Scientists at the Perelman School of Medicine, University of Pennsylvania, have developed an innovative DNA mapping technique that enables the accurate identification of specific DNA markings known as 5-methylcytosine (5mC). These markings play a vital role in regulating gene expression and are implicated in various health conditions, including cancer. The breakthrough method, named Direct Methylation Sequencing (DM-Seq), not only allows for profiling DNA using minimal samples but also avoids damage to the samples, making it potentially applicable to liquid biopsies for early cancer detection. The research findings were published in the journal Nature Chemical Biology.
In addition to the four primary bases of DNA (adenine, cytosine, guanine, and thymine), there exists an additional layer of information in the form of DNA modifications that control the activation or deactivation of genes in different cell types. Among these modifications, 5mC is considered one of the most significant, as it is the most prevalent type of DNA modification across mammals and is known to silence certain genes.
Rahul Kohli, MD, Ph.D., associate professor of Biochemistry and Biophysics at Penn Medicine and senior author of the study, explained, "5mC can act as a fingerprint for cell identity, so it’s important for scientists to have the power to isolate 5mC and only 5mC. DM-Seq uses two enzymes to map 5mC and can be applied to sparse DNA samples which means it could be used, for example, in blood tests that look for DNA released into the blood from tumors or other diseases tissues." The study was led by Tong Wang, an MD/Ph.D. student in Kohli's lab.
DNA modifications such as 5mC serve as epigenetic regulators that influence how DNA is read and processed. In the case of 5mC, a methyl group attaches to a specific site on a cytosine, represented as the letter "C" in the DNA alphabet. This modification can inhibit the expression of nearby DNA, affecting gene activity through direct and indirect mechanisms.
The presence or absence of 5mC can have significant implications for health, as abnormal patterns of 5mC are associated with various diseases, including cancer. Therefore, having an accurate and specific method to map 5mC is of utmost importance.
Existing methods for mapping 5mC rely on chemicals or enzymes that react differently with 5mC and unmodified cytosine, allowing for their differentiation. However, the conventional technique known as bisulfite sequencing (BS-Seq) damages DNA significantly and cannot distinguish 5mC from another essential type of methylation called 5-hydroxymethylcytosine (5hmC). Other recently developed methods also have limitations, such as the requirement for relatively large amounts of DNA.
DM-Seq, on the other hand, employs two enzymes, a designer DNA methyltransferase and a DNA deaminase, which together can directly and specifically detect 5mC. Moreover, the method is sensitive enough to work with minuscule amounts of DNA, making it suitable for liquid biopsy applications.
The researchers conducted DM-Seq on samples from glioblastoma-type brain tumors and demonstrated its superior ability, compared to traditional BS-Seq, to distinguish 5mC from 5hmC at critical genome sites where methylation levels can help predict patient outcomes.
In addition, the team compared DM-Seq with another emerging 5mC-sequencing technique called TAPS, which has potential applications in cancer diagnostics. The comparison revealed a previously unknown limitation in TAPS, which reduces its sensitivity in detecting 5mC.
Kohli emphasized, "These findings highlight ways in which direct detection of 5mC from DM-Seq, rather than traditional sequencing methods, could advance efforts to use epigenetic sequencing for prognostic purposes in cancer care."
In addition to the four primary bases of DNA (adenine, cytosine, guanine, and thymine), there exists an additional layer of information in the form of DNA modifications that control the activation or deactivation of genes in different cell types. Among these modifications, 5mC is considered one of the most significant, as it is the most prevalent type of DNA modification across mammals and is known to silence certain genes.
Rahul Kohli, MD, Ph.D., associate professor of Biochemistry and Biophysics at Penn Medicine and senior author of the study, explained, "5mC can act as a fingerprint for cell identity, so it’s important for scientists to have the power to isolate 5mC and only 5mC. DM-Seq uses two enzymes to map 5mC and can be applied to sparse DNA samples which means it could be used, for example, in blood tests that look for DNA released into the blood from tumors or other diseases tissues." The study was led by Tong Wang, an MD/Ph.D. student in Kohli's lab.
DNA modifications such as 5mC serve as epigenetic regulators that influence how DNA is read and processed. In the case of 5mC, a methyl group attaches to a specific site on a cytosine, represented as the letter "C" in the DNA alphabet. This modification can inhibit the expression of nearby DNA, affecting gene activity through direct and indirect mechanisms.
The presence or absence of 5mC can have significant implications for health, as abnormal patterns of 5mC are associated with various diseases, including cancer. Therefore, having an accurate and specific method to map 5mC is of utmost importance.
Existing methods for mapping 5mC rely on chemicals or enzymes that react differently with 5mC and unmodified cytosine, allowing for their differentiation. However, the conventional technique known as bisulfite sequencing (BS-Seq) damages DNA significantly and cannot distinguish 5mC from another essential type of methylation called 5-hydroxymethylcytosine (5hmC). Other recently developed methods also have limitations, such as the requirement for relatively large amounts of DNA.
DM-Seq, on the other hand, employs two enzymes, a designer DNA methyltransferase and a DNA deaminase, which together can directly and specifically detect 5mC. Moreover, the method is sensitive enough to work with minuscule amounts of DNA, making it suitable for liquid biopsy applications.
The researchers conducted DM-Seq on samples from glioblastoma-type brain tumors and demonstrated its superior ability, compared to traditional BS-Seq, to distinguish 5mC from 5hmC at critical genome sites where methylation levels can help predict patient outcomes.
In addition, the team compared DM-Seq with another emerging 5mC-sequencing technique called TAPS, which has potential applications in cancer diagnostics. The comparison revealed a previously unknown limitation in TAPS, which reduces its sensitivity in detecting 5mC.
Kohli emphasized, "These findings highlight ways in which direct detection of 5mC from DM-Seq, rather than traditional sequencing methods, could advance efforts to use epigenetic sequencing for prognostic purposes in cancer care."