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Sökning: WFRF:(Das Radhika)

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  • Tidskriftsartikel (refereegranskat)
  • Das, Radhika, et al. (författare)
  • Convergent and divergent evolution of genomic imprinting in the marsupial Monodelphis domestica
  • 2012
  • Ingår i: BMC Genomics. - 1471-2164 .- 1471-2164. ; 13, s. 394-
  • Tidskriftsartikel (refereegranskat)abstract
    • Background: Genomic imprinting is an epigenetic phenomenon resulting in parent-of-origin specific monoallelic gene expression. It is postulated to have evolved in placental mammals to modulate intrauterine resource allocation to the offspring. In this study, we determined the imprint status of metatherian orthologues of eutherian imprinted genes. Results: L3MBTL and HTR2A were shown to be imprinted in Monodelphis domestica (the gray short-tailed opossum). MEST expressed a monoallelic and a biallelic transcript, as in eutherians. In contrast, IMPACT, COPG2, and PLAGL1 were not imprinted in the opossum. Differentially methylated regions (DMRs) involved in regulating imprinting in eutherians were not found at any of the new imprinted loci in the opossum. Interestingly, a novel DMR was identified in intron 11 of the imprinted IGF2R gene, but this was not conserved in eutherians. The promoter regions of the imprinted genes in the opossum were enriched for the activating histone modification H3 Lysine 4 dimethylation. Conclusions: The phenomenon of genomic imprinting is conserved in Therians, but the marked difference in the number and location of imprinted genes and DMRs between metatherians and eutherians indicates that imprinting is not fully conserved between the two Therian infra-classes. The identification of a novel DMR at a non-conserved location as well as the first demonstration of histone modifications at imprinted loci in the opossum suggest that genomic imprinting may have evolved in a common ancestor of these two Therian infra-classes with subsequent divergence of regulatory mechanisms in the two lineages.
  • Mikkelsen, Tarjei S, et al. (författare)
  • Genome of the marsupial Monodelphis domestica reveals innovation in non-coding sequences
  • 2007
  • Ingår i: Nature. - 0028-0836 .- 1476-4687. ; 447:7141, s. 167-177
  • Tidskriftsartikel (refereegranskat)abstract
    • We report a high-quality draft of the genome sequence of the grey, short-tailed opossum (Monodelphis domestica). As the first metatherian ('marsupial') species to be sequenced, the opossum provides a unique perspective on the organization and evolution of mammalian genomes. Distinctive features of the opossum chromosomes provide support for recent theories about genome evolution and function, including a strong influence of biased gene conversion on nucleotide sequence composition, and a relationship between chromosomal characteristics and X chromosome inactivation. Comparison of opossum and eutherian genomes also reveals a sharp difference in evolutionary innovation between protein-coding and non-coding functional elements. True innovation in protein-coding genes seems to be relatively rare, with lineage-specific differences being largely due to diversification and rapid turnover in gene families involved in environmental interactions. In contrast, about 20% of eutherian conserved non-coding elements (CNEs) are recent inventions that postdate the divergence of Eutheria and Metatheria. A substantial proportion of these eutherian-specific CNEs arose from sequence inserted by transposable elements, pointing to transposons as a major creative force in the evolution of mammalian gene regulation.
  • Nandi, A., et al. (författare)
  • Accretion flow dynamics during 1999 outburst of XTE J1859+226—modeling of broadband spectra and constraining the source mass
  • 2018
  • Ingår i: Astrophysics and Space Science. - : Springer Netherlands. - 0004-640X .- 1572-946X. ; 363:5
  • Tidskriftsartikel (refereegranskat)abstract
    • We examine the dynamical behavior of accretion flow around XTE J1859+226 during the 1999 outburst by analyzing the entire outburst data (∼166 days) from RXTE Satellite. Towards this, we study the hysteresis behavior in the hardness intensity diagram (HID) based on the broadband (3–150 keV) spectral modeling, spectral signature of jet ejection and the evolution of Quasi-periodic Oscillation (QPO) frequencies using the two-component advective flow model around a black hole. We compute the flow parameters, namely Keplerian accretion rate (m˙ d), sub-Keplerian accretion rate (m˙ h), shock location (rs) and black hole mass (Mbh) from the spectral modeling and study their evolution along the q-diagram. Subsequently, the kinetic jet power is computed as Ljetobs∼3–6×1037ergs−1 during one of the observed radio flares which indicates that jet power corresponds to 8–16% mass outflow rate from the disc. This estimate of mass outflow rate is in close agreement with the change in total accretion rate (∼14%) required for spectral modeling before and during the flare. Finally, we provide a mass estimate of the source XTE J1859+226 based on the spectral modeling that lies in the range of 5.2–7.9 M⊙ with 90% confidence.
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