The intracellular cyanobacteria of Paulinella chromatophora: endosymbionts or organelles?

Endosymbiotic relationships are common across the tree of life and have had profound impacts on cellular evolution and diversity. Recent molecular investigations of the amoeba Paulinella chromatophora have raised a timely and important question: should obligatory intracellular cyanobacteria in Paulinella be considered new organelles, or do plastids and mitochondria hold a unique stature in the history of endosymbiotic events? We argue that drawing a sharp distinction between these two organelles and all other endosymbionts is not supported by accumulating data, neither is it a productive framework for investigating organelle evolution.     

How do pathogen evolution and host heterogeneity interact in disease emergence?

Heterogeneity in the parameters governing the spread of infectious diseases is a common feature of real-world epidemics. It has been suggested that for pathogens with basic reproductive number R(0)>1, increasing heterogeneity makes extinction of disease more likely during the early rounds of transmission. The basic reproductive number R(0) of the introduced pathogen may, however, be less than 1 after the introduction, and evolutionary changes are then required for R(0) to increase to above 1 and the pathogen to emerge. In this paper, we consider how host heterogeneity influences the emergence of both non-evolving pathogens and those that must undergo adaptive changes to spread in the host population. In contrast to previous results, we find that heterogeneity does not always make extinction more likely and that if adaptation is required for emergence, the effect of host heterogeneity is relatively small. We discuss the application of these ideas to vaccination strategies.     

How to measure Ca2+ in cellular organelles?

The review will aim to briefly summarise information on calcium measurements in cellular organelles with emphases on studies conducted in live cells using optical probes. When appropriate we will try to compare the effectiveness of different indicators for intraorganellar calcium measurements. We will consider calcium measurements in endoplasmic reticulum, Golgi apparatus, endosomes/lysosomes, nucleoplasm, nuclear envelope, mitochondria and secretory granules.     

How do regulatory networks evolve and expand throughout evolution?

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How did Death become a Saint in Mexico?

Over the last decade, the cult of La Santa Muerte (St Death) has attracted a remarkable number of followers in Mexico and the USA. Whereas the social context of her devotees, who tend to live on the fringes of society, has attracted ample attention from scholars and journalists, one of the principal puzzles is still how a skeleton image of death has come to be seen as a saint by large numbers of Catholics. How is it possible for this figure to embrace such antagonistic qualities as death and sainthood in a Christian context? In this semiotic-material exploration of the image's genealogy, I suggest that La Santa Muerte should be seen as a coalescing of two radically distinct images of death: the popular-secular Catrina and the occult-biblical Santísima Muerte. The St Death venerated today encompasses the ambiguities of the two and creates an exceptionally vibrant and popular Catholic image.     

Was the evolution of plastid genetic machinery discontinuous?

The plastid nucleoid consists of plastid DNA and various, mostly uncharacterized, DNA-binding proteins. The plastid DNA undoubtedly originated from an ancestral cyanobacterial genome, but the origin of the nucleoid proteins appears complex. Initial biochemical analysis of these proteins, as well as comparative genome informatics, suggest that proteins of eukaryotic origin replaced most of the original prokaryotic proteins during the evolution of plastids in the lineage of green plants.     

How to model the events in cutaneous fibrosis?

Skin fibrosis is classically seen as the consequence of chronic inflammation and altered healing response that is characterized by the differentiation of fibroblasts into secretory myofibroblasts and accumulation of connective tissue. Although fibrosis severely affects organ function and causes esthetic defects, no effective therapy is currently available to attenuate the fibrogenic process probably because the fibrogenic process is more complex than previously thought. Indeed, it might involve several interacting and mutually dependent cell types (fibroblasts, keratinocytes, endothelial cells, inflammatory cells), numerous paracrine factors, bio-active molecules and micro-environmental stimuli (growth factors, vasoactive peptides, balance between pro- and anti-inflammatory cytokines, coagulation system, reactive oxygen species, extracellular matrix...). In this perspective, the traditional approach that model individual cell response in simple cell culture system is probably inadequate and too simplistic. This article reviews the new models used to study skin fibrosis in vitro, in organotypic culture systems and in vivo and examines how these different models might be used to identify new molecular pathways involved in fibrogenesis. The monolayer cultures allow the study of fibrogenic signals induced by a single factor on a single cell type. Isolation of cells from fibrotic tissue allows to define the fibrogenic differentiation acquired in vivo. The organotypic models allow cell to cell and cell to matrix interaction and the experimental models in pigs and mice allowed studies in integrated physiological systems. These various and complementary models would also provide new tools to develop and test new drugs and treatments.     

