%0 Generic
%A Hartmann, Mark
%D 2018
%F heidok:23086
%R 10.11588/heidok.00023086
%T Centromeric tRNA and Dnmt2-mediated Methylation in Mitotic Chromosome Segregation
%U https://archiv.ub.uni-heidelberg.de/volltextserver/23086/
%X Centromeres are the primary constriction sites of mitotic chromosomes and a prereq- uisite for chromosome segregation during mitosis. Centromeres serve as a platform for kinetochore formation and spindle attachment and are epigenetically regulated. Specific proteins and protein modifications discriminate centromeric chromatin from the surrounding pericentromeric heterochromatin. Emerging evidence indicates that RNAs are important factors in centromere identity but the composition and regula- tion of centromeric transcripts are largely unknown. Surprisingly, the role of RNA modifications at centromeres is completely unknown. In this doctoral thesis, a subset of transfer RNAs (tRNAs) was found to localise to mitotic centromeres, as well as a number of different RNA processing enzymes. Among them were the cytosine-5 tRNA methyltransferases Dnmt2 and NSun2. Depletion of these enzymes caused severe chromosome segregation defects, suggesting a role of tRNA methylation in mitosis. Strikingly, analysis of enzymatically inactivated Dnmt2 indicated a direct role of cytosine-5 RNA methylation in the regulation of centromeres. Depletion of Dnmt2 affected (peri-) centromeric chromatin compositions, which presumably lead to the observed mitotic defects. The detection of components of the RNA poly- merase III (RNAPIII) transcription machinery suggested a role of active transcrip- tion at centromeres during mitosis. Indeed, inhibition of RNAPIII-mediated tran- scription caused comparable chromosome segregation defects as observed in tRNA methyltransferase mutant backgrounds. Strikingly, the centromeric localisation of RNAPIII appeared sensitive not only to transcriptional inhibition but also to cen- tromeric levels of Dnmt2. Vice versa, Dnmt2 was dependent on centromeric RNA and RNAPIII transcription, which suggests an interdependent role of RNAPIII tran- scription and tRNA methylation at centromeres. This thesis describes a novel role of RNAPIII transcription and tRNA methylation during mitosis in Drosophila, which functionally connects an epitranscriptomic mechanism and the epigenomic regulation of centromeres. Moreover, the mitotic function of Dnmt2 appeared to be conserved in mammalian cells, which suggests a conserved role of RNA modification in the regulation of centromeric chromatin.