The Opportunity Rover's Athena science investigation at Meridiani Planum, Mars

The Mars Exploration Rover Opportunity has investigated the landing site in Eagle crater and the nearby plains within Meridiani Planum. The soils consist of fine-grained basaltic sand and a surface lag of hematite-rich spherules, spherule fragments, and other granules. Wind ripples are common. Underlying the thin soil layer, and exposed within small impact craters and troughs, are flat-lying sedimentary rocks. These rocks are finely laminated, are rich in sulfur, and contain abundant sulfate salts. Small-scale cross-lamination in some locations provides evidence for deposition in flowing liquid water. We interpret the rocks to be a mixture of chemical and siliciclastic sediments formed by episodic inundation by shallow surface water, followed by evaporation, exposure, and desiccation. Hematite-rich spherules are embedded in the rock and eroding from them. We interpret these spherules to be concretions formed by postdepositional diagenesis, again involving liquid water.

Localization and physical property experiments conducted by Opportunity at Meridiani Planum

The location of the Opportunity landing site was determined to better than 10-m absolute accuracy from analyses of radio tracking data. We determined Rover locations during traverses with an error as small as several centimeters using engineering telemetry and overlapping images. Topographic profiles generated from rover data show that the plains are very smooth from meter- to centimeter-length scales, consistent with analyses of orbital observations. Solar cell output decreased because of the deposition of airborne dust on the panels. The lack of dust-covered surfaces on Meridiani Planum indicates that high velocity winds must remove this material on a continuing basis. The low mechanical strength of the evaporitic rocks as determined from grinding experiments, and the abundance of coarse-grained surface particles argue for differential erosion of Meridiani Planum.

The Spirit Rover's Athena science investigation at Gusev Crater, Mars

The Mars Exploration Rover Spirit and its Athena science payload have been used to investigate a landing site in Gusev crater. Gusev is hypothesized to be the site of a former lake, but no clear evidence for lacustrine sedimentation has been found to date. Instead, the dominant lithology is basalt, and the dominant geologic processes are impact events and eolian transport. Many rocks exhibit coatings and other characteristics that may be evidence for minor aqueous alteration. Any lacustrine sediments that may exist at this location within Gusev apparently have been buried by lavas that have undergone subsequent impact disruption.

Localization and physical properties experiments conducted by Spirit at Gusev Crater

The precise location and relative elevation of Spirit during its traverses from the Columbia Memorial station to Bonneville crater were determined with bundle-adjusted retrievals from rover wheel turns, suspension and tilt angles, and overlapping images. Physical properties experiments show a decrease of 0.2% per Mars solar day in solar cell output resulting from deposition of airborne dust, cohesive soil-like deposits in plains and hollows, bright and dark rock coatings, and relatively weak volcanic rocks of basaltic composition. Volcanic, impact, aeolian, and water-related processes produced the encountered landforms and materials.

Wind-related processes detected by the Spirit Rover at Gusev Crater, Mars

Wind-abraded rocks, ripples, drifts, and other deposits of windblown sediments are seen at the Columbia Memorial Station where the Spirit rover landed. Orientations of these features suggest formative winds from the north-northwest, consistent with predictions from atmospheric models of afternoon winds in Gusev Crater. Cuttings from the rover Rock Abrasion Tool are asymmetrically distributed toward the south-southeast, suggesting active winds from the north-northwest at the time (midday) of the abrasion operations. Characteristics of some rocks, such as a two-toned appearance, suggest that they were possibly buried and exhumed on the order of 5 to 60 centimeters by wind deflation, depending on location.

Tracing the pathways of neotropical migratory shorebirds using stable isotopes: a pilot study

We evaluated the potential use of stable isotopes to establish linkages between the wintering grounds and the breeding grounds of the Pectoral Sandpiper (Calidris melanotos), the White-rumped Sandpiper (Calidris fuscicollis), the Baird's Sandpiper (Calidris bairdii), and other Neotropical migratory shorebird species (e.g., Tringa spp.). These species molt their flight feathers on the wintering grounds and hence their flight feathers carry chemical signatures that are characteristic of their winter habitat. The objective of our pilot study was to assess the feasibility of identifying the winter origin of individual birds by: (1) collecting shorebird flight feathers from several widely separated Argentine sites and analyzing these for a suite of stable isotopes; and 2) analyzing the deuterium and 18O isotope data that were available from precipitation measurement stations in Argentina. Isotopic ratios (delta13C, delta15N and delta34S) of flight feathers were significantly different among three widely separated sites in Argentina during January 2001. In terms of relative importance in separating the sites, delta34S was most important, followed by delta15N, and then delta13C. In the complete discriminant analysis, the classification function correctly predicted group membership in 85% of the cases (jackknifed classification matrix). In a stepwise analysis delta13C was dropped from the solution, and site membership was correctly predicted in 92% of cases (jackknifed matrix). Analysis of precipitation data showed that both deltaD and delta18O were significantly related to both latitude and longitude on a countrywide scale (p < 0.001). Other variables, month, altitude, explained little additional variation in these isotope ratios. Several issues were identified that will likely constrain the degree of accuracy one can expect in predicting the geographic origin of birds from Argentina. There was unexplained variation in isotope ratios within and among the different wing feathers from individual birds. Such variation may indicate that birds are not faithful to a local site during their winter stay in Argentina. There was significant interannual variation in the deltaD and delta18O of precipitation. Hence, specific locations may not have a constant signature for some isotopes. Moreover, the fractionation that occurs in wetlands due to evaporation significantly skews local deltaD and delta18O values, which may undermine the strong large-scale gradients seen in the precipitation data. We are continuing the research with universities in Argentina with a focus on expanding the breadth of feather collection and attempting to resolve the identified issues.

