title: Haematopoietic stem cells retain long-term repopulating activity and multipotency in the absence of stem-cell leukaemia SCL/tal-1 gene.
abstract: The production of blood cells is sustained throughout the lifetime of an individual by haematopoietic stem cells (HSCs). Specification of HSCs from mesoderm during embryonic development requires the stem cell leukaemia SCL/tal-1 gene product. Forced expression of SCL/tal-1 strongly induces blood formation in embryos, indicating that this gene has a dominant role in commitment to haematopoiesis. In the adult haematopoietic system, expression of SCL/tal-1 is enriched in HSCs and multipotent progenitors, and in erythroid and megakaryocytic lineages, consistent with roles for this factor in adult haematopoiesis. Here we assess by conditional gene targeting whether SCL/tal-1 is required continuously for the identity and function of HSCs. We find that SCL/tal-1 is dispensable for HSC engraftment, self-renewal and differentiation into myeloid and lymphoid lineages; however, the proper differentiation of erythroid and megakaryocytic precursors is dependent on SCL/tal-1. Thus, SCL/tal-1 is essential for the genesis of HSCs, but its continued expression is not essential for HSC functions. These findings contrast with lineage choice mechanisms, in which the identity of haematopoietic lineages requires continuous transcription factor expression.
authors.affiliation: Department of Pediatric Oncology, Children's Hospital and the Dana Farber Cancer Institute, Harvard Medical School and Howard Hughes Medical Institute, Boston, Massachusetts 02115, USA.
authors.forename: Hanna K A
authors.initials: HK
authors.lastname: Mikkola
authors.forename: Jenny
authors.initials: J
authors.lastname: Klintman
authors.forename: Haidi
authors.initials: H
authors.lastname: Yang
authors.forename: Hanno
authors.initials: H
authors.lastname: Hock
authors.forename: Thorsten M
authors.initials: TM
authors.lastname: Schlaeger
authors.forename: Yuko
authors.initials: Y
authors.lastname: Fujiwara
authors.forename: Stuart H
authors.initials: SH
authors.lastname: Orkin
mesh_terms: D000818:Animals; D051792:Basic Helix-Loop-Helix Proteins; D002454:Cell Differentiation; D002455:Cell Division; D004268:DNA-Binding Proteins / Q000235:genetics* / Q000502:physiology; D006412:Hematopoietic Stem Cells / Q000166:cytology* / Q000502:physiology; D038041:Lymphopoiesis; D051379:Mice; D018345:Mice, Knockout; D039902:Multipotent Stem Cells / Q000166:cytology* / Q000502:physiology; D038042:Myelopoiesis; D011518:Proto-Oncogene Proteins / Q000235:genetics* / Q000502:physiology; D000073942:T-Cell Acute Lymphocytic Leukemia Protein 1; D014157:Transcription Factors / Q000235:genetics* / Q000502:physiology
chemical_list: D051792:Basic Helix-Loop-Helix Proteins; D004268:DNA-Binding Proteins; D011518:Proto-Oncogene Proteins; D000073942:T-Cell Acute Lymphocytic Leukemia Protein 1; D014157:Transcription Factors; C489366:Tal1 protein, mouse