Kabrun N, Bühring H J, Choi K, Ullrich A, Risau W, Keller G
National Jewish Medical and Research Center, Denver, CO 80206, USA.
Development. 1997 May;124(10):2039-48. doi: 10.1242/dev.124.10.2039.
We have investigated the expression pattern of the Flk-1 receptor tyrosine kinase in mouse embryonic and fetal hematopoietic tissues as well as on hematopoietic precursor cells derived from these tissues. RNA analysis indicated that flk-1 was expressed in the yolk sac at day 10 of gestation, in the whole embryo at day 10 and 12 of gestation, in the liver throughout fetal life and in embryoid bodies (EBs) generated from ES cells differentiated in culture. Flk-1 message was also detected in erythroid and macrophage colonies generated from precursors of yolk sac, fetal liver, adult marrow and EB origin. Using an antibody directed against the extracellular portion of the molecule we have found that up to 50% of cells from EBs differentiated for 4 days express Flk-1. Following the development of this early Flk-1+ population the number of receptor-positive cells declines progressively to represent less than 5% of the EBs by day 12 of differentiation. Kinetic analysis revealed that the establishment of the EB Flk-1+ population precedes the development of cells which express CD34, Ly6A (Sca-1) and AA4.1. Cell sorting experiments demonstrated that all day-4 EB-derived hematopoietic precursors are Flk-1+ whereas greater than 95% of those found within the day-12 EBs are Flk-1-, suggesting that the precursor population which expresses this receptor represents an early but transient wave of hematopoietic development. Analysis of yolk sac and whole embryos at day 8.5 of gestation revealed a small but distinct Flk-1+ population that contained hematopoietic precursors. Day-12.5 fetal liver contained few Flk-1+ cells that showed little hematopoietic potential. Together these findings indicate that Flk-1 is expressed on an early population of hematopoietic precursors that may represent the onset of embryonic hematopoiesis.
我们研究了Flk-1受体酪氨酸激酶在小鼠胚胎和胎儿造血组织以及源自这些组织的造血前体细胞上的表达模式。RNA分析表明，flk-1在妊娠第10天的卵黄囊中表达，在妊娠第10天和12天的整个胚胎中表达，在整个胎儿期的肝脏中表达，以及在培养中分化的ES细胞产生的胚状体（EBs）中表达。在源自卵黄囊、胎儿肝脏、成年骨髓和EB的前体细胞产生的红系和巨噬细胞集落中也检测到了Flk-1信息。使用针对该分子细胞外部分的抗体，我们发现分化4天的EBs中高达50%的细胞表达Flk-1。在这个早期Flk-1+群体发育之后，受体阳性细胞的数量逐渐下降，到分化第12天时占EBs的比例不到5%。动力学分析表明，EB Flk-1+群体的建立先于表达CD34、Ly6A（Sca-1）和AA4.1的细胞的发育。细胞分选实验表明，所有第4天EB来源的造血前体细胞都是Flk-1+，而在第12天EBs中发现的这些细胞中超过95%是Flk-1-，这表明表达该受体的前体细胞群体代表了造血发育的早期但短暂的阶段。对妊娠第8.5天的卵黄囊和整个胚胎的分析显示，有一小群但明显的Flk-1+群体，其中包含造血前体细胞。第12.天5的胎儿肝脏中含有很少的Flk-1+细胞，造血潜力很小。这些发现共同表明，Flk-1在早期造血前体细胞群体上表达，这可能代表胚胎造血的开始。
