Regulation of B cell development
Lymphocyte differentiation proceeds through multiple stages characterized by the expression of distinct sets of genes. Our goals include understanding how the nuclear proteins Early B cell Factor (EBF) and Pax5 (B cell-specific activator protein) regulate B lineage specification, commitment and the immune response. Early B cell Factor (EBF) is a DNA-binding protein required for B cell lymphopoiesis and for the expression of proteins essential for B cell receptor function. The absence of EBF results in a developmental blockade at a pre-pro-B cell-like stage resulting in a complete lack of functional B cells and immunoglobulins. Enforced expression of EBF in hematopoietic progenitors drives production of B lineage cells at the expense of other cell types. In the absence of upstream regulators of EBF expression (PU.1, E2A or IL-7Ra), enforced expression of EBF in progenitor cells activated transcription of B cell-specific genes. In accord with these observations, we have elucidated a central role for EBF in the specification of B lineage cells. We defined a new function of EBF as a ‘pioneer’ of epigenetic modifications necessary for gene activation. These modifications are necessary for the function of other transcriptional regulators, including Pax5. Our observations suggest a molecular basis for EBF’s role in the hierarchical network of factors necessary for B lymphopoiesis. We are currently continuing our studies by using molecular techniques and animal model systems to understand how EBF initiates the remodeling of chromatin, including demethylation and de-compaction of DNA.
Other work in our laboratory addresses functions of the transcription factor Pax5. Pax5 regulates B lineage commitment in two ways. First, it activates expression of genes that are essential for the B cell developmental program. Second, it represses the expression of other lineage programs. Together with EBF, Pax5 is essential for the rearrangement and expression of immunoglobulins and other components of the B cell receptor for antigen. We previously determined that functions of Pax5 are, in part, dependent on recruitment of Ets transcription factors to bind target genes. To better understand how these mechanisms, we are currently generating transgenic mice that will allow us to modulate the expression of Pax5 during B cell development. Other studies are using embryonic stem cell technology to introduce mutations directly into pax5 genes. These mutations are expected to impair the ability of Pax5 to modulate gene expression, and ultimately its ability to influence lineage decisions.