Given a passage with a context and an answer, construct a question on the basis of the information present in the passage. Construct the question in such a way that (i) it is unambiguous, (ii) it is answerable from the passage, (iii) its answer is unique (iv) it answer uses text phrases from the passage. Avoid creating questions that (i) can't be answered correctly without actually understanding the passage and (ii) uses the same words or phrases given in the passage.

Q: Context: DNA methylation is an important biological form of epigenetic modification, playing key roles in plant development and environmental responses.', 'In this study, we examined single-base resolution methylomes of Populus under control and drought stress conditions using high-throughput bisulfite sequencing for the first time. Our data showed methylation levels of methylated cytosines, upstream 2 kp, downstream 2kb, and repeatitive sequences significantly increased after drought treatment in Populus. Interestingly, methylation in 100 bp upstream of the transcriptional start site (TSS) repressed gene expression, while methylations in 100-2000 bp upstream of TSS and within the gene body were positively associated with gene expression. Integrated with the transcriptomic data, we found that all cis-splicing genes were non-methylated, suggesting that DNA methylation may not associate with cis-splicing. However, our results showed that 80% of trans-splicing genes were methylated. Moreover, we found 1156 transcription factors (TFs) with reduced methylation and expression levels and 690 TFs with increased methylation and expression levels after drought treatment. These TFs may play important roles in Populus drought stress responses through the changes of DNA methylation.
Answer: These findings may provide valuable new insight into our understanding of the interaction between gene expression and methylation of drought responses in Populus.

A: Do single-base-resolution methylomes of Populus trichocarpa reveal the association between DNA methylation and drought stress?
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Q: Context: To study the prevalence and age dependency of senile plaques (SP) and neurofibrillary tangles (NFT), the brain changes characteristic of Alzheimer disease (AD), and their association with apolipoprotein E (APOE) genotypes in a community-dwelling normal population.', 'This neuropathological study used both silver staining and A beta immunohistochemistry in brain tissue microarrays, including SP coverage and NFT counts from frontal cortex and hippocampus, and APOE genotyping, and was performed on a consecutive prospective series of 603 subjects (aged between 0 and 97 years) of an unselected population living outside of institutions. Cases were subjected to autopsy following sudden or unexpected out-of-hospital death, covering 22.1% of the mortality of Tampere, Finland and its surroundings. None died of AD, although 22 (3.7%) were demented and 10 (1.7%) had memory problems.', 'Of the series, 30.8% had SP, and 42.1% had NFT; these occurred more commonly among females and showed a strong relationship with age. Both changes had already appeared at around 30 years of age, reaching an occurrence of almost 100% in the oldest. SP were more frequent in APOE epsilon 4-carriers compared with noncarriers in every age group except the oldest (>90 years). The difference was most evident during the ages 50 to 59 years, where 40.7% of epsilon 4-carriers had SP, compared with 8.2% in noncarriers (odds ratio, 8.39; 95% confidence interval, 2.55-27.62). The difference in NFT prevalence between APOE genotypes was not statistically significant in any age group.
Answer: The brain changes associated with AD may already begin developing early in middle age, especially among APOE epsilon 4 carriers.

A: Does apolipoprotein E-dependent accumulation of Alzheimer disease-related lesions begin in middle age?
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Q: Context: Injection drug users (IDUs) are at risk of acquiring HIV through injection and sexual practices.', 'We analyzed data collected in five U.S. cities between 2002 and 2004 to identify correlates of HIV infection among 3285 IDUs ages 15-30 years.', 'Overall, HIV prevalence was 2.8% (95% CI 2.3-3.4), ranging from 0.8% in Chicago to 6.3% in Los Angeles. Mean age was 24 years, 70% were male, 64% non-Hispanic (NH) white, 7% NH black, 17% Hispanic, and 12% were other/mixed race. HIV infection was independently associated with: race/ethnicity (NH black [AOR 4.1, 95% CI 1.9-9.1], Hispanic [AOR 3.6, 95% CI 1.5-8.4], or other/mixed [AOR 2.3, 95% CI 1.1-5.2] vs. NH white); males who only had sex with males compared to males who only had sex with females (AOR 15.3, 95% CI 6.8-34.5); injecting methamphetamine alone or with heroin compared to heroin only (AOR 4.0, 95% CI 1.7-9.7); reporting inconsistent means of obtaining income compared to regular jobs (AOR 2.3, 95% CI 1.1-4.8); and having a history of exchanging sex for money/drugs (AOR 2.8, 95% CI 1.5-5.2).
Answer: More than two decades after injection and sexual practices were identified as risk factors for HIV infection, these behaviors remain common among young IDUs. While racial/ethnic disparities persist, methamphetamine may be replacing cocaine as the drug most associated with HIV seropositivity. HIV prevention interventions targeting young IDUs and address both sexual and injection practices are needed.

A:
Do young adult injection drug users in the United States continue to practice HIV risk behaviors?
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