Can maternally transmitted endosymbionts facilitate the evolution of haplodiploidy?

Whilst many invertebrate taxa are haplodiploid, the factors underlying the evolution of haplodiploidy remain unresolved. We investigate theoretically whether haplodiploidy might evolve as an outcome of the co-evolution between maternally inherited endosymbionts and their hosts. First, we substantially extend a recently developed model that involves maternally inherited endosymbionts that kill male offspring by eliminating the paternal genome. We also put forward a new hypothesis and develop a model that involves bacteria that induce cytoplasmic incompatibility (CI). Based on these models, we explore the co-evolutionary events that might occur between hosts and symbionts. We find that both with male-killers and CI-inducing endosymbionts, the hosts are likely to develop increased viability of haploid males, which can be considered a preadaptation to haplodiploidy. In addition, populations with haploidizing male-killers can in some cases evolve directly towards a genetic system of paternal genome elimination, a special form of haplodiploidy. These results are combined with consideration of mechanism and ecology to appraise the likelihood of male-killers and CI inducing bacteria being involved in the evolution of haplodiploidy.     

How do avian embryos breathe? Oxygen transport in the blood of early chick embryos

1. Chick embryos with primary circulation, up to about 3 days of development, show no hemoglobin-mediated transport of oxygen. 2. In embryos with secondary circulation, between 3 and 6 days of incubation, the vascular area acts as the respiratory organ. Its efficiency in the oxygen uptake is less than that of the chorioallantois of later embryos. On the contrary, oxygen release to the tissues is highly efficient. 3. A full efficient hematic uptake of oxygen is reached at about the 6th incubation day, when chorioallantois acts as the embryonic respiratory organ. 4. The different respiratory mechanisms of developing chick embryo are closely related to the functional properties of the various hemoglobins which are produced during the embryonic life.     

How symbiogenic is evolution?

When new entities are formed by the integration of individual organisms, these new entities possess characteristics which go beyond the sum of the individual properties of each element of the association, resulting in the development of new attributes and capacities as an integrated whole. In this process, these new entities also agglutinate and dynamize synergies not present in the individual organisms. In this sense, evolution is a dynamic process that evolves not in the way of perfection or progress, but in the way of adaptation to new conditions. Symbiogenesis, as an evolutionary mechanism, allows a coherent conceptual rupture with some evolutionary ideas of the past and, at the same time, shows and builds a new approach to life, based on solid evolutionary ideas, expanding evolution to an adequate level of integration with the more recent data in biology. These ideas and concepts should be integrated in a post-neodarwinian approach to evolution that needs further attention from the scientific community. The development of a Symbiogenic Theory of Evolution could contribute toward a new epistemological approach of the symbiotic phenomenon in the evolutionary context. This, in our point of view, could be the beginning of a new paradigm in science that rests almost unexplored.     

How do Parkin mutations result in neurodegeneration?

The gene product responsible for autosomal recessive juvenile Parkinsonism, Parkin, has been observed to have ubiquitin ligase activity. This finding has changed the direction of studies on Parkinson's disease by suggesting that abnormal protein turnover might be involved in its pathogenesis. A number of potentially neurotoxic Parkin-specific substrates have been identified. Further investigation of Parkin knockout mice will hopefully provide new evidence in the search for Parkin's substrates and further clarify their role in Parkinson's disease.     

How do dilatations form in mosquito ovarioles?

