459 research outputs found
Structure and expression of two nuclear receptor genes in marsupials: insights into the evolution of the antisense overlap between the Ī±-thyroid hormone receptor and Rev-erbĪ±
<p>Abstract</p> <p>Background</p> <p>Alternative processing of Ī±-thyroid hormone receptor (TRĪ±, NR1A1) mRNAs gives rise to two functionally antagonistic nuclear receptors: TRĪ±1, the Ī±-type receptor, and TRĪ±2, a non-hormone binding variant that is found only in mammals. TRĪ±2 shares an unusual antisense coding overlap with mRNA for Rev-erbĪ± (NR1D1), another nuclear receptor protein. In this study we examine the structure and expression of these genes in the gray short-tailed opossum, <it>Monodelphis domestica</it>, in comparison with that of eutherian mammals and three other marsupial species, <it>Didelphis virginiana, Potorous tridactylus </it>and <it>Macropus eugenii</it>, in order to understand the evolution and regulatory role of this antisense overlap.</p> <p>Results</p> <p>The sequence, expression and genomic organization of mRNAs encoding TRĪ±1 and Rev-erbĪ± are very similar in the opossum and eutherian mammals. However, the sequence corresponding to the TRĪ±2 coding region appears truncated by almost 100 amino acids. While expression of TRĪ±1 and Rev-erbĪ± was readily detected in all tissues of <it>M. domestica </it>ages 0 days to 18 weeks, TRĪ±2 mRNA was not detected in any tissue or stage examined. These results contrast with the widespread and abundant expression of TRĪ±2 in rodents and other eutherian mammals. To examine requirements for alternative splicing of TRĪ± mRNAs, a series of chimeric minigenes was constructed. Results show that the opossum TRĪ±2-specific 5' splice site sequence is fully competent for splicing but the sequence homologous to the TRĪ±2 3' splice site is not, even though the marsupial sequences are remarkably similar to core splice site elements in rat.</p> <p>Conclusions</p> <p>Our results strongly suggest that the variant nuclear receptor isoform, TRĪ±2, is not expressed in marsupials and that the antisense overlap between TRĪ± and Rev-erbĪ± thus is unique to eutherian mammals. Further investigation of the TRĪ± and Rev-erbĪ± genes in marsupial and eutherian species promises to yield additional insight into the physiological function of TRĪ±2 and the role of the associated antisense overlap with Rev-erbĪ± in regulating expression of these genes.</p
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A large-scale validation study of aircraft noise modeling for airport arrivals
In the U.S., the Federal Aviation Administration's Aviation Environmental Design Tool (AEDT) is approved to predict the impacts of aircraft noise and emissions. AEDT's critical role in regulatory compliance and evaluating the environmental impacts of aviation requires asking how accurate are its noise predictions. Previous studies suggest that AEDT's predictions lack desired accuracy. This paper reports on a large-scale study, using 200 000 flight trajectories paired with measured sound levels for arrivals to Runways 28L/28R at San Francisco International Airport, over 12 months. For each flight, two AEDT studies were run, one using the approved mode for regulatory filing and the other using an advanced non-regulatory mode with exact aircraft trajectories. AEDT's per aircraft noise predictions were compared with curated measured sound levels at two locations. On average, AEDT underestimated LAmax by -3.09 dB and SEL by -2.04 dB, combining the results from both AEDT noise-modeling modes. Discrepancies appear to result from limitations in the physical modeling of flight trajectories and noise generation, combined with input data uncertainties (aircraft weight, airspeed, thrust, and lift configuration) and atmospheric conditions
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