Cofilin-mediated F-actin severing is regulated by the Rap GTPase and controls the cytoskeletal dynamics that drive lymphocyte spreading and BCR microcluster formation

When lymphocytes encounter APCs bearing cognate Ag, they spread across the surface of the APC to scan for additional Ags. This is followed by membrane contraction and the formation of Ag receptor microclusters that initiate the signaling reactions that lead to lymphocyte activation. Breakdown of the submembrane cytoskeleton is likely to be required for the cytoskeleton reorganization that drives cell spreading and for removing physical barriers that limit Ag receptor mobility. In this report, we show that Ag receptor signaling via the Rap GTPases promotes the dephosphorylation and activation of the actin-severing protein cofilin and that this results in increased severing of cellular actin filaments. Moreover, we show that this cofilin-mediated actin severing is critical for the changes in actin dynamics that drive B and T cell spreading, for the formation of BCR microclusters, and for the increased mobility of BCR microclusters within the plasma membrane after BCR engagement. Finally, using a model APC, we show that activation of this Rap-cofilin signaling module controls the amount of Ag that is gathered into BCR microclusters and that this is directly related to the magnitude of the resulting BCR signaling that is initiated during B cell-APC interactions. Thus, Rap-dependent activation of cofilin is critical for the early cytoskeletal changes and BCR reorganization that are involved in APC-dependent lymphocyte activation.     

Origins of the nucleate organisms II

A revised version of an earlier phylogenetic model for the eukaryotes is presented. It is postulated that mitosis, phagotrophy, the mitochondrion, the flagellum, sexual reproduction, and the chloroplast are so complex that it is improbable that they evolved de novo more than once. It is assumed that their distribution among existing organisms is a reflection of their order of appearance in evolutionary history. Their distribution suggests that the nucleate organisms evolved through the sequence: amoeba, amoeboflagellate, sexual amoeboflagellate, and that the chloroplast first appeared in sexual flagellates. Sequence data indicate that the sexual amoeboflagellates gave rise to a line of holozoic protozoans that culminated in the metazoans. An amoeba-metazoan line can be envisaged as representing the mainstream of eukaryote evolution. Sequence data indicate that the sexual flagellates bearing mastigonemes, the eumycetes, and the metaphytes diverged from such a line, and in that order. Cytological and biochemical data strongly suggest that the rhodophytes and metaphytes derive from a common algal ancestor, that this ancestor would have arisen from a sexual, biflagellate, holozoic protozoan lacking mastigonemes, and that it would have been closely related to the most recent monocellular ancestor of the metazoans. Sequence data indicate that the chloroplast derives from an ancestral blue-green bacterium that was originally an endosymbiont within a phagotrophic protozoan. Thus the metaphytes may be secondary in a series of organisms able to produce chlorophyll a. There is evidence that subsequently a fully developed chloroplast able to produce chlorophylls a and b was transferred by a further symbiosis to a holozoic euglenoid protozoan; the chloroplast of the euglenophytes is so similar to that of the chlorophytes, but the morphologies of these algae are so different, it was postulated that euglenophytes arose through symbiosis between a euglenid and a chlorophyte. It is proposed here that the distribution of phylogenetic features among organisms bearing mastigonemes indicates that the euglenophytes gave rise to dinophytes, cryptophytes, and all other organisms bearing mastigonemes. Thus the algae bearing mastigonemes may be tertiary in a series of organisms able to produce chlorophyll a. It is postulated that the production of chlorophyll b in algae, and the stacking of thylakoids first appeared in a line from rhodophytes to chlorophytes, and that replacement of chlorophyll b by chlorophyll c₂ occurred in a line from euglenophytes to dinophytes. To account for the presence of biliproteins in rhodophytes and cryptophytes, it is proposed that the putative transfer of the chloroplast from chlorophytes to euglenophytes occurred before a loss of biliproteins in the metaphyte line, and that the primordial euglenophytes, dinophytes, and cryptophytes were able to produce biliproteins; subsequently, biliprotein production was abandoned in all algae except rhodophytes and cryptophytes. The interrelationships of the chytrids, eumycetes, and oomycetes remain obscure. However, the model is consistent with the hypothesis that the chytrids represent ancestors to the eumycetes, and that the eumycete line and the oomycete-hyphochytrid group of fungi arose independently. The distribution of phagotrophy, biflagellate form, and sexuality suggests that the paired form of flagella first appeared in asexual amoeboflagellates, and became stabilised in sexual amoeboflagellates. The overall model is in accord with sequence evidence that the genomes of the nucleus, mitochondrion, and chloroplast derive from different genetic sources in ancestral prokaryotes, and is consistent with the hypothesis that the mitochondrion and chloroplast were acquired through endosymbioses initiated by phagotrophic inclusion of an aerobic bacterium, and a blue-green bacterium, respectively. Avenues for phylogenetic and sequence investigation for testing the model are suggested.     

