title: HoxA3 is an apical regulator of haemogenic endothelium.
abstract: During development, haemogenesis occurs invariably at sites of vasculogenesis. Between embryonic day (E) 9.5 and E10.5 in mice, endothelial cells in the caudal part of the dorsal aorta generate haematopoietic stem cells and are referred to as haemogenic endothelium. The mechanisms by which haematopoiesis is restricted to this domain, and how the morphological transformation from endothelial to haematopoietic is controlled are unknown. We show here that HoxA3, a gene uniquely expressed in the embryonic but not yolk sac vasculature, restrains haematopoietic differentiation of the earliest endothelial progenitors, and induces reversion of the earliest haematopoietic progenitors into CD41-negative endothelial cells. This reversible modulation of endothelial-haematopoietic state is accomplished by targeting key haematopoietic transcription factors for downregulation, including Runx1, Gata1, Gfi1B, Ikaros, and PU.1. Through loss-of-function, and gain-of-function epistasis experiments, and the identification of antipodally regulated targets, we show that among these factors, Runx1 is uniquely able to erase the endothelial program set up by HoxA3. These results suggest both why a frank endothelium does not precede haematopoiesis in the yolk sac, and why haematopoietic stem cell generation requires Runx1 expression only in endothelial cells.
authors.affiliation: Lillehei Heart Institute and Department of Pediatrics, University of Minnesota, 312 Church St. SE, Minneapolis, MN 55455, USA.
authors.forename: Michelina
authors.initials: M
authors.lastname: Iacovino
authors.forename: Diana
authors.initials: D
authors.lastname: Chong
authors.forename: Istvan
authors.initials: I
authors.lastname: Szatmari
authors.forename: Lynn
authors.initials: L
authors.lastname: Hartweck
authors.forename: Danielle
authors.initials: D
authors.lastname: Rux
authors.forename: Arianna
authors.initials: A
authors.lastname: Caprioli
authors.forename: Ondine
authors.initials: O
authors.lastname: Cleaver
authors.forename: Michael
authors.initials: M
authors.lastname: Kyba
mesh_terms: D000818:Animals; D001483:Base Sequence; D002454:Cell Differentiation; D019070:Cell Lineage; D050676:Core Binding Factor Alpha 2 Subunit / Q000235:genetics / Q000378:metabolism; D004622:Embryo, Mammalian / Q000098:blood supply / Q000196:embryology / Q000378:metabolism*; D005434:Flow Cytometry; D020869:Gene Expression Profiling; D018507:Gene Expression Regulation, Developmental; D055018:Hemangioblasts / Q000166:cytology / Q000378:metabolism*; D006410:Hematopoiesis; D018398:Homeodomain Proteins / Q000235:genetics* / Q000378:metabolism; D017403:In Situ Hybridization; D008648:Mesoderm / Q000098:blood supply / Q000196:embryology / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D008969:Molecular Sequence Data; D020411:Oligonucleotide Array Sequence Analysis; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012689:Sequence Homology, Nucleic Acid; D013997:Time Factors; D015017:Yolk Sac / Q000098:blood supply / Q000196:embryology / Q000378:metabolism
chemical_list: D050676:Core Binding Factor Alpha 2 Subunit; D018398:Homeodomain Proteins; C080331:Hoxa3 protein, mouse; C493726:Runx1 protein, mouse