Department of Molecular Biology Umeå University
Umeå 2015
Epigenetics and targeting mechanisms in Drosophila melanogaster
Margarida Figueiredo
Akademisk avhandling
som med vederbörligt tillstånd av Rektor vid Umeå universitet för avläggande av filosofie doktorsexamen framläggs till offentligt försvar i Astrid Fagraeus Hörsal A 103 Unod R 1, NUS – Norrlands universitetssjukhus,
Torsdag den 4 June, kl. 09:00.
Avhandlingen kommer att försvaras på engelska.
Fakultetsopponent: Associate Professor Victoria Meller,
Department of Biological Sciences, Wayne State University, Detroit, MI, USA.
Organization Document type Date of publication Umeå University Doctoral thesis 2015-05-08 Department of Molecular Biology
SE-901 87 Umeå, Sweden
Author
Margarida Figueiredo
Title
Epigenetics and targeting mechanisms in Drosophila melanogaster
Abstract
Regulation of gene expression can occur at different levels, ranging from single genes to genomic regions and even to entire chromosomes. Understanding which epigenetic mechanisms are involved in this regulation, especially how protein regulators are targeted to chromatin, has been the focus of my thesis.
I show that genes in monosomic regions are buffered, i.e., expressed at a higher level than the expected 50% of the wild type level. The buffering is general, it is primarily affected by gene length and is not affected by the presence of other monosomic regions. Additionally, the expression of proteolysis genes is induced in aneuploidies.
Gene expression regulation at a chromosome-wide level has so far only been described for the X chromosome and for the 4th chromosome of Drosophila melanogaster. The 4th chromosome gene expression is regulated by both POF and HP1a, which target exons of active genes. Additionally, HP1a targets promoters. I found that Setdb1 and Su(var)3-9 recruit HP1a to the 4th chromosome and to pericentromeric regions, respectively, by di- and tri- methylation of H3K9. Importantly, HP1a is recruited to promoters of active genes independently of methylated H3K9. The promoters bound by HP1a are enriched in HP2, in A/T content and are DNase sensitive. We propose that HP1a is bound to the H3 histone core at promoters and that the promoter targeting functions as the nucleation site from which HP1a spreads via H3K9 methylation.
MSL complex targets the male X chromosome and is partially responsible for dosage compensation, by upregulation of X chromosome gene expression almost two times. The importance of roX long non-coding RNAs in MSL recruitment has been one important focus of this thesis. I found that in absence of roX, MSL targets high affinity sites on the X chromosome. Additionally, a complete and active MSL complex is bound to six genes of the 4th chromosome. Interestingly, when roX RNAs are not present, MSL targets genomic regions enriched in Hoppel transposable elements and repeats. We propose that the heterochromatic targeting represents an ancient function of the MSL complex and that the roX RNAs evolved to restrict MSL binding to the X chromosome. I further found that MSL associates with many different RNAs when roX are absent, including a set of snoRNAs.
Keywords
Heterochromatin, Drosophila, HP1a, POF, aneuplodies, dosage compensation, MSL.
Language ISBN Number of pages
English 978-91-7601-267-3 69 + 4 papers
