title: Changes in chromatin structure correlate with transcriptional activity of nucleolar rDNA in polytene chromosomes.
abstract: Ribosomal DNA genes (rDNA) are found in tandem arrays of hundreds of repeated genes, but only a fraction of these genes are actively transcribed. The regulatory mechanism controlling the transition between active and inactive rDNA in higher eukaryotes is vital for cell survival. Here, we show that the nucleolus from Drosophila salivary gland cells contains two levels of chromatin organization reflecting differences in transcriptional activity: Decondensed chromatin is highly occupied with TATA-box-binding protein (TBP), phosphorylated H3S10, and acetylated H3K14, suggesting that rDNA in decondensed nucleolar areas is actively transcribed. Condensed chromatin lacks TBP, phosphorylated H3S10, or acetylated H3K14 and is enriched in the rDNA retrotransposons R1 and R2. The data show that R1 and R2 retrotransposons are not actively transcribed in salivary glands and may lead to the epigenetic silencing of flanking rDNA genes and that the silencing mechanisms of these sequences might be partially independent of heterochromatin formation by methylation of histone H3 at lysine 9 and binding of heterochromatin protein 1.
authors.affiliation: Department of Biochemistry, Cellular and Molecular Biology, M407 Walters Life Sciences, The University of Tennessee, 1414 Cumberland Avenue, Knoxville, TN 37996, USA.
authors.forename: Maria Piedad
authors.initials: MP
authors.lastname: Plata
authors.forename: Hyuck Joon
authors.initials: HJ
authors.lastname: Kang
authors.forename: Shaofei
authors.initials: S
authors.lastname: Zhang
authors.forename: Srilalitha
authors.initials: S
authors.lastname: Kuruganti
authors.forename: Shih-Jui
authors.initials: SJ
authors.lastname: Hsu
authors.forename: Mariano
authors.initials: M
authors.lastname: Labrador
mesh_terms: D000818:Animals; D002466:Cell Nucleolus / Q000235:genetics* / Q000378:metabolism / Q000648:ultrastructure; D002843:Chromatin / Q000378:metabolism / Q000648:ultrastructure*; D002875:Chromosomes / Q000235:genetics* / Q000648:ultrastructure; D004275:DNA, Ribosomal / Q000235:genetics*; D004330:Drosophila / Q000235:genetics* / Q000502:physiology; D017344:Genes, Insect / Q000235:genetics / Q000502:physiology; D006657:Histones / Q000235:genetics / Q000378:metabolism / Q000648:ultrastructure; D018626:Retroelements / Q000235:genetics / Q000502:physiology; D012469:Salivary Glands / Q000378:metabolism; D035181:TATA-Box Binding Protein / Q000235:genetics / Q000378:metabolism
chemical_list: D002843:Chromatin; D004275:DNA, Ribosomal; D006657:Histones; D018626:Retroelements; D035181:TATA-Box Binding Protein