Intra-Aortic Clusters Undergo Endothelial to Hematopoietic Phenotypic Transition during Early Embryogenesis

Chiyo Mizuochi,Kenzaburo Tani,Katia Biasch,Manuela Tavian,Stuart T Fraser,Yoshikane Kikushige,Koichi Akashi,Daisuke Sugiyama,Yuka Horio,Alfons Navarro

doi:10.1371/journal.pone.0035763

Chiyo Mizuochi, Kenzaburo Tani + Show 8 more

Open Access

https://doi.org/10.1371/journal.pone.0035763

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Journal: PloS one	Publication Date: Apr 27, 2012
Citations: 71	License type: CC BY 4.0

Affiliation: Kyushu University, Inserm, University of Sydney

Abstract

Intra-aortic clusters (IACs) attach to floor of large arteries and are considered to have recently acquired hematopoietic stem cell (HSC)-potential in vertebrate early mid-gestation embryos. The formation and function of IACs is poorly understood. To address this issue, IACs were characterized by immunohistochemistry and flow cytometry in mouse embryos. Immunohistochemical analysis revealed that IACs simultaneously express the surface antigens CD31, CD34 and c-Kit. As embryos developed from 9.5 to 10.5 dpc, IACs up-regulate the hematopoietic markers CD41 and CD45 while down-regulating the endothelial surface antigen VE-cadherin/CD144, suggesting that IACs lose endothelial phenotype after 9.5 dpc. Analysis of the hematopoietic potential of IACs revealed a significant change in macrophage CFC activity from 9.5 to 10.5 dpc. To further characterize IACs, we isolated IACs based on CD45 expression. Correspondingly, the expression of hematopoietic transcription factors in the CD45(neg) fraction of IACs was significantly up-regulated. These results suggest that the transition from endothelial to hematopoietic phenotype of IACs occurs after 9.5 dpc.

Highlights

During mouse embryogenesis, hematopoiesis begins at the extra-embryonic yolk sac (YS) at 7.5 days post-coitum and shifts to fetal liver after mid-gestation, to spleen and to bone marrow shortly before birth
We used confocal microscopy to expand upon our previous study and characterize the cell types found within intra-aortic/arterial clusters (IACs) according to c-Kit, CD31 and CD34 expression (Figure 1)
IACs were observed in dorsal aorta (DA), omphalomesenteric (vitelline) artery (OMA) and umbilical artery (UA) at 10.5 dpc, and the size of IACs in the OMA and UA was significantly larger than those seen in the DA (Figure 1A, right)

Summary

Introduction

Hematopoiesis begins at the extra-embryonic yolk sac (YS) at 7.5 days post-coitum (dpc) and shifts to fetal liver after mid-gestation, to spleen and to bone marrow shortly before birth. Functional hematopoietic stem cells (HSCs) that can reconstitute adult recipients are first identified in the AGM region at 10.5 dpc after ex vivo organ culture [7]. Cell populations capable of reconstituting neonatal recipients are detected in the p-Sp/AGM region at 9.5 dpc [12,13]. These observations suggest that ancestor cells of HSC from the p-Sp/AGM region at 9.5 dpc require special microenvironments to acquire HSC activity and that HSCs undergo phenotypic changes from 9.5 to 10.5 dpc. IACs express both hematopoietic (CD41 and CD45) and endothelial (CD31, CD34 and VE-cadherin) surface markers [3,15,16] suggesting that IACs are likely equivalent to ancestor cells of HSC and/or pre-HSCs and are derived from endothelial cells (ECs) at aortic/arterial regions. Recent genetic approaches and novel tracing methods demonstrate that IACs are derived from ECs in zebrafish and mice, it is unclear how IACs form and acquire HSC activity [17,18,19,20,21,22,23,24,25]

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