Immunoglobulin kappa gene expression after stable integration. II. Role of the intronic MAR and enhancer in transgenic mice.

MOPC41 immunoglobulin kappa gene constructs have been stably introduced into the mouse germ line to investigate the effects of deleting the conserved intronic sequences on gene expression. Intact kappa genes containing 1.5 kilobase pairs of upstream and 8.5 kilobase pairs of downstream flanking sequences were highly expressed tissue-specifically, raising the total level of kappa mRNA in spleens severalfold in most transgenic animals. This high expression was often accompanied by marked suppression of endogenous kappa gene activity. Transgenes containing a deletion of the matrix association region (MAR) or both the MAR and enhancer were expressed tissue-specifically at mean levels only 2- and 3-fold lower, respectively, than that of intact transgenes. Therefore, while the intronic enhancer and MAR appear to play a quantitative role in gene expression, these sequences are not absolutely essential for transcriptional activation of rearranged kappa genes in a normal developmental environment.