While evidence in both sporadic and inherited human colorectal cancer and MIN mice implicate the tumor suppressor gene, APC, in the causation of colorectal carcinogenesis, this gene has not been confirmed to be involved in rodent chemically-induced colon cancer models (RCCM). These experimental models are widely used to elucidate mechanisms involved in colon carcinogenesis (initiation, promotion and progression) as well as studies on chemoprevention (dietary and other) and intervention. To validate the RCCM as relevant models for sporadic human colorectal cancer, and to facilitate research on the role of the APC gene in colon carcinogenesis, we investigated the role of APC in azoxymethane (AOM)-induced colorectal tumors in mice. Using an antibody that recognizes the carboxy terminus of APC, we have characterized the pattern of staining observed in normal mouse intestinal tissue, in MIN mouse intestinal adenomas and in AOM-induced mouse colon tumors. The APC protein was localized in the cytoplasm of normal colonic epithelial cells. In the small intestine there was APC immunoreactivity along the villous and staining of the Paneth cells at the base of the glands. In the proximal and distal colonic crypts there appeared to be a gradient of staining which increased towards the luminal surface. This gradient was not as apparent in the small intestinal villi. Nuclei and mucus in the goblet cells showed no immunoreactivity. MIN mouse small bowel and colonic adenomas, known to have lost APC, stained negatively for APC. AOM-induced adenomas and carcinomas also consistently stained negatively using this antibody. This study demonstrates for the first time the loss of wild-type APC protein in AOM-induced mouse colon tumors and suggests that alterations in expression of this tumor suppressor gene, which is so commonly mutated in human colon cancer, is also involved in this animal model of colon cancer.
[1] A new antenna layout for a Super Dual Auroral Radar Network (SuperDARN) HF radar has been developed. The new layout utilizes two auxiliary arrays; one behind and one in front of the main array, rather than the single auxiliary array that existing radars use. The rear auxiliary array consists of three antennas providing beam-steering capability while the front auxiliary array consists of a single antenna. This layout is expected to greatly improve the calculation of elevation angle of arrival. Simulations presented show the advantages and disadvantages of using twin-terminated folded dipole (TTFD) antennas and log-periodic dipole arrays in standard and modified SuperDARN array configurations. TTFD antennas are shown to have superior front-to-back ratio and beam-steering capability but suffer from shadowing effects due to the presence of corner reflectors. Impedance-matching techniques used in SuperDARN radars are discussed, and the results of a new matching method, exhibiting a superior voltage standing-wave ratio over the SuperDARN frequency band, are presented. Shadowing of the main array by the front auxiliary array is investigated, and it is shown that the impact of the front array on the main array gain pattern is significantly less for the case of a single front antenna than for a four-antenna front array. Radar phase calibration techniques are discussed, and it is proposed that the additional single-antenna front array be used for system-wide radar phase calibration. An algorithm for the determination of elevation angle of arrival using the new layout is also given.
The Tasman International Geospace Environment Radar (Radar) is a dual AF radar system with overlapping footprints designed to map ionospheric motions by detecting ionspheric scatter. The first radar was set up on Bmny Island, T a r mania at the end of 1999 and development of the second radar to be placed near Invercargill, NZ, has begun. TIGER is part of the Super Dual Auroral Radar Network (SuperDARN) wbieb CUIrently consists of 15 radars deployed in the northem and sonthern hemispheres. TIGER is located more equatolward than other SuperDARN radars enabling it to observe new phenomena, such as Auroral Westward Flow Channels (AWFCs). This paper describes TIGER'S capabilities and presents examples of observations, including an AWFC. Plans to develop digital transmitters and receivers are discussed as is a proposal to extend the network to even lower latitudes by deploying two additional radars.
[1] Calculations have been developed for the determination of elevation angle of arrival for a modified Super Dual Auroral Radar Network (SuperDARN) HF radar antenna layout consisting of dual auxiliary interferometer arrays: one behind and one in front of the main array. These calculations show that such a layout removes the 2 ambiguity or angle-of-arrival aliasing effect observed in existing SuperDARN HF radars. Ray tracing and simulation results are presented which show that there is significant potential for aliasing with existing SuperDARN radars and the standard interferometer algorithm under routine operating conditions. Citation: McDonald, A. J., J. Whittington, S. de Larquier, E. Custovic, T. A. Kane, and J. C. Devlin (2013), Elevation angle-of-arrival determination for a standard and a modified superDARN HF radar layout, Radio Sci., 48,[709][710][711][712][713][714][715][716][717][718][719][720][721]
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