The downstream enhancer, Ed, positively regulates Ig kappa gene expression and somatic hypermutation

Abstract

The mouse Ig kappa locus has three known enhancers: the MAR/intronic enhancer (MEi), the 3′enhancer (E3′) and the further downstream enhancer (Ed). Previous studies have shown that both MEi and E3′ enhancers are required for maximal gene rearrangement of the locus, and that E3′ is also required for maximal expression and somatic hypermutation (SHM). To functionally elucidate Ed in vivo, we generated knockout mice with a targeted germ line deletion of Ed. Ed deleted homozygous mice (Ed−/−) have moderately reduced numbers of kappa expressing B cells and correspondingly increased numbers of lambda expressing B cells in spleen. Ed−/− mice also have decreased kappa mRNA expression in resting and T‐cell dependent activated splenic B cells and reduced kappa chains in sera. However, our analysis indicates that kappa gene rearrangement is normal in Ed−/− mice. In addition, our results show that Ed−/− mice exhibit reduced SHM in the kappa gene J‐C intronic region in Peyer's patch germinal center B cells. We conclude that Ed positively regulates Ig kappa gene expression and SHM, but not gene rearrangement.Research supported by grants GM29935 and AI067906 from NIH and I‐0823 from the Robert A. Welch Foundation.