Identification of Pax5 Target Genes in Early B Cell Differentiation

Abstract

The transcription factor Pax5 is essential for B cell commitment in the mouse, where it represses lineage-inappropriate gene expression while simultaneously activating the B cell gene expression program. In this study we have performed a global gene expression screen of wild-type and Pax5-deficient pro-B cells in an attempt to identify the crucial Pax5 targets in early B lymphopoiesis. These studies have identified 109 Pax5 targets comprising 61% activated and 39% repressed genes. Interestingly, Pax5 directly regulates the genes encoding a number of transcription factors that are required at the pre-B cell stage of differentiation, including Irf8, Spib, and Ikzf3 (Aiolos), suggesting that a key function of Pax5 is to activate secondary transcription factors that further reinforce the B cell program. Pax5 is also required for the expression of many genes known to be involved in adhesion and signaling, indicating that Pax5 modulates the homing and or migration properties of B cell progenitors. Finally, Pax5 also represses a cohort of genes that are involved in multiple biological processes, many of which are not typically associated with B cells. These include the repression of the adhesion molecule Embigin, which is expressed in bone marrow progenitors, T cells, and myeloid cells but is specifically repressed by Pax5 in B cells.

Ebf1orPax5haploinsufficiency synergizes with STAT5 activation to initiate acute lymphoblastic leukemia

“…To further investigate changes in gene expression, we performed microarray analysis on samples from wild-type and Stat5b-CA progenitor B cells and Stat5b-CA x Ebf1 +/ leukemic B220 + CD19 + lymph node cells. We then compared our results with previously published datasets of EBF1-and PAX5-activated genes (Schebesta et al, 2007;Pongubala et al, 2008;Pridans et al, 2008;Treiber et al, 2010) and found that the majority of EBF1 and PAX5-induced genes (75.6 and 73.5%, respectively) were unaffected by twofold reductions in Ebf1 and Pax5 expression (Fig. 6 A and Table S2).…”

“…The most strongly derepressed of all genes in our analysis is Tnfsf11 (44-fold increase in expression), which encodes RANKL, a factor known to promote progenitor B cell proliferation (Kong et al, 1999). Both EBF1 and PAX5 repress expression of Tnfsf11 (Delogu et al, 2006;Pongubala et al, 2008;Pridans et al, 2008;Treiber et al, 2010). This prompted us to ask whether the list of significantly derepressed genes in our leukemias was enriched in genes regulated by both EBF1 and PAX5.…”

“…Reduced expression of EBF1 and PAX5 results in derepression of genes that promote proliferation or survival In addition to their role in activating genes required for B cell development, EBF1 and PAX5 have both been shown to play a key role in suppressing the expression of genes associated with other cell fates such as Notch1 or Tnsf11 (Delogu et al, 2006;Pridans et al, 2008;Treiber et al, 2010). These factors also appear to restrain expression of genes involved in cell survival, such as Bcl2, or cell proliferation, such as c-Myc (Nutt et al, 1998).…”

The reduced and altered activities of PAX5 are linked to the protein–protein interaction motif (coiled-coil domain) of the PAX5–PML fusion protein in t(9;15)-associated acute lymphocytic leukemia

“…Next, we extracted RNA from these transduced murine BM cells for quantitative real-time PCR analysis. The seven mouse Pax5 target genes, including CD19, Blnk, Rag2, Mb1/CD79a, Blk, Atp1b1 and Nedd9 (Kawamata et al, 2008;Pridans et al, 2008), were selected in our studies. We found that, compared with vector transduction only, introduction of PAX5 into murine BM cells remarkably enhanced the expression of these Pax5 target genes (Figure 1d), which supported these genes are positively regulated by PAX5 transcriptional factor as reported (Cobaleda et al, 2007).…”

The role of novel and known extracellular matrix and adhesion molecules in the homeostatic and regenerative bone marrow microenvironment

“…205 It is upregulated in short-term HSPCs compared to long-term HSCs, 11 and we found it higher expressed in MPB-compared to BM-derived HSPCs (Fig. 1).…”