ABSTRACT Despite decades of research, the identity of the cells generating the first haematopoietic cells in mammalian embryos is unknown1. Indeed, whether blood cells arise from mesodermal

cells, mesenchymal progenitors, bipotent endothelial–haematopoietic precursors or haemogenic endothelial cells remains controversial2,3,4,5,6,7,8,9. Proximity of endothelial and blood cells

at sites of embryonic haematopoiesis, as well as their similar gene expression, led to the hypothesis of the endothelium generating blood. However, owing to lacking technology10 it has been

impossible to observe blood cell emergence continuously at the single-cell level, and the postulated existence of haemogenic endothelial cells remains disputed1. Here, using new imaging and

morphology and multiple molecular and functional markers. Detachment of nascent blood cells from endothelium is not directly linked to asymmetric cell division, and haemogenic endothelial

cells are specified from cells already expressing endothelial markers. These results improve our understanding of the developmental origin of mammalian blood and the potential generation of

haematopoietic stem cells from embryonic stem cells. Access through your institution Buy or subscribe This is a preview of subscription content, access via your institution ACCESS OPTIONS

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institutional subscriptions * Read our FAQs * Contact customer support SIMILAR CONTENT BEING VIEWED BY OTHERS GASTRULOIDS AS IN VITRO MODELS OF EMBRYONIC BLOOD DEVELOPMENT WITH SPATIAL AND

TEMPORAL RESOLUTION Article Open access 04 August 2022 EFFICIENT GENERATION OF HUMAN NOTCH LIGAND-EXPRESSING HAEMOGENIC ENDOTHELIAL CELLS AS INFRASTRUCTURE FOR IN VITRO HAEMATOPOIESIS AND

LYMPHOPOIESIS Article Open access 04 September 2024 CD32 CAPTURES COMMITTED HAEMOGENIC ENDOTHELIAL CELLS DURING HUMAN EMBRYONIC DEVELOPMENT Article Open access 09 April 2024 REFERENCES *

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ACKNOWLEDGEMENTS We are grateful to S. Nishikawa, M. A. Rieger, A. Hermann and M. Yoder for technical advice and discussions, M. Ogawa and H. Niwa for the VEVC2 and EB3 ESC lines,

respectively, B. Schauberger for programming contributions, and A. Roth and C. Raithel for technical support. We thank M. Goetz, A. Hermann, M. A. Rieger and A. IJpenberg for critical

reading of the manuscript. Part of this study was financed by the Deutsche Forschungsgemeinschaft to T.S. and by the Leading Project for the Realization of Regenerative Medicine to S.-I.N.

AUTHOR CONTRIBUTIONS H.M.E. planned and performed experiments; S.-I.N. discussed results and commented on the manuscript; T.S. designed the study and experiments, developed the time-lapse

imaging and cell-tracking technology, performed initial experiments, analysed data with H.M.E. and wrote the paper with H.M.E. AUTHOR INFORMATION AUTHORS AND AFFILIATIONS * Institute of Stem

Cell Research, Helmholtz Center Munich—German Research Center for Environmental Health (GmbH), 85764 Neuherberg, Germany Hanna M. Eilken & Timm Schroeder * Laboratory for Stem Cell

Biology, RIKEN Center for Developmental Biology, 650-0047 Kobe, Japan Shin-Ichi Nishikawa Authors * Hanna M. Eilken View author publications You can also search for this author inPubMed 

Google Scholar * Shin-Ichi Nishikawa View author publications You can also search for this author inPubMed Google Scholar * Timm Schroeder View author publications You can also search for

this author inPubMed Google Scholar CORRESPONDING AUTHOR Correspondence to Timm Schroeder. SUPPLEMENTARY INFORMATION SUPPLEMENTARY INFORMATION This file contains Supplementary Figures 1-8

with Legends, Supplementary Tables 1-3 and Supplementary Movies Legends 1-8 (PDF 2443 kb) SUPPLEMENTARY VIDEO 1 This time-lapse movie, covering a period of about 4.5 days, shows that cells

with endothelial morphology can give rise to blood cells (see file s1 for full legend). (MOV 9773 kb) SUPPLEMENTARY VIDEO 2 This time-lapse movie, covering a period of about 1 day, proofs

the cell identity of endothelial and blood cells by molecular and functional markers (see file s1 for full legend). (MOV 3788 kb) SUPPLEMENTARY VIDEO 3 This time-lapse movie, covering a

period of about 2.5 days, shows that nascent blood cells generated by endothelial cells express the surface marker CD41 prior to CD45 expression (see file s1 for full legend). (MOV 4070 kb)

SUPPLEMENTARY VIDEO 4 This time-lapse movie, covering a period of about 1.5 days, shows that mesodermal cells purified from 7.5 dpc mouse embryos can generate hemogenic endothelial cells

(see file s1 for full legend). (MOV 3892 kb) SUPPLEMENTARY VIDEO 5 This time-lapse movie, covering a period of about 6.5 days, shows that nascent blood cells generated by endothelial cells

have colony forming potential with high proliferative potential and multilineage (including megakaryocytic) potential. (MOV 8815 kb) SUPPLEMENTARY VIDEO 6 This time-lapse movie, covering a

period of about 5 hours, demonstrates the temporal and optical resolution of the primary image sequences used for cell tracking (see file s1 for full legend). (MOV 2331 kb) SUPPLEMENTARY

VIDEO 7 This time-lapse movie, covering a period of about 8.5 hours, demonstrates the temporal and optical resolution of the primary image sequences used for cell tracking (see file s1 for

full legend). (MOV 6633 kb) POWERPOINT SLIDES POWERPOINT SLIDE FOR FIG. 1 POWERPOINT SLIDE FOR FIG. 2 POWERPOINT SLIDE FOR FIG. 3 POWERPOINT SLIDE FOR FIG. 4 RIGHTS AND PERMISSIONS Reprints

and permissions ABOUT THIS ARTICLE CITE THIS ARTICLE Eilken, H., Nishikawa, SI. & Schroeder, T. Continuous single-cell imaging of blood generation from haemogenic endothelium. _Nature_

457, 896–900 (2009). https://doi.org/10.1038/nature07760 Download citation * Received: 29 May 2008 * Accepted: 09 January 2009 * Published: 01 February 2009 * Issue Date: 12 February 2009 *

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