Our laboratory is interested in deciphering the functional and mechanistic role of homologous recombination in biology.
The Biology of Homologous Recombination
Homologous recombination (HR) governs genomic transactions. It represents a major chromosome repair tool that helps to eliminate deleterious lesions such as DNA double strand breaks (DSBs), mediate the restart of stalled or collapsed DNA replication forks, ensure proper meiotic chromosome segregation, as well as to maintain the length of telomeres in some circumstances (Fig. 1). As such, HR is indispensable for the maintenance of genome integrity. Studies in the past have provided compelling evidence for a tumor suppression role of HR. For instance, cell lines from familial breast cancer patients that harbor mutations in BRCA2 exhibit hypersensitivity to DNA damaging agents and a pronounced deficiency in HR. Aside from its genome maintenance and tumor suppression functions, HR also serves more specialized roles in various organisms, such as mating type switching in the budding yeast and V(D)J recombination in the immune system. In summary HR play an essential role in biology and dysregulation of HR causes severe disease such as cancer.
Homologous Recombination Pathway
HR is often induced via the formation of DSBs, which leads to the nucleolytic processing of DSB ends to generate 3′ single-stranded DNA (ssDNA) tails. Herein, the 3′ single-stranded tail associates with recombinases to form a nucleoprotein filament, which is then activated to invade a homologous duplex DNA molecule to form a displacement loop or D-loop. The 3′ invading strand is extended by DNA synthesis, followed by the pairing of the non-invading 3′ single-stranded tail with the homologous ssDNA strand in the enlarging D-loop (second end capture). The now paired second 3′ end is also extended by DNA synthesis and subsequent ligations generate a double Holliday Junction (dHJ) intermediate. Resolution of the dHJ intermediate can result in crossover or non-crossover recombinant products (Fig. 2). In summary, the HR pathway is constituted by a sequence of events that involve (1) DSBs formation; (2) end resection to create 3′ overhang ssDNA; (3) assembly of recombinase onto ssDNA; (4) D-loop mediated DNA synthesis; and (5) formation & resolution of dHJ intermediate.