Biomedical subjects

N Gorelick

Publications and source records attributed to N Gorelick.

6 recordsLinked to original sources

PubMed2005

Evidence for magmatic evolution and diversity on Mars from infrared observations.

Compositional mapping of Mars at the 100-metre scale with the Mars Odyssey Thermal Emission Imaging System (THEMIS) has revealed a wide diversity of igneous materials. Volcanic evolution produced compositions from low-silica basalts to high-silica dacite in the Syrtis Major caldera. The existence of dacite demonstrates that highly evolved lavas have been produced, at least locally, by magma evolution through fractional crystallization. Olivine basalts are observed on crater floors and in layers exposed in canyon walls up to 4.5 km beneath the surface. This vertical distribution suggests that olivine-rich lavas were emplaced at various times throughout the formation of the upper crust, with their growing inventory suggesting that such ultramafic (picritic) basalts may be relatively common. Quartz-bearing granitoid rocks have also been discovered, demonstrating that extreme differentiation has occurred. These observations show that the martian crust, while dominated by basalt, contains a diversity of igneous materials whose range in composition from picritic basalts to granitoids rivals that found on the Earth.

Journal Article↗

PubMed2004

Mineralogy at Meridiani Planum from the Mini-TES Experiment on the Opportunity Rover.

The Miniature Thermal Emission Spectrometer (Mini-TES) on Opportunity investigated the mineral abundances and compositions of outcrops, rocks, and soils at Meridiani Planum. Coarse crystalline hematite and olivine-rich basaltic sands were observed as predicted from orbital TES spectroscopy. Outcrops of aqueous origin are composed of 15 to 35% by volume magnesium and calcium sulfates [a high-silica component modeled as a combination of glass, feldspar, and sheet silicates (approximately 20 to 30%)], and hematite; only minor jarosite is identified in Mini-TES spectra. Mini-TES spectra show only a hematite signature in the millimeter-sized spherules. Basaltic materials have more plagioclase than pyroxene, contain olivine, and are similar in inferred mineral composition to basalt mapped from orbit. Bounce rock is dominated by clinopyroxene and is close in inferred mineral composition to the basaltic martian meteorites. Bright wind streak material matches global dust. Waterlain rocks covered by unaltered basaltic sands suggest a change from an aqueous environment to one dominated by physical weathering.

Calcium Sulfate↗

PubMed2004

Initial results from the Mini-TES experiment in Gusev Crater from the Spirit Rover.

The Miniature Thermal Emission Spectrometer (Mini-TES) on Spirit has studied the mineralogy and thermophysical properties at Gusev crater. Undisturbed soil spectra show evidence for minor carbonates and bound water. Rocks are olivinerich basalts with varying degrees of dust and other coatings. Dark-toned soils observed on disturbed surfaces may be derived from rocks and have derived mineralogy (+/-5 to 10%) of 45% pyroxene (20% Ca-rich pyroxene and 25% pigeonite), 40% sodic to intermediate plagioclase, and 15% olivine (forsterite 45% +/-5 to 10). Two spectrally distinct coatings are observed on rocks, a possible indicator of the interaction of water, rock, and airfall dust. Diurnal temperature data indicate particle sizes from 40 to 80 microm in hollows to approximately 0.5 to 3 mm in soils.

Carbonates↗

PubMed1998

Spontaneous mutation in lacI transgenic mice: a comparison of tissues.

The nature of spontaneous mutations in the lacI transgene of Big Blue mice was determined in selected tissues. The mutant frequencies ranged from 2.5 x 10(-5) to 7.1 x 10(-5) for liver, spleen, bladder, stomach, kidney, bone marrow, lung and skin. We also determined the DNA sequence alterations in the mutants recovered from these tissues. In all tissues the predominant class of mutations was G:C-->A:T transitions, most of which occurred at 5'-CpG-3' dinucleotide sequences. Bladder, kidney and skin display the highest contribution of G:C-->A:T transitions. The second most common class of mutations was G:C-->T:A transversions. All other base substitution classes contributed < 10% each. Of the non-substitution events, the loss of a single base pair was the most frequently occurring event (< 10%). The similarity of mutational spectra (in terms of kinds of mutations detected by the lacI transgenic system) in all tissues examined supports the idea that similar mutational pathways function in these tissues in the absence of chemical or physical stimulus.

Animals↗

PubMed1995

Genotoxicity in the rodent urinary bladder.

Elucidation of the mechanisms by which a chemical may induce urinary bladder tumours in rodents can be expected to provide insight into the relative risk from that agent. The methodologies for exploring whether tumour induction may be a response to direct genotoxic effect of the compound have been successfully applied to the bladders of both mice and rats. Thus, with experimental approaches that utilize adduct detection through the use of immunochemical and postlabelling techniques, unscheduled DNA synthesis and mutagenicity as studied with transgenic animals it is possible to obtain fundamental information on the genotoxic potential of carcinogens in the target bladder. Application of these experimental approaches to carcinogens for which the mechanisms of action are not known should permit assessment of the likelihood that genotoxic or non-genotoxic mechanisms are involved in the tumour induction process. Moreover, such studies may provide knowledge of the molecular pathways that are involved in the action of genotoxic agents, thus enabling judgements to be made as to whether humans are subject to tumour induction by the chemical.

Animals↗

PubMed1994

Development of a lambda-based complementation assay for the preliminary localization of lacI mutants from the Big Blue mouse: implications for a DNA-sequencing strategy.

The Big Blue transgenic mouse carrying the E. coli lacI gene as a mutational target in a lambda-based shuttle vector has been receiving increasing attention in genotoxicity testing because it offers the potential of studying mutation in a mammalian system in vivo. The system not only provides information on mutant frequency, but it also offers the potential of providing information about mutational specificity. Such data is not only important for studies of mutational mechanisms; it offers a critical advantage for determining the mutational response at levels where significant increases in mutant frequency have not been discerned. The repeated sequencing of the entire 1080-bp lacI target, however, remains a formidable task. Here we report on the adaptation of the "negative complementation" assay for the lacI-d phenotype to accommodate the lambda lacI recovered from the Big Blue transgenic animal. This assay permits the localization of mutations to an approximately 330-bp region to facilitate the production of mutational specificity data. The assay is based upon lysogenization of the lambda containing the lacI mutation into a lacI+ host. Of 107 sequenced lacI mutants recovered from Big Blue mice, 74 were identified as NC+ (lacI-d) using this assay. Of these 74, 49 occurred in the region 32-208 bp, which has traditionally been viewed as the NC+ domain. 33 of these mutations were previously identified as producing the NC+ phenotype while another 7 occurred at sites where NC+ mutants have been recovered, but involved a new base substitution. 9 mutants involved new sites. An additional 25 mutants located downstream of the presumed NC+ region were also found to be NC+ as determined by their blue colour on X-gal plates. Of these, 18 occurred in the 209-360-bp region. In parallel, 54 lacI mutants carrying unknown mutations were examined. 37 of these produced blue colonies in this assay. The sequencing of these mutants revealed that 20 (54%) of the 37 mutants were located in the 32-208-bp region. This complementation assay can potentially reduce the amount of DNA sequencing necessary to produce a mutational spectrum by optimising the choice of sequencing primers, and thus provide a significant saving of the material and time required. Furthermore, evidence indicates that the restriction of the mutational target to the NC+ region extends these savings without reducing the usefulness of the mutational specificity data.

Amino Acid Sequence↗