The necessary evil of V(D)J recombination

 V(D)J recombination occurs during early B- and T-lymphocytes development, assmebling the immunoglobulin (Ig) and T cell receptor (Tcr) genes from arrays of V,D and J gene segments. The diversity arising from his locus-specific recombination creates the basis for the immense variation in antigen recognition capacity of the mature lymphocytes population.

The RAG endonuclease initiates V(D)J recombination at antigen receptor (AgR) loci by introducing DNA breaks adjacent to the V,D and J segments constituting the variable region of the loci (A)

RAG ability to induce DNA breakage comprises harmful potential that necessitates a tight regulation to ensure the tunneling of its activity exclusively to the AgR. Our current understanding of RAG targeting outlines a two-tiered model, consists of DNA recognition and interactions with histones. This mechanism is initiated first by the recognition of the RAG1 substrate, consists of a conserved heptamer, and a less conserved nonamer separated by a non-conserved spacer of either 12 or 23 base pairs. Consequently, of RSS’s variability, sequences that contain heptamer or heptamer-like sequences are found to exist outside of the antigen receptor genes hence are susceptible to RAG1 cleavage. Further, beyond RAG1-DNA interactions, epigenetic post-translational modified (PTMs) histone tails are shown to control RAG localization.

While the basic mechanism of action of these DNA editors has been extensively studied, the rules that drive their specificity to the AgR, and at low levels-to oncogenic ” off-target” sites , have remained largely elusive.

In our lab we aim to elucidate the complex genomic language of the AgR loci by which regulate the localisation and activity of RAGs  and to  discern the role of RAG in tumorigenesis, by amending the canonical model of RAG-targeting, such that RAG off-target events along the genome can be predicted, as a function of cell lineage, cancer type, and inherited polymorphism.