A tale of two stories: astrocyte regulation of synaptic depression and facilitation

Short-term presynaptic plasticity designates variations of the amplitude of synaptic information transfer whereby the amount of neurotransmitter released upon presynaptic stimulation changes over seconds as a function of the neuronal firing activity. While a consensus has emerged that the resulting decrease (depression) and/or increase (facilitation) of the synapse strength are crucial to neuronal computations, their modes of expression in vivo remain unclear. Recent experimental studies have reported that glial cells, particularly astrocytes in the hippocampus, are able to modulate short-term plasticity but the mechanism of such a modulation is poorly understood. Here, we investigate the characteristics of short-term plasticity modulation by astrocytes using a biophysically realistic computational model. Mean-field analysis of the model, supported by intensive numerical simulations, unravels that astrocytes may mediate counterintuitive effects. Depending on the expressed presynaptic signaling pathways, astrocytes may globally inhibit or potentiate the synapse: the amount of released neurotransmitter in the presence of the astrocyte is transiently smaller or larger than in its absence. But this global effect usually coexists with the opposite local effect on paired pulses: with release-decreasing astrocytes most paired pulses become facilitated, namely the amount of neurotransmitter released upon spike i+1 is larger than that at spike i, while paired-pulse depression becomes prominent under release-increasing astrocytes. Moreover, we show that the frequency of astrocytic intracellular Ca(2+) oscillations controls the effects of the astrocyte on short-term synaptic plasticity. Our model explains several experimental observations yet unsolved, and uncovers astrocytic gliotransmission as a possible transient switch between short-term paired-pulse depression and facilitation. This possibility has deep implications on the processing of neuronal spikes and resulting information transfer at synapses.     

PUMA-mediated tumor suppression: A tale of two stories

Several recent studies provided evidence that PUMA, a pro-apoptotic member of the BH3-only protein subgroup of the Bcl-2 family, is critical for restricting survival and recovery of different cell types, including those of the hematopoietic system, after g-irradiation (IR)-triggered DNA damage. According to its pro-apoptotic function downstream of p53, PUMA is considered to act as a tumor suppressor. While this expectation was met in a model of oncogene-driven lymphomagenesis or carcinogen-driven tumor formation in the gut, studies on IR-driven tumor formation revealed surprising new insights into the role of p53-triggered and PUMA-mediated apoptosis in tumorigenesis and stem cell homeostasis.     

Relationships fade with time: a meta-analysis of temporal trends in publication in ecology and evolution.

Both significant positive and negative relationships between the magnitude of research findings (their 'effect size') and their year of publication have been reported in a few areas of biology. These trends have been attributed to Kuhnian paradigm shifts, scientific fads and bias in the choice of study systems. Here we test whether or not these isolated cases reflect a more general trend. We examined the relationship using effect sizes extracted from 44 peer-reviewed meta-analyses covering a wide range of topics in ecological and evolutionary biology. On average, there was a small but significant decline in effect size with year of publication. For the original empirical studies there was also a significant decrease in effect size as sample size increased. However, the effect of year of publication remained even after we controlled for sampling effort. Although these results have several possible explanations, it is suggested that a publication bias against non-significant or weaker findings offers the most parsimonious explanation. As in the medical sciences, non-significant results may take longer to publish and studies with both small sample sizes and non-significant results may be less likely to be published.     

Homeostasis and the physiological dimension of niche construction theory in ecology and evolution

Niche construction theory (NCT) has been represented as a new and comprehensive theory of evolution, one that breaks the constraints imposed by the dominant and largely gene-selectionist standard evolutionary model that is presently mischaracterized as “Darwinian.” I will argue that NCT is not so much a new theory, as it is a fruitful readmission of a venerable physiological perspective on adaptation, selection and evolution. This perspective is closer in spirit and philosophy to the original (and richer) Darwinian idea developed by Darwin himself, and that animated much of the rich late nineteenth century debate about evolution, heredity, adaptation and development, a debate that was largely eclipsed by the early twentieth century emergence of the Neodarwinian synthesis. I will argue that a full realization of the promise of NCT turns on a full understanding of another intellectual revolution of the nineteenth century, Claude Bernard’s conception of homeostasis, a profound statement of the nature of life that has, through the twentieth century, come to be widely misunderstood and trivialized.     

A tale of two worlds: molecular ecology and population structure of the threatened Florida scrub-jay

Elsewhere in this issue of Molecular Ecology , Coulon et al . provide a detailed analysis of population structure of the threatened Florida scrub-jay ( Aphelocoma coerulescens ) using genetic markers and compare it to that inferred from previous demographic surveys and observed dispersal behaviour in this species. In contrast to previous attempts at such comparisons, estimates from the two methods are reasonably congruent. Although challenges remain, Coulon et al .'s analyses demonstrate the potential for closing the gap between these alternative methodologies, and ultimately for future genetic surveys to be used confidently in conservation planning.     

