Antisense Intergenic transcription precedes Igh D-to-J recombination and is controlled by the intronic enhancer Eμ

V(D)J recombination is believed to be regulated by alterations in chromatin accessibility to the recombinase machinery, but the mechanisms responsible remain unclear. We previously proposed that antisense intergenic transcription, activated throughout the mouse Igh V-H region in pro-B cells, remodels chromatin for V-H-to-DJ(H) recombination. Using RNA fluorescence in situ hybridization, we now show that antisense intergenic transcription occurs throughout the Igh D(H)J(H) region before D-to-J recombination, indicating that this is a widespread process in V(D)J recombination. Transcription initiates near the Igh intronic enhancer E-mu and is abrogated in mice lacking this enhancer, indicating that E-mu regulates D-H antisense transcription. E-mu was recently demonstrated to regulate D-H-to-J(H) recombination of the Igh locus. Together, these data suggest that E-mu controls D-H-to-J(H) recombination by activating this form of germ line Igh transcription, thus providing a long-range, processive mechanism by which E-mu can regulate chromatin accessibility throughout the D-H region. In contrast, E-mu deletion has no effect on V-H antisense intergenic transcription, which is rarely associated with D-H antisense transcription, suggesting differential regulation and separate roles for these processes at sequential stages of V(D)J recombination. These results support a directive role for antisense intergenic transcription in enabling access to the recombination machinery.