3' IgH enhancer elements shift synergistic interactions during B cell development

IgH gene expression is tightly controlled over the course of B cell development, B cell activation, and the subsequent differentiation of these cells into Ig-secreting plasmacytes. There are several transcriptional enhancers that map within and downstream of the IgH locus, and some of these have been clearly implicated in the developmental regulation of IgH gene assembly and expression. While some of the individual enhancers from this locus have been studied extensively, the functional interactions possible among this group of enhancers have been largely unexplored. In the present study, we have measured the transcriptional activities of combinations of enhancers introduced into B-lineage cell lines at several different developmental stages. We detected a developmental progression in which the 3' enhancers are initially inactive, then become strongly active through synergistic interactions, and finally achieve a strong level of activity with little interdependency. The relative contributions of E mu (the intron enhancer) and of the 3' enhancers also change as a function of developmental stage. We discuss these results in light of parallel studies of developmental changes in transcription factor requirements.