Granular layer in the periplasmic space of gram-positive bacteria and fine structures of Enterococcus gallinarum and Streptococcus gordonii septa revealed by cryo-electron microscopy of vitreous sections.

High-resolution structural information on optimally preserved bacterial cells can be obtained with cryo-electron microscopy of vitreous sections. With the help of this technique, the existence of a periplasmic space between the plasma membrane and the thick peptidoglycan layer of the gram-positive bacteria Bacillus subtilis and Staphylococcus aureus was recently shown. This raises questions about the mode of polymerization of peptidoglycan. In the present study, we report the structure of the cell envelope of three gram-positive bacteria (B. subtilis, Streptococcus gordonii, and Enterococcus gallinarum). In the three cases, a previously undescribed granular layer adjacent to the plasma membrane is found in the periplasmic space. In order to better understand how nascent peptidoglycan is incorporated into the mature peptidoglycan, we investigated cellular regions known to represent the sites of cell wall production. Each of these sites possesses a specific structure. We propose a hypothetic model of peptidoglycan polymerization that accommodates these differences: peptidoglycan precursors could be exported from the cytoplasm to the periplasmic space, where they could diffuse until they would interact with the interface between the granular layer and the thick peptidoglycan layer. They could then polymerize with mature peptidoglycan. We report cytoplasmic structures at the E. gallinarum septum that could be interpreted as cytoskeletal elements driving cell division (FtsZ ring). Although immunoelectron microscopy and fluorescence microscopy studies have demonstrated the septal and cytoplasmic localization of FtsZ, direct visualization of in situ FtsZ filaments has not been obtained in any electron microscopy study of fixed and dehydrated bacteria.

An immuno-electron microscopical analysis of transcribing multinucleosomal templates: what happens to the histones?

Immuno-electron microscopy was used to visualize the structure of reconstituted chromatin after in vitro transcription by purified T7 RNA polymerase. T7 RNA polymerase disrupts the nucleosomal structure in the transcribed region. This disruption is not influenced by the template, linear or supercoiled, and the presence or absence of nucleosomal positioning sequences in the transcribed region. In this study, we used monoclonal autoantibodies reacting with the nucleosome core particles and epitopes within several regions of the four different core histones. Some of the residues recognized by the autoantibodies are accessible on the surface of the nucleosomes and some are more internal and therefore less exposed at the surface. We show that the loss of the nucleosomal configuration during transcription is due to the loss of histone/DNA binding and that at least part of the histones are transferred to the nascent RNA chains. Consequently, after in vitro transcription by T7 RNA polymerase, the nucleosomal template does not conserve its original configuration, and no interaction of antigen/antibodies is observed anymore in the region that has been transcribed. Therefore, we conclude that in our in vitro transcription assay, nucleosomes are detached from the template, and not simply unfolded with histones remaining attached to the DNA.

Polymorphism at a sex-linked transcription cofactor in European tree frogs (Hyla arborea): Sex-antagonistic selection or neutral processes?

Nascent sex chromosomes offer a unique opportunity to investigate the evolutionary fate of genesrecently trapped in non-recombining segments. A housekeeping gene (MED15) was recently shown to lie on the nascent sex-chromosomes of the European tree frog (Hyla arborea), with different alleles fixed on the X and the Y chromosomes. Here we document a polymorphism (glutamine deletion) in the X copy of the gene, and use population surveys and experimental crosses to test whether this polymorphism is neutral or maintained by sex-antagonistic selection. Tadpoles from parents of known genotypes revealed significant discrepancies from Mendelian inheritance, suggesting possible sex-antagonistic effects under laboratory conditions. Quantitatively, however, these effects did not meet the conditions for polymorphism maintenance. Furthermore, field estimates of female genotypic frequencies did not differ from Hardy-Weinberg equilibrium and allelic frequencies on the X chromosome did not differ between sexes. In conclusion, although sex antagonistic effects cannot be excluded given the laboratory conditions, the X-linked polymorphism under study appears neutral in the wild. Alternatively, sex-antagonistic selection might still account for the fixation of a male specific allele on the Y chromosome.

