Functional analysis of defined mutations in the immunoglobulin heavy-chain enhancer in transgenic mice

We have analyzed the effect of defined mutations in the mouse immunoglobulin heavy-chain enhancer after introduction into the germline of transgenic mice. We have tested a mutation of the enhancer octamer motif, a double mutation of the octamer motif and the microB-site, and a triple mutation in the microE2, microE3 and microE4-sites. All constructs are expressed in the spleen of transgenic mice. Furthermore, expression is exclusively detectable in lymphoid organs and not in several nonlymphoid tissues. Whereas mutations in the microE-sites have a more pronounced effect on transgene activity in thymocytes as compared to bone marrow and spleen cells, the octamer/microB double mutation shows significantly reduced expression levels only in B-cells. Finally, our results demonstrate that the intronic heavy-chain enhancer element does not contribute to the increase steady state levels of heavy-chain mRNA after stimulation of spleen cells with LPS.