SSiNGLe-ILM Method for Nucleotide-Precision DNA SSB Mapping
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Solution Overview
Problem
Current methods lack the capability to map single-strand breaks (SSBs) in DNA with nucleotide-level precision on a genome-wide scale, which is crucial for understanding their role in DNA damage and repair, as existing techniques either fail to provide nucleotide-level resolution or are limited in their ability to detect SSBs generated by various mechanisms.
Innovation Solution
The SSiNGLe-ILM method involves fragmenting DNA to generate 3' ends that cannot be tailed, adding tags to these ends, capturing and identifying SSB positions, and using next-generation sequencing to reveal their locations through linear amplification and PCR with specific primers, allowing for nucleotide-level mapping of SSBs across the genome.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If DNA is fragmented using conventional methods, then DNA can be processed for sequencing, but the 3' ends generated can be tailed which interferes with SSB detection
Solution Approach 1:
The DNA fragmentation is performed in situ within nuclei using micrococcal nuclease, which divides the genome into manageable fragments while preserving the spatial context of SSBs. This segmentation allows selective processing of fragments containing SSBs without being affected by other DNA regions
Solution Approach 2:
Instead of preventing tailing by chemical modification, the method inverts the approach by using the inability of MNase-generated 3' ends to be tailed as a selective feature. The TdT enzyme naturally fails to add tails to these ends, and this failure is exploited as a positive identifier for authentic SSB locations rather than treated as an obstacle
2Measurement precision
If existing SSB mapping methods are used, then some SSB information can be obtained, but nucleotide-level precision is not achieved
Solution Approach 1:
A poly(A) tail is introduced as an intermediary marker at the 3' end of DNA fragments containing SSBs. This tail serves as a unique identifier that can be captured and sequenced, allowing precise mapping of SSB positions to specific nucleotides in the genome without directly sequencing the break site itself
Solution Approach 2:
The TdT-mediated poly(A) tailing is performed preliminarily on DNA fragments before sequencing. This preliminary tagging action ensures that all SSB-containing fragments are marked with a uniform sequence motif, enabling high-precision localization during data analysis by identifying the exact position where the tail was added
3Adaptability or versatility
If comprehensive SSB detection is performed, then all SSB mechanisms can be studied, but the methodology becomes overly complex
Solution Approach 1:
The method uses a universal TdT enzyme that can add poly(A) tails to any 3' OH group regardless of the origin or mechanism of the SSB. This single enzymatic step provides universal detection capability for all types of SSBs (oxidative damage, replication stress, topoisomerase intermediates, etc.) without requiring different reagents or protocols for different damage mechanisms
Solution Approach 2:
The method extracts and isolates only the poly(A)-tailed DNA fragments containing SSBs from the total DNA population using magnetic beads or other capture methods. This extraction step simplifies the complex mixture of DNA fragments by selectively enriching only those with SSBs, making the subsequent sequencing and analysis manageable despite the comprehensiveness of the detection
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method enables the detection of SSBs with nucleotide precision genome-wide, identifying breaks produced by various mechanisms and can be applied to different species and conditions, providing comprehensive data on SSB patterns and potential biomarkers.
Implementation Method 1
fragmenting DNA to be tested with a method that generates 3' ends that cannot be tailed
Implementation Method 2
adding a first tail to available 3' ends of SSBs of the fragmented DNA corresponding to tag endogenous breaks
Implementation Method 3
linearly amplifying the tailed fragments using cycles of primer extension with a chimeric 5'-DNA-RNA-3' primer
Implementation Method 4
adding a second tail to 3' ends of the products of the primer extension to obtain desired products
Implementation Method 5
amplifying the desired products by a polymerase chain reaction (PCR) with oligonucleotides comprising adaptor sequences
Data Source
AI summary
The present disclosure discloses a method for detecting single strand breaks (SSBs) in DNA based on the following steps. First, DNA of interest is fragmented with a method that generates 3′ ends that cannot be tailed. Second, the available 3′ ends of the fragmented DNA corresponding to the pre-existing breaks are tailed. Third, SSBs are captured and their positions are identified genome-wide based on the following steps: (1) the tailed fragments are linearly amplified using a chimeric 5′-DNA-RNA-3′ primer; (2) the products of primer extension are tailed at the 3′ ends; (3) the desired products are amplified by PCR with oligonucleotides containing Illumina® adaptor sequences complementary to both tails and subjected to next-generation sequencing (NGS); 4) finally, positions of SSBs are revealed through the analysis of sequencing results.