Sequences affecting the v(d)j recombinational activity of the igh intronic enhancer in a transgenic substrate

Abstract

The immunoglobulin heavy chain intronic transcriptional enhancer (Eμ) is part of a complex cis-regulatory DNA region which has notably been shown to modulate V(D)J rearrangements of associated variable gene segments. We have used recombination substrates comprised of the Eμ enhancer together with various lengths of additional downstream μ sequences to assess the individual contribution of those sequences to the V(D)J recombinational regulatory activity. Surprisingly, in the absence of large amounts of μ. sequences, substrate rearrangements were not detected In Southern blot analyses of the lymphoid tissues from independent transgenic mice, but were readlly detectable following transfectlon into cultured pre-B cells. A short μ segment which includes matrix association regions (MARs) was not sufficient to restore high levels of rearrangements within the reporter transgenes. However, additional experiments demonstrated that the μ sequences are dispensable for V(D)J recombination in transgenic thymuses, implying a suppresslve effect exerted by the vector sequences left in the transgenic Insert, when they are attached near the Eμ regulatory region. This suppression of V(D)J recombination, which correlates with an hypermethylatlon of the transgenes, is discussed in view of previously reported transgenic and gene targeting experiments. © 1994 Oxford University Press.