Project description:Linker histones are involved in the formation of higher-order chromatin structure. Although linker histones have been implicated in the regulation of specific genes, it still remains unclear what their principal binding determinants are and how their repressive function in vitro can be reconciled with presumed broad binding in vivo. We generated a full genome, high resolution binding map of linker histone H1 in Drosophila Kc cells, using DamID. H1 binds at similar levels across much of the genome, both in classical euchromatin and heterochromatin. Strikingly, there are pronounced dips of low H1 occupancy around transcription start sites of active genes and at many distant cis-regulatory sites. H1 dips are not due to lack of nucleosomes. Rather, all regions with low binding of H1 show enrichment of the histone variant H3.3 which itself has been linked to high nucleosome turnover. Upon knockdown of H3.3, we find that H1 levels increase at sites previously not covered with H1 with a concomitant increase in nucleosome repeat length. These changes are independent of transcriptional changes. Our results show that the H3.3 protein counteracts association of H1 at genomic sites with high rates of histone turnover. This antagonism provides a mechanism to keep diverse genomic sites in an open chromatin conformation. For this study, we generated DamID profiles of histone H1 and RpII18 in Drosophila Kc167 cells. Additionally, we generated H1 profiles in cells treated with RNAi against white, H3.3B, or H3.3A and H3.3B. Nucleosome positioning profiles were generated in untreated cells and cells treated with RNAi against white, H3.3B, or H3.3A and H3.3B. Profiles of expression changes were generated for H3.3B RNAi and H3.3A and H3.3B RNAi. DamID experiments for H1 and RpII18 were performed in Drosophila cell cultures. Samples were hybridized to 380k NimbleGen arrays with 300 bp probe spacing. Formaldehyde-assisted isolation of regulatotry elements (FAIRE) was performed in Drosophila Kc167 cells. Samples were hybridized to 380k NimbleGen arrays with 300 bp probe spacing over non-crosslinked genomic DNA. Nucleosome positioning profiles were made by hybridizing mononucleosomal DNA over MNase digested purified genomic DNA on 380k NimbleGen arrays with 10 bp probe spacing. Expression profiles were made as H3.3 RNAi over white RNAi cohybridizations on spotted INDAC long oligo arrays. Every experiment was done in duplicate in the reverse dye orientation.

Project description:Insulators delimit independent transcriptional domains within genomes by constraining enhancer and silencer action. These transcriptional effects depend upon DNA recognition by insulator binding proteins that recruit partners that protect against inappropriate long range modulation of non-target promoters. Insulator binding proteins are broadly expressed during development, with largely constitutive binding to thousands of genomic sites. Yet, tissue-specific transcriptional changes result from the loss of individual insulator binding proteins. To understand the molecular basis for such effects, we are studying the classic Drosophila insulator protein Suppressor of Hairy-wing [Su(Hw)]. Genetic studies show that loss of this broadly expressed insulator protein prevents oocyte development. To determine the basis for the block in oogenesis, we coupled transcriptional analyses in su(Hw) mutant ovaries with genome-wide definition of Su(Hw) binding in this tissue. These studies identified 71 direct targets of Su(Hw) regulation, with nearly 70% of these genes showing increased RNA accumulation when Su(Hw) is lost. Surprisingly, derepressed Su(Hw) target genes correspond to genes normally highly expressed in neural tissues, suggesting that Su(Hw) has a critical role in silencing neural genes in the ovary. Support for this postulate was obtained by genetic studies. We found that oocyte production was restored in su(Hw) mutant females that carry a deletion of one allele of the elav family RNA binding protein 9 (Rbp9) gene. These su(Hw) null oocytes can be fertilized, with evidence that embryos lacking Su(Hw) show compromised development. Our studies extend the known transcriptional activities of Su(Hw), indicating that Su(Hw) can function as an insulator, activator and repressor, the latter function being essential for oogenesis. These findings highlight that insulator proteins are versatile transcriptional regulatory proteins, suggesting that tissue specific contributions to transcription result from direct regulation of individual genes.

Project description:Insulators delimit independent transcriptional domains within genomes by constraining enhancer and silencer action. These transcriptional effects depend upon DNA recognition by insulator binding proteins that recruit partners that protect against inappropriate long range modulation of non-target promoters. Insulator binding proteins are broadly expressed during development, with largely constitutive binding to thousands of genomic sites. Yet, tissue-specific transcriptional changes result from the loss of individual insulator binding proteins. To understand the molecular basis for such effects, we are studying the classic Drosophila insulator protein Suppressor of Hairy-wing [Su(Hw)]. Genetic studies show that loss of this broadly expressed insulator protein prevents oocyte development. To determine the basis for the block in oogenesis, we coupled transcriptional analyses in su(Hw) mutant ovaries with genome-wide definition of Su(Hw) binding in this tissue. These studies identified 71 direct targets of Su(Hw) regulation, with nearly 70% of these genes showing increased RNA accumulation when Su(Hw) is lost. Surprisingly, derepressed Su(Hw) target genes correspond to genes normally highly expressed in neural tissues, suggesting that Su(Hw) has a critical role in silencing neural genes in the ovary. Support for this postulate was obtained by genetic studies. We found that oocyte production was restored in su(Hw) mutant females that carry a deletion of one allele of the elav family RNA binding protein 9 (Rbp9) gene. These su(Hw) null oocytes can be fertilized, with evidence that embryos lacking Su(Hw) show compromised development. Our studies extend the known transcriptional activities of Su(Hw), indicating that Su(Hw) can function as an insulator, activator and repressor, the latter function being essential for oogenesis. These findings highlight that insulator proteins are versatile transcriptional regulatory proteins, suggesting that tissue specific contributions to transcription result from direct regulation of individual genes. Ovaries for RNA isolation were dissected from 4-6 hour old virgin females of wild type, su(Hw)f/v (fertile), su(Hw)2/v (sterile) and su(Hw)Pb/2 (sterile) Drosophila melanogaster. At this stage of development, ovaries only contain egg chamber stages 1-8. Loss of Su(Hw) causes apoptosis at stage 9. Thus, the experimental design compares transcriptionl changes in the ovary prior to induction nof apoptosis in su(Hw) mutants.

Dataset Information

The insulator protein SU(HW) modulates nuclear lamina interactions of the Drosophila genome: expression

Publications

The insulator protein SU(HW) fine-tunes nuclear lamina interactions of the Drosophila genome.

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