Multiple Mesoderm Subsets Give Rise to Endothelial Cells Whereas Hematopoietic Cells are Differentiated only From a Restricted Subset in ES Cell Differentiation Culture

¹ Laboratory for Stem Cell Biology, RIKEN Center for Development Biology, 2-2-3 Minatojima-minamimachi, Chuo-ku, Kobe, Hyogo, 650-0047, Japan.
² Department of Gastroenterology and Hepatology, Graduate school of Medicine, Kyoto University, 54 Shogoinkawara-cho, Sakyo-ku, Kyoto, 606-8507, Japan.

^* To whom correspondence should be addressed. E-mail: tera{at}cdb.riken.jp.

	Abstract

In the developing mouse, vascular endothelial (EC) and hematopoietic cell (HPC) lineages are two initial cell lineages that diverge from mesodermal cells which has been sub-divided roughly into three subtypes according to their geographical location - the organizer, embryonic mesoderm in the primitive streak, and extra-embryonic mesoderm during gastrulation. While the initial progenitors that become the two lineages appear in both VEGFR2⁺ lateral and extra-embryonic mesoderm, little is known about the underlying molecular events that regulate the derivation of ECs and HPCs. Here, we describe an experimental system consisting of two types of ES cell lines capable of distinguishing between organizer and the middle section of the primitive streak region. Using this system, we were able to establish a defined culture condition that can separately induce distinct types of mesoderm. While we were able to differentiate EC from all mesoderm subsets, however, the potential of HPC was restricted to the VEGFR2⁺ cells derived from primitive streak-type mesodermal cells. We also show that the culture condition for the progenitors of primitive erythrocytes is separated from that for the progenitors of definitive erythrocytes. These results suggest the dominant role of extrinsic regulation during diversification of mesoderm.

Key Words. ES cell, Brachyury, goosecoid, PDGFR and VEGFR2