Bioethics and conflicts of interest

Bioethics has been subject to considerable social criticism in recent years. One criticism that has caused particular discomfort in the bioethics community is that bioethicists, because of the way their work is funded, are involved in profound conflicts of interest that undermine their title to be considered independent moral commentators on developments in biomedicine and biotechnology. This criticism draws its force from the assumption that bioethics is, or ought to be, a type of normative social criticism. Versions of this criticism come from both the political left and right. For instance, such criticisms include allegations that bioethics is inherently socially conservative, that it is inherently “pro-technology”, that it lays spurious claims to moral and social authority and expertise, that its focus on autonomy links it to neoliberal theories of choice, and that it is an ideological mystification of real social relationships and political power. This commentary paper analyses the problem of bioethical conflict of interest, and argues that the types of conflict of interest facing bioethics are inherent to the role of “public intellectual” that bioethicists generally wish to assume. The paper defends this conception of the role of the bioethicist, arguing that bioethicists should be interested and openly so.     

Autopoiesis, Life, Mind and Cognition: Bases for a Proper Naturalistic Continuity

The strong version of the life-mind continuity thesis claims that mind can be understood as an enriched version of the same functional and organizational properties of life. Contrary to this view, in this paper I argue that mental phenomena offer distinctive properties, such as intentionality or representational content, that have no counterpart in the phenomenon of life, and that must be explained by appealing to a different level of functional and organizational principles. As a strategy, and following Maturana’s autopoietic theory of cognition, I introduce a conceptual distinction between mind and cognition. I argue that cognition corresponds to the natural behaviour that every living being exhibits in the realization of its existence, and that, viewed in that way, cognition is a dynamic process of structural coupling that, unlike mental phenomena, involves no representational contents. On the basis of this distinction, I try to show that while life suffices for cognition, it does not suffice for mind. That is, that the strong continuity is not between life and mind but between life and cognition.     

Mature glycosylation and trafficking of nicastrin modulate its binding to presenilins

Nicastrin is an integral component of the high molecular weight presenilin complexes that control proteolytic processing of the amyloid precursor protein and Notch. We report here that nicastrin is most probably a type 1 transmembrane glycoprotein that is expressed at moderate levels in the brain and in cultured neurons. Immunofluorescence studies demonstrate that nicastrin is localized in the endoplasmic reticulum, Golgi, and a discrete population of vesicles. Glycosidase analyses reveal that endogenous nicastrin undergoes a conventional, trafficking-dependent maturation process. However, when highly expressed in transfected cells, there is a disproportionate accumulation of the endo-beta-N-acetylglucosaminidase H-sensitive, immature form, with no significant increase in the levels of the fully mature species. Immunoprecipitation revealed that presenilin-1 interacts preferentially with mature nicastrin, suggesting that correct trafficking and co-localization of the presenilin complex components are essential for activity. These findings demonstrate that trafficking and post-translational modifications of nicastrin are tightly regulated processes that accompany the assembly of the active presenilin complexes that execute gamma-secretase cleavage. These results also underscore the caveat that simple overexpression of nicastrin in transfected cells may result in the accumulation of large amounts of the immature protein, which is apparently unable to assemble into the active complexes capable of processing amyloid precursor protein and Notch.     

