Interaction of RNA polymerase II and the RNA silencing machinery in heterochromatin formation of Drosophila

Abstract

[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT AUTHOR'S REQUEST.] The eukaryotic chromosome is composed of two structurally and functionally distinct compartments. The loosely packaged region is known as the euchromatin, a region that shows a high rate of active transcription. The tightly packaged region of the genome is known as the heterochromatin. There are very few genes in this region and hence there is a paucity of active transcription. Although heterochromatin is transcriptionally inert it has an important role to play in many important biological processes such as meiotic recombination, genomic stability and separation of sister chromatids in mitosis. Heterochromatin is thought to be formed by transcription via RNA Pol II of aberrant/repeated regions such as those found in the centromeric regions that enter into the RNAi silencing pathway and guide chromatin modification for gene silencing. Recent evidence in S. pombe indicates that mutations in the RNA Pol II second largest subunit affect the production of siRNA and the subsequent histone modifications associated with centromeric heterochromatin. We examined this issue in Drosophila. Our initial results indicate genetic and biochemical interactions between RNAi related components in Drosophila and the second largest subunit of RNA Pol II. The interaction between mutations in the RNAi silencing machinery and RNA pol II results in a strong suppression of PEV (Position Effect Variegation) indicating a possible effect on heterochromatin formation in Drosophila. The analysis of polytene chromosomes revealed a compromised chromocenter in the double heterozygous mutant when compared with wild type and single heterozygotes. This study suggests a link between RNA Pol II and small RNA mediated heterochromatin assembly in higher metazoan cells. The structure of centromeric heterochromatin is very crucial for normal cell division. The study of small RNA mediated heterochromatin structure and the crucial role of RNA Pol II will lead to a better understanding of cell cycle regulation. Aberrations in cell cycle regulation can lead to various types of malignant cancer. The study of heterochromatin structure will shed light on this important aspect of human health.--From public.pdf