Transposable elements (TEs) are mobile genetic elements with the ability to replicate themselves throughout the host genome. In some taxa TEs reach copy numbers in hundreds of thousands and can occupy more than half of the genome. The increasing number of reference genomes from nonmodel species has begun to outpace efforts to identify and annotate TE content and methods that are used vary significantly between projects. Here, we demonstrate variation that arises in TE annotations when less than optimal methods are used. We found that across a variety of taxa, the ability to accurately identify TEs based solely on homology decreased as the phylogenetic distance between the queried genome and a reference increased. Next we annotated repeats using homology alone, as is often the case in new genome analyses, and a combination of homology and de novo methods as well as an additional manual curation step. Reannotation using these methods identified a substantial number of new TE subfamilies in previously characterized genomes, recognized a higher proportion of the genome as repetitive, and decreased the average genetic distance within TE families, implying recent TE accumulation. Finally, these finding—increased recognition of younger TEs—were confirmed via an analysis of the postman butterfly (Heliconius melpomene). These observations imply that complete TE annotation relies on a combination of homology and de novo–based repeat identification, manual curation, and classification and that relying on simple, homology-based methods is insufficient to accurately describe the TE landscape of a newly sequenced genome.

Environmental factors profoundly affect the addictive potential of drugs of abuse and may also modulate the neuro-anatomical/neuro-chemical impacts of uncontrolled drug use and relapse propensity. This study examined the impact of environmental enrichment on heroin self-administration, addiction-related behaviors, and molecular processes proposed to underlie these behaviors. Male Sprague-Dawley rats in standard and enriched housing conditions intravenously self-administered similar amounts of heroin over 14 days. However, environmental enrichment attenuated progressive ratio, extinction, and reinstatement session responding after 14 days of enforced abstinence. Molecular mechanisms, namely DNA methylation and gene expression, are proposed to underlie abstinence-persistent behaviors. A global reduction in methylation is reported to coincide with addiction, but no differences in total genomic methylation or repeat element methylation were observed in CpG or non-CpG (CH) contexts across the mesolimbic circuitry as assessed by multiple methods including whole genome bisulfite sequencing. Immediate early gene expression associated with drug seeking, taking, and abstinence also were examined. EGR1 and EGR2 were suppressed in mesolimbic regions with heroin-taking and environmental enrichment. Site-specific methylation analysis of EGR1 and EGR2 promoter regions using bisulfite amplicon sequencing (BSAS) revealed hypo-methylation in the EGR2 promoter region and EGR1 intragenic CpG sites with heroin-taking and environmental enrichment that was associated with decreased mRNA expression. Taken together, these findings illuminate the impact of drug taking and environment on the epigenome in a locus and gene-specific manner and highlight the need for positive, alternative rewards in the treatment and prevention of drug addiction.

Background Alterations to cellular and molecular programs with brain aging result in cognitive impairment and susceptibility to neurodegenerative disease. Changes in DNA methylation patterns, an epigenetic modification required for various CNS functions are observed with brain aging and can be prevented by anti-aging interventions, but the relationship of altered methylation to gene expression is poorly understood. Results Paired analysis of the hippocampal methylome and transcriptome with aging of male and female mice demonstrates that age-related differences in methylation and gene expression are anti-correlated within gene bodies and enhancers. Altered promoter methylation with aging was found to be generally un-related to altered gene expression. A more striking relationship was found between methylation levels at young age and differential gene expression with aging. Highly methylated gene bodies and promoters in early life were associated with age-related increases in gene expression even in the absence of significant methylation changes with aging. As well, low levels of methylation in early life were correlated to decreased expression with aging. This relationship was also observed in genes altered in two mouse Alzheimer’s models. Conclusion DNA methylation patterns established in youth, in combination with other epigenetic marks, were able to accurately predict changes in transcript trajectories with aging. These findings are consistent with the developmental origins of disease hypothesis and indicate that epigenetic variability in early life may explain differences in aging trajectories and age-related disease.

Alterations to cellular and molecular programs with brain aging result in cognitive impairment and susceptibility to neurodegenerative disease. Changes in DNA methylation patterns, an epigenetic modification required for various CNS functions, are observed with aging and can be prevented by anti-aging interventions, but the functional outcomes of altered methylation on transcriptome profiles are poorly understood with brain aging.Integrated analysis of the hippocampal methylome and transcriptome with aging of male and female mice demonstrates that age-related differences in methylation and gene expression are anti-correlated within gene bodies and enhancers, but not promoters. Methylation levels at young age of genes altered with aging are positively associated with age-related expression changes even in the absence of significant changes to methylation with aging, a finding also observed in mouse Alzheimer's models. DNA methylation patterns established in youth, in combination with other epigenetic marks, are able to predict changes in transcript trajectories with aging. These findings are consistent with the developmental origins of disease hypothesis and indicate that epigenetic variability in early life may explain differences in age-related disease.