Vasoactive intestinal polypeptide and glucagon: stimulation of adenylate cyclase activity via distinct receptors in liver and fat cell membranes

Vasoactive intestinal polypeptide (VIP), a peptide hormone that is chemically and biologically related to glucagon and secretin, stimulates the activity of adenylate cyclase in liver and fat cell membranes. Effects of combinations of VIP with glucagon and secretin at concentrations that maximally activate adenylate cyclase suggest that in adipose tissue, the three hormones act on the same enzyme, whereas in liver, VIP and secretin activate a common enzyme that is distinct from that responding to glucagon. Studies with radioiodinated derivatives of VIP and glucagon indicate that these hormones interact with separate receptors. Secretin, which gives a maximal stimulation of adenylate cyclase activity virtually identical to that elicited by VIP, inhibits the binding of the latter to its receptor. However, the apparent affinity of secretin for adenylate cyclase and for the VIP receptor is about two order of magnitude lower than that of VIP. It is suggested that VIP and secretin may activate adenylate cyclase via a common receptor.     

Dissociation of conditioned taste avoidance from conditioned disgust reactions induced by wheel running in rats

It is well established that wheel running in rats produces conditioned taste avoidance; that is, rats that run in wheels after consuming a novel-tasting solution later consume less of that solution than rats that do not run. In experiment 1, we found that wheel running also produces conditioned disgust reactions, indicated by gapes elicited by both the taste and context that were experienced before running. Experiment 2 showed that the conditioned disgust reactions were likely not due to running itself but to a by-product of running, the rocking of the wheel that occurs when the running stops. When rocking was reduced, the disgust reactions were also reduced, but consumption of the taste solution was not changed, showing dissociation of conditioned taste avoidance and disgust. These findings indicate that the taste avoidance induced by wheel running itself is more like the taste avoidance produced by rewarding drugs than that produced by nausea-inducing drugs.     

Optimal Information Transfer in the Cortex through Synchronization

In recent experimental work it has been shown that neuronal interactions are modulated by neuronal synchronization and that this modulation depends on phase shifts in neuronal oscillations. This result suggests that connections in a network can be shaped through synchronization. Here, we test and expand this hypothesis using a model network. We use transfer entropy, an information theoretical measure, to quantify the exchanged information. We show that transferred information depends on the phase relation of the signal, that the amount of exchanged information increases as a function of oscillations in the signal and that the speed of the information transfer increases as a function of synchronization. This implies that synchronization makes information transport more efficient. In summary, our results reinforce the hypothesis that synchronization modulates neuronal interactions and provide further evidence that gamma band synchronization has behavioral relevance.     

Progress toward a general species concept

New insights in the speciation process and the nature of "species" that accumulated in the past decade demand adjustments of the species concept. The standing of some of the most broadly accepted or most innovative species concepts in the light of the growing evidence that reproductive barriers are semipermeable to gene flow, that species can differentiate despite ongoing interbreeding, that a single species can originate polyphyletically by parallel evolution, and that uniparental organisms are organised in units that resemble species of biparental organisms is discussed. As a synthesis of ideas in existing concepts and the new insights, a generalization of the genic concept is proposed that defines species as groups of individuals that are reciprocally characterized by features that would have negative fitness effects in other groups and that cannot be regularly exchanged between groups upon contact. The benefits of this differential fitness species concept are that it classifies groups that keep differentiated and keep on differentiating despite interbreeding as species, that it is not restricted to specific mutations or mechanisms causing speciation, and that it can be applied to the whole spectrum of organisms from uni- to biparentals.     

The Sonic Hedgehog-Gli pathway regulates dorsal brain growth and tumorigenesis.

The mechanisms that regulate the growth of the brain remain unclear. We show that Sonic hedgehog (Shh) is expressed in a layer-specific manner in the perinatal mouse neocortex and tectum, whereas the Gli genes, which are targets and mediators of SHH signaling, are expressed in proliferative zones. In vitro and in vivo assays show that SHH is a mitogen for neocortical and tectal precursors and that it modulates cell proliferation in the dorsal brain. Together with its role in the cerebellum, our findings indicate that SHH signaling unexpectedly controls the development of the three major dorsal brain structures. We also show that a variety of primary human brain tumors and tumor lines consistently express the GLI genes and that cyclopamine, a SHH signaling inhibitor, inhibits the proliferation of tumor cells. Using the in vivo tadpole assay system, we further show that misexpression of GLI1 induces CNS hyperproliferation that depends on the activation of endogenous Gli1 function. SHH-GLI signaling thus modulates normal dorsal brain growth by controlling precursor proliferation, an evolutionarily important and plastic process that is deregulated in brain tumors.     

