This information is current as through the Regulation of MAD 2 Expression Critical Role of Pcid 2 in B Cell Survival

The mitotic checkpoint is essential for maintaining genomic stability in differentiating B cells undergoing genetic alterations of the Ig gene. In this study, using real-time RT-PCR and in situ RNA hybridization, we demonstrated that MAD2 mRNA export is selectively regulated by Pcid2/Thp1. Pcid2 small interfering RNA induced a cell-cycle abnormality with increased apoptosis and polyploidy, as previously observed in MAD2-knockdown cells. Pcid2 small interfering RNA reduced MAD2 expression, but not the expression of other cell-cycle checkpoint proteins, such as MAD1 and BUBR1, or the cell-cycle–associated proteins, cyclin A, cyclin B1, and cyclin-dependent kinase 1. In mouse B lineage cells, Pcid2 transcripts appeared in a stage-dependent manner at high levels in bone marrow pre-B and immature B cells, and in spleen transitional 1 and follicular B cells, but at lower levels in pro-B, transitional 2, and marginal zone B cells, suggesting a stage-dependent requirement for MAD2 regulation. Cd19-cre–derived targeting of the Pcid2 gene induced a mature B cell deficiency in mice. These findings indicate that Pcid2 is essential for B cell survival through the regulation of MAD2 expression during B cell differentiation. B cell development is characterized by the configuration of Ig genes and the expression of surface Ags that differentiate B lineage cells as pro-B, pre-B, and surface IgM + immature B cells in the bone marrow, and transitional (T) 1, T2, follicular (FO), and marginal zone (MZ) B cells in the spleen (1). The primary B cell repertoire is created by the initial growth and survival of B cells that comprise diverse Ag-specific clones. Ag stimulation induces rapid proliferation and differentiation of B cells in the germinal center (GC) of peripheral lymphoid organs. During early and mature B cell differentiation, Ig genes of B cells undergo three major genetic alterations: gene rearrangements in the bone marrow (2), V-region somatic hypermutation (SHM), and C-region class switch recombination (CSR) in the GC of the peripheral lym-phoid organs (3–5). The Ig gene rearrangements are carried out mainly by the expression of RAG1, RAG2, DNA-PKcs, Artemis, and XRCC4. Ig genes SHM and CSR are initiated in GC B cells by the expression of activation-induced cytidine deaminase, followed by uracil-DNA glycosylase, apurinic/apyrimidinic endonuclease, Msh2/Msh6, and various DNA polymerases (6, 7). Although these processes target different DNA segments of the Ig genes, B cells inevitably show transient DNA cleavages, including dsDNA breaks (8, 9). The genetic alterations occurring in B cells must be sensed and …