Effects of formalin-fixation on FAIRE-Seq and MNase-Seq signatures in yeast (RNA-Seq)
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PROVIDER: PRJNA1078351 | ENA |
REPOSITORIES: ENA
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Project description:Formalin induces inter- and intra-molecular crosslinks within exposed cells. This cross-linking can be exploited to characterise chromatin state as in the FAIRE (Formaldehyde-Assisted Isolation of Regulatory Elements) and MNase (micrococcal nuclease) assays. Our team aims to optimise these assays for application in museum preserved formalin-exposed specimens. To do so, we first sought to understand the effect of prolonged formalin fixation on the read alignment signatures resulting from FAIRE and MNase treatment. Here we cultured yeast (Saccharomyces cerevisiae) under normal and heat-shock conditions then fixed the cells with formalin for 15 minutes, 1 hour, 6 hours, and 24 hours. We found that heavy formalin fixation modulates rather than eliminates signatures of differential chromatin accessibility and enables semi-quantitative estimates of relative gene expression in this yeast model.
2024-03-01 | GSE256156 | GEO
Project description:Formalin induces inter- and intra-molecular crosslinks within exposed cells. This cross-linking can be exploited to characterise chromatin state as in the FAIRE (Formaldehyde-Assisted Isolation of Regulatory Elements) and MNase (micrococcal nuclease) assays. Our team aims to optimise these assays for application in museum preserved formalin-exposed specimens. To do so, we first sought to understand the effect of prolonged formalin fixation on the read alignment signatures resulting from FAIRE and MNase treatment. Here we cultured yeast (Saccharomyces cerevisiae) under normal and heat-shock conditions then fixed the cells with formalin for 15 minutes, 1 hour, 6 hours, and 24 hours. We found that heavy formalin fixation modulates rather than eliminates signatures of differential chromatin accessibility and enables semi-quantitative estimates of relative gene expression in this yeast model.
2024-03-01 | GSE256160 | GEO
Project description:Formalin induces inter- and intra-molecular crosslinks within exposed cells. This cross-linking can be exploited to characterise chromatin state as in the FAIRE (Formaldehyde-Assisted Isolation of Regulatory Elements) and MNase (micrococcal nuclease) assays. Here, we optimised the FAIRE and MNase assays for application upon heavily-fixed tissues as is typically found in historical formalin-preserved museum specimens. We demonstrate these assays in formalin-fixed mouse specimens and compare the chromatin signatures to specimen-matched fresh tissues. We found that heavy formalin fixation modulates rather than eliminates signatures of differential chromatin accessibility and that these chromatin profiles are reproducible, tissue-specific and sex-specific in vertebrate specimens.
2024-03-15 | GSE261169 | GEO
Project description:Effects of formalin-fixation on FAIRE-Seq and MNase-Seq signatures in yeast
| PRJNA1078344 | ENA
Project description:Formalin induces inter- and intra-molecular crosslinks within exposed cells. This cross-linking can be exploited to characterise chromatin state as in the FAIRE (Formaldehyde-Assisted Isolation of Regulatory Elements) and MNase (micrococcal nuclease) assays. Here, we optimised the FAIRE and MNase assays for application upon heavily-fixed tissues as is typically found in historical formalin-preserved museum specimens. We demonstrate these assays in formalin-fixed mouse specimens and compare the chromatin signatures to specimen-matched fresh tissues. We found that heavy formalin fixation modulates rather than eliminates signatures of differential chromatin accessibility and that these chromatin profiles are reproducible, tissue-specific and sex-specific in vertebrate specimens.