Role of the Spatzle Pro-domain in the generation of an active toll receptor ligand

The cytokine Sp?tzle is the ligand for Drosophila Toll, the prototype of an important family of membrane receptors that function in embryonic patterning and innate immunity. A dimeric precursor of Sp?tzle is processed by an endoprotease to produce a form (C-106) that cross-links Toll receptor ectodomains and establishes signaling. Here we show that before processing the pro-domain of Sp?tzle is required for correct biosynthesis and secretion. We mapped two loss-of-function mutations of Sp?tzle to a discrete site in the pro-domain and showed that the phenotype arises because of a defect in biosynthesis rather than signaling. We also report that the pro-domain and C-106 remain associated after cleavage and that this processed complex signals with the same characteristics as the C-terminal fragment. These results suggest that before activation the determinants on C-106 that bind specifically to Toll are sequestered by the pro-domain and that proteolytic processing causes conformational rearrangements that expose these determinants and enables binding to Toll. Furthermore, we show that the pro-domain is released when the Toll extracellular domain binds to the complex, a finding that has implications for the generation of a signaling-competent Toll dimer.     

Energy allocation in the cladoceran Daphnia magna Straus,under starvation and refeeding

Summary Models incorporating the energetics of individual daphnids (Cladocera) have been developed to predict the effect of environmental variables, particularly food availability, on population dynamics. One of them, that of Kooijman (1986), assumes that all assimilated energy enters a storage compartment prior to use in production and metabolism, and that under starvation the stores are used to support maintenance, reproduction and somatic growth, in that order of priority. This predicts that, under starvation, reproduction and growth will continue for a time, and that after they cease death will be immediate. Another model, that of McCauley et al. (1990), assumes that assimilated energy is used directly for maintenance and production, and that stores are accumulated to support maintenance metabolism under starvation. This predicts that growth and reproduction should cease immediately upon starvation and that death will not be immediate. We have carried out laboratory experiments, manipulating starvation time, on Daphnia magna to distinguish between these two models. The results support features of both models in that reproduction, but not growth, ceases upon starvation. We therefore developed a third model in which both maintenance and growth are supported from stores under starvation, with maintenance taking priority over growth under these conditions.     

Control of meta-cleavage degradation of 4-hydroxyphenylacetate in Pseudomonas putida.

Synthesis of enzymes of the 4-hydroxyphenylacetate meta-cleavage pathway was studied in Pseudomonas putida wild-type strain P23X1 (NCIB 9865) and mutant strains which had either structural or regulatory gene mutations. Induction studies with mutant strains each defective in an enzyme of the pathway showed that 4-hydroxyphenylacetate induced the hydroxylase and that 3,4-dihydroxyphenylacetate induced the 2,3-oxygenase, aldehyde dehydrogenase, isomerase, decarboxylase, and hydratase. This showed that the hydroxylase structural gene does not exist in an operon that contains any other structural gene of this meta pathway. Studies of mutant strains that synthesized constitutively the 2,3-oxygenase and subsequent enzymes suggested that the regulation of synthesis of these enzymes was coincident, and, in such strains, the hydroxylase was inducible only. Observations made with a putative polarity mutant that lacked 2,3-oxygenase activity suggested that the structural genes encoding this enzyme and subsequent enzymes of the pathway exist in the same operon. Studies of a regulatory mutant strain that was defective in the induction of the 2,3-oxygenase and subsequent enzymes suggest that the 2,3-oxygenase operon is under positive control.     

Are We all Natural Dualists? A Cognitive Developmental Approach*

The article takes to task the well-established anthropological claim that non-Western peoples are free from the traps of dualistic thinking. Although Vezo informants in Madagascar produce statements that could be used to support such a claim, experimental procedures that target their inferential reasoning reveal that they systematically differentiate between mind and body, between the biological processes that determine the organism and the social processes that shape personhood. This suggests that there is a significant discrepancy between people's explicit linguistic statements and their implicit theoretical knowledge. Moreover, developmental data show that such implicit theoretical presuppositions are essential to the production and transmission of cultural knowledge. Thus, Vezo children, who do not as yet differentiate between the biological mechanism of birth and the social mechanism of nurture, are still unable to grasp a salient aspect of Vezo culture, namely the causally integrated set of ideas that guide the way adults classify the social world. These findings have significant theoretical and methodological implications for the constitution of anthropological knowledge.     

