Fig. 4

Mechanisms of double-strand break (DSB) repair. A Canonical Non-Homologous End-Joining (c-NHEJ) mechanism: The repair of (a) the DSB is done by molecularly bridging and rejoining the broken ends. This can happen (b) without nucleotide edition or through the editing of the broken ends with (c) addition or (d) loss of nucleotides. B Microhomology-Mediated End-Joining (MMEJ) mechanism: After (a) the DSB, (b) a 5′ to 3′ resection results in two 3′ single-stranded overhangs with exposed nucleotides of microhomology (purple), which (c) anneal. (d) After the trimming of the 3′ strands, the gaps are filled (light orange) and ligated, resulting in the repair with a deletion. C Homologous Recombination (HR) mechanism: after (a) a DSB in one of the sister chromatids, (b) a 5′ to 3′ resection creates a 3′ overhang with an exposed region of homology (yellow), (c) which helps the broken end to invade its sister chromatid and anneal, allowing for the start of DNA synthesis. (d) The DSB can be solved using homologous chromosomes without errors, therefore without the creation of rearrangements. It is important to note that HR can lead to rearrangements when it uses repetitive elements and not the homology located at the sister chromatid