High-frequency generation of conditional mutations affecting Drosophila melanogaster development and life span

Genome sequencing reveals that a large percentage of Drosophila genes have homologs in humans, including many human disease genes. The goal of this research was to develop methods to efficiently test Drosophila genes for functions in vivo. An important challenge is the fact that many genes function at more than one point during development and during the life cycle. Conditional expression systems such as promoters regulated by tetracycline (or its derivative doxycycline) are often ideal for testing gene functions. However, generation of transgenic animals for each gene of interest is impractical. Placing the doxycycline-inducible ("tet-on") promoter directed out of the end of the P transposable element produced a mobile, doxycycline-inducible promoter element, named PdL. PdL was mobilized to 228 locations in the genome and was found to generate conditional (doxycycline-dependent), dominant mutations at high frequency. The temporal control of gene overexpression allowed generation of mutant phenotypes specific to different stages of the life cycle, including metamorphosis and aging. Mutations characterized included inserts in the alpha-mannosidase II (dGMII), ash1, and pumilio genes. Novel phenotypes were identified for each gene, including specific developmental defects and increased or decreased life span. The PdL system should facilitate testing of a large fraction of Drosophila genes for overexpression and misexpression phenotypes at specific developmental and life cycle stages.

The Drosophila chiffon gene is required for chorion gene amplification, and is related to the yeast Dbf4 regulator of DNA replication and cell cycle

The Drosophila chorion genes encode the major protein components of the chorion (eggshell) and are arranged in two clusters in the genome. To meet the demand for rapid chorion synthesis, Drosophila ovary follicle cells amplify the chorion gene clusters approximately 80-fold. Amplification proceeds through repeated firing of one or more DNA replication origins located near the center of each gene cluster. Hypomorphic mutant alleles of the chiffon gene cause thin, fragile chorions and female sterility, and were found to eliminate chorion gene amplification. Null alleles of chiffon had the additional phenotypes of rough eyes and thin thoracic bristles: phenotypes often associated with disruption of normal cell cycle. The chiffon locus was cloned by chromosomal walking from the nearby cactus locus. A 6.5 kb transcript was identified and confirmed to be chiffon by sequencing of mutant alleles and by phenotypic rescue with genomic transformation constructs. The protein predicted by translation of the 5.1 kb chiffon ORF contains two domains related to the S. cerevisiae Dbf4 regulator of DNA replication origin firing and cell cycle progression: a 44 residue domain designated CDDN1 (43% identical) and a 41 residue domain designated CDDN2 (12% identical). The CDDN domains were also found in the S. pombe homolog of Dbf4, Dfp1, as well as in the proteins predicted by translation of the Aspergillus nimO gene and specific human and mouse clones. The data suggest a family of eukaryotic proteins related to Dbf4 and involved in initiation of DNA replication.

The k43 gene, required for chorion gene amplification and diploid cell chromosome replication, encodes the Drosophila homolog of yeast origin recognition complex subunit 2

Lethal alleles of the Drosophila k43 gene result in small or missing imaginal discs, greatly reduced mitotic index, and fragmented and abnormally condensed chromosomes. A female-sterile allele of k43 specifically reduces chorion gene amplification in ovarian follicle cells. k43 was cloned by chromosomal walking, and the identification of the k43 gene was confirmed by phenotypic rescue and sequence analysis of mutant alleles. The sequence analyses reveal that the k43 gene encodes the Drosophila homolog of the yeast origin recognition complex subunit 2 (Orc2p), a protein required for replication origin function and transcriptional silencing in yeast. These results suggest an evolutionarily conserved role for Orc2p in eukaryotic chromosomal DNA replication.

Diagnosis of breast implant rupture: imaging findings and relative efficacies of imaging techniques

OBJECTIVE

The purpose of this study was to compare the efficacies of mammography, sonography, CT, and MR imaging in the detection of breast implant rupture and to analyze the imaging findings.

