The emergence of haematopoietic stem cells (HSCs) from the aorta-gonad-mesenephros (AGM) region requires the coordinated activity of multiple transcriptional networks. The transcription factor stem cell leukemia (SCL) is necessary for this process; however, multiple scl isoforms exist and the exact stage at which each is required is unknown. In this issue (p. 3977), Zilong Wen and colleagues deconstruct the stage-specific requirement of scl isoforms scl-α and scl-β during the emergence of HSCs from the ventral wall of the dorsal aorta in zebrafish, which is equivalent to the AGM. Using dual fluorescent reporters coupled with in vivo time-lapse imaging, the authors show that scl-β is expressed in the haemogenic endothelial cells, whereas scl-α is expressed after the endothelial-to-haematopoietic transition has occurred. In loss-of-function studies, the authors show that scl-β is necessary for the specification of the haemogenic endothelial cells, whereas scl-α acts to maintain the newly born HSCs. This study represents an important step in teasing apart the transcriptional complexity that governs HSC development.
- © 2013. Published by The Company of Biologists Ltd