siRNAs from an X-linked satellite repeat promote X-chromosome recognition in Drosophila melanogaster

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 111; no. 46; pp. 16460 - 16465
• Main Authors: Menon, Debashish U., Coarfa, Cristian, Xiao, Weimin, Gunaratne, Preethi H., Meller, Victoria H.
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 18.11.2014; National Acad Sciences
• Subjects: Animals; Animals, Genetically Modified; Base Pairing; Base Sequence; Biological Sciences; Chromatin; Chromosome Mapping; Chromosomes; DNA, Satellite - genetics; DNA-Binding Proteins - analysis; Dosage Compensation, Genetic; Drosophila; Drosophila - classification; Drosophila - genetics; Drosophila melanogaster; Drosophila melanogaster - embryology; Drosophila melanogaster - genetics; Drosophila melanogaster - growth & development; Drosophila melanogaster - ultrastructure; Drosophila Proteins - analysis; Drosophila Proteins - genetics; Drosophila Proteins - physiology; Euchromatin - genetics; Female; females; Gene expression; Gene Expression Regulation, Developmental; Genes; Genes, Lethal; Insects; Larva; Larvae; Male; Male animals; males; Molecular Sequence Data; Nuclear Proteins - analysis; Repetitive Sequences, Nucleic Acid; Ribonucleic acid; RNA; RNA Interference; RNA, Small Interfering - biosynthesis; RNA, Small Interfering - genetics; RNA, Small Interfering - pharmacology; RNA, Small Interfering - physiology; RNA-Binding Proteins - genetics; RNA-Binding Proteins - physiology; Sequence Alignment; Sequence Homology, Nucleic Acid; Sex chromosomes; Small interfering RNA; Species Specificity; Survival analysis; Tandem Repeat Sequences; Transcription Factors - analysis; Transcription Factors - genetics; Transcription Factors - physiology; Transgenes; X chromosome; X Chromosome - genetics; roX RNA; siRNA; X chromosome recognition; dosage compensation; epigenetics
• ISSN: 0027-8424; 1091-6490; 1091-6490
• DOI: 10.1073/pnas.1410534111

Significance Modulation of X-linked gene expression is essential in organisms with XX females and XY males. Various strategies for global regulation of X chromosomes have been proposed, but all require highly selective recognition of X chromatin. How this is achieved is not understood. The siRNA pathway contributes to X recognition in a well-studied Drosophila model. We now show that ectopic production of siRNA from a repetitive sequence that is limited to the X chromosome also promotes X recognition. Differential activities of X-linked repeats suggest a control region model, in which siRNA produced by a few repeats acts on widely distributed X-linked target sequences to promote selective recognition, and modification, of a single chromosome. Highly differentiated sex chromosomes create a lethal imbalance in gene expression in one sex. To accommodate hemizygosity of the X chromosome in male fruit flies, expression of X-linked genes increases twofold. This is achieved by the male- specific lethal (MSL) complex, which modifies chromatin to increase expression. Mutations that disrupt the X localization of this complex decrease the expression of X-linked genes and reduce male survival. The mechanism that restricts the MSL complex to X chromatin is not understood. We recently reported that the siRNA pathway contributes to localization of the MSL complex, raising questions about the source of the siRNAs involved. The X-linked 1.688 g/cm ³ satellite related repeats (1.688 X repeats) are restricted to the X chromosome and produce small RNA, making them an attractive candidate. We tested RNA from these repeats for a role in dosage compensation and found that ectopic expression of single-stranded RNAs from 1.688 X repeats enhanced the male lethality of mutants with defective X recognition. In contrast, expression of double-stranded hairpin RNA from a 1.688 X repeat generated abundant siRNA and dramatically increased male survival. Consistent with improved survival, X localization of the MSL complex was largely restored in these males. The striking distribution of 1.688 X repeats, which are nearly exclusive to the X chromosome, suggests that these are cis -acting elements contributing to identification of X chromatin.