A chemical survey of exoplanets with ARIEL

Thousands of exoplanets have now been discovered with a huge range of masses, sizes and orbits: from rocky Earth-like planets to large gas giants grazing the surface of their host star. However, the essential nature of these exoplanets remains largely mysterious: there is no known, discernible pattern linking the presence, size, or orbital parameters of a planet to the nature of its parent star. We have little idea whether the chemistry of a planet is linked to its formation environment, or whether the type of host star drives the physics and chemistry of the planet’s birth, and evolution. ARIEL was conceived to observe a large number (~1000) of transiting planets for statistical understanding, including gas giants, Neptunes, super-Earths and Earth-size planets around a range of host star types using transit spectroscopy in the 1.25–7.8 μm spectral range and multiple narrow-band photometry in the optical. ARIEL will focus on warm and hot planets to take advantage of their well-mixed atmospheres which should show minimal condensation and sequestration of high-Z materials compared to their colder Solar System siblings. Said warm and hot atmospheres are expected to be more representative of the planetary bulk composition. Observations of these warm/hot exoplanets, and in particular of their elemental composition (especially C, O, N, S, Si), will allow the understanding of the early stages of planetary and atmospheric formation during the nebular phase and the following few million years. ARIEL will thus provide a representative picture of the chemical nature of the exoplanets and relate this directly to the type and chemical environment of the host star. ARIEL is designed as a dedicated survey mission for combined-light spectroscopy, capable of observing a large and well-defined planet sample within its 4-year mission lifetime. Transit, eclipse and phase-curve spectroscopy methods, whereby the signal from the star and planet are differentiated using knowledge of the planetary ephemerides, allow us to measure atmospheric signals from the planet at levels of 10–100 part per million (ppm) relative to the star and, given the bright nature of targets, also allows more sophisticated techniques, such as eclipse mapping, to give a deeper insight into the nature of the atmosphere. These types of observations require a stable payload and satellite platform with broad, instantaneous wavelength coverage to detect many molecular species, probe the thermal structure, identify clouds and monitor the stellar activity. The wavelength range proposed covers all the expected major atmospheric gases from e.g. H2O, CO2, CH4 NH3, HCN, H2S through to the more exotic metallic compounds, such as TiO, VO, and condensed species. Simulations of ARIEL performance in conducting exoplanet surveys have been performed – using conservative estimates of mission performance and a full model of all significant noise sources in the measurement – using a list of potential ARIEL targets that incorporates the latest available exoplanet statistics. The conclusion at the end of the Phase A study, is that ARIEL – in line with the stated mission objectives – will be able to observe about 1000 exoplanets depending on the details of the adopted survey strategy, thus confirming the feasibility of the main science objectives.Peer reviewedFinal Published versio

Genotypic and allelic variability in CYP19A1 among populations of African and European ancestry.

CYP19A1 facilitates the bioconversion of estrogens from androgens. CYP19A1 intron single nucleotide polymorphisms (SNPs) may alter mRNA splicing, resulting in altered CYP19A1 activity, and potentially influencing disease susceptibility. Genetic studies of CYP19A1 SNPs have been well documented in populations of European ancestry; however, studies in populations of African ancestry are limited. In the present study, ten 'candidate' intronic SNPs in CYP19A1 from 125 African Americans (AA) and 277 European Americans (EA) were genotyped and their frequencies compared. Allele frequencies were also compared with HapMap and ASW 1000 Genomes populations. We observed significant differences in the minor allele frequencies between AA and EA in six of the ten SNPs including rs10459592 (p<0.0001), rs12908960 (p<0.0001), rs1902584 (p = 0.016), rs2470144 (p<0.0001), rs1961177 (p<0.0001), and rs6493497 (p = 0.003). While there were no significant differences in allele frequencies between EA and CEU in the HapMap population, a 1.2- to 19-fold difference in allele frequency for rs10459592 (p = 0.004), rs12908960 (p = 0.0006), rs1902584 (p<0.0001), rs2470144 (p = 0.0006), rs1961177 (p<0.0001), and rs6493497 (p = 0.0092) was observed between AA and the Yoruba (YRI) population. Linkage disequilibrium (LD) blocks and haplotype clusters that is unique to the EA population but not AA was also observed. In summary, we demonstrate that differences in the allele frequencies of CYP19A1 intron SNPs are not consistent between populations of African and European ancestry. Thus, investigations into whether CYP19A1 intron SNPs contribute to variations in cancer incidence, outcomes and pharmacological response seen in populations of different ancestry may prove beneficial

Characteristics of <i>CYP19A1</i> SNPs and predicted binding sites and associated regulatory proteins.

<p>Characteristics of <i>CYP19A1</i> SNPs and predicted binding sites and associated regulatory proteins.</p

Genomic organization of <i>CYP19A1</i> showing the 10 SNPs used in the haplotype analysis.

<p>Presented is the <i>CYP19A1</i> gene and locations of the 10 <i>CYP19A1</i> SNPs on chromosome 15 coordinates 51, 536,349–51,338,598 estimated using UCSC Genome Browser February 2009 (GRCh37/hg19). SNPs are indicated by the rs number highlighted in red. Illustrated below the <i>CYP19A1</i> gene are the LD blocks and common haplotypes (≥ 2%) estimated using all SNPs across AA and EA groups separately. The red dotted lines denote the SNPs defined within the corresponding LD block. The lines between blocks link haplotypes that are transmitted with ≥ 2% frequency across blocks. LD blocks constructed in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0117347#pone.0117347.g001" target="_blank">Fig. 1</a> match haplotype blocks generated in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0117347#pone.0117347.g002" target="_blank">Fig. 2</a>.</p

Ethnic differences in <i>CYP19A1</i> minor allele frequency distribution across populations of European (EA) and African (AA) ancestry.

<p>*p<0.05;</p><p>**p<0.01;</p><p>***p<0.001</p><p>Ethnic differences in <i>CYP19A1</i> minor allele frequency distribution across populations of European (EA) and African (AA) ancestry.</p

Haplotype block structures for genotyped <i>CYP19A1</i> SNPs on chromosome 15q for EA and AA subjects from Arkansas.

<p>Shown above are the approximate locations of each of the ten <i>CYP19A1</i> SNPs (identified by their dbSNP rs number) among EA and AA populations. The values within the figure refer to the D’ values for each pairwise comparison. The color gradient from red to white indicates higher to lower LD with the darker color indicating higher LD between the SNP pairs.</p

Allele and genotype frequencies of the <i>CYP19A1</i> SNPs in various populations.

<p>African Americans; EA: European Americans; CEU: Utah residents with Northern and European ancestry; YRI: Yoruba in Ibadan, Nigeria; HCB: Hans Chinese in Beijing, China; JPT: Japanese in Tokyo, Japan; and GIH Gujarat Indians in Houston, TX</p><p>^a African Americans and European Americans in present study</p><p>^b HapMap data according to NCBI Entrez database</p><p>^c Umamaheswaran et al. (9)</p><p>^d Lee et al. (10)</p><p>^e 1000 Genomes ASW: Population of African ancestry from southwest USA</p><p>Minor allele frequency (in bold)</p><p>Allele and genotype frequencies of the <i>CYP19A1</i> SNPs in various populations.</p