title: Hes repressors are essential regulators of hematopoietic stem cell development downstream of Notch signaling.
abstract: 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.
authors.affiliation: Program in Cancer Research, Hospital del Mar Medical Research Institute, IMIM, Barcelona Biomedical Research Park, 08003 Barcelona, Spain.
authors.forename: Jordi
authors.initials: J
authors.lastname: Guiu
authors.forename: Ritsuko
authors.initials: R
authors.lastname: Shimizu
authors.forename: Teresa
authors.initials: T
authors.lastname: D'Altri
authors.forename: Stuart T
authors.initials: ST
authors.lastname: Fraser
authors.forename: Jun
authors.initials: J
authors.lastname: Hatakeyama
authors.forename: Emery H
authors.initials: EH
authors.lastname: Bresnick
authors.forename: Ryoichiro
authors.initials: R
authors.lastname: Kageyama
authors.forename: Elaine
authors.initials: E
authors.lastname: Dzierzak
authors.forename: Masayuki
authors.initials: M
authors.lastname: Yamamoto
authors.forename: Lluis
authors.initials: L
authors.lastname: Espinosa
authors.forename: Anna
authors.initials: A
authors.lastname: Bigas
mesh_terms: D000818:Animals; D001011:Aorta / Q000166:cytology / Q000196:embryology; D051792:Basic Helix-Loop-Helix Proteins / Q000235:genetics / Q000378:metabolism*; D001665:Binding Sites; D050676:Core Binding Factor Alpha 2 Subunit / Q000235:genetics / Q000378:metabolism; D004622:Embryo, Mammalian; D004730:Endothelium, Vascular / Q000196:embryology; D005260:Female; D050989:GATA2 Transcription Factor / Q000235:genetics / Q000378:metabolism; D018507:Gene Expression Regulation, Developmental; D006412:Hematopoietic Stem Cells / Q000166:cytology / Q000502:physiology*; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism*; D051819:Immunoglobulin J Recombination Signal Sequence-Binding Protein / Q000235:genetics / Q000378:metabolism; D008650:Mesonephros / Q000166:cytology / Q000254:growth & development; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D011401:Promoter Regions, Genetic; D020598:Proto-Oncogene Proteins c-myb / Q000235:genetics / Q000378:metabolism; D051880:Receptors, Notch / Q000235:genetics / Q000378:metabolism*; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D000072056:Transcription Factor HES-1
chemical_list: D051792:Basic Helix-Loop-Helix Proteins; D050676:Core Binding Factor Alpha 2 Subunit; D050989:GATA2 Transcription Factor; D018398:Homeodomain Proteins; D051819:Immunoglobulin J Recombination Signal Sequence-Binding Protein; D020598:Proto-Oncogene Proteins c-myb; D051880:Receptors, Notch; D012097:Repressor Proteins; D000072056:Transcription Factor HES-1; C494712:Gata2 protein, mouse; C489734:Hes1 protein, mouse; C489685:Hes5 protein, mouse; C497571:Rbpj protein, mouse; C493726:Runx1 protein, mouse