Sharing competences in strategic alliances: a case study of the Cosan and Shell biofuel venture

In a competitive world, the way a firm establishes its organizational arrangements may determine the enhancement of its core competences and the possibility of reaching new markets. Firms that find their skills to be applicable in just one type of market encounter constraints in expanding their markets, and through alliances may find a competitive form of value capture. Hybrid forms of organization appear primarily as an alternative to capturing value and managing joint assets when the market and hierarchy modes do not present any yields for the firm's competitiveness. As a result, this form may present other challenging issues, such as the allocation of rights and principal-agent problems. The biofuel market has presented a strong pattern of changes over the last 10 years. New intra-firm arrangements have appeared as a path to participate or survive among global competition. Given the need for capital to achieve better results, there has been a consistent movement of mergers and acquisitions in the Biofuel sector, especially since the 2008 financial crisis. In 2011 there were five major groups in Brazil with a grinding capacity of more than 15 million tons per year: Raízen (joint venture formed by Cosan and Shell), Louis Dreyfus, Tereos Petrobras, ETH, and Bunge. Major oil companies have implemented the strategy of diversification as a hedge against the rising cost of oil. Using the alliance of Cosan and Shell in the Brazilian biofuel market as a case study, this paper analyses the governance mode and challenging issues raised by strategic alliances when firms aim to reach new markets through the sharing of core competences with local firms. The article is based on documentary research and interviews with Cosan's Investor Relations staff, and examines the main questions involving hybrid forms through the lens of the Transaction Cost Economics (TCE), Agency Theory, Resource Based View (RBV), and dynamic capabilities theoretical approaches. One focal point is knowledge "appropriability" and the specific assets originated by the joint venture. Once the alliance is formed, it is expected that competences will be shared and new capabilities will expand the limits of the firm. In the case studied, Cosan and Shell shared a number of strategic assets related to their competences. Raízen was formed with economizing incentives, as well to continue marshalling internal resources to enhance the company's presence in the world energy sector. Therefore, some challenges might be related to the control and monitoring agents' behavior, considering the two-part organism formed by distinctive organizational culture, tacit knowledge, and long-term incentives. The case study analyzed illustrates the hybrid arrangement as a middle form for organizing the transaction: neither in the market nor in the hierarchy mode, but rather a more flexible commitment agreement with a strategic central authority. The corporate governance devices are also a challenge, since the alignment between the parent companies in the joint ventures is far more complex. These characteristics have led to an organism with bilateral dependence, offering favorable conditions for developing dynamic capabilities. However, these conditions might rely on the partners' long-term interest in the joint venture.

Stable complexes involving acetylcholinesterase and amyloid-ß-peptide change the biochemical properties of the enzyme and increase the neurotoxicity of Alzheimer's fibrils

Brain acetylcholinesterase (AChE) forms stable complexes with amyloid-beta peptide (Abeta) during its assembly into filaments, in agreement with its colocalization with the Abeta deposits of Alzheimer's brain. The association of the enzyme with nascent Abeta aggregates occurs as early as after 30 min of incubation. Analysis of the catalytic activity of the AChE incorporated into these complexes shows an anomalous behavior reminiscent of the AChE associated with senile plaques, which includes a resistance to low pH, high substrate concentrations, and lower sensitivity to AChE inhibitors. Furthermore, the toxicity of the AChE-amyloid complexes is higher than that of the Abeta aggregates alone. Thus, in addition to its possible role as a heterogeneous nucleator during amyloid formation, AChE, by forming such stable complexes, may increase the neurotoxicity of Abeta fibrils and thus may determine the selective neuronal loss observed in Alzheimer's brain.

An Illustrated Guide for Monitoring and Protecting Bridge Waterways Against Scour - Project TR-515 - Final Report, March 2006

