Methylation profile analysis of Of DNA-HALO structure by synchrotron-based FTIR spectroscopy

Abstract

Introduction: DNA methylation is a major regulator of transcriptional activity and alongside other epigenetic modifications it introduces specific level of chromatin complexity. Fourier transform infrared (FTIR) spectroscopy is a rapid, non-destructive, and label-free technique for identifying subtle changes in all bio-macromolecules, and it has been used as a method of choice for studying DNA conformation. The present study was designed to explore the use of synchrotron-based FTIR spectroscopy to monitor the subtle changes on molecular level regarding the DNA methylation status of cytosine in the whole genome. Methods: For FTIR-based DNA methylation analysis in situ, DNA-HALO samples were prepared using slightly modified methodology for nuclear HALO preparations where DNA-HALOs are liberated of any protein residues but preserve higher order chromatin structure. Results: Using FTIR spectroscopy we analysed and compared methylation profiles of isolated genomic DNA and DNA-HALO samples. DNA-HALO structure shows more distinct peaks in fingerprint region of spectra. DNA-HALO structure is more accurate for detecting bonds in unmemthylated cytosine as specific infrared peaks are defined as vibrations of bonds in unmethylated cytosine at 1151 cm-1 and 1357 cm-1. The ratio of integrated area under the peak 1151 cm-1 over integrated area under the peak that represents PO2-backbone vibrations can be used to assess level of unmethylated cytosine and thus methylation rate in the DNA-HALO samples. Conclusion: This study demonstrates potential of FTIR spectroscopy to detect DNA methylation in DNA-HALO samples more precisely compared to classical DNA extraction procedure that yield unstructured whole genomic DNA.