Velo-cardio-facial syndrome (VCFS)/DiGeorge syndrome (DGS) is a human disorder characterized by a number of phenotypic features including cardiovascular defects. Most VCFS/DGS patients are hemizygous for a 1.5-3.0 Mb region of 22q11. To investigate the etiology of this disorder, we used a cre-loxP strategy to generate mice that are hemizygous for a 1.5 Mb deletion corresponding to that on 22q11. These mice exhibit significant perinatal lethality and have conotruncal and parathyroid defects. The conotruncal defects can be partially rescued by a human BAC containing the TBX1 gene. Mice heterozygous for a null mutation in Tbx1 develop conotruncal defects. These results together with the expression patterns of Tbx1 suggest a major role for this gene in the molecular etiology of VCFS/DGS.
B cells producing high-affinity antibodies are destined to differentiate into memory B cells and plasma cells, but the mechanisms leading to those differentiation pathways are mostly unknown. Here we report that the transcription factor IRF4 is required for the generation of plasma cells. Transgenic mice with conditional deletion of Irf4 in germinal center B cells lacked post-germinal center plasma cells and were unable to differentiate memory B cells into plasma cells. Plasma cell differentiation required IRF4 as well as the transcriptional repressor Blimp-1, which both acted 'upstream' of the transcription factor XBP-1. In addition, IRF4-deficient B cells had impaired expression of activation-induced deaminase and lacked class-switch recombination, suggesting an independent function for IRF4 in this process. These results identify IRF4 as a crucial transcriptional 'switch' in the generation of functionally competent plasma cells.
Chronic lymphocytic leukemia (CLL) is a malignancy of B cells of unknown etiology. Deletions of the chromosomal region 13q14 are commonly associated with CLL, with monoclonal B cell lymphocytosis (MBL), which occasionally precedes CLL, and with aggressive lymphoma, suggesting that this region contains a tumor-suppressor gene. Here, we demonstrate that deletion in mice of the 13q14-minimal deleted region (MDR), which encodes the DLEU2/miR-15a/16-1 cluster, causes development of indolent B cell-autonomous, clonal lymphoproliferative disorders, recapitulating the spectrum of CLL-associated phenotypes observed in humans. miR-15a/16-1-deletion accelerates the proliferation of both human and mouse B cells by modulating the expression of genes controlling cell-cycle progression. These results define the role of 13q14 deletions in the pathogenesis of CLL.
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