SUBJECTS AND METHODS

Thirty-two women with 63 silicone breast implants participated in the study. All but one had signs and symptoms suggestive of rupture, and all had requested that their implants be removed before they were enrolled in this imaging study. All patients had film-screen mammography, sonography, CT, and MR imaging. Twenty-two ruptures were found at surgery; 21 were intracapsular and one was extracapsular. The relative efficacies of the imaging studies were determined, and the imaging findings were compared with the surgical results.

RESULTS

Of the 32 women with 63 implants, mammographic sensitivity for detecting implant rupture was only 23% but the specificity was 98%. Sonography had a higher sensitivity (59%), but its specificity was significantly lower (79%). CT had a sensitivity of 82% and a specificity of 88%. MR was the only imaging technique that consistently provided evidence that enabled the evaluation of intracapsular and extracapsular ruptures. The sensitivity and specificity of MR imaging were 95% and 93%, respectively.

CONCLUSION

Our results show that MR imaging is more sensitive and specific for the detection of breast implant rupture than is mammography, CT, or sonography.

Ring substituted and other conformationally constrained tyrosine analogues of [D-Pen2,D-Pen5]enkephalin with delta opioid receptor selectivity

The conformationally restricted, cyclic disulfide-containing delta opioid receptor selective enkephalin analogue [D-Pen2,D-Pen5] enkephalin (DPDPE) was modified by 2' (CH3) and 3' (I, OCH3, NO2, NH2) ring substitutions and by beta-methyl conformationally constrained beta-methyltyrosine derivatives in the 1 position. The potency and selectivity of these analogues were evaluated by bioassay in the mouse vas deference (MVD, delta receptor assay) and guinea pig ileum (GPI, mu receptor assay) assays and by radioreceptor binding assays in the rat brain using [3H]CTOP (mu ligand) and [3H][p-ClPhe4]DPDPE (delta ligand). The analogues showed highly variable potencies in the binding assays and in the bioassays. Aromatic ring substituents with positive Hammett constants had decreased potency, while substituents with negative Hammett constraints has increased potency for the opioid receptor. The most potent and most selective compound based on the binding was [2'-MeTyr1]DPDPE (IC50 = 0.89 nM and selectivity ratio 1310 in the binding assays). The 6-hydroxy-2-aminotetralin-2-carboxylic acid-containing analogue, [Hat1]DPDPE, also was highly potent and selective in both assays, demonstrating that significant modifications of tyrosine in enkephalins are possible with maintenance of high potency and delta opioid receptor selectivity. Of the beta-methyl-substituted Tyr1 analogues, [(2S,3R)-beta-MeTyr1]DPDPE was the most potent and the delta receptor selective. The results with substitution of beta-MeTyr or Hat instead of Tyr also demonstrate that topographical modification in a conformationally restricted ligand can significantly modulate both potency and receptor selectivity of peptide ligands that have multiple sites of biological activity.

Synthesis of highly mu and delta opioid receptor selective peptides containing a photoaffinity group

A series of cyclic, conformationally constrained photolabile peptides related to the enkephalins and to somatostatin were designed and synthesized in an effort to develop highly selective and potent peptides for the delta and mu opioid receptors. The following new peptides were prepared and tested for their delta opioid receptor potency and selectivity in the guinea pig ileum assay, the mouse vas deferens assay, and the rat brain binding assay: H-Tyr-D-Pen-Gly-p-NH2Phe-D-Pen-OH (1, [p-NH2Phe4]DPDPE) and H-Tyr-D-Pen-Gly-p-N3Phe-D-Pen-OH (2, [p-N3Phe4]-DPDPE). The following new peptides were prepared and tested for their mu opioid receptor potency and selectivity in the same assays: H-D-Phe-Cys-p-NH2Phe-D-Trp-Lys-Thr-Pen-Thr-NH2 (3, [p-NH2Phe3]CTP) and D-Phe-Cys-p-N3Phe-D-Trp-Lys-Thr-Pen-Thr-NH2 (4, [p-N3Phe3]CTP). The delta selective photoaffinity peptide 2 displayed both high affinity (IC50 = 9.5 nM) and good selectivity (IC50 mu/IC50 delta = 1053) as an agonist at delta opioid receptors in bioassays, and 2 also displayed moderate affinity (33 nM) and excellent selectivity (IC50 mu/IC50 delta = 110) for rat brain delta opioid receptors. The mu selective photoaffinity peptide 4 displayed very weak affinity (8% contraction at 300 nM) at mu opioid receptors in bioassays, but good affinity (IC50 = 48.6 nM) and excellent selectivity (IC50 delta/IC50 mu = 412) for the rat brain mu opioid receptors. These conformationally constrained cyclic photoaffinity peptides may be useful tools to investigate the pharmacology of delta and mu opioid receptors.