2024-03-01 | GSE256158 | GEO
Project description:Archival chromatin sequencing in formalin-fixed mouse specimens [FAIRE and Mnase]
| PRJNA1085716 | ENA
Project description:INTRODUCTION. Fixation with formalin, a widely adopted procedure to preserve tissue samples, leads to extensive degradation of nucleic acids and thereby compromises procedures like microarray-based gene expression profiling. We hypothesized that RNA fragmentation is caused by activation of RNAses during the interval between formalin penetration and tissue fixation. To prevent RNAse activation, a series of tissue samples were kept under-vacuum at 4°C until fixation and then fixed at 4°C, for 24 hours, in formalin followed by 4 hours in ethanol 95%. RESULTS. The cold-fixation (CF) procedure preserved DNA and RNA, so that RNA segments up to 660 bp were efficiently amplified. Histological and immunohistochemical features were fully comparable with those of standard fixation. Microarray-based gene expression profiles were comparable with those obtained on matched frozen samples for probes hybridizing within 700 bases from the reverse transcription start site. In conclusion, CF preserves tissues and nucleic acids, enabling reliable gene expression profiling of fixed tissues. Thirty samples from human cancers processed in different ways before RNA extraction: (i) Fresh-Freezing (FF), (ii) Standard Fixation with formalin (SF), (iii) Cold-Fixation (CF), a new formalin fixation procedure preserving nucleic acids. The first six samples compare CF with SF and FF in one colorectal cancer (CRC) specimen and one breast cancer (BRCa) specimen. The subsequent 24 samples compare only CF with FF in various cancer specimens. Expression data are neither normalized nor backound subtracted to preserve the original signal distribution for each sample, which is essential to compare expression profiles obtained after different tissue preservation methods.
2011-09-04 | E-GEOD-27175 | biostudies-arrayexpress
Project description:Archival formalin-fixed paraffin-embedded (FFPE) tissue samples hold a wealth of transcriptomic information; however, little is known about potential artifacts. Previously, we identified a consistent shift in global RNA-sequencing profiles between matching frozen and FFPE samples. We hypothesized that this shift was from fixing fresh tissue in formalin. To test this idea, RNA-sequencing was performed on liver samples collected from male mice treated with 600 ppm of a reference chemical (phenobarbital, 600 ppm phenobarbital) or vehicle control for 7 days. Samples were divided into: (1) fresh-frozen (FR); (2) directly fixed in 10% buffered formalin for 18 hours followed by paraffin embedding (FFPE); (3) frozen then fixed as FFPE (FR>FFPE); or (4) frozen then fixed in 70% ethanol followed by paraffin embedding (FR>OH) (n=6/group/condition). Direct fixation resulted in 2946 differentially expressed genes (DEGs), 98% of which were down-regulated. Freezing prior to fixation resulted in ≥95% fewer DEGs vs. FR, indicating that most formalin-derived transcriptional effects occurred with fixation. This was supported by follow-up studies, which identified consistent enrichment in oxidative stress, mitochondrial dysfunction, and transcription elongation pathways with formalin fixation. Notably, formalin fixation in the parent study did not significantly impact chemical response profiles, which were consistent with CAR/PXR activation and 600 ppm phenobarbital exposure. Our results demonstrate distinct transcriptional effects of formalin fixation that could impact gene expression studies using FFPE samples.
2020-09-08 | GSE148174 | GEO
Project description:INTRODUCTION. Fixation with formalin, a widely adopted procedure to preserve tissue samples, leads to extensive degradation of nucleic acids and thereby compromises procedures like microarray-based gene expression profiling. We hypothesized that RNA fragmentation is caused by activation of RNAses during the interval between formalin penetration and tissue fixation. To prevent RNAse activation, a series of tissue samples were kept under-vacuum at 4°C until fixation and then fixed at 4°C, for 24 hours, in formalin followed by 4 hours in ethanol 95%. RESULTS. The cold-fixation (CF) procedure preserved DNA and RNA, so that RNA segments up to 660 bp were efficiently amplified. Histological and immunohistochemical features were fully comparable with those of standard fixation. Microarray-based gene expression profiles were comparable with those obtained on matched frozen samples for probes hybridizing within 700 bases from the reverse transcription start site. In conclusion, CF preserves tissues and nucleic acids, enabling reliable gene expression profiling of fixed tissues.
2011-09-05 | GSE27175 | GEO