The miR-15a/16-1 and miR-15b/16-2 clusters regulate early B cell development by limiting IL-7 receptor expression II

Pleiotropic functions of miRNAs as transcriptional repressors have been reported for multiple biological processes. One prominent miRNA family is the miR-15 family, which is a well-established tumor-suppressor in B-cell chronic lymphocytic leukemia (CLL). The miR-15 family consists of three bicistronic clusters, miR-15a/16-1, miR-15b/16-2 and miR-497/195, all sharing the same seed sequence suggesting that loss one cluster can be functionally compensated by the remaining miR-15 family members. Thus, a combined deletion may be necessary to reveal its physiological function in vivo. A combined knockout of the most prominent miR-15 clusters, miR-15a/16-1 and miR-15b/16-2 in the hematopoietic system reveals a novel role of the miR-15 family in early B cell development highlighted by an increase of the pro-B cell compartment. Mechanistically, this effect is mediated by enhanced IL-7 receptor expression, which we identified as direct miR-15 target gene. Notably, elevated IL-7 receptor levels were sufficient to trigger increased activation of the STAT5 and PI3K/AKT pathways. Moreover, derepression of directly targeted cell cycle regulators such as Ccne1, Chek1 and Wee1 further facilitates G-to-S transition. Thus, by deregulating a target gene network of cell cycle and signaling mediators, loss of the miR-15 family establishes a pro-proliferative milieu manifesting in an enlarged pro-B cell pool. RNA sequencing data of FACS-sorted pro-B cells of 4 miR-15a/b+/+ Vav-Cre mice (controls) and 4 miR-15a/bfl/fl Vav-Cre mice.

作为转录抑制因子的微小RNA（microRNA, miRNA）的多效性功能已在多种生物学过程中被报道。其中极具代表性的miR-15家族，作为B细胞慢性淋巴细胞白血病（B-cell chronic lymphocytic leukemia, CLL）中公认的抑癌基因已得到充分验证。miR-15家族包含三个双顺反子基因簇：miR-15a/16-1、miR-15b/16-2以及miR-497/195，三者共享完全一致的种子序列，这意味着单个基因簇的功能缺失可由其余miR-15家族成员实现功能代偿。因此，若要揭示该家族在体内的生理功能，往往需要对多个基因簇进行联合敲除。
在造血系统中联合敲除最具代表性的miR-15基因簇——miR-15a/16-1与miR-15b/16-2，揭示了miR-15家族在早期B细胞发育中的全新功能：前B细胞区室的显著扩增即为该功能的典型特征。机制层面，该效应通过上调白细胞介素7受体（IL-7 receptor, IL-7R）的表达介导，本研究证实IL-7R是miR-15的直接靶基因。值得注意的是，升高的IL-7R水平足以触发STAT5与PI3K/AKT通路的过度激活。此外，Ccne1、Chek1与Wee1等直接靶向的细胞周期调控因子的去抑制，进一步促进了G1期向S期的细胞周期转换。综上，通过失调细胞周期与信号通路介质的靶基因网络，miR-15家族的缺失构建了促增殖微环境，最终表现为前B细胞池的扩增。
本数据集包含经荧光激活细胞分选（FACS）获得的4只miR-15a/b+/+ Vav-Cre小鼠（对照组）与4只miR-15a/bfl/fl Vav-Cre小鼠的前B细胞RNA测序数据。