Immunobiology & Cancer Program, Oklahoma Medical Research Foundation, Oklahoma City, OK 73104, USA.
J Immunol. 2009 Dec 15;183(12):7768-77. doi: 10.4049/jimmunol.0902333.
Changes in cell surface markers and patterns of gene expression are commonly used to construct sequences of events in hematopoiesis. However, the order may not be as rigid as once thought and it is unclear which changes represent the best milestones of differentiation. We developed a fate-mapping model where cells with a history of RAG-1 expression are permanently marked by red fluorescence. This approach is valuable for appreciating lymphoid-lineage relationships without need for irradiation and transplantation. Hematopoietic stem cells (HSC) as well as myeloid and dendritic cell progenitors were unlabeled. Also as expected, most previously identified RAG-1(+) early lymphoid progenitors in bone marrow and all lymphoid-affiliated cells were marked. Of particular interest, there was heterogeneity among canonical common lymphoid progenitors (CLP) in bone marrow. Labeled CLP expressed slightly higher levels of IL-7Ralpha, displayed somewhat less c-Kit, and generated CD19(+) lymphocytes faster than the unlabeled CLP. Furthermore, CLP with a history of RAG-1 expression were much less likely to generate dendritic and NK cells. The RAG-1-marked CLP were lineage stable even when exposed to LPS, while unlabeled CLP were redirected to become dendritic cells in response to this TLR4 ligand. These findings indicate that essential events in B lymphopoiesis are not tightly synchronized. Some progenitors with increased probability of becoming lymphocytes express RAG-1 while still part of the lineage marker-negative Sca-1(+)c-Kit(high) (LSK) fraction. Other progenitors first activate this locus after c-Kit levels have diminished and cell surface IL-7 receptors are detectable.
细胞表面标志物的变化和基因表达模式通常用于构建造血过程中的事件序列。然而，顺序可能不像以前认为的那样严格，也不清楚哪些变化代表分化的最佳里程碑。我们开发了一种命运映射模型，其中具有 RAG-1 表达史的细胞被红色荧光永久标记。这种方法对于在不需要照射和移植的情况下欣赏淋巴谱系关系非常有价值。造血干细胞（HSC）以及髓系和树突状细胞祖细胞均未标记。正如预期的那样，骨髓中大多数先前鉴定的 RAG-1（+）早期淋巴祖细胞和所有与淋巴相关的细胞均被标记。特别有趣的是，骨髓中的典型共同淋巴祖细胞（CLP）存在异质性。标记的 CLP 表达稍高水平的 IL-7Ralpha，显示稍低水平的 c-Kit，并且比未标记的 CLP 更快地产生 CD19（+）淋巴细胞。此外，具有 RAG-1 表达史的 CLP 产生树突状细胞和 NK 细胞的可能性较小。即使暴露于 LPS，具有 RAG-1 标记的 CLP 也保持谱系稳定，而未标记的 CLP 则在响应这种 TLR4 配体时被重新定向为树突状细胞。这些发现表明 B 淋巴细胞生成中的基本事件没有紧密同步。一些具有增加成为淋巴细胞可能性的祖细胞表达 RAG-1，而仍属于谱系标记阴性 Sca-1（+）c-Kit（高）（LSK）部分。其他祖细胞在 c-Kit 水平降低并且细胞表面 IL-7 受体可检测之后首先激活该基因座。
