Extensive evaluation of ATAC-seq protocols for native or formaldehyde-fixed nuclei
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PROVIDER: PRJNA729079 | ENA |
REPOSITORIES: ENA
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Project description:The "Assay for Transposase Accessible Chromatin sequencing" (ATAC-seq) is an efficient and easy to implement protocol to measure chromatin accessibility that has been widely used in multiple applications studying gene regulation. While several modifications or variants of the protocol have been published since it was first described, there has not yet been an extensive evaluation of the effects of specific protocol choices head-to-head in a consistent experimental setting. In this study, we tested multiple protocol options for major ATAC-seq components (including three reaction buffers, two reaction temperatures, two enzyme sources, and the use of either native or fixed nuclei) in a well-characterized cell line. In addition, the native conditions were tested in a primary sample type (mouse lung tissue) with two different input amounts. In general, native samples yielded more peaks (particularly at loci not overlapping transcription start sites) than fixed samples, and the temperature at which the enzymatic reaction was carried out had a major impact on data quality metrics for both fixed and native nuclei. However, the effect of various conditions tested was not always consistent between the native and fixed samples. For example, the Nextera and Omni buffers were largely interchangeable across all other conditions, while the THS buffer resulted in markedly different profiles in native samples. In-house and commercial enzymes performed similarly. We found that the relationship between commonly used measures of library quality differed across temperature and fixation, and so evaluating multiple metrics in assessing the quality of a sample is recommended. Notably, we also found that these choices can bias the functional class of elements profiled and so we recommend evaluating several formulations in any new experiments. Finally, we hope the ATAC-seq workflow formulated in this study on crosslinked samples will help to profile archival clinical specimens.
2022-03-23 | GSE174280 | GEO
Project description:Fluorescence-activated cell sorting (FACS) is a sensitive and valuable technique to characterize cellular subpopulations and great advances have been made using this approach. Cells are often fixed with formaldehyde prior to the sorting process to preserve cell morphology and maintain the expression of surface molecules, as well as to ensure safety in the sorting of infected cells. It is widely recognized that formaldehyde fixation alters RNA and DNA structure and integrity, thus analyzing gene expression in these cells has been difficult. We therefore examined the effects of formaldehyde fixation on the stability and quantitation of nucleic acids in cell lines, primary leukocytes and also cells isolated from SIV-infected pigtailed macaques. We developed a method to extract RNA from fixed cells that yielded the same amount of RNA as our common method of RNA isolation from fresh cells. Quantitation of RNA by RT-qPCR in fixed cells was not always comparable with that in unfixed cells. In comparison, when RNA was measured by the probe-based NanoString system, there was no significant difference in RNA quantitation. In addition, we demonstrated that quantitation of proviral DNA in fixed cells by qPCR is comparable to that in unfixed cells when normalized by a single-copy cellular gene. These results provide a systematic procedure to quantitate gene expression in cells that have been fixed with formaldehyde and sorted by FACS.
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Project description:In crosslinked MINUTE-ChIP, formaldehyde-fixed chromatin is fragmented using sonication, blunted and ligated to double-stranded DNA adaptors that include a T7 RNA polymerase promoter and a sample barcode sequence. Finally, samples are combined and subsequent ChIP reactions are performed with the pooled samples. ChIP material is prepared into an Illumina-compatible library using linear amplification by virtue of T7 RNA polymerase, reverse transcription and a low-cycle library PCR amplification. Here, we demonstrate a MINUTE-ChIP for Nanog from formaldehyde-fixed cells using fragmentation by sonication.
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Project description:Fluorescence-activated cell sorting (FACS) is a sensitive and valuable technique to characterize cellular subpopulations and great advances have been made using this approach. Cells are often fixed with formaldehyde prior to the sorting process to preserve cell morphology and maintain the expression of surface molecules, as well as to ensure safety in the sorting of infected cells. It is widely recognized that formaldehyde fixation alters RNA and DNA structure and integrity, thus analyzing gene expression in these cells has been difficult. We therefore examined the effects of formaldehyde fixation on the stability and quantitation of nucleic acids in cell lines, primary leukocytes and also cells isolated from SIV-infected pigtailed macaques. We developed a method to extract RNA from fixed cells that yielded the same amount of RNA as our common method of RNA isolation from fresh cells. Quantitation of RNA by RT-qPCR in fixed cells was not always comparable with that in unfixed cells. In comparison, when RNA was measured by the probe-based NanoString system, there was no significant difference in RNA quantitation. In addition, we demonstrated that quantitation of proviral DNA in fixed cells by qPCR is comparable to that in unfixed cells when normalized by a single-copy cellular gene. These results provide a systematic procedure to quantitate gene expression in cells that have been fixed with formaldehyde and sorted by FACS. We compared RNA quantitation between unfixed and formaldehyde-fixed cells using the NanoString nCounter system. This analysis was performed using two cell lines, K562 and CEMx174, and human PBMCs. Three biological replicates were performed for each cell type. We also performed this comparison using human PBMCs sorted by FACS. For this analysis, we isolated PBMCs from two donors and performed two technical replicates for each donor sample.
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Project description:To profile the interactome of cell nucleus,a formaldehyde-CBDPS double chemical-crosslinking method was combined with mass spectrometry to perform quantitative interactomics on the in vivo fixed nuclei.
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Project description:We have developed a methodology for isolation of high-quality RNA from cells that are fixed, stained and sorted by flow cytometry that allows routine transcriptomic analysis of highly purified cell populations and single cells. This method, essentially developed by modifying existing staining and sorting protocols, involves fixation of cells with glyoxal, an alternative fixative to commonly used formaldehyde, followed by methanol permeabilization, a 2-step primary and secondary antibody staining and sorting by flow cytometry. The advantage of using glyoxal is that it does not crosslink RNA to proteins nor form stable RNA adducts, ensuring that RNA remains accessible and amenable to enzymatic manipulation after glyoxal fixation. The dataset comprising mRNA seq libraries from unprocessed or fixed and stained human cancer cells demonstrate that RNA recovered from glyoxal-fixed cells does not retain sufficient glyoxal adducts to impair reverse transcription, and also reveal very few differentially expressed genes between the 2 groups. The dataset derived from fixed and stained cells that were sorted into CCNB1 positive or negative fractions show the applicability of this method for sorting highly purified cell fractions as the CCNB1 positive fractions show strong enrichment for G2-phase cells according to the GO analysis.
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