Notch activation and downstream targets in embryonic hematopoiesis
Loading...
Document Type
Document Version
Author
Director
Bigas Salvans, Anna
Espinosa Blay, Lluís
Espinosa Blay, Lluís
Tutor
Other authors
Publication Date
Pages
224 p.
Embargo date
Citation
Guiu Sagarra, J. Notch activation and downstream targets in embryonic hematopoiesis. Universitat Pompeu Fabra; 2012. handle: http://hdl.handle.net/10803/98475
This citation was generated automatically.
Citation
Doctoral program
Programa de doctorat en Biomedicina
Abstract
La regió de l’aorta-gonada-mesonefros (AGM) és el primer nínxol de les cèl·lules mare hematopoètiques. Està descrit que la via de Notch és necessària per generar artèries i cèl·lules mare hematopoètiques. Les cèl·lules mare hematopoètiques es generen a partir de les artèries durant el desenvolupament embrionari. Tenint en compte que els vasos arterials es formen abans que les cèl·lules mare hematopoètiques, durant molt temps ha estat controvertit si la via de Notch només indueix la formació d’artèries i en canvi l’abscència de cèl·lules mare hematopoètiques és un efecte secundari o si per contra, la via de Notch participa activament en la inducció d’ambdós programes genètics, l’arterial i l’hematopoètic. Moltes de les funcions descrites de la via de Notch són conseqüència de l’expressió de les seves dianes transcripcionals: Hes i Hesrelated (Hrt). No obstant cada cop s’estan identificant noves dianes transcripcionals de la via de Notch que són específiques de teixit. En aquesta tesis doctoral, demostrem que l’activació de la via de Notch per part del lligand Jagged1 és necessària per activar el programa hematopoètic però no cal per establir el programa arterial. Aquest fet demostra que la via de Notch juga un paper clau i directe en l’hematopoèsi embrionaria. Per sota de la via de Notch mostrem que els embrions deficients en Hes1 i Hes5 mantenen intacte el programa arterial. Cal remarcar que també generen més quantitat de cèl·lules mare hematopoètiques però que no són funcionals. A més tal mutants, tenen nivells més alts d’expressió dels gens Runx1, Myb i Gata2; els quals són importants reguladors de l’hematopoèsi. Per acabar demostrem que Notch activa la transcripció de Gata2 i que HES-1 l’inhibeix. Això genera un Incoherent Feed-Fordward loop, el qual regula estretament els nivells de Gata2 necessàris per generar cèl·lules mare hematopoètiques.
The aorta-gonad-mesonephros (AGM) is the first Hematopoietic Stem Cell (HSC) niche. It was previously shown that Notch pathway is required to induce the arterial fate as well as to generate Hematopoietic Stem Cells. HSC emerge at the site of arterial vessels during embryonic development. Since arterial fate precedes HSC generation, it has long been controversial whether Notch exclusively induces the arterial program and the lack of HSC is a secondary defect; or Notch is directly involved in activating both genetic programs, arterial and hematopoietic. The best-characterized Notch targets are Hes and Hesrelated genes (Hrt) since they are involved in most of described Notch functions, however there is a growing number of tissue-specific transcriptional Notch-targets. In this thesis, we found that Jagged-mediated activation of Notch is required for the correct execution of the definitive hematopoietic program but not for the establishment of the arterial fate, thus demonstrating that Notch exerts a specific hematopoietic function in the embryo. Downstream of Notch pathway, we also show that embryos deficient for Hes1 and Hes5 alleles contain an intact arterial program but produce increased numbers of non-functional hematopoietic stem cells associated to higher levels of the hematopoietic regulators Runx1, Myb and Gata2. Moreover, Gata2 transcription is positively regulated by Notch and negatively controlled by HES-1. This creates an incoherent feed-forward loop that tightly controls Gata2 levels to generate HSC.
The aorta-gonad-mesonephros (AGM) is the first Hematopoietic Stem Cell (HSC) niche. It was previously shown that Notch pathway is required to induce the arterial fate as well as to generate Hematopoietic Stem Cells. HSC emerge at the site of arterial vessels during embryonic development. Since arterial fate precedes HSC generation, it has long been controversial whether Notch exclusively induces the arterial program and the lack of HSC is a secondary defect; or Notch is directly involved in activating both genetic programs, arterial and hematopoietic. The best-characterized Notch targets are Hes and Hesrelated genes (Hrt) since they are involved in most of described Notch functions, however there is a growing number of tissue-specific transcriptional Notch-targets. In this thesis, we found that Jagged-mediated activation of Notch is required for the correct execution of the definitive hematopoietic program but not for the establishment of the arterial fate, thus demonstrating that Notch exerts a specific hematopoietic function in the embryo. Downstream of Notch pathway, we also show that embryos deficient for Hes1 and Hes5 alleles contain an intact arterial program but produce increased numbers of non-functional hematopoietic stem cells associated to higher levels of the hematopoietic regulators Runx1, Myb and Gata2. Moreover, Gata2 transcription is positively regulated by Notch and negatively controlled by HES-1. This creates an incoherent feed-forward loop that tightly controls Gata2 levels to generate HSC.
Keywords
Notch, Jagged, Hes, Gata2, Hematopoiesis, AGM, Embrió, Embryo
Subjects
612 - Physiology
Publisher
Universitat Pompeu Fabra
