Regulation of B cell early development by CNOT3

The CCR4-NOT complex, bearing poly(A) deadenylation activity, is a highly conserved regulator that is involved in biological control; however its action mechanisms and physiological targets remain unclear. Using genetic deletion of the CNOT3 subunit of this complex in early B cell progenitors, we show that CNOT3 plays a critical role in pro- to pre-B cell transition. CNOT3 participated in controlling germline transcription, compaction of the immunoglobulin heavy chain (Igh) locus, and Igh rearrangement, and in destabilizing tumor suppressor p53 mRNA. Moreover, by genetic ablation of p53 or introduction of pre-rearranged Igh transgene, the B cell developmental defect in the Cnot3 knockout background could be partly rescued, suggesting that CCR4-NOT complex exerts critical control in B cell differentiation processes by co-utilizing transcriptional and post-transcriptional mechanisms. Pro-B cells mRNA profiles of Mb1(cre/+) and Cnot3(fl/fl)Mb1(cre/+) mice were generated by deep sequencing using Illumina HiSeq 1500具备多聚腺苷酸脱腺苷化（poly(A) deadenylation）活性的CCR4-NOT复合物（CCR4-NOT complex）是一类高度保守的生物学调控因子，广泛参与生命过程的调控，但其具体作用机制与生理靶标仍未明确。本研究通过在早期B细胞前体中对该复合物的CNOT3亚基（CNOT3 subunit）实施基因敲除，证实CNOT3在祖B细胞（pro-B cell）向未成熟前B细胞（pre-B cell）的转化进程中发挥关键调控作用。CNOT3参与调控生殖系转录、免疫球蛋白重链（Igh）基因座的染色质压缩以及Igh基因重排，同时还可介导肿瘤抑制因子p53的mRNA发生去稳定化。进一步研究显示，通过敲除p53基因或引入预重排的Igh转基因，可部分挽救Cnot3基因敲除小鼠的B细胞发育缺陷，这表明CCR4-NOT复合物可通过协同转录与转录后调控机制，对B细胞分化过程施加关键调控。本研究采用Illumina HiSeq 1500平台进行深度测序，成功获取了Mb1(cre/+)与Cnot3(fl/fl)Mb1(cre/+)小鼠的祖B细胞mRNA表达谱。