Genome-wide Mapping of Sister Chromatid Exchange in Single Cells Using 5hmC

DNA double stranded breaks can lead to genome instability and improper DNA repair. Genome instability refers to the rearrangements of genetic code such as translocations and inversions. Improper DNA repair results in deletions and insertions of genetic code causing mutations. Mutations and genome rearrangements give rise to a plethora of medical syndromes that make a person highly susceptible to genetic diseases such as cancer. The frequency of sister chromatid exchange events has been shown to be a strong indicator of genomic instability, and thus can indicate the risk level of an individual to develop such genetic diseases. A sister chromatid exchange can happen as a result of a double stranded break reparation. A novel technique, recently developed by the Dey lab, uses the epigenetic mark, 5-hydroxymethylcytosine, to deduce the presence of a double stranded break by directly detecting sister chromatid exchange. The ability to determine strand specific 5hmC at a single cell level allows for the creation of strand bias as a parameter. Strand bias is defined as the number of 5hmC marks detected on the chromosome’s plus strand divided by the total number of 5hmC marks detected. A computational algorithm was created, using data generated from Aba-seq genome sequencing, to determine changes in strand bias. The changes in strand bias are evidence of a sister chromatid exchange and thus a double stranded break.