Transcriptional and Post-Transcriptional Control of Ig-Gene Expression in Murine B-Cells Activated by LPS and Anti-Receptor Antibodies

Abstract

Bacterial Lipopdysaccharide (LPS) induces normal resting B-cells to proliferate and to differentiate into immunoglobulin (Ig)-secreting plasma cells. We have studied the transcriptional control of Ig-gene expression in this system by an in vitro transcriptional run-on assay (1). Fig. 1 shows the relative RNA transcriptional rates in nuclei isolated from resting B-cells and from B-cells 1 to 4 days after LPS stimulation. There are very few if any transcripts demonstrable in resting B-cells with the probes tested (C/u, Igh-enhancer, and kappa). Even actin and H-2 probes do not give strong signals. Upon LPS stimulation, there is a rapid and strong enhancement of RNA Polymerase II activities until day 4, giving 30–50 fold increases. The /u- and kappa-transcripts detectable are about equal, indicating also a balanced distribution of RNA Polymerase II along both heavy and light chain loci. The 30–50 fold increases of transcription upon LPS induction account for the strong accumulation of Ig-mRNAs found in day-4 LPS cultures. The data demonstrate that Ig-gene expression in normal activated B-lymphocytes is regulated primarily at the level of transcription.