Abstract
In adult mice, the VpreB genes are expressed in bone marrow progenitor (pro‐) and precursor (pre‐) B cells. As part of the pre‐B cell receptor, the proteins are crucial for the proliferation of these cells and consequently normal B lymphocyte development. Using cell lines, we identified a lineage‐ and developmental‐stage‐specific VpreB1 enhancer. Here, we analyze its specificity in vivo by generating transgenic mice in which expression of a reporter gene (human CD122) is regulated by the VpreB1 enhancer in the context of its own promoter. All transgenic lines expressed thereporter gene in the bone marrow in a copy number‐independent manner, whereas expression levels were integration site‐dependent. While the enhancer is not tissue specific, within the B cell lineage the expression pattern of human CD122 mimicked that of endogenous VpreB1. Thus, low levels were detected in pro‐B cells, high levels in pre‐BI and slightly lower levels in pre‐BII cells; no expression was detected in immature/mature B cells. Furthermore, when in vitro cultured transgenic pre‐B cells differentiated into immature B cells there was concomitant down‐regulation of human CD122 andendogenous VpreB1. Thus the VpreB1 enhancer is sufficient to ensure developmental stage‐specific expression of a reporter gene in B lymphocytes in vivo.