Localized gene-specific induction of accessibility to V(D)J recombination induced by E2A and early B cell factor in nonlymphoid cells

Accessibility of immunoglobulin (Ig) gene segments to V(D)J recombination i s highly regulated and is normally only achieved in B cell precursors. We p reviously showed that ectopic expression of E2A or early B cell factor (EBF ) with recombination activating gene (RAG) induces rearrangement of IgH and IgL genes in nonlymphoid cells. V kappaI genes throughout the locus were i nduced to rearrange after transfection with E2A, suggesting that the entire V kappa locus was accessible. However, here we show that Ig loci are not o pened globally but that recombination is localized. Gene families are inter spersed in the D-H, V kappa, and V lambda loci, and we show that certain fa milies and individual genes undergo high levels of recombination after ecto pic expression of E2A or EBF, while other families within the same locus ar e not induced to rearrange. Furthermore, in some families, induction of ger mline transcription correlates with the level of induced recombination, whi le in others there is no correlation, suggesting that recombination is not simply initiated by induction of germline transcription. The induced repert oire seen at 24 hours does not change significantly over time indicating th e absence of many secondary rearrangements and also suggesting a direct tar geting mechanism. We propose that accessibility occurs in a local manner, a nd that binding sites for factors facilitating accessibility are therefore likely to be associated with individual gene segments.