The scl +18/19 Stem Cell Enhancer Is Not Required for Hematopoiesis: Identification of a 5′ Bifunctional Hematopoietic-Endothelial Enhancer Bound by Fli-1 and Elf-1

Abstract

Analysis of cis-regulatory elements is central to understanding the genomic program for development. The scl/tal-1 transcription factor is essential for lineage commitment to blood cell formation and previous studies identified an scl enhancer (the ؉18/19 element) which was sufficient to target the vast majority of hematopoietic stem cells, together with hematopoietic progenitors and endothelium. Moreover, expression of scl under control of the ؉18/19 enhancer rescued blood progenitor formation in scl ؊/؊ embryos. However, here we demonstrate by using a knockout approach that, within the endogenous scl locus, the ؉18/19 enhancer is not necessary for the initiation of scl transcription or for the formation of hematopoietic cells. These results led to the identification of a bifunctional 5 enhancer (؊3.8 element), which targets expression to hematopoietic progenitors and endothelium, contains conserved critical Ets sites, and is bound by Ets family transcription factors, including Fli-1 and Elf-1. These data demonstrate that two geographically distinct but functionally related enhancers regulate scl transcription in hematopoietic progenitors and endothelial cells and suggest that enhancers with dual hematopoietic-endothelial activity may represent a general strategy for regulating blood and endothelial development.

A previously unrecognized promoter of LMO2 forms part of a transcriptional regulatory circuit mediating LMO2 expression in a subset of T-acute lymphoblastic leukaemia patients

“…It has long been noted that genes critical for blood and endothelial development contain functional ETSbinding sites, and using a combination of approaches, expression of numerous ETS factors, including FLI1, SPI1/PU.1, ELF1and ETS1, has been shown to control the expression of SCL/TAL1 (Gottgens et al, 2004), LYL1 , LMO2 and GATA2 . What has been less well studied, however, is how dysregulation of this same constellation of genes might facilitate leukaemogenesis.…”

Organ-injury-induced reactivation of hemangioblastic precursor cells

“…Finally, considering into that SCL 3 0 enhancer is dispensable for hematopoietic development, 50 it remains to be determined whether the observed 3 0 enhancer-mediated upregulation of SCL in injured kidneys is mandatory for vascular repair.…”

Role of a 5′-enhancer in the transcriptional regulation of the human endothelial cell protein C receptor gene

“…In transgenic embryos, high-level reporter gene expression was reproducibly directed to ECs, demonstrating that, by itself, the Ϫ5.5HS enhancer contains the regulatory sequences necessary to impart vascular specificity and thus functions as an autonomous EC-specific enhancer. Other enhancers have been shown to autonomously direct transcription to the endothelium of transgenic embryos, 29,34,[40][41][42] but Ϫ5.5HS is the first human enhancer capable of targeting transcription to both embryonic and adult ECs. Moreover, to our knowledge, Ϫ5.5HS is the first regulatory element capable of specifically targeting transcription to large-vessel ECs.…”

“…42 Interestingly, the Tal1, Flk1, Fli1, and PRH genes are all governed by autonomous enhancers with dual HSC/EC activity. 34,[40][41][42] Furthermore, the activity of each of these enhancers is dependent on cis-elements similar to those present within Ϫ5.5HS, namely Ets, GATA, and Tal1 motifs. In light of this, we propose a model in which Ϫ5.5HS targets hEPCR expression to primitive stem cells with dual specification potential, and in which hEPCR expression is progressively lost as these cells embark into hematopoietic specification.…”