[Human immunoglobulin heavy-chain gene intronic enhancer segment HE2 (microB) functions as a major B-cell specific cis-element at cellular level as well as in transgenic mice].

Immunoglobulin heavy-chain (IgH) gene expression is regulated in a large part of the IgH gene intronic enhancer which is composed of certain protein-binding motifs. These motifs act as a DNA element which is important for the regulation of the IgH gene transcription. Two of these motifs, HE2 and E6 in the human IgH gene intronic enhancer, are considered to affect the B cell-specific gene expression. To examine the true function of the HE2 and E6 motifs in vivo, we established transgenic mouse lines. A 3'deletion mutant of the IgH gene intronic enhancer which includes an active HE2 motif showed almost the same degree of transcriptional activity and tissue-specificity as the whole IgH gene intronic enhancer. Still more, using the luciferase-assay, it was confirmed at cellular level that the HE2 motif plays an important role in the tissue-specific activity of the IgH gene intronic enhancer. On the other hand, the E6 motif was unable to sufficiently produce the B cell-specific expression in vivo and showed enhancer activity in some non-B cells. In transgenic mice, the IgH gene intronic enhancer functioned not only in B-lymphocytes but also in chorid plexus cells which are similar to glial cells. This suggests the existence of common gene expression control mechanisms between the immune system and the nervous system.