title: Involvement of Runx1 in the down-regulation of fetal liver kinase-1 expression during transition of endothelial cells to hematopoietic cells.
abstract: During early mouse embryogenesis, fetal liver kinase-1 (Flk-1), a receptor for vascular endothelial growth factor, and Runx1, a runt domain transcription factor, have prerequisite roles in the generation of hematopoietic lineages. Flk-1 expression is maintained in successive stages from mesodermal to endothelial cells and is down-regulated in nascent hematopoietic cells, whereas Runx1 (Runt-related transcription factor 1) is expressed in embryonic sites of hematopoietic cell de novo generation and in practically all hematopoietic organs. Here we show that Runx1 represses Flk-1 during the development of hemogenic endothelial cells into hematopoietic cells. We established embryonic stem cell clones carrying the Venus gene, a modified version of yellow fluorescence protein, in the Runx1 locus and cultured them on OP9 cells. Flk-1+ cells appeared on day 3.5, and Runx1+ cells first appeared from the Flk-1+ fraction on day 4.5. The Flk-1+Runx1+ cells rapidly stopped expressing Flk-1 with further incubation and eventually gave rise to CD45+ or TER119+ cells. Runx1 repressed Flk-1 promoter transcriptional activity in an endothelial cell line, and this repression required intact DNA-binding and transactivating domains of Runx1 protein. The repressor activity of Runx1 endogenous Flk-1 was also confirmed overexpressing Runx1 in embryonic stem cell differentiation cultures. These results provide novel insight into the role Runx1 during the development of hematopoietic cell lineages.
authors.affiliation: Department of Microbiology, Kyoto Prefectural University of Medicine, Kamigyo-ku, Kyoto 602-8566, Japan. hhirai@koto.kpu-m.ac.jp
authors.forename: Hideyo
authors.initials: H
authors.lastname: Hirai
authors.forename: Igor M
authors.initials: IM
authors.lastname: Samokhvalov
authors.forename: Tetsuhiro
authors.initials: T
authors.lastname: Fujimoto
authors.forename: Satomi
authors.initials: S
authors.lastname: Nishikawa
authors.forename: Jiro
authors.initials: J
authors.lastname: Imanishi
authors.forename: Shin-Ichi
authors.initials: S
authors.lastname: Nishikawa
mesh_terms: D000818:Animals; D002417:Cattle; D002454:Cell Differentiation / Q000235:genetics*; D019070:Cell Lineage; D050676:Core Binding Factor Alpha 2 Subunit; D004268:DNA-Binding Proteins / Q000032:analysis / Q000502:physiology*; D015536:Down-Regulation / Q000235:genetics; D004622:Embryo, Mammalian / Q000166:cytology; D042783:Endothelial Cells / Q000166:cytology*; D004730:Endothelium, Vascular / Q000166:cytology / Q000378:metabolism; D006412:Hematopoietic Stem Cells / Q000166:cytology*; D051379:Mice; D011518:Proto-Oncogene Proteins / Q000032:analysis / Q000502:physiology*; D013234:Stem Cells / Q000166:cytology / Q000378:metabolism; D014157:Transcription Factors / Q000032:analysis / Q000502:physiology*; D014158:Transcription, Genetic; D040301:Vascular Endothelial Growth Factor Receptor-2 / Q000032:analysis / Q000235:genetics*
chemical_list: D050676:Core Binding Factor Alpha 2 Subunit; D004268:DNA-Binding Proteins; D011518:Proto-Oncogene Proteins; C493726:Runx1 protein, mouse; D014157:Transcription Factors; D040301:Vascular Endothelial Growth Factor Receptor-2