Ovariolar dilatations have been used to estimate parity status in mosquitoes for over 40 years. The theoretical basis for this parity-diagnostic method, which was established for mosquitoes by Polovodova 1, has been challenged by a number of Russian researchers. The findings of this new school of researchers have elicited little response from those currently using the method outside Russia, except for a recent paper by Hoc and Charlwood2. This has stimulated Andrew Fox and Reinhart Brust to review the formation of ovariolar dilatations here, and compare what they term the Old and the New Schools. Although the basic application of Polovodova's method is unaffected by the premise of either School, a clear understanding of ovarian dynamics is needed to understand the method and its limits.     

How do neurons die in neurodegenerative diseases?

Given that neurons are post-mitotic cells, their life span is generally long enough to reach that of humans. However, sometimes neurons die without recognizable causes, as a result of a process called neurodegeneration. Apart from when gene mutations can be correlated with disease, it is difficult to pinpoint molecules that are responsible for neuronal death. Therefore, neurons living in a 'sick state' for many years might reveal important information about neuronal death. Systematic and extensive single-neuron analysis of 'sick' neurons is expected to provide clues to the mechanisms of neurodegeneration. Moreover, the elimination of putative triggering and promoting factors involved in neurodegenerative disease might prevent disease progression.     

How was teleology eliminated in early molecular biology?

This paper approaches the issue of the status of teleological reasoning in contemporary biology through a historical examination of events of the 1930s that surrounded Niels Bohr’s efforts to introduce ‘complementarity’ into biological discussions. The paper examines responses of three theoretical physicists who engaged boundary questions between the biological and physical sciences in this period in response to Bohr—Ernst Pascual Jordan (1902–80), Erwin Schrödinger (1887–1961), and Max Delbrück (1906–81). It is claimed that none of these physicists sufficiently understood Bohr’s ‘critical’ teleological arguments, which are traced to the lineage of Kant and Harald Høffding and their respective resolutions of the Antinomy of Teleological Judgment. The positions of these four historical actors are discussed in terms of Ernst Mayr’s distinction of ‘teleological,’ ‘teleomatic,’ and ‘teleonomic’ explanations. A return to some of the views articulated by Bohr, and behind him, to Høffding and Kant, is claimed to provide a framework for reintroducing a ‘critical’ teleology into biological discussions.     

How do grazers affect periphyton heterogeneity in streams?

The effects of grazing by stream invertebrates on algal biomass and spatial heterogeneity were tested experimentally in flow-through microcosms with natural substrates (rocks). One experiment tested the effects of fixed densities of three species of grazers (the caddisfly Allomyia sp. and two mayflies, Epeorus deceptivus and Baetis bicaudatus) on periphyton. Baetis was tested with and without chemical cues from fish predators, which reduced grazer foraging activity to levels similar to the less mobile mayfly (Epeorus). Mean algal biomass (chlorophyll a; chl a) was reduced in grazer treatments compared to ungrazed controls, but there were no differences among grazer treatments. Algal heterogeneity (Morisita index) increased with grazer mobility, with the highest heterogeneity occurring in the Baetis-no fish treatment (most mobile grazer) and the lowest in the caddisfly treatment (most sedentary grazer). A second experiment used a three factorial design, and tested whether initial resource distribution (homogeneous vs. heterogeneous), Baetis density (high vs. low) and fish odor (present vs. absent) affected grazer impact on algal resources. Abundances of Baetis and chl a on individual rocks were recorded to explore the mechanisms responsible for the observed distributions of algae. Initial resource heterogeneity was maintained despite being subjected to grazing. Mean chl a was highest in controls, as in experiment I, and effects of Baetis on algal biomass increased with grazer density. There were no fish effects on algal biomass and no effects of grazer density or fish on algal heterogeneity. At the scale of individual rocks Baetis was unselective when food was homogeneously distributed, but chose high-food rocks when it was heterogeneously distributed. Results of these mechanistic experiments showed that Baetis can track resources at the scale of single rocks; and at moderate densities mobile grazers could potentially maintain periphyton distributions observed in natural streams.