RESUMO
Planetary rings are observed not only around giant planets1, but also around small bodies such as the Centaur Chariklo2 and the dwarf planet Haumea3. Up to now, all known dense rings were located close enough to their parent bodies, being inside the Roche limit, where tidal forces prevent material with reasonable densities from aggregating into a satellite. Here we report observations of an inhomogeneous ring around the trans-Neptunian body (50000) Quaoar. This trans-Neptunian object has an estimated radius4 of 555 km and possesses a roughly 80-km satellite5 (Weywot) that orbits at 24 Quaoar radii6,7. The detected ring orbits at 7.4 radii from the central body, which is well outside Quaoar's classical Roche limit, thus indicating that this limit does not always determine where ring material can survive. Our local collisional simulations show that elastic collisions, based on laboratory experiments8, can maintain a ring far away from the body. Moreover, Quaoar's ring orbits close to the 1/3 spin-orbit resonance9 with Quaoar, a property shared by Chariklo's2,10,11 and Haumea's3 rings, suggesting that this resonance plays a key role in ring confinement for small bodies.
RESUMO
Hitherto, rings have been found exclusively around the four giant planets in the Solar System. Rings are natural laboratories in which to study dynamical processes analogous to those that take place during the formation of planetary systems and galaxies. Their presence also tells us about the origin and evolution of the body they encircle. Here we report observations of a multichord stellar occultation that revealed the presence of a ring system around (10199) Chariklo, which is a Centaur--that is, one of a class of small objects orbiting primarily between Jupiter and Neptune--with an equivalent radius of 124 ± 9 kilometres (ref. 2). There are two dense rings, with respective widths of about 7 and 3 kilometres, optical depths of 0.4 and 0.06, and orbital radii of 391 and 405 kilometres. The present orientation of the ring is consistent with an edge-on geometry in 2008, which provides a simple explanation for the dimming of the Chariklo system between 1997 and 2008, and for the gradual disappearance of ice and other absorption features in its spectrum over the same period. This implies that the rings are partly composed of water ice. They may be the remnants of a debris disk, possibly confined by embedded, kilometre-sized satellites.
RESUMO
Here we report the discovery of a novel HLA-B allele, named B*4212 in a Brazilian volunteer bone marrow donor. The new sequence has nucleotide variation at position 496 (TâG) as compared with B*4201. This variation results in a conservative amino acid substitution from valine to glycine at codon 165 of exon 3.
Assuntos
Antígenos HLA-B/genética , Alelos , Sequência de Aminoácidos , Substituição de Aminoácidos , Sequência de Bases , Medula Óssea , Brasil , Antígenos HLA-B/química , Antígenos HLA-B/imunologia , Teste de Histocompatibilidade , Humanos , Dados de Sequência Molecular , Mutação Puntual , Análise de Sequência de DNA , Doadores de TecidosRESUMO
Major histocompatibility complex class I chain-related gene A (MICA) was identified within the human leukocyte antigen (HLA) class I region and was located 46 kb centromeric from HLA-B locus. It functions as a ligand for human gammadelta T, CD8 T and natural killer (NK) cells by binding the NKG2D receptor. The aims of the present study were to determine the distribution of MICA alleles and MICA-HLA-B haplotypes in a sample of Euro-Brazilians. Through the combination of three typing methods, polymerase chain reaction (PCR)-sequence-specific oligonucleotide probe, PCR-sequence-specific primer and PCR-restriction fragment length polymorphism, 19 alleles were detected besides a MICA gene deletion in a sample composed by 204 unrelated Euro-Brazilians. The most commonly observed alleles were: MICA*00801 (25.3%), MICA*00201 (17.7%) and MICA*00901 (13.7%). The GCT repeat polymorphism variant A6 was the most commonly found. The most frequent haplotype found in this study was MICA*00901-B*51 (8.1%), followed by haplotypes MICA*00201-B*35 (6.1%) and MICA*00801-B*07 (6.1%). MICA*00801 truncated product, and its low affinity for NKG2D receptor may work as an inhibitor in its putative soluble form. It may also be that selective forces may favor MICA*00801 heterozygosity with NKG2D high affinity MICA alleles enabling activation and inhibition of cytotoxic activity of cells expressing the NKG2D receptor. The possibility of selective neutrality or of balancing selection still provides no explanation for MICA gene polymorphisms. Is it maintained by genetic drift or by the influence of migratory waves? Are there favored alleles while others present the same adaptive value?
