Mechanotransduction from the ECM to the genome: Are the pieces now in place?

A multitude of biochemical signaling processes have been characterized that affect gene expression and cellular activity. However, living cells often need to integrate biochemical signals with mechanical information from their microenvironment as they respond. In fact, the signals received by shape alone can dictate cell fate. This mechanotrasduction of information is powerful, eliciting proliferation, differentiation, or apoptosis in a manner dependent upon the extent of physical deformation. The cells internal "prestressed" structure and its "hardwired" interaction with the extra-cellular matrix (ECM) appear to confer this ability to filter biochemical signals and decide between divergent cell functions influenced by the nature of signals from the mechanical environment. In some instances mechanical signaling through the tissue microenvironment has been shown to be dominant over genomic defects, imparting a normal phenotype on cells that otherwise have transforming genetic lesions. This mechanical control of phenotype is postulated to have a central role in embryogenesis, tissue physiology as well as the pathology of a wide variety of diseases, including cancer. We will briefly review studies showing physical continuity between the external cellular microenvironment and the interior of the cell nucleus. Newly characterized structures, termed nuclear envelope lamina spanning complexes (NELSC), and their interactions will be described as part of a model for mechanical transduction of extracellular cues from the ECM to the genome.     

Echoes from the past--are we still in an RNP world?

Availability of the human genome sequence and those of other species is unmeasured in their value for a comprehensive understanding of the architecture, function and evolution of genomes and cells. Various mechanisms keep genomes in flux and generate intra- and interspecies variation. The conversion of RNA modules into DNA and their more or less random integration into chromosomes (retroposition) is in many lineages including our own the most pervasive and perhaps the most enigmatic. The proclivity of such events in extant multicellular eukaryotes, even in more recent evolutionary times, gives the impression that the transition period from the RNP (ribonucleoprotein) world to the emergence of modern cells, where DNA became the predominant carrier of genetic information, has lasted billions of years and is an endlessly drawn-out process rather than the punctuated event one might expect. Apart from the impact of such RNA-mediated processes as retroposition, the role of RNA in a wide variety of cellular functions has only recently become more widely appreciated.     

What to expect from MRI in the investigation of the central nervous system?

Functional magnetic resonance imaging (fMRI) has appeared as a new tool that is very powerful for cognitive neuroscience, offering the potential to look at the dynamics of cerebral processes underlying cognition, non-invasively and on an individual basis. Work remains to be done to optimize the technique and to better understand its basic mechanisms, but one may expect to build in a foreseeable future a functional list of the main brain cortical networks implicated in sensory-motor or cognitive processes. Still, the real understanding of brain function requires direct access to the functional unit consisting of the neuron, so that one may look at the transient temporal relationships that exist between largely distributed groups of hundreds or thousands of neurons. Furthermore, communication pathways between networks, which are carried by brain white matter, must be identified to establish connectivity maps at the individual scale, taking into account individual variability resulting from genetic factors and cerebral plasticity. In this respect, MRI of molecular diffusion is very sensitive to water molecular motion and, thus, to tissue dynamic microstructure, such as cell size and geometry. Preliminary data suggest that diffusion MRI visualizes dynamic tissue changes associated with large neuronal activation and space orientation of large bundles of myelinated axons in the white matter.     

Are Antarctic suspension-feeding communities different from those elsewhere in the world?

This paper reviews the trophic ecology of benthic suspension feeders in Antarctic shelf communities, studied within SCAR's EASIZ Programme, in comparison with published information from other seas. Dense benthic suspension-feeder communities capture large quantities of particles and may directly regulate primary, and indirectly, secondary production in littoral food chains. Most work has been performed in temperate and tropical seas; however, little is known about suspension feeders in cold environments. Recent studies on Antarctic littoral benthic suspension feeders suggest the period of winter inactivity may last only a few weeks. This contrasts with the hypothesis that in Antarctic communities there is a prolonged period of minimal activity lasting at least 6 months during the austral winter. Results from other oceans may explain how dense benthic communities could develop under such conditions. Alternative food sources, i.e. the "fine fraction", sediment resuspension, lateral advection and efficient food assimilation may play a significant role in the development of suspension-feeder dominated, very diversified, high biomass and three-dimensionally structured communities on the Antarctic shelf.     

