Cristina Porcheri, Ohad Golan, Fernando J.Calero-Nieto, Roshana Thambyrajah, Cristina Ruiz-Herguido, Xiaonan Wang, Francesca Cato, Yolanda Guillén, Roshani Sinha, Jessica González, Sarah J.Kinston, Samanta Mariani, Antonio Maglitto, Chris Vink, Elaine Dzierzak, Pierre Charbord, Bertie Gottgens, Lluis Espinosa, David Sprinzak, Anna Bigas
Notch ligand Dll4 impairs cell recruitment into aortic clusters and limits hematopoietic stem cells
EMBO J . 2020 Apr 15;39(8):e104270 , . Hematopoietic stem cells (HSCs) develop from the hemogenic endothelium in cluster structures that protrude into the embryonic aortic lumen. Although much is known about the molecular characteristics of the developing hematopoietic cells, we lack a complete understanding of their origin and the three-dimensional organization of the niche. Here, we use advanced live imaging techniques of organotypic slice cultures, clonal analysis, and mathematical modeling to show the two-step process of intra-aortic hematopoietic cluster (IACH) formation. First, a hemogenic progenitor buds up from the endothelium and undergoes division forming the monoclonal core of the IAHC. Next, surrounding hemogenic cells are recruited into the IAHC, increasing their size and heterogeneity. We identified the Notch ligand Dll4 as a negative regulator of the recruitment phase of IAHC. Blocking of Dll4 promotes the entrance of new hemogenic Gfi1+ cells into the IAHC and increases the number of cells that acquire HSC activity. Mathematical modeling based on our data provides estimation of the cluster lifetime and the average recruitment time of hemogenic cells to the cluster under physiologic and Dll4-inhibited conditions.
Més informacióChristos Gekas, Teresa D’Altri, Rosa Aligué, Jessica González1, Lluis Espinosa, Anna Bigas
β-Catenin is required for T cell leucemia initiation and MYC transcription downstream of Notch1
Leukemia . 2016 Oct;30(10):2002-2010 , . Notch activation is instrumental in the development of most T-cell acute lymphoblastic leukemia (T-ALL) cases, yet Notch mutations alone are not sufficient to recapitulate the full human disease in animal models. We here found that Notch1 activation at the fetal liver (FL) stage expanded the hematopoietic progenitor population and conferred it transplantable leukemic-initiating capacity. However, leukemogenesis and leukemic-initiating cell capacity induced by Notch1 was critically dependent on the levels of β-Catenin in both FL and adult bone marrow contexts. In addition, inhibition of β-Catenin compromised survival and proliferation of human T-ALL cell lines carrying activated Notch1. By transcriptome analyses, we identified the MYC pathway as a crucial element downstream of β-Catenin in these T-ALL cells and demonstrate that the MYC 3' enhancer required β-Catenin and Notch1 recruitment to induce transcription. Finally, PKF115-584 treatment prevented and partially reverted leukemogenesis induced by active Notch1.
Més informacióGama-Norton, Leonor; Ferrando, Eva; Ruiz-Herguido, Cristina; Liu, Zenhy; Guiu, Jordi; Islam, Abul BMMK; Lee, Sung-Uk; Yan, Minhong; Guidos, Cynthia J; Lopez-Bigas, Nuria; Takahiro Maeda, Lluis Espinosa, Raphael Kopan, Anna Bigas
Notch signal strength controls cell fate in the haemogenic endothelium
Nat Commun . 2015 Oct 14;6:8510 , . Acquisition of the arterial and haemogenic endothelium fates concurrently occur in the aorta-gonad-mesonephros (AGM) region prior to haematopoietic stem cell (HSC) generation. The arterial programme depends on Dll4 and the haemogenic endothelium/HSC on Jag1-mediated Notch1 signalling. How Notch1 distinguishes and executes these different programmes in response to particular ligands is poorly understood. By using two Notch1 activation trap mouse models with different sensitivity, here we show that arterial endothelial cells and HSCs originate from distinct precursors, characterized by different Notch1 signal strengths. Microarray analysis on AGM subpopulations demonstrates that the Jag1 ligand stimulates low Notch strength, inhibits the endothelial programme and is permissive for HSC specification. In the absence of Jag1, endothelial cells experience high Dll4-induced Notch activity and select the endothelial programme, thus precluding HSC formation. Interference with the Dll4 signal by ligand-specific blocking antibodies is sufficient to inhibit the endothelial programme and favour specification of the haematopoietic lineage.
Més informacióJordi Guiu, Ritsuko Shimizu, Teresa D’Altri, Stuart T. Fraser, Jun Hatakeyama, Emery H. Bresnick, Ryoichiro Kageyama, Elaine Dzierzak, Masayuki Yamamoto, Lluis Espinosa and Anna Bigas (*equal contribution
Hes repressors are essential regulators of Hematopoietic Stem Cell Development downstream of Notch signaling
J Exp Med . 2013 Jan 14;210(1):71-84 , . Previous studies have identified Notch as a key regulator of hematopoietic stem cell (HSC) development, but the underlying downstream mechanisms remain unknown. The Notch target Hes1 is widely expressed in the aortic endothelium and hematopoietic clusters, though Hes1-deficient mice show no overt hematopoietic abnormalities. We now demonstrate that Hes is required for the development of HSC in the mouse embryo, a function previously undetected as the result of functional compensation by de novo expression of Hes5 in the aorta/gonad/mesonephros (AGM) region of Hes1 mutants. Analysis of embryos deficient for Hes1 and Hes5 reveals an intact arterial program with overproduction of nonfunctional hematopoietic precursors and total absence of HSC activity. These alterations were associated with increased expression of the hematopoietic regulators Runx1, c-myb, and the previously identified Notch target Gata2. By analyzing the Gata2 locus, we have identified functional RBPJ-binding sites, which mutation results in loss of Gata2 reporter expression in transgenic embryos, and functional Hes-binding sites, which mutation leads to specific Gata2 up-regulation in the hematopoietic precursors. Together, our findings show that Notch activation in the AGM triggers Gata2 and Hes1 transcription, and next HES-1 protein represses Gata2, creating an incoherent feed-forward loop required to restrict Gata2 expression in the emerging HSCs.
Més informacióEspinosa L, Cathelin S, D’Altri T, Trimarchi T, Guiu J, Rodilla V, Inglés-Esteve J, Nomdedeu J, Bellosillo B, Besses C, Rajewsky K, Aifantis I* and Bigas A* (*equal contribution)
The Notch/Hes1 pathway sustains NFkB activation through CYLD repression in T cell leukemia
Cancer Cell . 2010 Sep 14;18(3):268-81 , . It was previously shown that the NF-κB pathway is downstream of oncogenic Notch1 in T cell acute lymphoblastic leukemia (T-ALL). Here, we visualize Notch-induced NF-κB activation using both human T-ALL cell lines and animal models. We demonstrate that Hes1, a canonical Notch target and transcriptional repressor, is responsible for sustaining IKK activation in T-ALL. Hes1 exerts its effects by repressing the deubiquitinase CYLD, a negative IKK complex regulator. CYLD expression was found to be significantly suppressed in primary T-ALL. Finally, we demonstrate that IKK inhibition is a promising option for the targeted therapy of T-ALL as specific suppression of IKK expression and function affected both the survival of human T-ALL cells and the maintenance of the disease in vivo
Més informació
