Effects of simulated weightlessness on meiosis. Fertilization, and early development in mice

The initial goal was to construct a clinostat which could support mammalian cell culture. The clinostat was selected as a means by which to simulate microgravity conditions within the laboratory, by constant re-orientation of cells with respect to the gravity vector. The effects of this simulated microgravity on in-vitro meiotic maturation of oocytes, using mouse as the model system, was investigated. The effects of clinostat rotation on fertilization in-vitro was then examined. Specific endpoints included examining the timely appearance of male and female pronuclei (indicating fertilization) and the efficiency of extrusion of the second polar body. Particular attention was paid to detecting anomalies of fertilization, including parthenogenetic activation and multiple pronuclei. Finally, for the preliminary studies on mouse embryogenesis, a key feature of the clinostat was modified, that of the position of the cells during rotation. A means was found to immobilize the cells during the clinostat reotation, permitting the cells to remain at the axis of rotation yet not interfering with cellular development

Applied Qualitative Data Analysis After the Ontological Turn

In this article we demonstrate the use and usefulness of new materialism as an analytic lens in applied qualitative inquiry. Intended as a possible entry point to applied inquiry after the ontological turn, we draw on Barad’s agential realism to analyze three existing transcripts of focus groups conducted with healthcare workers, traditional birth attendants, and mothers to explore the postnatal care referral behavior of traditional birth attendants in Nigeria. We describe elements of our data analysis process including deep reading, summoning of the inquiry, delaying the inquiry, attuning to glowing data, and writing. We explore how the research phenomenon enacted agential cuts that distinguished participants (healthcare workers, traditional birth attendants, and mothers) and relayed their participation in the focus group. We show how the inclusion of the mothers’ babies and the transcripts themselves made available some understandings at the possible exclusion of others. Our Baradian, new materialist analysis shows the inextricability of interview materials (things) and language (discourse) and demonstrates that all applied research is bounded and affected by its material conditions. As a point of entry, we hope our illustration sensitizes applied qualitative researchers to how research decisions, research materials, and research cultures produce what can be known and lived within and beyond the research encounter

The introduction of the TMPG fails charge for U.S. Treasury securities

The TMPG fails charge for U.S. Treasury securities provides that a buyer of Treasury securities can claim monetary compensation from the seller if the seller fails to deliver the securities on a timely basis. The charge was introduced in May 2009 and replaced an existing market convention of simply postponing—without any explicit penalty and at an unchanged invoice price—a seller’s obligation to deliver Treasury securities if the seller fails to deliver the securities on a scheduled settlement date. This article explains how a proliferation of settlement fails following the insolvency of Lehman Brothers Holdings Inc. in September 2008 led the Treasury Market Practices Group (TMPG)—a group of market professionals committed to supporting the integrity and efficiency of the U.S. Treasury market—to promote a change in the existing market convention. The change—the introduction of the fails charge—was significant because it mitigated an important dysfunctionality in the secondary market for U.S. Treasury securities and because it stands as an example of the value of cooperation between the public and private sectors in responding to altered market conditions in a flexible, timely, and innovative fashion.Treasury bonds ; Government securities ; Clearing of securities ; Secondary markets

Elasticity and Biochemistry of Growth Relate Replication Rate to Cell Length and Cross-link Density in Rod-Shaped Bacteria

AbstractIn rod-shaped bacteria, cell morphology is correlated with the replication rate. For a given species, cells that replicate faster are longer and have less cross-linked cell walls. Here, we propose a simple mechanochemical model that explains the dependence of cell length and cross-linking on the replication rate. Our model shows good agreement with existing experimental data and provides further evidence that cell wall synthesis is mediated by multienzyme complexes; however, our results suggest that these synthesis complexes only mediate glycan insertion and cross-link severing, whereas recross-linking is performed independently

How Myxobacteria Glide

BackgroundMany microorganisms, including myxobacteria, cyanobacteria, and flexibacteria, move by gliding. Although gliding always describes a slow surface-associated translocation in the direction of the cell's long axis, it can result from two very different propulsion mechanisms: social (S) motility and adventurous (A) motility. The force for S motility is generated by retraction of type 4 pili. A motility may be associated with the extrusion of slime, but evidence has been lacking, and how force might be generated has remained an enigma. Recently, nozzle-like structures were discovered in cyanobacteria from which slime emanated at the same rate at which the bacteria moved. This strongly implicates slime extrusion as a propulsion mechanism for gliding.ResultsHere we show that similar but smaller nozzle-like structures are found in Myxococcus xanthus and that they are clustered at both cell poles, where one might expect propulsive organelles. Furthermore, light and electron microscopical observations show that slime is secreted in ribbons from the ends of cells. To test whether the slime propulsion hypothesis is physically reasonable, we construct a mathematical model of the slime nozzle to see if it can generate a force sufficient to propel M. xanthus at the observed velocities. The model assumes that the hydration of slime, a cationic polyelectrolyte, is the force-generating mechanism.ConclusionsThe discovery of nozzle-like organelles in various gliding bacteria suggests their role in prokaryotic gliding. Our calculations and our observations of slime trails demonstrate that slime extrusion from such nozzles can account for most of the observed properties of A motile gliding

