Transcriptional Regulation of the SCL Locus: Identification of an Enhancer That Targets the Primitive Erythroid Lineage In Vivo

Abstract

The stem cell leukemia (SCL) gene, also known as TAL-1, encodes a basic helix-loop-helix protein that is essential for the formation of all hematopoietic lineages, including primitive erythropoiesis. Appropriate transcriptional regulation is essential for the biological functions of SCL, and we have previously identified five distinct enhancers which target different subdomains of the normal SCL expression pattern. However, it is not known whether these SCL enhancers also regulate neighboring genes within the SCL locus, and the erythroid expression of SCL remains unexplained. Here, we have quantitated transcripts from SCL and neighboring genes in multiple hematopoietic cell types. Our results show striking coexpression of SCL and its immediate downstream neighbor, MAP17, suggesting that they share regulatory elements. A systematic survey of histone H3 and H4 acetylation throughout the SCL locus in different hematopoietic cell types identified several peaks of histone acetylation between SIL and MAP17, all of which corresponded to previously characterized SCL enhancers or to the MAP17 promoter. Downstream of MAP17 (and 40 kb downstream of SCL exon 1a), an additional peak of acetylation was identified in hematopoietic cells and was found to correlate with expression of SCL but not other neighboring genes. This ؉40 region is conserved in human-dog-mouse-rat sequence comparisons, functions as an erythroid cell-restricted enhancer in vitro, and directs ␤-galactosidase expression to primitive, but not definitive, erythroblasts in transgenic mice. The SCL ؉40 enhancer provides a powerful tool for studying the molecular and cellular biology of the primitive erythroid lineage.

Identifying gene regulatory elements by genomic microarray mapping of DNaseI hypersensitive sites

“…Previous systematic analysis of the 50 kb of the mouse Tal1/ Pdzk1ip1 coregulatory domain ‫01מ(‬ kb to +40 kb relative to promoter 1a) has identified multiple Tal1 regulatory elements Sinclair et al 1999;Göttgens et al 2000Göttgens et al , 2002aDelabesse et al 2005). Within this well-characterized region, two novel DNaseI hypersensitive sites were identified as significantly enriched (+29 and +32) and investigated in functional assays.…”

“…Elements at +1 and +3, relative to the mouse exon 1a, have been shown to target the expression of Tal1 to the developing spinal cord in transgenic mice , while the +23 directs expression to specific regions within the brain (Göttgens et al 2000). The region at ‫9מ‬ functions as an enhancer in hematopoietic cell lines , and the +40 region is active in the primitive erythroid lineage (Delabesse et al 2005). The mouse +12 region is homologous to the human +14 region, which has been identified as an TAL1 transcriptional repressor (Courtes et al 2000).…”

“…The Tal1 (formerly known as Scl) locus was used to establish the protocol, which was then further validated by successfully mapping known DNaseI hypersensitive sites across 240 kb of the human ␣-globin locus. Previous studies have systematically dissected the transcriptional regulation of the mouse Tal1 locus and have identified multiple conserved regulatory elements that direct expression in transgenic mice to subdomains of the Tal1 expression pattern (Göttgens et al , 2000(Göttgens et al , 2002bSanchez et al 1999Sanchez et al , 2001Sinclair et al 1999;Delabesse et al 2005). Similarly, the regulatory elements within the ␣-globin locus have been extensively characterized using both biological and bioinformatics approaches (Yagi et al 1986;Higgs et al 1990;Vyas et al 1992;Hughes et al 2005).…”

Identification of Biologically Relevant Enhancers in Human Erythroid Cells

“…Previous studies, such as those of the globin gene loci (77)(78)(79)(80)(81), the GATA1 and SCL/Tal1 gene loci (82)(83)(84)(85)(86)(87)(88)(89)(90)(91)(92)(93), and the erythropoietin gene locus (83), characterized enhancers as distantly located, positively acting cis-regulatory elements (77,80). Recent studies have shown that enhancers have additional, complex roles in cellular gene regulation.…”

Gene regulatory networks governing haematopoietic stem cell development and identity

“…If the regulatory proteins of a cell as a whole are considered an input, the output is determined by the DNA sequences of the CRMs and their accessibility to transcription factor complex binding. Therefore in terms of a pression that mirrors the developmental and spatial expression patterns of the endogenous genes they regulate (Delabesse et al, 2005;Gottgens et al, 2000;Gottgens et al, 2004;Sanchez et al, 1999;Silberstein et al, 2005). Genes are equipped with multiple, disparate CRMs, each several hundred base pairs long.…”