Igh nuclear speckle association promotes V(D)J recombination

Igh locus positioning in the nuclear center is correlated with V to DJ recombination. However, the mechanisms that dictate radial positioning remain undefined. Deletion of the highly transcribed V_H14-2 led to reduced V to DJ rearrangements and increased locus contraction that facilitates V(D)J recombination. To reconcile these findings, we imaged Igh radial position by DNA fluorescence in situ hybridization and found that V_H14-2 deleted alleles locate in the nuclear periphery implying that nuclear compartmentalization may be linked to nuclear body association. We found that Igh loci associate with nuclear speckles (NS) and these contacts are reduced for V_H14-2 deleted alleles. Knockdown of NS constituents or treatment with a drug inhibitor led to disaggregation of speckles and impaired Igh radial positioning. Chemical disruption of speckles also caused reduced V to DJ recombination. Igh transcription and V_H chromatin accessibility are diminished in V_H14-2 deleted alleles linking function to NS association.