A method for the enrichment of auxotrophic mutants of Serratia marcescens with the antibiotic azthreonam

A new method for the enrichment of cultures of Serratia marcescens for auxotrophic mutants has been developed. The method is based on the formation of filaments by growing cells in minimal medium M70 containing azthreonam. Auxotrophic mutants unable to grow in M70 do not form filaments. Mutants are collected from the culture by filtration.     

SIMPROT: Using an empirically determined indel distribution in simulations of protein evolution

Background  

General protein evolution models help determine the baseline expectations for the evolution of sequences, and they have been extensively useful in sequence analysis and for the computer simulation of artificial sequence data sets.     

Respiration and Protein Synthesis in Dormant and After-ripened Seeds of Avena fatua

Dormant seeds of Avena fatua, which do not germinate when allowed to imbibe water, have a respiration rate only about 20% less than that of imbibed nondormant (after-ripened) seeds in the period before actual germination and are capable of synthesizing protein at a rate comparable to that of the nondormant seeds. An increase of protein synthesis is observed in nondormant seeds at the beginning of root protrusion. Autoradiography of seeds administered ³H-leucine shows that protein synthesis occurs in the axis part of the embryo, the scutellum, the coleorhiza, and the aleurone layer. Dormancy in seeds is not a state of general inactivity; rather, it must be due to some specific metabolic block.     

Tracking morphogenetic tissue deformations in the early chick embryo

Embryonic epithelia undergo complex deformations (e.g. bending, twisting, folding, and stretching) to form the primitive organs of the early embryo. Tracking fiducial markers on the surfaces of these cellular sheets is a well-established method for estimating morphogenetic quantities such as growth, contraction, and shear. However, not all surface labeling techniques are readily adaptable to conventional imaging modalities and possess different advantages and limitations. Here, we describe two labeling methods and illustrate the utility of each technique. In the first method, hundreds of fluorescent labels are applied simultaneously to the embryo using magnetic iron particles. These labels are then used to quantity 2-D tissue deformations during morphogenesis. In the second method, polystyrene microspheres are used as contrast agents in non-invasive optical coherence tomography (OCT) imaging to track 3-D tissue deformations. These techniques have been successfully implemented in our lab to study the physical mechanisms of early head fold, heart, and brain development, and should be adaptable to a wide range morphogenetic processes.     

<Emphasis Type="Italic">In vivo</Emphasis> assessment of the impedance ratio method used in electronic foramen locators

Background  

The results of an in vivo study on the "ratio method" used in electronic foramen locators (EFL) are presented. EFLs are becoming widely used in the determination of the working length (WL) during the root canal treatment. The WL is the distance from a coronal reference point to the point at which canal preparation and filling should terminate. The "ratio method" was assessed by many clinicians with the aim of determining its ability to locate the apical foramen (AF). Nevertheless, in vivo studies to assess the method itself and to explain why the "ratio method" is able to locate the apical foramen and is unable to determine intermediate distances were not published so far.     

The challenge of cross-cultural clinical trials research: case report from the Tibetan Autonomous Region, People's Republic of China

Efforts to conduct Western clinical research in non-Western medical settings with little or no familiarity with such methodologies are on the rise, but documented accounts of the ways that biomedical science requires negotiation and translation across cultures are not plentiful. This article adds to this literature through analysis of an NICHD-funded collaborative research effort in women's health carried out in the Tibetan Autonomous Region of the People's Republic of China. The research involved a feasibility study for an eventual clinical trial comparing Tibetan medicine with misoprostol for preventing postpartum hemorrhage in delivering women. It explores strategies of negotiation and translation in and around notions of the scientific method, informed consent procedures, randomization, blinding, placebo, and concepts of medical standardization.