Evi1 regulates Notch activation to induce zebrafish hematopoietic stem cell emergence

Abstract

During development, hematopoietic stem cells (HSCs) emerge from aortic endothelial cells (ECs) through an intermediate stage called hemogenic endothelium by a process known as endothelial-tohematopoietic transition (EHT). While Notch signaling, including its upstream regulator Vegf, is known to regulate this process, the precise molecular control and temporal specificity of Notch activity remain unclear. Here, we identify the zebrafish transcriptional regulator evi1 as critically required for Notch-mediated EHT. In vivo live imaging studies indicate that evi1 suppression impairs EC progression to hematopoietic fate and therefore HSC emergence. evi1 is expressed in ECs and induces these effects cell autonomously by activating Notch via pAKT. Global or endothelialspecific induction of notch, vegf, or pAKT can restore endothelial Notch and HSC formations in evi1 morphants. Significantly, evi1 overexpression induces Notch independently of Vegf and rescues HSC numbers in embryos treated with a Vegf inhibitor. In sum, our results unravel evi1-pAKT as a novel molecular pathway that, in conjunction with the shh-vegf axis, is essential for activation of Notch signaling in VDA endothelial cells and their subsequent conversion to HSCs.

Twist1 regulates embryonic hematopoietic differentiation through binding to Myb and Gata2 promoter regions

“…Gata2 is reportedly essential for differentiation of hematopoietic precursors 35 and for the ETH cell transition 14 in mouse embryos. Although Mecom has been recently implicated in embryonic HSPC generation by regulating that transition, 16 we did not observe changes in levels of Mecom transcripts in Twist1 2/2 embryos ( Figure 3B), suggesting that impairment of the ETH transition is likely because of downregulated Gata2 gene expression. Myb, also known as c-Myb, is required for HSPC differentiation in mouse embryos and adults.…”

“…Next we focused on representative hematopoietic transcription factor genes, namely, Myb, 13,32 Gata2, 14 Runx1, 12 Tal1 (Scl), 15 and Mecom (Evi-1), 16,17 as these factors play important roles in HSPC generation and differentiation. Among them, levels of Myb, Gata2, and Mecom were higher than those of Runx1 and Tal1 in microarrays of c-Kit 1 CD31 1 CD34 1 cells derived from AGM of 10.5-dpc WT embryos ( Figure 3A, white bars).…”

“…5 Generation of IACs is intrinsically regulated by transcription factors such as Runx1, 11,12 Myb, 13 Gata2, 14 Scl/Tal1, 15 and Mecom (Evi-1). 16,17 A transcription switch reportedly occurs at 9.5 to 10.5 dpc, based on cap analysis of gene expression. 18 By contrast, IAC differentiation is extrinsically regulated by the AGM region niche.…”

Extracellular bone morphogenetic protein modulator BMPER and twisted gastrulation homolog 1 preserve arterial‐venous specification in zebrafish blood vessel development and regulate Notch signaling in endothelial cells

“…Our findings add that silencing of BMPER in endothelial cells decreases Notch signaling as well as silencing of BMPER and TWSG1 promotes expression of the venous differentiation marker EPHB4/ephnb4a at the expense of arterial blood vessel differentiation marker EFNB2/efnb2a in endothelial cells and zebrafish embryos (Figs 1, 2, and 4). Recently, activation of the PI3K/AKT pathway was also shown to act upstream of the Notch signaling pathway [52,53]. Indeed, stimulation with BMP4 augmented the effect of BMPER on the Notch signaling pathway, whereas inhibition of the ALK2 receptor with DMH1 prevented Notch pathway activation by BMPER (Fig.…”

Mutations in signal recognition particle SRP54 cause syndromic neutropenia with Shwachman-Diamond–like features

“…WISH was performed as described in Konantz et al (54). Briefly, c-myb riboprobes were generated using pBK-CMV as a plasmid template (a gift of Caroline E. Burns, Massachusetts General Hospital, Boston, Massachusetts, USA), EcoRI for DNA linearization, and T7 RNA polymerase for further antisense probe production.…”