The B-cell identity factor Pax5 regulates distinct transcriptional programmes in early and late B lymphopoiesis

Abstract

Pax5 controls the identity and development of B cells by repressing lineage-inappropriate genes and activating B-cell-specific genes. Here, we used genome-wide approaches to identify Pax5 target genes in pro-B and mature B cells. In these cell types, Pax5 bound to 40% of the cisregulatory elements defined by mapping DNase I hypersensitive (DHS) sites, transcription start sites and histone modifications. Although Pax5 bound to 8000 target genes, it regulated only 4% of them in pro-B and mature B cells by inducing enhancers at activated genes and eliminating DHS sites at repressed genes. Pax5-regulated genes in pro-B cells account for 23% of all expression changes occurring between common lymphoid progenitors and committed pro-B cells, which identifies Pax5 as an important regulator of this developmental transition. Regulated Pax5 target genes minimally overlap in pro-B and mature B cells, which reflects massive expression changes between these cell types. Hence, Pax5 controls B-cell identity and function by regulating distinct target genes in early and late B lymphopoiesis. The EMBO Journal (2012) (Nutt and Kee, 2007). The helix-loop-helix protein E2A and the early B-cell factor EBF1 specify the B-cell lineage by activating the expression of B-lymphoid genes in pre-pro-B cells Treiber et al, 2010). Pax5 subsequently controls B-cell commitment at the transition to the pro-B cell stage by restricting the developmental potential of lymphoid progenitors to the B-cell lineage, as shown by the fact that Pax5-deficient pro-B cells are still able to differentiate into most hematopoietic cell types in vitro and in vivo (Nutt et al, 1999;Medvedovic et al, 2011). At the molecular level, Pax5 fulfills a dual role by repressing B-lineage-inappropriate genes to suppress alternative lineage options and by simultaneously activating B-cell-specific genes to promote B-cell development (Nutt et al, 1999;Medvedovic et al, 2011). Gene expression analyses of wild-type and Pax5-deficient pro-B cells identified 110 Pax5-repressed and 170 Pax5-activated genes, which code for key regulatory and structural proteins involved in transcriptional control, receptor signalling, adhesion, migration and immune function (Delogu et al, 2006;Schebesta et al, 2007;Pridans et al, 2008). Pax5 regulates these gene expression changes by inducing active chromatin at activated target genes and eliminating active chromatin at repressed genes in pro-B cells . Notably, Pax5 induces these chromatin and transcription changes by recruiting chromatin-remodelling, histone-modifying and basal transcription factor complexes to its target genes, which identifies Pax5 as an epigenetic regulator of B-cell commitment .Pax5 is expressed throughout B-cell development from pro-B cells in the bone marrow to mature B cells in peripheral lymphoid organs (Fuxa and Busslinger, 2007), where it plays an important role in the generation and function of distinct mature B-cell types (Horcher et al, 2001;Medvedovic et al, 2011). Pax5 is essential for maintaining the B-cell gene exp...

Transcription factors regulating B cell fate in the germinal centre

“…PAX5 binds directly to thousands of DNA sites in B cells and functions by both activating and repressing gene expression [40]. During early B cell development PAX5 is absolutely required for the initial commitment of lymphoid progenitors to the B cell fate [43] and V-DJ recombination of the Ig locus [44,45].…”

“…During early B cell development PAX5 is absolutely required for the initial commitment of lymphoid progenitors to the B cell fate [43] and V-DJ recombination of the Ig locus [44,45]. In mature B cells it regulates the expression of genes critical to B cell identity, including components of the B cell receptor (Ig heavy chain and CD79A), CD19, CD21, B lymphocyte kinase (BLK), interferon regulatory factor (IRF)4 and IRF8 [40]. In addition, PAX5 further reinforces B cell identity by repressing the expression of lineage inappropriate genes, including Fmslike tyrosine kinase 3 (FLT3), CCR2 and CD28, which are expressed in PCs following PAX5 down-regulation, and macrophage colony-stimulating factor (M-CSF) receptor, NOTCH1, RAMP1, LMO2 and CCL3, which are expressed in common lymphoid progenitors and myeloid cells [46].…”

“…Paired box protein 5 (PAX5) is the master regulator of B cell identity and is expressed throughout B cell development [40], from pro-B cells [41] to mature GC B cells [42]. PAX5 binds directly to thousands of DNA sites in B cells and functions by both activating and repressing gene expression [40].…”

The ADP-ribosyl cyclases - the current evolutionary state of the ARCs

“…The principal defects were observed in the B cell lineage; among them, alteration of peritoneal B-1 cell development, and decreased serum and mucosal antibody production (62). Further data pointing to an important role for Bst1 in B lymphocyte development and migration is that the Bst1 gene has been identified as a target of the transcription factor Pax5, the B-cell identity factor, in murine pro-B cells (63).…”

One missense mutation in exon 2 of the PAX5 gene in Iran

“…Analysis of gene expression of wild-type and PAX5 knock-out pro-B cells revealed that 110 and 170 genes are repressed and activated, respectively, by PAX5 and that these genes encode essential proteins that participate in several important cell process. PAX5 regulates expression of these genes through induction or elimination of active chromatins (Revilla-i-Domingo et al, 2012). Importantly, PAX5 has also been associated with human B-cell tumors.…”