Department of Immunology, Mayo Clinic College of Medicine, Rochester, MN, USA; Mayo Graduate School, Mayo Clinic College of Medicine, Rochester, MN, USA.
Department of Immunology, Mayo Clinic College of Medicine, Rochester, MN, USA.
Exp Hematol. 2014 May;42(5):380-393.e3. doi: 10.1016/j.exphem.2014.01.001. Epub 2014 Jan 18.
Flt3 signaling plays a crucial role in regulating the survival and differentiation of lymphoid progenitors into B cell precursors (BCPs) in bone marrow. To define further the role of Flt3 signaling in lymphoid progenitor survival, mice deficient in Flt3 ligand that also expressed a Bcl2 transgene (Eμ-bcl2tg flt3l(-/-)) were generated. Intracellular flow cytometry established transgene expression in primitive hematopoietic progenitors, including lineage-negative Sca-1(+) c-kit(+) (LSK(+)) CD27(-) cells enriched for functional hematopoietic stem cells. Compared with flt3l(-/-) mice, Eμ-bcl2tg flt3l(-/-) mice had significantly increased multipotential progenitors (MPPs), IL-7R(+) common lymphoid progenitors, and B cell precursors. To determine whether forced expression of Bcl2 was sufficient to restore lymphoid priming in the absence of Flt3 signaling Eμ-bcl2tg flt3l(-/-)rag1-gfp(+) mice were generated. Analysis of Eμ-bcl2tg flt3l(-/-)rag1-gfp(+) mice revealed that the Bcl2 transgene had no effect on lymphoid priming before CD19 expression. Thus, forced expression of a survival gene can bypass the requirement for threshold levels of Flt3 signaling requisite for lymphoid priming. Temporal Flt3 ligand (FL) replacement therapy in flt3l(-/-) mice revealed specific requirements for Flt3 signaling in the expansion and maintenance of Flt3(+hi) MPP and Flt3(+) all lymphoid progenitors, but not Flt3(+) B lymphoid progenitors (BLPs), the immediate precursors of BCPs. BCPs were restored after temporal in vivo FL treatment, albeit with delayed kinetics. Together, these results show that Flt3 regulates the proliferation, survival, and maintenance of developmental stage-specific hematopoietic progenitors that give rise to BCPs.
Flt3 信号在调节骨髓中淋巴祖细胞向 B 细胞前体（BCP）分化和存活中起着至关重要的作用。为了进一步确定 Flt3 信号在淋巴祖细胞存活中的作用，生成了表达 Bcl2 转基因的 Flt3 配体缺陷（Eμ-bcl2tg flt3l(-/-)）的小鼠。细胞内流式细胞术确定了原始造血祖细胞中转基因的表达，包括谱系阴性 Sca-1(+) c-kit(+)（LSK(+)）CD27(-)细胞，其富含功能性造血干细胞。与 flt3l(-/-)小鼠相比，Eμ-bcl2tg flt3l(-/-)小鼠具有显著增加的多潜能祖细胞（MPP）、IL-7R(+)共同淋巴祖细胞和 B 细胞前体。为了确定在缺乏 Flt3 信号的情况下强制表达 Bcl2 是否足以恢复淋巴祖细胞的启动，生成了 Eμ-bcl2tg flt3l(-/-)rag1-gfp(+)小鼠。对 Eμ-bcl2tg flt3l(-/-)rag1-gfp(+)小鼠的分析表明，在 CD19 表达之前，Bcl2 转基因对淋巴祖细胞的启动没有影响。因此，生存基因的强制表达可以绕过对淋巴祖细胞启动所必需的 Flt3 信号的阈值水平的要求。在 flt3l(-/-)小鼠中进行的时间性 Flt3 配体（FL）替代治疗显示 Flt3 信号在 Flt3(+hi)MPP 和 Flt3(+)所有淋巴祖细胞的扩增和维持中具有特定的要求，但不是 Flt3(+)B 淋巴祖细胞（BLP），BCP 的直接前体。尽管动力学延迟，但在体内进行时间性 FL 治疗后恢复了 BCP。总之，这些结果表明 Flt3 调节产生 BCP 的发育阶段特异性造血祖细胞的增殖、存活和维持。