This report is a well illustrated and practical Guide intended to aid engineers and engineering technicians in monitoring, maintaining, and protecting bridge waterways so as to mitigate or prevent scour from adversely affecting the structural performance of bridge abutments, piers, and approach road embankments. Described and illustrated here are the scour processes affecting the stability of these components of bridge waterways. Also described and illustrated are methods for monitoring waterways, and the various methods for repairing scour damage and protecting bridge waterways against scour. The Guide focuses on smaller bridges, especially those in Iowa. Scour processes at small bridges are complicated by the close proximity of abutments, piers, and waterway banks, such that scour processes interact in ways difficult to predict and for which reliable design relationships do not exist. Additionally, blockage by woody debris or by ice, along with changes in approach channel alignment, can have greater effects on pier and abutment scour for smaller bridges. These considerations tend to cause greater reliance on monitoring for smaller bridges. The Guide is intended to augment and support, as a source of information, existing procedures for monitoring bridge waterways. It also may prompt some adjustments of existing forms and reports used for bridge monitoring. In accord with increasing emphasis on effective management of public facilities like bridges, the Guide ventures to include an example report format for quantitative risk assessment applied to bridge waterways. Quantitative risk assessment is useful when many bridges have to be evaluated for scour risk and damage, and priorities need to be determined for repair and protection work. Such risk assessment aids comparison of bridges at risk. It is expected that bridge inspectors will implement the Guide as a concise, handy reference available back at the office. The Guide also likely may be implemented as an educational primer for new inspectors who have yet to become acquainted with waterway scour. Additionally, the Guide may be implemented as a part of process to check whether existing bridge-inspection forms or reports adequately encompass bridge-waterway scour.

Excess Entry, Ambiguity Seeking, and Competence: An Experimental Investigation

Excess entry refers to the high failure rate of new entrepreneurial ventures. Economic explanations suggest 'hit and run' entrants and risk-seeking behavior. A psychological explanation is that people (entrepreneurs) are overconfident in their abilities (Camerer & Lovallo, 1999). Characterizing entry decisions as ambiguous gambles, we alternatively suggest following Heath and Tversky (1991) that people seek ambiguity when the source of uncertainty is related to their competence. Overconfidence, as such, plays no role. This hypothesis is confirmed in an experimental study that also documents the phenomenon of reference group neglect. Finally, we emphasize the utility that people gain from engaging in activities that contribute to a sense of competence. This is an important force in economic activity that deserves more explicit attention.

Evolution of Y chromosomes : lessons from mammals and amphibians

RÉSUMÉ : Le sexe des individus peut être déterminé par l'environnement ou la génétique. Lorsque la détermination du sexe est génétique, il y a dans le génome, la présence de chromosomes spécifiques qui détermineront le sexe. Dans cette thèse, j'ai étudié l'évolution des chromosomes sexuels et dans quel contexte des marqueurs sur ces chromosomes peuvent être utilisés. Pour explorer la formation du chromosome Y, nous avons étudié les caractéristiques des chromosomes sexuels chez la rainette verte, Hyla arborea. Dans un premier temps, nous avons utilisé un marqueur situé sur les chromosomes sexuels X et Y chez plusieurs espèces appartenant au groupe de la rainette verte. Cela nous a permis de révéler chez toutes ces espèces une hétérogamétie mâle. Dans un deuxième temps, nous avons tiré profit de deux autres marqueurs situés sur les chromosomes sexuels pour montrer que la recombinaison est supprimée chez les mâles mais pas chez les femelles. Pour expliquer la réduction de la variabilité sur le chromosome Y, il n'est pas nécessaire d'invoquer le balayage sélectif ou la sélection d'arrière-plan : le nombre de copies plus petit du chromosome Y dans le génome et l'absence de recombinaison suffisent à l'expliquer. Nous avons également analysé plus en détail la suppression de la recombinaison chez les mâles de H. arborea. Les modèles classiques de l'évolution des chromosomes sexuels supposent que la taille de la région non-recombinante augmente progressivement pendant l'évolution du chromosome Y, due à l'accumulation de changements structuraux. Dans cette étude, nous montrons un modèle différent, à savoir que la recombinaison est supprimée ou diminuée non seulement sur les chromosomes sexuels mais aussi sur les autosomes chez les mâles, dû à l'action de modificateurs généraux. En utilisant des marqueurs localisés sur le chromosome Y, ainsi que sur l'ADN mitochondrial et le chromosome X, nous avons étudié l'histoire évolutive de la musaraigne musette, Crocidura russula. Cette étude illustre que les analyses génétiques avec plusieurs types de marqueurs génétiques peuvent faciliter l'interprétation de l'histoire évolutive des espèces, mais que l'utilisation des marqueurs sur les chromosomes X et Y pour des études phylogéographiques est limitée par le peu de polymorphisme observé sur ces deux types de marqueurs. Le même jeu de données combiné avec des simulations a été employé pour comprendre les facteurs responsables de la faible variabilité sur le chromosome Y qui peut être expliqué, dans notre étude, par la démographie et les traits d'histoire de vie de C. russula. SUMMARY The sex of an individual is determined either by its environment or its genetics. Genetic sex determination relies on the presence of specific chromosomes that will determine the sex of their bearer. In this thesis, I studied the evolution of the sex chromosomes and the context in which markers on this type of chromosomes can be used. To explore the evolution of a Y chromosome, we studied the nascent sex chromosomes in the European tree frog Hyla arborea. First; we amplified a sex specific marker in several related species of European tree frog and found a homogeneous pattern of male heterogamety. Secondly, we used two additional sex-specific markers to show that recombination is suppressed in males but not in females. There is, therefore, no need to invoke background selection or selective sweeps to explain the reduced genetic variability on the Y chromosome, because the lower number of copies of the Y chromosomes per breeding pair and the absence of recombination are sufficient. To further analyze the suppression of recombination in male European. tree frogs, we constructed a microsatellite linkage map for this species. Classical models of sex-chromosome evolution assume that the non-recombining region expands progressively during the long-term evolution of the Y chromosome, owing to the accumulation of structural changes. Here we show a strikingly different pattern: recombination is suppressed or depressed both on sex chromosomes and autosomes in the heterogametic sex, presumably due to the action of general modifiers. We investigated the evolutionary history of the greater white-toothed shrew, Crocidura russula, using markers on both sex chromosomes and mtDNA. This study illustrates that multilocus genetic analyses facilitates the interpretation of a species' evolutionary history. It also demonstrates that phylogeographic inferences from X and Y chromosomal markers are restricted by the low levels of observed polymorphism. Combining this genetic study with simulations, we determined that the demography and the life-history traits of this species can alone be responsible for the low Y diversity. In conclusion, this thesis shows that sex chromosomes, in combination with autosomes or mtDNA, are necessary to understand the evolution of sex chromosomes and to precisely infer the population history of a species.