Assuntos
Frequência do Gene/genética , Antígenos HLA-B/genética , Antígenos de Histocompatibilidade Classe I/genética , Desequilíbrio de Ligação/genética , Subfamília K de Receptores Semelhantes a Lectina de Células NK/genética , Alelos , Brasil , Europa (Continente)/etnologia , Frequência do Gene/imunologia , Antígenos HLA-B/imunologia , Haplótipos , Antígenos de Histocompatibilidade Classe I/imunologia , Humanos , Desequilíbrio de Ligação/imunologia , Subfamília K de Receptores Semelhantes a Lectina de Células NK/imunologia , Polimorfismo GenéticoRESUMO
MICA is a nonclassical polymorphic MHC molecule. We investigated MICA allelic frequencies and MICA-HLA-B-HLA-C haplotypes in Brazilian Amerindians to describe the polymorphism and to extract information about the evolution of MICA gene. Kaingang is the first population described to have a high frequency of MICA*020, found associated with HLA-B*3505-HLA-Cw*0401. Allele MICA*020 probably originated de novo in South America. The Guarani population had high frequencies of MICA*027. Allele MICA*00801 is common worldwide but rare among Amerindians, occurring only because of gene flow. The analysis of the 64 described MICA alleles revealed that in exons 2 and 4, synonymous substitutions are in excess, a result compatible with purifying selection. The opposite was observed for exons 3 and 6 and the excess of nonsynonymous substitutions was significant for exon 3, indicating positive selection. Few of the alleles described so far had exon 6 sequenced, impeding conclusions for the corresponding portion of the molecule. The analysis of the entire gene is required for a better understanding of the evolution of MICA's polymorphism and its functional consequences. This knowledge is of prime importance in view of the increasing awareness of the functional and medical implications of MICA gene variability.
Assuntos
Antígenos de Histocompatibilidade Classe I/genética , Indígenas Sul-Americanos/genética , Alelos , Evolução Molecular , Éxons , Frequência do Gene , Genética Populacional , Haplótipos , Humanos , Filogenia , Polimorfismo GenéticoRESUMO
AIMS: The aim of this research was to determine the suitability of coliphages (bacteriophages) for assessing the microbial quality of groundwater. METHODS AND RESULTS: The number of several bacterial indicators (faecal coliforms, Escherichia coli, enterococci and spores of sulfite-reducing clostridia) and bacteriophages (somatic coliphages, F-specific RNA bacteriophages and bacteriophages infecting Bacteroides fragilis) were determined in groundwater of aquifers in various geographical areas. Results show that the relative abundance, determined as percentages of positive detections, of the bacterial indicators and bacteriophages varies depending on the aquifer. CONCLUSIONS: A single bacterial indicator may not be enough to assess microbiological quality in certain aquifers. One bacterial indicator and a bacteriophage parameter provide more information than two bacterial indicators. SIGNIFICANCE AND IMPACT OF THE STUDY: Coliphages (CPH) provide different information from that provided by bacterial indicators on the microbial quality of groundwater in different geographical areas. Easy, fast and inexpensive methods for the detection of CPH are feasible in both industrialized and developing countries.
Assuntos
Bactérias/isolamento & purificação , Enterovirus/isolamento & purificação , Monitoramento Ambiental/métodos , Microbiologia da Água , Poluição da Água , Argentina , Colômbia , Contagem de Colônia Microbiana , França , Água Doce , Técnicas Microbiológicas , Esgotos , EspanhaRESUMO
Bone Marrow Transplant (BMT) is a lifesaving procedure for several diseases. Histocompatibility between host and donor is crucial for the success of this therapy. Since human leukocyte antigen (HLA) genes are the most polymorphic in humans, a foreknowledge of their frequencies and a vast register of volunteer donors are important for patients who need an unrelated donor. This research evaluated data from 3500 HLA-typed donors using PCR-SSP (One Lambda ABDRX kits, low/medium resolution). The allele and haplotype frequencies were calculated from the donor HLA typings. Among the total sample we observed that the allelic groups HLA-A*02, -B*35, and -DRB1*11 had frequencies of 0.228, 0.112, and 0.125, respectively. The haplotype HLA-A*01-B*08-DRB1*03 was the most frequent (0.024). We also compared our results with another study conducted in a Northeastern Brazilian population. The identification of the most common allelic groups and haplotypes is of great interest, not only to know the HLA composition of the population but also to search for the best HLA match for a transplant. However, the search for the perfect match depends on the eventual registration of every specific donor in the national registers for bone marrow donation.
Assuntos
Transplante de Medula Óssea/imunologia , Antígenos HLA/genética , Antígenos HLA/imunologia , Haplótipos , Doadores Vivos , Brasil , Antígenos HLA-B/genética , Antígenos HLA-B/imunologia , Antígenos HLA-DR/genética , Antígenos HLA-DR/imunologia , Cadeias HLA-DRB1 , Teste de Histocompatibilidade , Humanos , Reação em Cadeia da Polimerase , Polimorfismo Conformacional de Fita SimplesRESUMO
The authors carried out a literature review of the subject "stillbirth", with special emphasis on its conceptual and epidemiological features, aimed at highlighting its importance as a perinatal health indicator.