GFI1 proteins orchestrate the emergence of haematopoietic stem cells through recruitment of LSD1

Abstract

In vertebrates, the first haematopoietic stem cells (HSCs) with multi-lineage and long-term repopulating potential arise in the AGM (aorta-gonad-mesonephros) region. These HSCs are generated from a rare and transient subset of endothelial cells, called haemogenic endothelium (HE), through an endothelial-to-haematopoietic transition (EHT). Here, we establish the absolute requirement of the transcriptional repressors GFI1 and GFI1B (growth factor independence 1 and 1B) in this unique trans-differentiation process. We first demonstrate that Gfi1 expression specifically defines the rare population of HE that generates emerging HSCs. We further establish that in the absence of GFI1 proteins, HSCs and haematopoietic progenitor cells are not produced in the AGM, revealing the critical requirement for GFI1 proteins in intra-embryonic EHT. Finally, we demonstrate that GFI1 proteins recruit the chromatin-modifying protein LSD1, a member of the CoREST repressive complex, to epigenetically silence the endothelial program in HE and allow the emergence of blood cells.

Atoh1 in sensory hair cell development: constraints and cofactors

“…Despite these varied interactions, a single mutation in the SNAG domain, which disrupts the interactions with the LSD1/CoRest complex, leads to a phenotype apparently identical to that observed in Gfi1 null mice in both hematopoietic and non-hematopoietic systems (57,58). Further support for this mode of Gfi1 function comes from a recent study showing that LSD1 deficiency phenocopies the developmental arrest of the haematopoietic stem cells observed in Gfi1 null mice (59).…”

Human haematopoietic stem cell development: from the embryo to the dish

“…In contrast to non-haematogenic vascular cells, hPSC-derived haematogenic endothelium lacks expression of CD73 (NT5E) (Choi et al, 2012;Ditadi et al, 2015), CXCR4 and DLL4 (Ditadi et al, 2015). Also, both mouse (North et al, 1999;Thambyrajah et al, 2016) and human (Choi et al, 2012;Ng et al, 2016) haematogenic endothelium are distinguished by their expression of the key transcription factors RUNX1 and GFI1, which are required for the endothelial to haematopoietic transition. Interestingly, hPSCs differentiated with a protocol that induces HOXA gene expression produce SOX17-expressing endothelial cells that bear similarity at the transcriptional level to developing dorsal aorta endothelium, and a SOX17…”

Interplay between SOX7 and RUNX1 regulates hemogenic endothelial fate in the yolk sac

“…The expression of the RUNX1b isoform is low in HE but it increases during EHT before the subsequent rapid upregulation of RUNX1c in emerging hematopoietic progenitors (Sroczynska et al, 2009a;Swiers et al, 2013). RUNX1 is a master regulator of EHT: activating the expression of hematopoietic genes, while switching off the endothelial transcriptional program via activation of GFI1 expression (Lancrin et al, 2012;Lie-A-Ling et al, 2014;Tanaka et al, 2012;Thambyrajah et al, 2016). We propose that in the early stages of HE differentiation, SOX7 can outcompete CBFβ for RUNX1 binding, while also preventing RUNX1 binding to its hematopoietic target genes (Fig.…”

“…For dissociated yolk sac cultures, E9.5 yolk sacs were dissociated with collagenase dispase (Roche) diluted to 1 mg/ml in PBS for 20 min at 37°C. Yolk sac cell suspensions were cultured for 4 days on OP9 cells in HE differentiation media previously described for AGM culture (Thambyrajah et al, 2016). Doxycycline was added to all yolk sac cultures at 1 µg/ml.…”

“…It is now widely accepted that the hematopoietic transcription factor RUNX1 is a key master regulator of this process (Chen et al, 2009;Lancrin et al, 2009;Lie-A-Ling et al, 2014). RUNX1 is expressed in HE and emerging HSPCs both in the yolk sac and in the embryo proper (Frame et al, 2015;Lancrin et al, 2009;North et al, 1999), and controls the downregulation and upregulation of endothelial and hematopoietic transcriptional programs, respectively (Lancrin et al, 2012;Tanaka et al, 2012;Thambyrajah et al, 2016). RUNX1 has been shown to act in a heptad of interacting transcription factors in hematopoietic progenitor cells (HPCs) comprising FLI1, ERG, TAL1, LYL1, LMO2 and GATA2 (Wilson et al, 2010).…”