What is in the intercellular spaces of roots? Evidence from the cryo-analytical-scanning electron microscope

The schizogenous intercellular spaces (i. e. those small spaces formed by cell walls coming apart) in the cortex of the roots of field-grown maize ( Zea mays L.) were studied in planed transverse faces of frozen tissue, very lightly etched and coated with Al. The spaces were mostly filled with either fluid or, in the drier roots, with a flaky deposit. This deposit may have been left behind when water was withdrawn, or may have been debris dislodged by the planing. Even in roots with mostly dry spaces, some wet, fluid-filled spaces remained. X-ray microanalysis of the wet spaces revealed that the fluid contained K (average concentration 230 m M , range 50–750 m M ) and Ca (average concentration 100 m M , range 15 to 550 m M ), and occasionally small amounts of S, P or Cl. No other balancing inorganic anions were detected. Concentrations in the wet intercellular spaces showed considerable variation between one space and the next, and were often quite different from those in the vacuoles of adjacent cells. However, overall the vacuoles of the cells surrounding the spaces showed mean concentrations, and distributions of concentrations, indistinguishable from those of the wet spaces. Analyses of the deposits in the dry spaces were less reliable because of their uneven surface, but the same ions in about the same amounts were found there. The contents of the spaces showed no correlation with either the time of collection of the roots, or with distance from the root tip. Nor was there any change in concentration of these ions in the spaces when the roots were grown for 19 h in distilled water mist. Experiments and evidence are presented suggesting that the observed distribution of ions is probably not an artefact. Pilot experiments showed similar distributions of extracellular ions in roots of barley, Sudan grass and soybean     

Renewable resources in the chemical industry – Breaking away from oil?

Rising prices for fossil-based raw materials suggest that sooner or later renewable raw materials will, in principle, become economically viable. This paper examines this widespread paradigm. Price linkages like those seen for decades particularly in connection with petrochemical raw materials are now increasingly affecting renewable raw materials. The main driving force is the competing utilisation as an energy source because both fossil-based and renewable raw materials are used primarily for heat, electrical power and mobility. As a result, prices are determined by energy utilisation. Simple observations show how prices for renewable carbon sources are becoming linked to the crude oil price. Whether the application calls for sugar, starch, virgin oils or lignocellulose, the price for the raw material rises with the oil price. Consequently, expectations regarding price trends for fossil-based energy sources can also be utilised for the valuation of alternative processes. However, this seriously calls into question the assumption that a rising crude oil price will favour the economic viability of alternative products and processes based on renewable raw materials. Conversely, it follows that these products and processes must demonstrate economic viability today. Especially in connection with new approaches in white biotechnology, it is evident that, under realistic assumptions, particularly in terms of achievable yields and the optimisation potential of the underlying processes, the route to utilisation is economically viable. This makes the paradigm mentioned at the outset at least very questionable.     

B chromosomes in plants: escapees from the A chromosome genome?

B chromosomes are dispensable elements that do not recombine with the A chromosomes of the regular complement and that follow their own evolutionary track. In some cases, they are known to be nuclear parasites with autonomous modes of inheritance, exploiting "drive" to ensure their survival in populations. Their "selfishness" brings them into conflict with their host nuclear genome and generates a host-parasite relationship, with anti-B-chromosome genes working to ameliorate the worst of their excesses in depriving their hosts of genetic resources. Molecular studies are homing in on their sequence organization to give us an insight into the origin and evolution of these enigmatic chromosomes, which are, with rare exceptions, without active genes.     

Synaptic Plasticity in the Hippocampus: Effects of Estrogen from the Gonads or Hippocampus?

Different effects of estrogen on synaptic plasticity have [corrected] been reported. Here, we summarise effects of low, gonad-derived serum estrogen concentrations, of intermediate concentrations, provided by hippocampal cells, and of pharmacological doses of estrogen on synapses and spines and on the expression of synaptic proteins. No effects of low concentrations were found. To study the effects of hippocampus-derived estradiol, we inhibited hippocampal estrogen synthesis by treatment of hippocampal cell cultures with letrozole, an aromatase inhibitor. Alternatively, we used siRNA against Steroidogenic acute regulatory protein (StAR). Spines, synapses, and synaptic proteins were significantly down regulated in response to letrozole and in siRNA-StAR transfected cells. Application of high pharmacological doses of estradiol promoted only synaptophysin expression, a presynaptic protein, but did not increase the number of boutons. Our results point to an essential role of endogenous hippocampal estrogen in hippocampal synaptic plasticity rather than to a direct influence of estrogens derived from peripheral sources, such as the gonads.     

Do Turkish women in the diaspora build social capital? Evidence from the Low countries

Abstract

Ever since Putnam (2000) made social capital a concept that should be mourned for its decline in the USA, researchers and policy makers in some western countries have adopted it as a solution to what they believe to be the failed practices of multiculturalism. Instead of preserving their individual cultures and traditions, critics would have them build social capital by bridging to people and institutions in their new countries and adopt the ‘shared values’ of the host countries and become ‘integrated’. This study, based on a study conducted in the Netherlands in 2006, and supplemented with survey findings from Flanders at the same time, examines whether this perspective is accurate, focusing on women migrants who live in the Low Countries (Netherlands and Flanders in Belgium), of the networks they have built or not and the reasons for that, and of the role of media and the internet in that process.     