Increased mobility of major histocompatibility complex I-peptide complexes decreases the sensitivity of antigen recognition.

CD8(+) cytotoxic T lymphocytes (CTL) can recognize and kill target cells expressing only a few cognate major histocompatibility complex (MHC) I-peptide complexes. This high sensitivity requires efficient scanning of a vast number of highly diverse MHC I-peptide complexes by the T cell receptor in the contact site of transient conjugates formed mainly by nonspecific interactions of ICAM-1 and LFA-1. Tracking of single H-2K(d) molecules loaded with fluorescent peptides on target cells and nascent conjugates with CTL showed dynamic transitions between states of free diffusion and immobility. The immobilizations were explained by association of MHC I-peptide complexes with ICAM-1 and strongly increased their local concentration in cell adhesion sites and hence their scanning by T cell receptor. In nascent immunological synapses cognate complexes became immobile, whereas noncognate ones diffused out again. Interfering with this mobility modulation-based concentration and sorting of MHC I-peptide complexes strongly impaired the sensitivity of antigen recognition by CTL, demonstrating that it constitutes a new basic aspect of antigen presentation by MHC I molecules.

Lack of Smad3 signaling leads to impaired skeletal muscle regeneration.

Smad3 is a key intracellular signaling mediator for both transforming growth factor-β and myostatin, two major regulators of skeletal muscle growth. Previous published work has revealed pronounced muscle atrophy together with impaired satellite cell functionality in Smad3-null muscles. In the present study, we have further validated a role for Smad3 signaling in skeletal muscle regeneration. Here, we show that Smad3-null mice had incomplete recovery of muscle weight and myofiber size after muscle injury. Histological/immunohistochemical analysis suggested impaired inflammatory response and reduced number of activated myoblasts during the early stages of muscle regeneration in the tibialis anterior muscle of Smad3-null mice. Nascent myofibers formed after muscle injury were also reduced in number. Moreover, Smad3-null regenerated muscle had decreased oxidative enzyme activity and impaired mitochondrial biogenesis, evident by the downregulation of the gene encoding mitochondrial transcription factor A, a master regulator of mitochondrial biogenesis. Consistent with known Smad3 function, reduced fibrotic tissue formation was also seen in regenerated Smad3-null muscle. In conclusion, Smad3 deficiency leads to impaired muscle regeneration, which underscores an essential role of Smad3 in postnatal myogenesis. Given the negative role of myostatin during muscle regeneration, the increased expression of myostatin observed in Smad3-null muscle may contribute to the regeneration defects.