Innate Ideas as a Naturalistic Source of Metaphysical Knowledge

This article starts from the assumption that there are various innate contributions to our view of the world and explores the epistemological implications that follow from this. Specifically, it explores the idea that if certain components of our worldview have an evolutionary origin, this implies that these aspects accurately depict the world. The simple version of the argument for this conclusion is that if an aspect of mind is innate, it must be useful, and the most parsimonious explanation for its usefulness is that it accurately depicts the world. There are a number of important criticisms of this argument. These include the idea that evolutionary justifications are circular, that evolved mental content and principles are not necessarily accurate, and that, if the argument is taken seriously, it has some highly dubious consequences. These criticisms necessitate various qualifications to the initial argument. Nonetheless, it is argued that, in some cases, important conclusions can be drawn about the world from an analysis of evolved contributions to our view of the world. An evolutionary approach cannot provide an ultimate justification for any belief; however, in certain circumstances, it supports the conclusion that a given belief is a reasonable first approximation. To the extent that innate content and principles pertain to topics in metaphysics, they can be viewed as a naturalistic source of metaphysical knowledge.     

Endosomal microdomains: Formation and function

It is widely recognized that after endocytosis, internalized cargo is delivered to endosomes that act as sorting stations. The limiting membrane of endosomes contain specialized subregions, or microdomains, that represent distinct functions of the endosome, including regions competing for cargo capture leading to degradation or recycling. Great progress has been made in defining the endosomal protein coats that sort cargo in these domains, including Retromer that recycles transmembrane cargo, and ESCRT (endosomal sorting complex required for transport) that degrades transmembrane cargo. In this review, we discuss recent work that is beginning to unravel how such coat complexes contribute to the creation and maintenance of endosomal microdomains. We highlight data that indicates that adjacent microdomains do not act independently but rather interact to cross-regulate. We posit that these interactions provide an agile means for the cell to adjust sorting in response to extracellular signals and intracellular metabolic cues.     

Enhancements, easy shortcuts, and the richness of human activities

One argument that is frequently invoked against the technological enhancement of human functioning is that it is morally suspect, or even wrong, to take an easy shortcut. Some things that usually take effort, endurance or struggle can come easily with the use of an enhancer. This paper analyses the various arguments that circle round the idea that enhancement of human functioning is problematic because of the 'easy shortcut' that it offers. It discusses the concern that quick fixes lead to corrosion of character and the idea that suffering, pain, hard work and effort are essential for real and worthy achievements, and argues that these views are largely mistaken. Next, the paper argues that the core worry about taking an easy shortcut is that it makes us lose sight of the complexities of our means and ends; in other words, the argument warns against reducing the richness of human activities. A vocabulary of 'practices', 'internal goods' and 'focal engagement' will be used to articulate this argument further. The conclusion is that the easy shortcut argument has no general validity as an argument against enhancement 'as such'. The paper urges us, however, to evaluate enhancement technologies not only in terms of their efficiency in reaching certain goals but also in terms of their contribution to intrinsically worthwhile human activities. It can point out some of the caveats, as well as the opportunities, of the use of enhancement technologies.     

The fallacy of the Principle of Procreative Beneficence

The claim that we have a moral obligation, where a choice can be made, to bring to birth the 'best' child possible, has been highly controversial for a number of decades. More recently Savulescu has labelled this claim the Principle of Procreative Beneficence. It has been argued that this Principle is problematic in both its reasoning and its implications, most notably in that it places lower moral value on the disabled. Relentless criticism of this proposed moral obligation, however, has been unable, thus far, to discredit this Principle convincingly and as a result its influence shows no sign of abating. I will argue that while criticisms of the implications and detail of the reasoning behind it are well founded, they are unlikely to produce an argument that will ultimately discredit the obligation that the Principle of Procreative Beneficence represents. I believe that what is needed finally and convincingly to reveal the fallacy of this Principle is a critique of its ultimate theoretical foundation, the notion of impersonal harm. In this paper I argue that while the notion of impersonal harm is intuitively very appealing, its plausibility is based entirely on this intuitive appeal and not on sound moral reasoning. I show that there is another plausible explanation for our intuitive response and I believe that this, in conjunction with the other theoretical criticisms that I and others have levelled at this Principle, shows that the Principle of Procreative Beneficence should be rejected.