Drug resistance in D. discoideum: isolation of 4-nitroquinoline 1-oxide resistant mutants

The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file.Title from title screen of research.pdf file viewed on (July 14, 2006)Includes bibliographical references.Thesis (M.A.) University of Missouri-Columbia 2005.Dissertations, Academic -- University of Missouri--Columbia -- Biological sciences.The drug 4-nitroquinoline 1-oxide (4NQO) displays both carcinogenic and antitumor effects, a well known characteristic of many chemotherapeutic drugs. In addition 4NQO shares a similar operating mechanism with the commonly used chemotherapeutic drug cisplatin. Previously, using the model organism Dictyostelium discoideum, we have shown that we can alter sensitivity to cisplatin by deleting or overexpressing enzymes in the sphingolipid metabolic pathway. Similarly, this work analyzed the cellular response to 4NQO in Dictyostelium discoideum. To study the molecular basis of 4NQO resistance in Dictyostelium, I used restriction enzyme mediated integration (REMI), a direct insertional mutagenesis approach, to isolate 4NQO resistant mutants. This study lead to the isolation of two Dictyostelium mutants showing about 1.5 to 4.5 fold more resistance than the wild-type. Using inverse PCR and DA sequencing one mutant disruption was found to be in a retrotransposon and in the second mutant the disruption was fond to be in an intergenic region between a S-adenosylmethionine-dependent methyltransferase gene and a retrotransposon. This study confirmed that Dictyostelium discoideum can be used as a model system to study the molecular basis of resistance to anticancer drugs

External field control of donor electron exchange at the Si/SiO2 interface

We analyze several important issues for the single- and two-qubit operations in Si quantum computer architectures involving P donors close to a SiO2 interface. For a single donor, we investigate the donor-bound electron manipulation (i.e. 1-qubit operation) between the donor and the interface by electric and magnetic fields. We establish conditions to keep a donor-bound state at the interface in the absence of local surface gates, and estimate the maximum planar density of donors allowed to avoid the formation of a 2-dimensional electron gas at the interface. We also calculate the times involved in single electron shuttling between the donor and the interface. For a donor pair, we find that under certain conditions the exchange coupling (i.e. 2-qubit operation) between the respective electron pair at the interface may be of the same order of magnitude as the coupling in GaAs-based two-electron double quantum dots where coherent spin manipulation and control has been recently demonstrated (for example for donors ~10 nm below the interface and \~40 nm apart, J~10^{-4} meV), opening the perspective for similar experiments to be performed in Si.Comment: 11 pages, 15 figures. Changes in Eq. 24 plus minor typo

Electron Paramagnetic Resonance of Boron Acceptors in Isotopically Purified Silicon

The electron paramagnetic resonance (EPR) linewidths of B acceptors in Si are found to reduce dramatically in isotopically purified 28Si single crystals. Moreover, extremely narrow substructures in the EPR spectra are visible corresponding to either an enhancement or a reduction of the absorbed microwave on resonance. The origin of the substructures is attributed to a combination of simultaneous double excitation and spin relaxation in the four level spin system of the acceptors. A spin population model is developed which qualitatively describes the experimental results.Comment: 4 pages, 3 figure

Using MGA to shorten the beef breeding season (2002)

Modified conventional synchronization systems for beef cows boost fertility and increase the total number of females that can be inseminated.New March 2002 -- Extension website

The Stability Balloon for Two-dimensional Vortex Ripple Patterns

Patterns of vortex ripples form when a sand bed is subjected to an oscillatory fluid flow. Here we describe experiments on the response of regular vortex ripple patterns to sudden changes of the driving amplitude a or frequency f. A sufficient decrease of f leads to a "freezing" of the pattern, while a sufficient increase of f leads to a supercritical secondary "pearling" instability. Sufficient changes in the amplitude a lead to subcritical secondary "doubling" and "bulging" instabilities. Our findings are summarized in a "stability balloon" for vortex ripple pattern formation.Comment: 4 pages, 5 figure

Proteomics of canine lymphoma identifies potential cancer-specific protein markers

Purpose: Early diagnosis of cancer is crucial for the success of treatment of the disease, and there is a need for markers whose differential expression between disease and normal tissue could be used as a diagnostic tool. Spontaneously occurring malignancies in pets provide a logical tool for translational research for human oncology. Lymphoma, one of the most common neoplasms in dogs, is similar to human non-Hodgkin's lymphoma and could serve as an experimental model system. Experimental Design: Thirteen lymph nodes from normal dogs and 11 lymph nodes from dogs with B-cell lymphoma were subjected to proteomic analysis using two-dimensional PAGE separation and matrix-assisted laser desorption/ionization time-of-flight analysis. Results: A total of 93 differentially expressed spots was subjected to matrix-assisted laser desorption/ionization time-of-flight tandem mass spectrometry analysis, and several proteins that showed differential expression were identified. Of these, prolidase (proline dipeptidase), triosephosphate isomerase, and glutathione S-transferase were down-regulated in lymphoma samples, whereas macrophage capping protein was up-regulated in the lymphoma samples. Conclusions: These proteins represent potential markers for the diagnosis of lymphoma and should be further investigated in human samples for validation of their utility as diagnostic markers

Dynamical models for sand ripples beneath surface waves

We introduce order parameter models for describing the dynamics of sand ripple patterns under oscillatory flow. A crucial ingredient of these models is the mass transport between adjacent ripples, which we obtain from detailed numerical simulations for a range of ripple sizes. Using this mass transport function, our models predict the existence of a stable band of wavenumbers limited by secondary instabilities. Small ripples coarsen in our models and this process leads to a sharply selected final wavenumber, in agreement with experimental observations.Comment: 9 pages. Shortened version of previous submissio