Telomeres:Linking stress and survival,ecology and evolution

Telomeres are protective structures at the ends of eukaryotic chromosomes. The loss of telomeres through cell division and oxidative stress is related to cellular aging, organismal growth and disease. In this way, telomeres link molecular and cellular mechanisms with organismal processes, and may explain variation in a number of important life-history traits. Here, we discuss how telomere biology relates to the study of physiological ecology and life history evolution. We emphasize current knowledge on how ...     

Chitinolytic functions in actinobacteria: ecology,enzymes, and evolution

Applied Microbiology and Biotechnology - Actinobacteria, a large group of Gram-positive bacteria, secrete a wide range of extracellular enzymes involved in the degradation of organic compounds and...     

Sponge-associated microorganisms: evolution, ecology, and biotechnological potential.

Marine sponges often contain diverse and abundant microbial communities, including bacteria, archaea, microalgae, and fungi. In some cases, these microbial associates comprise as much as 40% of the sponge volume and can contribute significantly to host metabolism (e.g., via photosynthesis or nitrogen fixation). We review in detail the diversity of microbes associated with sponges, including extensive 16S rRNA-based phylogenetic analyses which support the previously suggested existence of a sponge-specific microbiota. These analyses provide a suitable vantage point from which to consider the potential evolutionary and ecological ramifications of these widespread, sponge-specific microorganisms. Subsequently, we examine the ecology of sponge-microbe associations, including the establishment and maintenance of these sometimes intimate partnerships, the varied nature of the interactions (ranging from mutualism to host-pathogen relationships), and the broad-scale patterns of symbiont distribution. The ecological and evolutionary importance of sponge-microbe associations is mirrored by their enormous biotechnological potential: marine sponges are among the animal kingdom's most prolific producers of bioactive metabolites, and in at least some cases, the compounds are of microbial rather than sponge origin. We review the status of this important field, outlining the various approaches (e.g., cultivation, cell separation, and metagenomics) which have been employed to access the chemical wealth of sponge-microbe associations.     

Current status of the tardigrada: evolution and ecology

The Tardigrada are bilaterally symmetrical micrometazoans withfour pairs of lobopod legs terminating in claws or sucking disks.They occupy a diversity of niches in marine, freshwater, andterrestrial environments throughout the world. Some have a cosmopolitandistribution, while others are endemic. About 900 species havebeen described thus far, but many more species are expectedas additional habitats are investigated. Most are less than1 mm in body length and are opaque or translucent, exhibitingcolors such as brown, green, orange, yellow, red, or pink inthe cuticle and/or gut. Marine species are more variable inbody shape and overall appearance and generally exhibit lowpopulation density with high species diversity. Reproductivemodes include sexual reproduction and parthenogenesis, but muchremains to be known about development. Tardigrades have a hemocoel-typeof fluid-filled body cavity, a complete digestive tract, anda lobed dorsal brain with a ventral nerve cord with fused ganglia.Recent molecular analyses and additional morphological studiesof the nervous system have confirmed the phylogenetic positionof tardigrades as a sister group of the arthropods. The abilityof tardigrades to undergo cryptobiosis has long intrigued scientists.Although tardigrades are active only when surrounded by a filmof water, they can enter latent states in response to desiccation(anhydrobiosis), temperature (cryobiosis), low oxygen (anoxybiosis),and salinity changes (osmobiosis). Cryptobiotic states aid indispersal.     

OCBIL theory: towards an integrated understanding of the evolution, ecology and conservation of biodiversity on old, climatically buffered, infertile landscapes

OCBIL theory aims to develop an integrated series of hypotheses explaining the evolution and ecology of, and best conservation practices for, biota on very old, climatically buffered, infertile landscapes (OCBILs). Conventional theory for ecology and evolutionary and conservation biology has developed primarily from data on species and communities from young, often disturbed, fertile landscapes (YODFELs), mainly in the Northern Hemisphere. OCBILs are rare, but are prominent in the Southwest Australian Floristic Region, South Africa’s Greater Cape, and Venezuela’s Pantepui Highlands. They may have been more common globally before Pleistocene glaciations. Based on the premise that natural selection has favoured limited dispersability of sedentary organisms, OCBILs should have elevated persistence of lineages (Gondwanan Heritage Hypothesis) and long-lived individuals (Ultimate Self Hypothesis), high numbers of localised rare endemics and strongly differentiated population systems. To counter such natural fragmentation and inbreeding due to small population size, ecological, cytogenetic and genetic mechanisms selecting for the retention of heterozygosity should feature (the James Effect). The climatic stability of OCBILs should be paralleled by persistence of adjacent semi-arid areas, conducive to speciation (Semiarid Cradle Hypothesis). Special nutritional and other biological traits associated with coping with infertile lands should be evident, accentuated in plants, for example, through water-foraging strategies, symbioses, carnivory, pollination and parasitism. The uniquely flat landscapes of southwestern Australia have had prolonged presence of saline lakes along palaeoriver systems favouring evolution of accentuated tolerance to salinity. Lastly, unusual resiliences and vulnerabilities might be evident among OCBIL organisms, such as enhanced abilities to persist in small fragmented populations but great susceptibility to major soil disturbances. In those places where it is most pertinent, OCBIL theory hopefully lays a foundation for future research and for better informed conservation management.