Did desmid assemblages in Dutch moorland pools recover from acidification in the past century?

Hydrobiologia - In order to monitor recovery from acidification caused by acid atmospheric deposition, desmids and water chemistry were sampled in three Dutch moorland pools regularly from 1978 to...     

What can we still learn from the electrochromic band-shifts in Photosystem II?

Electrochromic band-shifts have been investigated in Photosystem II (PSII) from Thermosynechoccocus elongatus. Firstly, by using Mn-depleted PsbA1-PSII and PsbA3-PSII in which the Q_X absorption of Phe_D1 differs, a band-shift in the Q_X region of Phe_D2 centered at ~ 544 nm has been identified upon the oxidation, at pH 8.6, of Tyr_D. In contrast, a band-shift due to the formation of either Q_A^•- or Tyr_Z^• is observed in PsbA3-PSII at ~ 546 nm, as expected with E130 H-bonded to Phe_D1 and at ~ 544 nm as expected with Q130 H-bonded to Phe_D1. Secondly, electrochromic band-shifts in the Chla Soret region have been measured in O₂-evolving PSII in PsbA3-PSII, in the PsbA3/H198Q mutant in which the Soret band of P_D1 is blue shifted and in the PsbA3/T179H mutant. Upon Tyr_Z^•Q_A^•- formation the Soret band of P_D1 is red shifted and the Soret band of Chl_D1 is blue shifted. In contrast, only P_D1 undergoes a detectable S-state dependent electrochromism. Thirdly, the time resolved S-state dependent electrochromism attributed to P_D1 is biphasic for all the S-state transitions except for S₁ to S₂, and shows that: i) the proton release in S₀ to S₁ occurs after the electron transfer and ii) the proton release and the electron transfer kinetics in S₂ to S₃, in T. elongatus, are significantly faster than often considered. The nature of S₂Tyr_Z^• is discussed in view of the models in the literature involving intermediate states in the S₂ to S₃ transition.     

The Cape element in the Afrotemperate flora: from Cape to Cairo?

The build-up of biodiversity is the result of immigration and in situ speciation. We investigate these two processes for four lineages (Disa, Irideae p.p., the Pentaschistis clade and Restionaceae) that are widespread in the Afrotemperate flora. These four lineages may be representative of the numerous clades which are species rich in the Cape and also occur in the highlands of tropical Africa. It is as yet unclear in which direction the lineages spread. Three hypotheses have been proposed: (i) a tropical origin with a southward migration towards the Cape, (ii) a Cape origin with a northward migration into tropical Africa, and (iii) vicariance. None of these hypotheses has been thoroughly tested. We reconstruct the historical biogeography of the four lineages using likelihood optimization onto molecular phylogenies. We find that tropical taxa are nested within a predominantly Cape clade. There is unidirectional migration from the Cape into the Drakensberg and from there northwards into tropical Africa. The amount of in situ diversification differs between areas and clades. Dating estimates show that the migration into tropical East Africa has occurred in the last 17 Myr, consistent with the Mio-Pliocene formation of the mountains in this area.     

Where are the Caribs? Ancient DNA from ceramic period human remains in the Lesser Antilles

The identity and history of the indigenous groups who occupied the Lesser Antilles during the ceramic periods remain highly controversial. Although recent archaeological evidence has challenged hypotheses concerning the organization of human groups in this region, more biological data are needed to fully inform the discussion. Our study provides, to our knowledge, the first palaeogenetic data for Late Ceramic groups of the Guadeloupe archipelago, yielding crucial information concerning the identities of these groups. Despite the generally poor DNA preservation in the tested remains, we were able to retrieve Hypervariable Region 1 sequences from 11 individuals and mitochondrial single-nucleotide polymorphisms from 13 individuals. These novel data provide interesting preliminary results in favour of a common origin for all Saladoid Caribbean communities, i.e. the first ceramic groups of the region, as well as for a local continuity between the Saladoid and post-Saladoid groups. A combination of the genetic data obtained and several pieces of cultural evidence allows us to propose that two different groups inhabited the Guadeloupe archipelago during the Late Ceramic period, with the possible occupation of the La Désirade and Marie-Galante islands by groups affiliated with the Taíno communities. The working hypotheses proposed here appear consistent with recent archaeological evidence.