TASK DEFINITION: In this task, you are given a passage which has a question and the context. You have to generate an answer to the question based on the information present in the context.
PROBLEM: Context: Chromatin epigenetics participate in control of gene expression during metazoan development. DNA methylation and post-translational modifications (PTMs) of histones have been extensively characterised in cell types present in, or derived from, mouse embryos. In embryonic stem cells (ESCs) derived from blastocysts, factors involved in deposition of epigenetic marks regulate properties related to self-renewal and pluripotency. In the germ lineage, changes in histone PTMs and DNA demethylation occur during formation of the primordial germ cells (PGCs) to reset the epigenome of the future gametes. Trimethylation of histone H3 on lysine 27 (H3K27me3) by Polycomb group proteins is involved in several epigenome-remodelling steps, but it remains unclear whether these epigenetic features are conserved in non-mammalian vertebrates. To investigate this question, we compared the abundance and nuclear distribution of the main histone PTMs, 5-methylcytosine (5mC) and 5-hydroxymethylcytosine (5hmC) in chicken ESCs, PGCs and blastodermal cells (BCs) with differentiated chicken ESCs and embryonic fibroblasts. In addition, we analysed the expression of chromatin modifier genes to better understand the establishment and dynamics of chromatin epigenetic profiles.', 'The nuclear distributions of most PTMs and 5hmC in chicken stem cells were similar to what has been described for mammalian cells. However, unlike mouse pericentric heterochromatin (PCH), chicken ESC PCH contained high levels of trimethylated histone H3 on lysine 27 (H3K27me3). In differentiated chicken cells, PCH was less enriched in H3K27me3 relative to chromatin overall. In PGCs, the H3K27me3 global level was greatly reduced, whereas the H3K9me3 level was elevated. Most chromatin modifier genes known in mammals were expressed in chicken ESCs, PGCs and BCs. Genes presumably involved in de novo DNA methylation were very highly expressed. DNMT3B and HELLS/SMARCA6 were highly expressed in chicken ESCs, PGCs and BCs compared to differentiated chicken ESCs and embryonic fibroblasts, and DNMT3A was strongly expressed in ESCs, differentiated ESCs and BCs.\Question: Do chicken embryonic stem cells and primordial germ cells display different heterochromatic histone marks than their mammalian counterparts?

SOLUTION: Chicken ESCs and PGCs differ from their mammalian counterparts with respect to H3K27 methylation. High enrichment of H3K27me3 at PCH is specific to pluripotent cells in chicken. Our results demonstrate that the dynamics in chromatin constitution described during mouse development is not universal to all vertebrate species.

PROBLEM: Context: In this study, we compared the diagnostic performance of the standard SPECT with motion-frozen (MF) myocardial perfusion SPECT (MPS) in obese patients.', 'A total of 90 consecutive obese patients (body mass index, 30.1-46.8, average, 34.3 +/- 3.6; age, 63 +/- 12 y; 30% women) underwent standard supine rest (201)Tl/stress (99m)Tc dual-isotope gated MPS and cardiac catheterization within 3 mo. MF images were obtained by nonlinear warping of cardiac phases to the end-diastolic position. Total perfusion deficit (TPD) was obtained for summed (S-TPD) and motion-frozen (MF-TPD) datasets with sex-specific standard and MF normal limits.', 'The area under the receiver-operating-characteristic (ROC) curve for detection of coronary artery disease (CAD) by MF-TPD was significantly larger than that for S-TPD (0.93 +/- 0.25 vs. 0.88 +/- 0.32, P < 0.05). MF-TPD had higher specificity (77% vs. 55%, P < 0.05) and accuracy (89% vs. 80%, P < 0.05) than did S-TPD.\Question: Does motion-frozen myocardial perfusion SPECT improve detection of coronary artery disease in obese patients?

SOLUTION: MF processing of MPS improves CAD detection in obese patients.

PROBLEM: Context: The incidence of hydronephrosis due to ureteropelvic junction obstruction is approx. 0.5%. During the last decade, the management of non-symptomatic hydronephrosis has become much more conservative, but the long-term physiological consequences of this policy are not clear. Previously, we have shown that animals with chronic partial unilateral ureteral obstruction develop salt-sensitive hypertension. In this study, the effects of ipsilateral and contralateral nephrectomy and ureterovesicostomy on blood pressure were studied in hydronephrotic animals.', 'Partial unilateral ureteral obstruction was created in 3-week-old male Sprague-Dawley rats and blood pressure was measured telemetrically 4-6 weeks later during a normal and high salt diet before and after uninephrectomy or ureterovesicostomy. Plasma samples for renin assay were collected during both diets before and after ipsilateral nephrectomy.', 'All hydronephrotic animals developed salt-sensitive hypertension, of different degrees. Before nephrectomy the plasma renin concentration was significantly higher in the hydronephrotic animals than in controls (160 +/- 15 microGU mL(-1) vs. 96 +/- 12 microGU mL(-1), respectively), but after the ipsilateral nephrectomy no differences were found between the groups. In the hydronephrotic animals both ipsilateral nephrectomy and ureterovesicostomy reduced the blood pressure and salt-sensitivity but the former still differed significantly from the controls. In contralaterally, nephrectomized hydronephrotic animals the salt-sensitive hypertension became more pronounced.\Question: Does relief of chronic partial ureteral obstruction attenuate salt-sensitive hypertension in rats?

SOLUTION:
Hydronephrosis in rats causes salt-sensitive hypertension that can be markedly reduced by removing the hydronephrotic kidney or relieving the obstruction by ureterovesicostomy. The mechanisms appear to be intrarenal and primarily located in the diseased kidney, but a secondary mechanism is also present.