The organization of research corporations and researcher ability

This paper analyzes the formation of Research Corporations as an alternative governance structure for performing R&D compared to pursuing in-house R&D projects. Research Corporations are privatefor-profit research centers that bring together several firms with similar research goals. In a Research Corporation formal authority over the choice of projects is jointly exercised by the top management of the member firms. A private for-profit organization cannot commit not to interfere with the project choice of the researchers. However, increasing the number of member firms of the Research Corporation reduces the incentive of member firms to meddle with the research projects of researchers because exercising formal authority over the choice of research projects is a public good. The Research Corporation thus offers researchers greater autonomy than a single firm pursuing an identical research program in its in-house R&D department. This attracts higher ability researchers to the Research Corporation compared to the internal R&D department. The paper uses the theoretical model to analyze the organization of the Microelectronics and Computer Technology Corporation (MCC). The facts of this case confirm the existence of a tension between control over the choice of research projects and the ability of researchers that the organization is able to attract or hold onto.

Influence activity and the organization of research and development

The organizational design of research and development conditions theincentives of the researchers of the research project. In particular,the organizational form determines the allocation of effort of theresearcher between time spent on research and time spent lobbying management. Researchers prefer to spend their time on research. However,the researchers only get utility from performing research if theproject is approved for its full duration. Spending time lobbyingmanagement for the continuation of the researcher s project increasesthe probability that the management observes a favorable signal aboutthe project. Organizing a research joint venture increases theflexibility of the organizational form with respect to the continuationdecision. For low correlation between the signals of the partners aboutthe expected profitability of the project, we find that the organizationof a research joint venture reduces influence activity by the researchersand increases expected profits of the partners. For high correlationbetween the signals, internal research projects lower influence activityby the researchers. We try to relate the correlation of the partnerssignals to the characteristics of basic research versus more appliedresearch projects, and find that the model is consistent with theobservation that research joint ventures seem involved in more basicresearch projects compared to internal R&D departments, whichconcentrate on more applied research.

Excess entry, ambiguity seeking and competence: An experimental investigation

Excess entry refers to the high failure rate of new entrepreneurial ventures. Economic explanations suggest 'hit and run' entrants and risk-seeking behavior. A psychological explanation is that people (entrepreneurs) are overconfident in their abilities (Camerer & Lovallo, 1999). Characterizing entry decisions as ambiguous gambles, we alternatively suggest following Heath and Tversky (1991) that people seek ambiguity when the source of uncertainty is related to their competence. Overconfidence, as such, plays no role. This hypothesis is confirmed in an experimental study that also documents the phenomenon of reference group neglect. Finally, we emphasize the utility that people gain from engaging in activities that contribute to a sense of competence. This is an important force in economic activity that deserves more explicit attention.

Managing Social-Business Tensions: A Review and Research Agenda for Social Enterprise

In a world filled with poverty, environmental degradation, and moral injustice, social enterprises offer a ray of hope. These organizations seek to achieve social missions through business ventures. Yet social missions and business ventures are associated with divergent goals, values, norms, and identities. Attending to them simultaneously creates tensions, competing demands, and ethical dilemmas. Effectively understanding social enterprises therefore depends on insight into the nature and management of these tensions. While existing research recognizes tensions between social missions and business ventures, we lack any systematic analysis. Our paper addresses this issue. We first categorize the types of tensions that arise between social missions and business ventures, emphasizing their prevalence and variety. We then explore how four different organizational theories offer insight into these tensions, and we develop an agenda for future research. We end by arguing that a focus on social-business tensions not only expands insight into social enterprises, but also provides an opportunity for research on social enterprises to inform traditional organizational theories. Taken together, our analysis of tensions in social enterprises integrates and seeks to energize research on this expanding phenomenon.

Poor, hungry and ignorant: Numeracy and the impact of high food prices in industrializing Britain, 1780-1850

This paper uses the ability to recall one s age correctly as an indicator of numeracy.We show that low levels of nutrition impaired numeracy in industrializing England, 1780-1850.Numeracy declined markedly among those born during the war years, especially where wheatwas dear. England s nascent welfare state mitigated the negative effect of high food prices oncognitive skills. Nutrition during early development mattered for labor market outcomes:individuals born in periods or countries with high age heaping were more likely to sort intooccupations with limited intellectual requirements.