S16-05 Conserved function of STAT3 in mouse and rat embryonic stem cell self-renewal

MECHANISMS OF DEVELOPMENT 126 (2009)

S16-05

S43

S 4 2 –S 4 3

The University of Auckland, Auckland, New Zealand

Conserved function of STAT3 in mouse and rat embryonic stem cell self-renewal Qi-Long Ying University of Southern California, CA, United States STAT3 belongs to the signal transducers and activators of transcription (STAT) family. Activation of STAT3 via the LIF receptor/ gp130 signaling complex allows the derivation and propagation of embryonic stem (ES) cells from mouse blastocysts in the presence of feeders. Intriguingly, ES cells have not been established from some strains of mice, and not at all from rats under the LIF/feeder condition. We hypothesized that the STAT3 activation level is critical for regulating ES cell self-renewal. We introduced an STAT3 transgene and an artificial gp130 chimeric receptor into feeder-dependent mouse ES cells. This allows us to modulate STAT3 activity within a wider range in ES cells. We demonstrated that feeder-dependent mouse ES cells can be maintained in feeder-free conditions simply by modulating STAT3 activation level. We also showed that long-term self-renewal of rat ES cells can be sustained by increasing STAT3 activation, whereas LIF alone can not. These data suggest that the STAT3 activation level plays a key role in sustaining ES cell self-renewal and its function may be conserved among different strains of mice and rats.

The identity of the cells that give rise to the first haematopoietic stem cells (HSCs) in the developing embryo has long been controversial. HSCs have been proposed to emerge from mesenchymal progenitors, a bipotential endothelial-haematopoietic precursor (the haemangioblast) or the haemogenic endothelium. There is now evidence for the central role of haemogenic endothelial cells in the generation of primitive and definitive blood of mammalian embryos using long-term imaging of the cell fates of single mouse mesodermal cells in culture. However, definitive proof that HSCs originate from a haemogenic endothelium within an organism is still lacking. Here, we provide the first demonstration of the direct emergence of definitive HSCs from the haemogenic endothelium in a living embryo. The haematopoietic program is highly conserved in vertebrates. Runx1, a transcription factor essential for the development of HSCs in all vertebrates is also required for the transition from haemogenic endothelium to HSCs in mouse and zebrafish. We have generated a zebrafish Runx1 transgenic line, Tg(runx1P2:EGFP) marking definitive HSCs in the aortagonad-mesonephros (AGM) that later populate the pronephros and thymus. Kdr (Flk-1) is expressed in haemangioblasts and in early endothelial cells. Double Tg(runx1P2:EGFP/kdrl:nlsmCherry) transgenic lines express mCherry in the nuclei of endothelial cells, while HSCs emerging from the AGM express

doi:10.1016/j.mod.2009.06.1022

EGFP. Time-lapse imaging of these embryos reveal that all of the cells that initiate EGFP expression in the AGM were red fluorescent mCherry-expressing endothelial cells. This demon-

S16-03 Live imaging reveals that definitive haematopoietic stem cells emerge directly from haemogenic endothelial cells in zebrafish

strates

that

HSCs

arise

from

ogenic endothelium’.

embryos Enid Yi Ni Lam, Kathy Crosier, Chris Hall, Phil Crosier, Maria Vega Flores

further

differentiation

of

endothelial cells, providing strong in vivo evidence for a ‘haem-

doi:10.1016/j.mod.2009.06.1085