Abstract
The Drosophila genome encodes three BEN-solo proteins including Insensitive (Insv), Elba1 and Elba2 that possess activities in transcriptional repression and chromatin insulation. A fourth protein—Elba3—bridges Elba1 and Elba2 to form an ELBA complex. Here, we report comprehensive investigation of these proteins in Drosophila embryos. We assess common and distinct binding sites for Insv and ELBA and their genetic interdependencies. While Elba1 and Elba2 binding generally requires the ELBA complex, Elba3 can associate with chromatin independently of Elba1 and Elba2. We further demonstrate that ELBA collaborates with other insulators to regulate developmental patterning. Finally, we find that adjacent gene pairs separated by an ELBA bound sequence become less differentially expressed in ELBA mutants. Transgenic reporters confirm the insulating activity of ELBA- and Insv-bound sites. These findings define ELBA and Insv as general insulator proteins in Drosophila and demonstrate the functional importance of insulators to partition transcription units.
Highlights
The Drosophila genome encodes three BEN-solo proteins including Insensitive (Insv), Elba[1] and Elba[2] that possess activities in transcriptional repression and chromatin insulation
Class I insulators are mainly bound by CP190, BEAF-32, and CTCF in active chromatin regions proximal to promoters, while class II insulators are mostly bound by Su(Hw) located in distal intergenic loci
We intended to broaden this perspective by generating chromatin immunoprecipitation (ChIP)-seq data for each of the three ELBA factors from the blastoderm stage of embryos, which covers the peak expression of the ELBA factors[23]
Summary
The Drosophila genome encodes three BEN-solo proteins including Insensitive (Insv), Elba[1] and Elba[2] that possess activities in transcriptional repression and chromatin insulation. Transgenic reporters confirm the insulating activity of ELBA- and Insv-bound sites. These findings define ELBA and Insv as general insulator proteins in Drosophila and demonstrate the functional importance of insulators to partition transcription units. Several BEN-containing proteins including mammalian BANP/SMAR114,15, NAC116,17, BEND318, and the C isoform of Drosophila Mod(mdg4)[12,19] have chromatin-associated functions and have been linked to transcriptional silencing. Mammalian RBB, a BEN and BTB domain protein, binds to and directly represses expression of the HDM2 oncogene through interaction with the nucleosome remodeling and deacetylase (NuRD) complex[20]
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