Provision of the immunoglobulin heavy chain enhancer downstream of a test gene is sufficient to confer lymphoid‐specific expression in transgenic mice

To test whether the immunoglobulin heavy chain enhancer is sufficient to direct lymphoid specific gene expression in vivo, we have incorporated into the mouse germ line a test gene (chloramphenicol-acetyl transferase) whose transcription is potentiated by the enhancer. Analysis of transgenic mice bearing single-copy integrations of the injected DNA indicates that provision of the enhancer downstream of the test gene (beyond the polyadenylation site) is sufficient to direct lymphoid-specific expression. The tissue specificity is considerable as judged by the fact that transgene expression is at least one thousandfold higher in spleen than in liver. Within the lymphoid family, expression of the transgene is much higher in surface IgM+ spleen cells than in thymocytes high in Thy-1 expression, suggesting that the enhancer preferentially directs expression to cells of the B lineage.