receptor systems. Instead, metabolic defects in the pathways of macromolecular synthesis may be the basis of altered cellular responsiveness during ageing. (shrink)

Mitochondria have been fundamental to the eco‐physiological success of eukaryotes since the last eukaryotic common ancestor (LECA). They contribute essential functions to eukaryotic cells, above and beyond classical respiration. Mitochondria interact with, and complement, metabolic pathways occurring in other organelles, notably diversifying the chloroplast metabolism of photosynthetic organisms. Here, we integrate existing literature to investigate how mitochondrial metabolism varies across the landscape of eukaryotic evolution. We illustrate the mitochondrial remodelling and proteomic changes undergone in conjunction with major evolutionary transitions. We (...) explore how the mitochondrial complexity of the LECA has been remodelled in specific groups to support subsequent evolutionary transitions, such as the acquisition of chloroplasts in photosynthetic species and the emergence of multicellularity. We highlight the versatile and crucial roles played by mitochondria during eukaryotic evolution, extending from its huge contribution to the development of the LECA itself to the dynamic evolution of individual eukaryote groups, reflecting both their current ecologies and evolutionary histories. (shrink)

Cellular Automata (CA) based simulations are widely used in a great variety of domains, fromstatistical physics to social science. They allow for spectacular displays and numerical predictions. Are they forall that a revolutionary modeling tool, allowing for “direct simulation”, or for the simulation of “the phenomenon itself”? Or are they merely models "of a phenomenological nature rather than of a fundamental one”? How do they compareto other modeling techniques? In order to answer these questions, we present a systematic exploration (...) of CA’s various uses. (shrink)

Conceptual developments have defined concrete questions about the timing and precise location of cellular pattern formation. Plants in general, and the trichomes of Arabidopsis in particular, are remarkably suited for research on these problems. Genetic analysis requires the quantitative characterizations of the developmental processes by which patterning occurs. Larkin et al.(1) have provided measures of the non‐random distances between trichomes. They have also obtained evidence about the cell lineages leading to trichome development, and this evidence constrains the possible role (...) of intracellular programs. Continued genetic analysis may call for the identification of mutations that are expressed only during development and whose effects are corrected before the phenotype matures. (shrink)

The molecular cloning of new neuroactive growth factors and their receptors has greatly enhanced our understanding of important interactions among receptors and singnaling molecules. These studies have begun to illuminate some of the mechanisms that allow for specificity in neuronal signaling. Model cell systems, such as the PC‐12 pheochromocytoma cell line, express receptors for these different neurotirophic factors, leading to comparisons of signaling pathways for these factors. Upon binding their ligands, these receptors undergo phosphorylation on tyrosine residues, which directs their (...) interaction with signaling proteins containing src homology (SH2) domains, sequences that mediate associations with tyrosine‐phosphorylated proteins. These SH2 proteins translate the tyrosine kinase activity of receptors into downstream events that result in the specific cellular response. Investigations such as these have revealed that molecular specificity in signaling pathways may arise from combinatorial diversity in interactions between receptors and key regulatory proteins. (shrink)

To cope with the water deficit resulting from saline environment, plant cells accumulate three kinds of osmotica: salts, small organic solutes and hydrophillic, glycine-rich proteins. Salts such as NaCl are cheap and available but has ion toxicity in high concentrations. Small organic solutes are assistant osmotica, their main function is to protect cytoplasmic enzymes from ionic toxicity and maintain the integrity of cellular membranes. Hydrophillic, glycine-rich proteins are the most effective osmotica, they have some characteristics to avoid crystallization even (...) in high concentration, but because they are expensive they are not as commonly used as salts or organic solutes. In addition there is the question of whether the genetic information for growth in saline environment is present in all kinds of plants, both halophytes and nonhalophytes. (shrink)

In this paper I explore the question of how artificial life might be used to get a handle on philosophical issues concerning the mind-body problem. I focus on questions concerning what the physical precursors were to the earliest evolved versions of intelligent life. I discuss how cellular automata might constitute an experimental platform for the exploration of such issues, since cellular automata offer a unified framework for the modeling of physical, biological, and psychological processes. I discuss what it (...) would take to implement in a cellular automaton the evolutionary emergence of cognition from non-cognitive artificial organisms. I review work on the artificial evolution of minimally cognitive organisms and discuss how such projects might be translated into cellular automata simulations. (shrink)

Let T be an infinite pseudo-tree. In [2], we showed that the cellularity of the pseudo-tree algebra Treealg(T) was the maximum of four cardinals cT, lT, ϕT, and μT: roughly, cT is the "tallness" of T; lT is the "width" of T; ϕ is the number of "points of finite branching" in T; and μ is the number of "sections of no branching" in T. Here we ask: which inequalities among these four cardinals may be satisfied, in some sense, by (...) a pseudo-tree? We show that the possible inequalities among cT, lT, ϕT, and μT attained by pseudo-trees T are closely related to the existence of generalized Suslin trees. (shrink)

Mesodermal cell differentiation begins in response to an inductive interaction early in frog development. In parallel with the recent finding that certain peptide growth factors can induce mesoderm, early cellular and genetic responses to the induction have been discovered. I review here recent work on these responses, work that aims to understand how cells respond to inducers to form the complex pattern of the vertebrate mesoderm.

