Clonal separation and regionalisation during formation of the medial and lateral myotomes in the mouse embryo.

In vertebrates, muscles of the back (epaxial) and of the body wall and limbs (hypaxial) derive from precursor cells located in the dermomyotome of the somites. In this paper, we investigate the mediolateral regionalisation of epaxial and hypaxial muscle precursor cells during segmentation of the paraxial mesoderm and myotome formation, using mouse LaacZ/LacZ chimeras. We demonstrate that precursors of medial and lateral myotomes are clonally separated in the mouse somite, consistent with earlier studies in birds. This clonal separation occurs after segmentation of the paraxial mesoderm. We then show that myotome precursors are mediolaterally regionalised and that this regionalisation precedes clonal separation between medial and lateral precursors. Strikingly, the properties of myotome precursors are remarkably similar in the medial and lateral domains. Finally, detailed analysis of our clones demonstrates a direct spatial relationship between the myocytes in the myotome and their precursors in the dermomyotome, and earlier in the somite and presomitic mesoderm, refuting several models of myotome formation, based on permanent stem cell systems or extensive cell mingling. This progressive mediolateral regionalisation of the myotome at the cellular level correlates with progressive changes in gene expression in the dermomyotome and myotome.     

Lysozyme inactivation and aggregation in stirred-reactor

Mechanisms of enzyme inactivation and aggregation are still poorly understood. In this work, we are considering the characterisation of both inactivation and aggregation in stirred tank reactor, with lysozyme as the model enzyme.

The inactivation kinetics are first order. For stirring speeds in the range of 0–700 rpm, the kinetic constant is found to be proportional to the power brought by the impeller. It suggests that inactivation depends on collisions between enzyme molecules. Efficient collisions between native and inactive molecules induce native molecules to turn into inactive molecules and lead to lysozyme aggregation.

During inactivation, enzymes are found to aggregate as shown by light scattering measurements. The structure of aggregates was studied on samples treated for chemical denaturation and reduction. The aggregates are supramolecular edifices, mainly made up of inactivated enzymes linked by weak forces. But aggregates are also made up of dimers and trimers of lysozyme, linked by disulfide bridges. Dimers and trimers are 18% and 5%, respectively, of the total amount of lysozyme aggregates.

Whatever the stage of aggregate formation and the initial enzyme concentration are, these aggregates are irreversibly inactivated. Enzyme activity is definitely lost even if stirring is stopped and/or temperature decreased.

This study points out the importance of hydrodynamics in bioreactors and highlights the nature of the aggregates resulting from the interactions between native and inactive enzymes.     

Stereospecific binding of MRI contrast agents to human serum albumin: the case of Gd-(S)-EOB-DTPA (Eovist) and its (R) isomer

The water proton relaxation rate enhancement of the hepatospecific Gd-(S)-EOB-DTPA (Eovist) and of its (R) isomer in aqueous solutions free of protein, in serum and in 4% human serum albumin solution, are compared. In the absence of proteins, both compounds exhibit, as expected, the same proton relaxivity, as measured by the nuclear magnetic relaxation dispersion (NMRD) profiles. In serum and albumin solution, non-covalent binding of the paramagnetic complexes to macromolecules is observed. Both isomers are likely to bind to the same site of human serum albumin, but the affinity of the (S) isomer is larger than for the (R) isomer.     

Reliable estimation of the key variables and of their rates of change in alcoholic fermentation

The paper establishes a rigorous probabilistic framework for the reconciliation of apparently conflicting data from various physical and chemical measurements related to the key biological variables of alcoholic fermentation: the ethanol and the residual sugar concentrations. The analysis is carried out on a database consisting of 15 beer fermentation experiments, for which off-line determinations of ethanol concentration, fermentable sugar concentration, wort density and refractive index are available, as well as on-line records of evolved CO₂. The basic reconciliation method uses mass balance and monotonicity constraints derived from the biological knowledge of the fermentation process. In order to provide interpolated values and rate estimates, smoothness requirements are added. The reconciliation procedure gives more reliable estimates than any given measurement, detects outliers, helps fixing problems in the experimental setting and is also applicable on line.     

The effects of environment and ownership on children's innovation of tools and tool material selection

Research indicates that in experimental settings, young children of 3–7 years old are unlikely to devise a simple tool to solve a problem. This series of exploratory studies done in museums in the US and UK explores how environment and ownership of materials may improve children''s ability and inclination for (i) tool material selection and (ii) innovation. The first study takes place in a children''s museum, an environment where children can use tools and materials freely. We replicated a tool innovation task in this environment and found that while 3–4 year olds showed the predicted low levels of innovation rates, 4–7 year olds showed higher rates of innovation than the younger children and than reported in prior studies. The second study explores the effect of whether the experimental materials are owned by the experimenter or the child on tool selection and innovation. Results showed that 5–6 year olds and 6–7 year olds were more likely to select tool material they owned compared to tool material owned by the experimenter, although ownership had no effect on tool innovation. We argue that learning environments supporting tool exploration and invention and conveying ownership over materials may encourage successful tool innovation at earlier ages.     

Intra- and inter-observer analysis in the morphological assessment of early-stage embryos

Background  

The aim of this study was to determine the intra- and inter-observer variability in the evaluation of embryo quality. Multilevel images of embryos on day 1, day 2 and day 3, were analysed using different morphological parameters.     

Are patients with abnormal cervical smears adequately managed?

The outcome was assessed for all 1062 women in Nottingham who had a first report of abnormal cervical cytology in 1981. Satisfactory follow up could be found for only 628 (59%) of them. For 275 (26%) one subsequent normal smear had been reported but no further follow up requested. For 43 (4%), no subsequent test, after the abnormal smear, had been requested by the patient''s general practitioner. Thirty patients (3%), 22 of whom had been tested at a special clinic, had not responded to a request for follow up. Even after extensive efforts we could not find the outcome in the remaining 86 (8%) of the patients. Adequate follow up of patients with abnormal cervical cytology is not being achieved. Improvements in the records systems and some changes in procedure should be made to reduce this problem.     

Direct anabolic metabolism of three-carbon propionate to a six-carbon metabolite occurs in vivo across tissues and species

Anabolic metabolism of carbon in mammals is mediated via the one- and two-carbon carriers S-adenosyl methionine and acetyl-coenzyme A. In contrast, anabolic metabolism of three-carbon units via propionate has not been shown to extensively occur. Mammals are primarily thought to oxidize the three-carbon short chain fatty acid propionate by shunting propionyl-CoA to succinyl-CoA for entry into the TCA cycle. Here, we found that this may not be absolute as, in mammals, one nonoxidative fate of propionyl-CoA is to condense to two three-carbon units into a six-carbon trans-2-methyl-2-pentenoyl-CoA (2M2PE-CoA). We confirmed this reaction pathway using purified protein extracts provided limited substrates and verified the product via LC-MS using a synthetic standard. In whole-body in vivo stable isotope tracing following infusion of ¹³C-labeled valine at steady state, 2M2PE-CoA was found to form via propionyl-CoA in multiple murine tissues, including heart, kidney, and to a lesser degree, in brown adipose tissue, liver, and tibialis anterior muscle. Using ex vivo isotope tracing, we found that 2M2PE-CoA also formed in human myocardial tissue incubated with propionate to a limited extent. While the complete enzymology of this pathway remains to be elucidated, these results confirm the in vivo existence of at least one anabolic three- to six-carbon reaction conserved in humans and mice that utilizes propionate.