Biology subjects

Andrew P Feinberg

Publications and source records attributed to Andrew P Feinberg.

4 recordsLinked to original sources

bioRxiv2016

Choice of reference genome can introduce massive bias in bisulfite sequencing data

In the study of DNA methylation, genetic variation between species, strains, or individuals can result in CpG sites that are exclusive to a subset of samples, and insertions and deletions can rearrange the spatial distribution of CpGs. How to account for this variation in an analysis of the interplay between sequence variation and DNA methylation is not well understood, especially when the number of CpG differences between samples is large. Here we use whole-genome bisulfite sequencint data on two highly divergent inbred mouse strains to study this problem. We find that while the large number of strain-specific CpGs necessitates considerations regarding the reference genomes used during alignment, properties such as CpG density are surprisingly conserved across the genome. We introduce a method for including strain-specific CpGs in differential analysis, and show that accounting for strain-specific CpGs increases the power to find differentially methylated regions between the strains. Our method uses smoothing to impute methylation levels at strain-specific sites, thereby allowing strain-specific CpGs to contribute to the analysis, and also allowing us to account for differences in the spatial occurrences of CpGs. Our results have implications for analysis of genetic variation and DNA methylation using bisulfite-converted DNA.

Genomics↗

bioRxiv2016

Whole genome analysis of the methylome and hydroxymethylome in normal and malignant lung and liver

DNA methylation at the 5-postion of cytosine (5mC) is a well-established epigenetic modification which regulates gene expression and cellular plasticity in development and disease. The ten-eleven translocation (TET) gene family is able to oxidize 5mC to 5-hydroxymethyl-cytosine (5hmC), providing an active mechanism for DNA demethylation, and may also provide its own regulatory function. Here we applied oxidative bisulfite sequencing to generate whole-genome DNA methylation and hydroxymethylation maps at single-base resolution in paired human liver and lung normal and cancer. We found that 5hmC is significantly enriched in CpG island (CGI) shores while depleted in CGIs themselves, in particular at active genes, resulting in a 5hmC but not 5mC bimodal distribution around CGI corresponding to H3K4me1 marks. Hydroxymethylation on promoters, gene bodies, and transcription termination regions showed strong positive correlation with gene expression within and across tissues, suggesting that 5hmC is a mark of active genes and could play a role gene expression mediated by DNA demethylation. Comparative analysis of methylomes and hydroxymethylomes revealed that 5hmC is significantly enriched in both tissue specific DMRs (t-DMRs) and cancer specific DMRs (c-DMRs), and 5hmC is negatively correlated with methylation changes, particularly in non-CGI associated DMRs. Together these findings indicate that changes in 5mC as well as in 5hmC and coupled to H3K4me1 correspond to differential gene expression in tissues and matching tumors, revealing an intricate gene expression regulation through interplay of methylome, hydroxyl-methylome, and histone modifications.

Genomics↗

bioRxiv2016

Potential energy landscapes reveal the information-theoretic nature of the epigenome

Epigenetics is defined as genomic modifications carrying information independent of DNA sequence heritable through cell division. In 1940, Waddington coined the term \"epigenetic landscape\" as a metaphor for pluripotency and differentiation, but epigenetic potential energy landscapes have not yet been rigorously defined. Using well-grounded biological assumptions and principles of statistical physics and information theory, we derive potential energy landscapes from whole genome bisulfite sequencing data that allow us to quantify methylation stochasticity genome-wide and discern epigenetic differences using Shannons entropy and the Jensen-Shannon distance. We discover a \"developmental wheel\" of germ cell lineages and an association between entropy and chromatin structure. Viewing methylation maintenance as a communications system, we introduce methylation channels and show that higher-order chromatin organization can be predicted from their informational properties. Our results provide a fundamental understanding of the information-theoretic nature of the epigenome and a powerful methodology for studying its role in disease and aging.

Genetics↗

bioRxiv2016

Evaluation of Techniques for Performing Cellular Isolation and Preservation during Microgravity Conditions

Genomic and epigenomic studies require the precise transfer of small volumes from one container to another. Epigenomic and transcriptional analysis require separation of purified cell types, and long term preservation of cells requires their isolation and transfer into appropriate freezing media. There are currently no protocols for these procedures on the ISS. Currently samples are either frozen as mixed cell populations, with poor yield, or returned under ambient conditions, requiring timing with Soyuz missions. Here, we evaluate the feasibility of translating terrestrial cell purification techniques to the ISS. Our evaluations were performed in microgravity conditions during parabolic atmospheric flight. The pipetting of open liquids in microgravity was evaluated using analog blood fluids and several types of pipette hardware. The best performing pipettes were used to evaluate the pipetting steps required for peripheral blood mononuclear cell (PBMC) isolation via density gradient centrifugation (DGC). Evaluation of actual blood products was performed for both the overlay of diluted blood, and the extraction of isolated PBMCs. We also validated magnetic purification of cells. We found that positive displacement pipettes avoided air bubbles, and the tips allowed the strong surface tension of water, glycerol and blood to maintain a patent meniscus and withstand robust pipetting in microgravity. These procedures will greatly increase the breadth of research that can be performed onboard the ISS, and allow improvised experimentation on extraterrestrial missions.

Scientific Communication and Education↗