Developmental activation of the lysozyme gene in chicken macrophage cells is linked to core histone acetylation at its enhancer elements

Abstract

Native chromatin IP assays were used to define changes in core histone acetylation at the lysozyme locus during developmental maturation of chicken macrophages and stimulation to high-level expression by lipo-polysaccharide. In pluripotent precursors the lysozyme gene (Lys) is inactive and there is no acetylation of core histones at the gene, its promoter or at the upstream cis-control elements. In myeloblasts, where there is a very low level of Lys expression, H4 acetylation appears at the cis-control elements but not at the Lys gene or its promoter: neither H3 nor H2B become significantly acetylated in myeloblasts. In mature macrophages, Lys expression increases 5-fold: H4, H2B and H2A.Z are all acetylated at the cis-control elements but H3 remains unacetylated except at the −2.4 S silencer. Stimulation with LPS increases Lys expression a further 10-fold: this is accompanied by a rise in H3 acetylation throughout the cis-control elements; H4 and H2B acetylation remain substantial but acetylation at the Lys gene and its promoter remains low. Acetylation is thus concentrated at the cis-control elements, not at the Lys gene or its immediate promoter. H4 acetylation precedes H3 acetylation during development and H3 acetylation is most directly linked to high-level Lys expression.

The Chromatin Remodeling Protein, SRCAP, Is Critical for Deposition of the Histone Variant H2A.Z at Promoters

“…These studies indicated that acetylated H2A.Z levels within the SP-1 promoter are uniform over a wide region, Ϫ3457 to Ϫ1109, with a slight peak at Ϫ1241 and two prominent peaks at Ϫ859 and ϩ7 directly adjacent to but not overlapping the peak site of SRCAP binding. Consistent with reports of acetylated H2A.Z distribution on other genes, greatly reduced levels of acetylated H2A.Z were also observed in the coding region of the SP-1 (12,13).…”

“…H2A.Z is lost following activation, suggesting a model in which the SWR-C complex is preferentially associated with inactive promoters (3)(4)(5). The recent finding that increased levels of acetylated H2A.Z occur at active promoters (7,12,13) suggests a model in which non-acetylated H2A.Z deposited at inactive promoters becomes acetylated upon activation. An alternative model is that the SWR-C complex is present at active promoters, where it catalyzes deposition of non-acetylated H2A.Z, which becomes acetylated, or that it catalyzes deposition of acetylated H2A.Z.…”

“…The Peak of Acetylated H2A.Z Deposition Occurs Adjacent to the Peak of SRCAP Binding-Recent studies indicate the deposition of acetylated H2A.Z occurs at active promoters (7,12,13). This observation led us to ask whether SRCAP mediates deposition of acetylated H2A.Z at the SP-1 promoter.…”

“…In mammals, H2A.Z is essential for embryonic development and chromosome segregation, and increased H2A.Z expression is implicated in cardiac hypertrophy (9 -11). Studies done in chicken cells suggest that deposition of both H2A.Z and acetylated H2A.Z in higher eukaryotes differs from that observed in S. cerevisiae and occurs at active promoters but not at inactive promoters (12,13). The specific role that H2A.Z plays at active promoters in higher eukaryotes has not been established.…”

“…Histone modifications found in promoters of active genes, e.g. triMeH3K4, acetylated H2B, and acetylated H4 have been reported to be enriched in H2A.Z-containing nucleosomes purified from chicken and HeLa cells (12,13,19). The loss of specific histone acetyltransferases GCN5 and Sas3 has also been reported to reduce H2A.Z deposition (5).…”