The development of B lymphocytes is characterized by ordered changes in gene expression. The overall goal of this research is to understand the mechanisms responsible for the increase in heavy chain (mu) and light chain (kappa) synthesis and expression during the differentiation of immunoglobulin-producing cells. A murine B lymphoma cell line, 7OZ/3 is the model system. 7OZ/3 expresses both the membrane specific form and the secretion specific forms of heavy chains as intracellular proteins. The cells can be induced to synthesize kappa chains and express membrane IgM by treatment with the polyclonal B cell mitogen LPS, interleukin-1, supernatant from concanavalin A stimulated spleen cells, or gamma interferon. Variants have been isolated which fail to respond to either LPS or interferon, and their responses to the other inducers have been characterized by somatic, genetic, cellular and molecular biological methods. The results indicate that the pathways of induction by the four inducers are different, but that the induction of kappa transcription is a common target of all pathways. Cloned kappa and mu chains have been introduced into both wild type and mutant 7OZ/3 cells. The wild type cell lines transfected with the introduced genes express them both transiently and as stable clones, and the introduced kappa gene is inducible. One of the mutants is unable to express kappa transiently and only a few stable subclones can express the introduced kappa gene even at low levels. The next goals of this project are to determine which missing factor(s) prevent kappa expression in this mutant. Mutant and wild type kappa genes will be introduced into previously characterized variant 7OZ/3 cells to determine whether the cellular activation system or endogenous kappa gene is responsible for the mutant phenotype. The results of this research will enhance understanding of the regulation of B cell development and, more generally, of the regulation of gene expression.
