Formalin Fixation at Low Temperature Better Preserves Nucleic Acid Integrity
Ontology highlight
ABSTRACT:
ORGANISM(S): Homo sapiens
PROVIDER: GSE27175 | GEO | 2011/09/05
SECONDARY ACCESSION(S): PRJNA137377
REPOSITORIES: GEO
Similar Datasets
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: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.
2013-09-09 | GSE50690 | GEO
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: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.
2013-09-09 | E-GEOD-50690 | biostudies-arrayexpress
Project description:AIM: To analyze the expression profiles of premalignant and/or preclinical lesions of gastric cancers. METHODS: We analyzed the expression profiles of normal gastric pit, tubular adenoma and carcinoma in situ using microdissected cells from routine gastric biopsies. For the DNA microarray analysis of formalin-fixed samples, we developed a simple and reproducible RNA extraction and linear amplification procedure applying two polymerase-binding sites. The amplification procedure took only 8 h and yielded comparable DNA microarray data between formalin-fixed tissues and unfixed controls. RESULTS: In comparison with normal pit, adenoma/carcinoma showed 504 up-regulated and 29 down-regulated genes at the expected false significance rate 0.15%. The differential expression between adenoma and carcinoma in situ was subtle: 50 and 22 genes were up-, and down-regulated in carcinomas at the expected false significance rate of 0.61%, respectively. Differentially expressed genes were grouped according to patterns of the sequential changes for the 'tendency analysis' in the gastric mucosa-adenoma-carcinoma sequence. CONCLUSION: Groups of genes are shown to reflect the sequential expression changes in the early carcinogenic steps of stomach cancer. It is suggested that molecular carcinogenic pathways could be analyzed using routinely processed biopsies. Keywords: other
2004-04-06 | GSE1279 | GEO
Project description:Formalin Fixation at Low Temperature Better Preserves Nucleic Acid Integrity
| PRJNA137377 | 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.
2024-03-15 | GSE261169 | 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.
2024-03-01 | GSE256158 | GEO
Project description:Chromatin immunoprecipitation (ChIP) has allowed the study of protein-DNA interactions in chromatin, bringing new insights into the role of histone post-translational modifications (HPTMs) in cancer and other diseases. The coupling of ChIP with next-generation sequencing (NGS) techniques has revealed the distribution of HPTMs over the entire genome allowing the identification of altered epigenetic profiles in pathological conditions. However, until recently, these studies have been limited to cultured cells or fresh/frozen tissues. The development of a new technique named PAT-ChIP has enabled chromatin studies in formalin-fixed paraffin-embedded (FFPE) tissues, opening the doors to a huge number of samples stored in pathology archives and related clinical information. However, chromatin studies in FFPE archival samples can be hindered by the extensive formalin fixation to which these tissues are routinely subjected. Here, we describe enhanced PAT-ChIP (EPAT-ChIP), a new ChIP procedure that facilitates epigenomic studies in archival FFPE tissues. EPAT-ChIP improves the extraction of soluble chromatin, allowing the study of multiple histone marks from limited amounts of starting material. In addition, EPAT-ChIP assures higher yields of final immunoselected DNA, especially when poorly represented histone marks (e.g. narrow peaks of H3K4me3) are investigated, and the consequent production of reliable NGS libraries. In this procedure, FFPE samples are subjected to heat-mediated limited reversal of crosslinking (LRC) which predisposes the tissue to better release soluble chromatin after sonication without altering the antigenic potential of its biomolecules. After investigating differentially-fixed normal colon specimens specifically produced for this study, ePAT-ChIP was successfully used to study three different HPTMs (H3K4me3, K3K27me3, H3K27ac) at genome-wide level in an archival invasive breast carcinoma (IBC) sample.
2018-11-20 | GSE117752 | 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 | GSE256156 | GEO