The establishment of a functional vascular system requires multiple complex steps throughout embryogenesis, from endothelial cell (EC) specification to vascular patterning into venous and arterial hierarchies. Following the initial assembly of ECs into a network of cord‐like structures, vascular expansion and remodeling occur rapidly through morphogenetic events including vessel sprouting, fusion, and pruning. In addition, vascular morphogenesis encompasses the process of lumen formation, critical for the transformation of cords into perfusable vascular tubes. Studies in mouse, zebrafish, frog, and human endothelial (...) cells have begun to outline the cellular and molecular requirements underlying lumen formation. Although the lumen can be generated through diverse mechanisms, the coordinated participation of multiple conserved molecules including transcription factors, small GTPases, and adhesion and polarity proteins remains a fundamental principle, leading us closer to a more thorough understanding of this complex event. (shrink)

Brain arteriovenous malformations (bAVMs) are abnormal vessels that are prone to rupture, causing life-threatening intracranial bleeding. The mechanism of bAVM formation is poorly understood. Nevertheless, animal studies revealed that gene mutation in endothelial cells (ECs) and angiogenic stimulation are necessary for bAVM initiation. Evidence collected through analyzing bAVM specimens of human and mouse models indicate that cells other than ECs also are involved in bAVM pathogenesis. Both human and mouse bAVMs vessels showed lower mural cell-coverage, suggesting a role of pericytes (...) and vascular smooth muscle cells (vSMCs) in bAVM pathogenesis. Perivascular astrocytes also are important in maintaining cerebral vascular function and take part in bAVM development. Furthermore, higher inflammatory cytokines in bAVM tissue and blood demonstrate the contribution of inflammatory cells in bAVM progression, and rupture. The goal of this paper is to provide our current understanding of the roles of different cellular loci in bAVM pathogenesis. (shrink)

The ability to memorize changes in the environment is present at all biological levels, from social groups and individuals, down to single cells. Trans‐generational memory is embedded subcellularly through genetic and epigenetic mechanisms. Evidence that cells process and remember features of the immediate environment using protein sensors is reviewed. It is argued that this mnemonic ability is encapsulated within the protein conformational space and lasts throughout its lifetime, which can overlap with the lifespan of the organism. Means to determine diachronic (...) changes in protein activity are presented. (shrink)

During the early Cambrian period metazoan life forms diverged at an accelerated rate to occupy multiple ecological niches on earth. A variety of explanations have been proposed to address this major evolutionary phenomenon termed the “Cambrian explosion.” While most hypotheses address environmental, developmental, and ecological factors that facilitated evolutionary innovations, the biological basis for accelerated emergence of species diversity in the Cambrian period remains largely conjectural. Herein, we posit that morphogenesis by self‐organization enables the uncoupling of genomic mutational landscape from (...) phenotypic diversification. Evidence is provided for a two‐tiered interpretation of genomic changes in metazoan animals wherein mutations not only impact upon function of individual cells, but also alter the self‐organization outcome during developmental morphogenesis. We provide evidence that the morphological impacts of mutations on self‐organization could remain repressed if associated with an unmet negative energetic cost. We posit that accelerated morphological diversification in transition to the Cambrian period has occurred by emergence of dormant (i.e., reserved) morphological novelties whose molecular underpinnings were seeded in the Precambrian period. (shrink)

Oxycholesterols (OS) are formed from cholesterol or its immediate precursors by enzymatic or free radical action in vivo, or they may be derived from food. OS exhibit a wide spectrum of biological activities. In OS cytotoxicity, several mechanisms seem to be involved: e.g. inhibition of HMG‐CoA reductase activity, antiproliferative action, apoptosis induction, replacement of cholesterol by OS in membranes followed by changes in cellular membrane structure and functionality, and immune system functions alteration. Furthermore, OS may be mutagenic and carcinogenic (...) and may serve as intracellular signaling or regulatory molecules. Here we review OS cellular activities with special attention to the cytotoxic action in vivo and in vitro using experimental models. BioEssays 28: 387–398, 2006. © 2006 Wiley Periodicals, Inc. (shrink)

