Deletion of the Scl +19 enhancer increases the blood stem cell compartment without affecting the formation of mature blood lineages

Exp Hematol. 2012 Jul;40(7):588-598.e1. doi: 10.1016/j.exphem.2012.02.006. Epub 2012 Mar 5.


The stem cell leukemia (Scl)/Tal1 gene is essential for normal blood and endothelial development, and is expressed in hematopoietic stem cells (HSCs), progenitors, erythroid, megakaryocytic, and mast cells. The Scl +19 enhancer is active in HSCs and progenitor cells, megakaryocytes, and mast cells, but not mature erythroid cells. Here we demonstrate that in vivo deletion of the Scl +19 enhancer (Scl(Δ19/Δ19)) results in viable mice with normal Scl expression in mature hematopoietic lineages. By contrast, Scl expression is reduced in the stem/progenitor compartment and flow cytometry analysis revealed that the HSC and megakaryocyte-erythroid progenitor populations are enlarged in Scl(Δ19/Δ19) mice. The increase in HSC numbers contributed to enhanced expansion in bone marrow transplantation assays, but did not affect multilineage repopulation or stress responses. These results affirm that the Scl +19 enhancer plays a key role in the development of hematopoietic stem/progenitor cells, but is not necessary for mature hematopoietic lineages. Moreover, active histone marks across the Scl locus were significantly reduced in Scl(Δ19/Δ19) fetal liver cells without major changes in steady-state messenger RNA levels, suggesting post-transcriptional compensation for loss of a regulatory element, a result that might be widely relevant given the frequent observation of mild phenotypes after deletion of regulatory elements.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Base Sequence*
  • Basic Helix-Loop-Helix Transcription Factors / genetics
  • Basic Helix-Loop-Helix Transcription Factors / metabolism*
  • Enhancer Elements, Genetic / physiology*
  • Gene Expression Regulation / physiology*
  • Hematopoiesis / physiology
  • Hematopoietic Stem Cells / cytology
  • Hematopoietic Stem Cells / metabolism*
  • Mice
  • Mice, Mutant Strains
  • Proto-Oncogene Proteins / genetics
  • Proto-Oncogene Proteins / metabolism*
  • Sequence Deletion*
  • Stress, Physiological / physiology
  • T-Cell Acute Lymphocytic Leukemia Protein 1


  • Basic Helix-Loop-Helix Transcription Factors
  • Proto-Oncogene Proteins
  • T-Cell Acute Lymphocytic Leukemia Protein 1
  • Tal1 protein, mouse