Helgason C D, Sauvageau G, Lawrence H J, Largman C, Humphries R K
Department of Medicine, University of British Columbia, Vancouver, BC, Canada.
Blood. 1996 Apr 1;87(7):2740-9.
Little is known about the molecular mechanisms controlling primitive hematopoietic stem cells, especially during embryogenesis. Homeobox genes encode a family of transcription factors that have gained increasing attention as master regulators of developmental processes and recently have been implicated in the differentiation and proliferation of hematopoietic cells. Several Hox homeobox genes are now known to be differentially expressed in various subpopulations of human hematopoietic cells and one such gene, HOXB4, has recently been shown to positively determine the proliferative potential of primitive murine bone marrow cells, including cells with long-term repopulating ability. To determine if this gene might influence hematopoiesis at the earliest stages of development, embryonic stem (ES) cells were genetically modified by retroviral gene transfer to overexpress HOXB4 and the effect on their in vitro differentiation was examined. HOXB4 overexpression significantly increased the number of progenitors of mixed erythroid/myeloid colonies and definitive, but not primitive, erythroid colonies derived from embryoid bodies (EBs) at various stages after induction of differentiation. There appeared to be no significant effect on the generation of granulocytic or monocytic progenitors, nor on the efficiency of EB formation or growth rate. Analysis of mRNA from EBs derived from HOXB4-transduced ES cells on different days of primary differentiation showed a significant increase in adult beta-globin expression, with no detectable effect on GATA-1 or embryonic globin (beta H-1). Thus, HOXB4 enhances the erythropoietic, and possibly more primitive, hematopoietic differentiative potential of ES cells. These results provide new evidence implicating Hox genes in the control of very early stages in the development of the hematopoietic system and highlight the utility of the ES model for gaining insights into the molecular genetic regulation of differentiation and proliferation events.
关于控制原始造血干细胞的分子机制，人们了解甚少，尤其是在胚胎发育过程中。同源框基因编码一类转录因子，作为发育过程的主要调节因子，它们越来越受到关注，最近还被认为与造血细胞的分化和增殖有关。现在已知几种Hox同源框基因在人类造血细胞的各种亚群中差异表达，其中一个这样的基因HOXB4，最近已被证明能正向决定原始小鼠骨髓细胞的增殖潜力，包括具有长期重建能力的细胞。为了确定该基因是否可能在发育的最早阶段影响造血作用，通过逆转录病毒基因转移对胚胎干细胞（ES细胞）进行基因改造，使其过表达HOXB4，并检测其对体外分化的影响。在诱导分化后的不同阶段，HOXB4过表达显著增加了混合红系/髓系集落的祖细胞数量，以及源自胚状体（EBs）的确定性红系集落而非原始红系集落的数量。对粒细胞或单核细胞祖细胞的生成、EB形成效率或生长速率似乎没有显著影响。对来自HOXB4转导的ES细胞在初次分化不同天数的EBs的mRNA分析表明，成人β-珠蛋白表达显著增加，而对GATA-1或胚胎珠蛋白（βH-1）没有可检测到的影响。因此，HOXB4增强了ES细胞的红细胞生成以及可能更原始的造血分化潜力。这些结果提供了新的证据，表明Hox基因参与了造血系统发育非常早期阶段的控制，并突出了ES模型在深入了解分化和增殖事件的分子遗传调控方面的实用性。