Louise Brown's birth in 1978 heralded a new era not just in reproductive technology, but in the relationship between science, cells, and society. For the first time, human embryos could be created, selected, studied, manipulated, frozen, altered, or destroyed, outside the human body. But with this possibility came a plethora of ethical questions. Is it acceptable to destroy a human embryo for the purpose of research? Or to create an embryo with the specific purpose of destroying it for research? In (...) an attempt to construct ethical and legal frameworks for the new era of cellular reprogramming, legislators and ethicists have tried to distinguish between different kinds of biological entity. We treat cells differently depending on whether they are human or animal, somatic cells or gametes, and on whether they are embryos or not. But this approach to the ethics of cellular reprogramming is doomed to failure for the simple reason that cellular reprogramming in itself destroys the distinctions that the law requires to function. In this article, we explore the historical trajectory of cellular reprogramming and its relationship with ethics and society. We suggest that the early hype of embryo research has not obviously fulfilled expectations, but since new avenues of research are continuously opening, it is hard to say definitely that these promises have been broken. We explore the forthcoming challenges posed by the creation of DNA from scratch in the laboratory, and the implications of this for understandings of identity, privacy, and reproduction. We conclude that while ethics used to seek answers in biological facts, this is no longer possible, and a new approach is required. (shrink)

Methods developed in a previous paper are employed to define an exact correspondence between the states of a deterministic cellular automaton in 1+1 dimensions and those of a bosonic quantum field theory. The result may be used to argue that quantum field theories may be much closer related to deterministic automata than what is usually thought possible.

Most cells communicate with their immediate neighbors through the exchange of cytosolic molecules such as ions, second messengers and small metabolites. This activity is made possible by clusters of intercellular channels called gap junctions, which connect adjacent cells. In terms of molecular architecture, intercellular channels consist of two channels, called connexons, which interact to span the plasma membranes of two adjacent cells and directly join the cytoplasm of one cell to another. Connexons are made of structural proteins named connexins, which (...) compose a multigene family. Connexin channels participate in the regulation of signaling between developing and differentiated cell types, and recently there have been some unexpected findings. First, unique ionic‐ and size‐selectivities are determined by each connexin; second, the establishment of intercellular communication is defined by the expression of compatible connexins; third, the discovery of connexin mutations associated with human diseases and the study of knockout mice have illustrated the vital role of cell‐cell communication in a diverse array of tissue functions. (shrink)

The introduction of electron microscopy profoundly altered biomedical research, providing a tool for a more detailed but at the same time a spatially and temporally more restricted visual analysis. Examining the case study of Golgi apparatus research in the 1950s and 1960s, it will be shown how microscopists handled these challenges, and how these confrontations modified the general concept of cellular organization. This will also shed light on the artifact debate and on the question of scientific realism in the (...) field of microscopy. (shrink)

This article reviews recent findings that bear on the mechanism(s) of tumor‐specific Lyt‐1+2− T cell‐mediated tumor eradication in vivo A tumor‐immune Lyt‐1+2− T cell subset has been identified which is distinct from T cells mediating in vitro cytotoxicity (Lyt‐1+2+/1−2+). The Lyt‐1+2− cells have a crucial role in rejecting tumor cells when adoptively transferred into T cell‐deprived B cell mice. This indicates that Lyt‐1+2− T cells do not necessarily require recruitment of the host's cytotoxic T cell precursors for implementation of in (...) vivo immunity. Instead, this T cell subset exerts its anti‐tumor effect in collaboration with macrophages as shown with an in vivo tumor cell culture system utilizing a diffusion chamber. A pathway of Lyt‐1+2− T cell‐macrophage interaction leading to tumor cell killing is discussed in terms of its probable relevance to the eradication of tumor cell masses consisting of tumor cells expressing quantitatively and/or qualitatively different tumor antigens. (shrink)

A comparison of six alternative definitions of the term 'cellular pathway' against the background of ontological realism.

Alzheimer's disease results from the degeneration of neurons. Degenerating nerve cells express atypical proteins, and amyloid is deposited. We suggest that some of these events are strongly influenced by genetic factors and age. Animal models should be useful in investigating the pathogenic mechanisms that lead to the brain abnormalities seen in this disease.

The study of adhesion plaques in normal and transformed cells provides a series of phenotypic markers by which the process of transformation can be followed. Several proteins which are concentrated in adhesion plaques have now been identified; a few of these can act as targets for tyrosine kinase. In an attempt to characterize the relationship between tyrosine phosphorylation and cell transformation, the reactions of three such proteins – vinculin, talin and integrin – with a range of tyrosine kinase oncogene products (...) have been studied in detail. (shrink)