The coupling between enhancer activity and hypomethylation of kappa immunoglobulin genes is developmentally regulated.

Abstract

Previous studies have indicated that immunoglobulin enhancers are essential for establishing transcriptional competence but not for maintaining the activity of constitutively transcribed genes. To understand the basis for this developmental shift away from dependence on enhancer function, we have investigated the relationship between transcriptional activity and methylation status of the immunoglobulin K light-chain genes (K genes) in mouse cell lines representing different stages of B-cel maturation. Using pre-B-cell lines in which the level of a critical K enhancer-binding factor, NF-KB, was controlled by the administration or withdrawal of lipopolysaccharide and plasmacytoma lines that either contain or lack this factor, we studied the properties of endogenous K genes and of transfected K genes which were stably integrated into the genomes of these cells. In the pre-B ceUls, the exogenous (originally unmethylated) K genes, as well as the endogenous K genes, were fully methylated and persistently dependent on enhancer function, even after more than 30 generations in a transcriptionally active state. In plasmacytoma cels, the endogenous K genes were invariably hypomethylated, whereas exogenous K genes were hypomethylated only in cells that contain NF-KB and are thus permissive for K enhancer function. These results indicate that the linkage of hypomethylation to enhancer-dependent activation of K transcription occurs after the pre-B-cell stage of development. The change in methylation status, together with associated changes in chromatin structure, may suffice to eliminate or lessen the importance of the enhancer for the maintenance of the transcriptionally active state.

The Role of Methylation in the Phenotype-dependent Modulation of Epstein-Barr Nuclear Antigen 2 and Latent Membrane Protein Genes in Cells Latently Infected with Epstein-Barr Virus

“…Several studies in other systems have shown that methylation of 5' flanking regulatory sequences is more critical in gene regulation than is methylation of the coding exons (Kelley et al, 1988 ;Bonnerot et al, 1988;Keshet et al, 1985;Toniolo et al, 1988). We have analysed the methylation pattern of several such regions.…”

Chromatin remodeling directly activates V(D)J recombination

“…Hypermethylation has been correlated with the existence of a repressed state, refractory to V(D)J recombination (5,10). Antigen receptor loci become demethylated as they are rendered recombinationally active (11,12). A transgenic model system was able to recapitulate the dependence on hypomethylation for recombination, suggesting that changes in CpG methylation may be another potentially important switch for Rag-mediated recombinational accessibility (13).…”

A novel enhancer in the immunoglobulin lambda locus is duplicated and functionally independent of NF kappa B.

“…The generation of productive H-chain rearrangement (Alt et al 1986), followed by the interaction of the Ki enhancer with NFKB, may be prerequisites for the recombination of VK and JK gene segments (Kelley et al 1988). At a later stage, and independent of productive K expression, unique factors may bind to activate the h enhancers.…”