Selection for transgene homozygosity in embryonic stem cells results in extensive loss of heterozygosity

Embryonic stem cells offer unprecedented opportunities for random or targeted genome alterations in the mouse. We present here an efficient strategy to create chromosome-specific loss of heterozygosity in embryonic stem cells. The combination of this method with genome-wide mutagenesis in ES cells (using chemical mutagens or gene-trap vectors) opens up the possibility for in vitro or in vivo functional screening of recessive mutations in the mouse.     

Effets immédiats de quelques antibiotiques sur l'électro-osmose chezNitella flexilis L.

Summary The short term effects of chloramphenicol, polymyxin sulfate and oligomycin A + B (the latter in 0,5M alcoholic solution) on the basic flow and the electrosmosis inNitella were studied. Both chloramphenicol and polymyxin increase the basic flow but only polymyxin increases the electro-osmotic efficiency.     

Variations de la différence de potentiel électrochimique des chlorures chezNitella en présence de benzène sulphonate

Summary The chloride electrochemical potential difference between the inside of cells ofNitella translucens and some external solutions, where Cl has been progressively replaced by benzenesulphonate, has been measured by means of Ag-AgCl electrodes. It appears that benzenesulphonate moves into the cell by an electrogenic pump and that the uptake of Cl byNitella is not in contradiction with a carrier hypothesis.

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This work was supported by grants from the F.N.R.S. and was carried out in the Biophysics Section of the Edinburgh University. We are indebted to Dr. E. J.Williams and Dr.Hogg for having sponsored this research and kindly provided the material.     

Inhibition of human pancreatic elastase II activity on human aortic elastin by human alpha 2-macroglobulin

Human alpha 2-macroglobulin-human pancreatic elastase II binding were investigated using a homologous substrate, human aortic elastin, in order to test the enzymatic activity. We demonstrated that two moles of alpha 2-M are required to inhibit one mole of HPEII when the enzyme is added to a mixture of elastin and alpha 2-M. In addition, when the elastase-alpha 2-M complex is prepared under some circumstances, it exhibits an elastinolytic activity.     

Shell microlaminations of the freshwater bivalveHyridella depressa as an archival monitor of manganese water concentration: Experimental investigation by depth profiling using secondary ion mass spectrometry (SIMS)

Specimens of the freshwater unionid bivalveHyridella depressa were experimentally exposed to a synthetic river water containing an elevated Mn water concentration (20 mg l^–1) for 2 or 6 days. SIMS depth profiles through the incremental nacre microlaminations or tablets (0.6 m breadth) of the shells of these bivalves showed increases in the signal intensity of Ca-normalised Mn that corresponded to the period of exposure. These results support the proposition that bivalve shells can be used as retrospective monitors of water chemistry. They also indicate that 1) there is a lag phase between exposure to the elevated Mn water concentration and its expression in the shell, and 2) the period for Mn in the shell to reach equilibrium with the aquatic medium is greater that 2 to 6 days.     

A laser-plasma accelerator producing monoenergetic electron beams

Particle accelerators are used in a wide variety of fields, ranging from medicine and biology to high-energy physics. The accelerating fields in conventional accelerators are limited to a few tens of MeV m(-1), owing to material breakdown at the walls of the structure. Thus, the production of energetic particle beams currently requires large-scale accelerators and expensive infrastructures. Laser-plasma accelerators have been proposed as a next generation of compact accelerators because of the huge electric fields they can sustain (>100 GeV m(-1)). However, it has been difficult to use them efficiently for applications because they have produced poor-quality particle beams with large energy spreads, owing to a randomization of electrons in phase space. Here we demonstrate that this randomization can be suppressed and that the quality of the electron beams can be dramatically enhanced. Within a length of 3 mm, the laser drives a plasma bubble that traps and accelerates plasma electrons. The resulting electron beam is extremely collimated and quasi-monoenergetic, with a high charge of 0.5 nC at 170 MeV.