The SCL 3' enhancer responds to Hedgehog signaling during hemangioblast specification.
OBJECTIVE
The Hedgehog family of intercellular proteins has a crucial role in embryonic development. Recent experimental data suggests that the Hedgehog pathway may play a role in early hematopoiesis and angiogenesis. Stem cell leukemia (SCL), a basic helix-loop-helix (bHLH) transcription factor, is essential for the specification and function of the hemangioblast. SCL expression in early hematopoietic precursors and endothelium is directed by a 3' enhancer. We hypothesized that the SCL 3' enhancer is regulated by Hedgehog signaling during specification of mesoderm towards hemangioblastic fate.


METHODS
Whole embryos derived from transgenic mouse lines carrying reporter genes under the regulation of SCL 3' enhancer were cultured in the presence of active Hedgehog peptide. Hedgehog transcriptional regulation of SCL 3' enhancer was studied by in vitro and in vivo binding and reporter assays.


RESULTS
Hedgehog induced expansion of cells in which the SCL 3' enhancer was transcriptionally activated. A Gli-binding site within the 3' enhancer of SCL was identified and Gli1 was demonstrated to bind and transactivate this enhancer in a sequence-dependent manner. We further demonstrated that the core region of the SCL 3' enhancer is transcriptionally regulated by Hedgehog in-vivo and that the Gli-binding site located in this enhancer is essential for Hedgehog transcriptional regulation in vitro.


CONCLUSIONS
These findings suggest that SCL may be a direct target of Hedgehog signaling during hemangioblast specification.
Hochman
Eldar
E
The Research Section of Pediatric Malignancies, The Sheba Cancer Research Center, Safra Children's Hospital, Sheba Medical Center and Faculty of Medicine, Tel-Aviv University, Tel Hashomer, Israel.
Kinston
Sarah
S
Harmelin
Alon
A
Göttgens
Berthold
B
Izraeli
Shai
S
D000818:Animals; D051792:Basic Helix-Loop-Helix Proteins / Q000235:genetics* / Q000378:metabolism; D001665:Binding Sites; D002478:Cells, Cultured; D053595:Embryonic Stem Cells / Q000378:metabolism; D004742:Enhancer Elements, Genetic / Q000187:drug effects / Q000235:genetics*; D053823:Hedgehog Proteins / Q000494:pharmacology / Q000502:physiology*; D006410:Hematopoiesis / Q000502:physiology*; D006412:Hematopoietic Stem Cells / Q000187:drug effects / Q000378:metabolism*; D006801:Humans; D051741:Kruppel-Like Transcription Factors / Q000378:metabolism; D051379:Mice; D008822:Mice, Transgenic; D011518:Proto-Oncogene Proteins / Q000235:genetics* / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*; D000073942:T-Cell Acute Lymphocytic Leukemia Protein 1; D000071676:Zinc Finger Protein GLI1
D051792:Basic Helix-Loop-Helix Proteins; D053823:Hedgehog Proteins; D051741:Kruppel-Like Transcription Factors; D011518:Proto-Oncogene Proteins; D000073942:T-Cell Acute Lymphocytic Leukemia Protein 1; D000071676:Zinc Finger Protein GLI1; C498520:Gli1 protein, mouse; C489366:Tal1 protein, mouse