title: Perturbation analysis of heterochromatin-mediated gene silencing and somatic inheritance.
abstract: Repetitive sequences in eukaryotic genomes induce chromatin-mediated gene-silencing of juxtaposed genes. Many components that promote or antagonize silencing have been identified, but how heterochromatin causes variegated and heritable changes in gene expression remains mysterious. We have used inducible mis-expression in the Drosophila eye to recover new factors that alter silencing caused by the bw(D) allele, an insertion of repetitive satellite DNA that silences a bw(+) allele on the homologous chromosome. Inducible modifiers allow perturbation of silencing at different times in development, and distinguish factors that affect establishment or maintenance of silencing. We find that diverse chromatin and RNA processing factors can de-repress silencing. Most factors are effective even in differentiated cells, implying that silent chromatin remains plastic. However, over-expression of the bantam microRNA or the crooked-legs (crol) zinc-finger protein only de-repress silencing when expressed in cycling cells. Over-expression of crol accelerates the cell cycle, and this is required for de-repression of silencing. Strikingly, continual over-expression of crol converts the speckled variegation pattern of bw(D) into sectored variegation, where de-repression is stably inherited through mitotic divisions. Over-expression of crol establishes an open chromatin state, but the factor is not needed to maintain this state. Our analysis reveals that active chromatin states can be efficiently inherited through cell divisions, with implications for the stable maintenance of gene expression patterns through development.
authors.affiliation: Department of BCMP, Harvard Medical School, Boston, Massachusetts, United States of America.
authors.forename: Jonathan I
authors.initials: JI
authors.lastname: Schneiderman
authors.forename: Sara
authors.initials: S
authors.lastname: Goldstein
authors.forename: Kami
authors.initials: K
authors.lastname: Ahmad
mesh_terms: D000818:Animals; D002453:Cell Cycle; D029721:Drosophila Proteins / Q000378:metabolism; D004331:Drosophila melanogaster / Q000166:cytology / Q000235:genetics*; D004742:Enhancer Elements, Genetic / Q000235:genetics; D005123:Eye / Q000166:cytology / Q000378:metabolism; D020868:Gene Silencing; D006570:Heterochromatin / Q000378:metabolism*; D040582:Inheritance Patterns / Q000235:genetics*; D035683:MicroRNAs / Q000378:metabolism; D009687:Nuclear Proteins / Q000378:metabolism; D034622:RNA Interference; D012097:Repressor Proteins / Q000378:metabolism; D014157:Transcription Factors / Q000378:metabolism
chemical_list: D029721:Drosophila Proteins; D006570:Heterochromatin; D035683:MicroRNAs; D009687:Nuclear Proteins; D012097:Repressor Proteins; D014157:Transcription Factors; C471146:bantam microRNA, Drosophila; C112763:crol protein, Drosophila