Helices at Interfaces

Helically coiled filaments are a frequent motif in nature. In situations commonly encountered in experiments coiled helices are squeezed flat onto two dimensional surfaces. Under such 2-D confinement helices form "squeelices" - peculiar squeezed conformations often resembling looped waves, spirals or circles. Using theory and Monte-Carlo simulations we illuminate here the mechanics and the unusual statistical mechanics of confined helices and show that their fluctuations can be understood in terms of moving and interacting discrete particle-like entities - the "twist-kinks". We show that confined filaments can thermally switch between discrete topological twist quantized states, with some of the states exhibiting dramatically enhanced circularization probability while others displaying surprising hyperflexibility

Meiotic failure in cyclin A1-deficient mouse spermatocytes triggers apoptosis through intrinsic and extrinsic signaling pathways and 14-3-3 proteins

Cyclin A1 (Ccna1), a member of the mammalian A type cyclins, is most abundantly expressed in spermatocytes and is essential for spermatogenesis in the mouse. Ccna1- deficient spermatocytes arrest at late meiotic prophase and undergo apoptosis. To further delineate the mechanisms and key factors involved in this process, we have examined changes in expression of genes involved in both intrinsic and extrinsic signaling pathways that trigger apoptosis in the mutant spermatocytes. Our results show that both pathways are involved, and that the factors involved in the intrinsic pathway were expressed earlier than those involved in the extrinsic pathway. We have also begun to identify in vivo Ccna1- interacting proteins, using an unbiased biochemical approach, and identified 14-3-3, a key regulator of apoptosis, as a Ccna1-interacting protein. Expression levels of 14-3-3 proteins remain unchanged between wild type and mutant testes but there were differences in the subcellular distribution. In wild type control, 14-3-3 is detected in both cytosolic and nuclear fractions whereas it is restricted to the cytoplasm in mutant testes. This differential distribution of 14-3-3 may contribute to the induction of apoptosis in Ccna1-deficient spermatocytes. These results provide insight into the apoptotic mechanisms and pathways that are triggered when progression through the meiotic cell cycle is defective in male gametogenesis

Dietary intake, nutritional status and mental wellbeing of homeless adults in Reading, UK

Malnutrition has been reported in the homeless, yet the specific nutritional issues faced by each homeless community are unclear. This is in part due to nutrient intake often being compared with dietary reference values as opposed to a comparative housed population. In addition, the complex interplay between nutrient intake, reward mediated behaviour and mental illness is frequently overlooked. This study aimed to compare the dietary intake, nutritional status and mental wellbeing of homeless and housed adults. Homeless (n 75) and matched housed (n 75) adults were recruited from Reading (UK). Nutrient intake was determined using the European Prospective Investigation into Cancer and Nutrition Norfolk FFQ. The Patient Health Questionnaire: Somatic Anxiety Depressive Symptoms (PHQ-SADS) assessed for signs of mental illness. Demographic, behavioural and physiological information was collected using closed-ended questions and anthropometric measurements. Overall, dietary intake was poorer in homeless adults who reported higher intakes of salt (8·0 v. 6·4 g, P=0·017), SFA (14·6 v. 13·0 %, P=0·002) and alcohol (5·3 v. 1·9 %, P<0·001) and lower intakes of fibre (13·4 v. 16·3 g, P<0·001), vitamin C (79 v. 109 mg, P<0·001) and fruit (96 v. 260 g, P<0·001) than housed. Smoking, substance misuse and PHQ-SADS scores were also higher in the homeless (P<0·001). Within the homeless population, street homeless (n 24) had lower SFA (13·7 v.15·0 %, P=0·010), Ca (858 v. 1032 mg, P=0·027) and milk intakes (295 v. 449 g, P=0·001) than hostel residents (n 51), which may reflect the issues with food storage. This study highlights the disparity between nutritional status in homeless and housed populations and the need for dietary intervention in the homeless community