The transcription factor Pax5 regulates its target genes by recruiting chromatin-modifying proteins in committed B cells.

Pax5 is a critical regulator of B-cell commitment. Here, we identified direct Pax5 target genes by streptavidin-mediated ChIP-chip analysis of pro-B cells expressing in vivo biotinylated Pax5. By binding to promoters and enhancers, Pax5 directly regulates the expression of multiple transcription factor, cell surface receptor and signal transducer genes.

The distal V(H) gene cluster of the Igh locus contains distinct regulatory elements with Pax5 transcription factor-dependent activity in pro-B cells.

V(H)-DJ(H) recombination of the immunoglobulin heavy chain (Igh) locus is temporally and spatially controlled during early B cell development, and yet no regulatory elements other than the V(H) gene promoters have been identified throughout the entire V(H) gene cluster. Here, we discovered regulatory sequences that are interspersed in the distal V(H) gene region. These conserved repeat elements were characterized by the presence of Pax5 transcription factor-dependent active chromatin by binding of the regulators Pax5, E2A, CTCF, and Rad21, as well as by Pax5-dependent antisense transcription in pro-B cells.

STAT5 in B cell development and leukemia.

Early B cell development depends on a network of transcription factors, whereby E2A and EBF1 regulate B cell specification and Pax5 controls B-lineage commitment. In contrast, activation of the transcription factor STAT5 in response to IL-7R signaling promotes cell survival by activating the prosurvival gene Mcl1 and orders immunoglobulin gene rearrangement by repressing Igk recombination in pro-B cells. Subsequently, it cooperates with the pre-B cell receptor to facilitate pre-B cell expansion.

Role of STAT5 in controlling cell survival and immunoglobulin gene recombination during pro-B cell development.

STAT5 and interleukin 7 (IL-7) signaling are thought to control B lymphopoiesis by regulating the expression of key transcription factors and by activating variable (V(H)) gene segments at the immunoglobulin heavy-chain (Igh) locus. Using conditional mutagenesis to delete the gene encoding the transcription factor STAT5, we demonstrate that the development of pro-B cells was restored by transgenic expression of the prosurvival protein Bcl-2, which compensated for loss of the antiapoptotic protein Mcl-1. Expression of the genes encoding the B cell-specification factor EBF1 and the B cell-commitment protein Pax5 as well as V(H) gene recombination were normal in STAT5- or IL-7 receptor alpha-chain (IL-7Ralpha)-deficient pro-B cells rescued by Bcl-2.

Stepwise activation of enhancer and promoter regions of the B cell commitment gene Pax5 in early lymphopoiesis.

Pax5 is an essential regulator of B cell identity and function. Here, we used transgenesis and deletion mapping to identify a potent enhancer in intron 5 of the Pax5 locus. This enhancer in combination with the promoter region was sufficient to recapitulate the B lymphoid expression of Pax5.

Transcription factor Pax5 activates the chromatin of key genes involved in B cell signaling, adhesion, migration, and immune function.

The transcription factor Pax5 represses B lineage-inappropriate genes and activates B cell-specific genes in B lymphocytes. Here we have identified 170 Pax5-activated genes. Conditional mutagenesis demonstrated that the Pax5-regulated genes require continuous Pax5 activity for normal expression in pro-B and mature B cells.