Symposiums (S1-1 – S2-7)
Genes & Genetic Systems
Molecular mechanisms of piRNA-mediated transposon silencing PIWI-interacting RNAs (piRNAs) mediate retrotransposon silencing at transcriptional or post-transcriptional level in animal gonads. In the Drosophila ovary, the Piwi-piRNA complexes (Piwi-piRISCs) repress retrotransposons by modifying chromatins. Here, we demonstrate involvement of linker histone H1 in this repression. H1 physically interacts with Piwi. Depleting Piwi decreases H1 density on retrotransposon locus in a cultured
... a cultured Drosophila ovarian somatic cell line (OSC) where Piwi-piRISCmediated transposon silencing occurs. Targeted piRNA production induces de novo H1 association to the target locus. Thus, we propose that Piwi-piRISCs silence their targets by recruiting H1 in a sequence-specific (piRNA-dependent) manner. The genomes of vertebrates and plants contain a substantial number of transposable elements (TEs), which are silenced by repressive epigenetic modifications such as cytosine methylation and methylation of lysine 9 of histone H3. Although active cellular genes often contain TEs within their transcribed regions, epigenetic regulation of the intragenic TEs and its impacts on gene expression remain largely unexplored. In this study, we show that in Arabidopsis thaliana, about 7% of TEs are located within gene bodies, almost equally distributed between intronic and exonic regions. Most of them are shorter and less methylated than their intergenic copies. Interestingly, while exonic TEs are epigenetically regulated as genes, intronic TEs are regulated similarly to intergenic TEs. Moreover, expression analysis showed that heterochromatic epigenetic marks associated with intronic TEs are critical for proper transcription of the associated genes. These results suggest the importance of epigenetic mechanisms for regulation of TEs within transcriptional gene units. S1 -3 JANGID, Rahul 1 , JAYANI, Ranveer 1 , GALANDE, Sanjeev 1 ( 1 Indian Inst. Sci. Education and Res.) Chromatin organizer SATB1 recruits Set9 histone methyltransferase to regulate global gene expression The global chromatin organizer SATB1 has emerged as a key factor integrating higher-order chromatin architecture with gene regulation. We set out to understand how SATB1 collaborates with the histone modifying machinery to accomplish this task. Knockdown of SATB1 resulted in alterations in the methylation marks across multiple loci, suggesting that SATB1 is involved in defining the epigenetic landscape of multiple loci. Immunofluorescence analysis revealed that SATB1 and H3K4(me)3 occupy the same regions within thymocyte nuclei. However, there was virtually no overlap of SATB1 with H3K9(me)3 modified regions. Furthermore, co-immunoprecipitation analysis indicated that SATB1 specifically interacts with SET 9 histone methyltransferase but not with Suv39H1. In vitro pull-down assays revealed that SATB1 interacts with SET9 via its N-terminal PDZ-like domain. Genome-wide occupancy analysis for SATB1 and SET9 further revealed large number of shared targets. Collectively, our findings suggest that SATB1 plays an important role in gene regulation via organization of transcriptionally poised chromatin. S1 -4 HORI, Tetsuya 1 , FUKAGAWA, Tatsuo 1 ( 1 Dept. Molec. Genet., Natl. Inst. Genet.) Molecular switch for kinetochore assembly The centromere is an essential genome region where the kinetochore is formed for faithful chromosome segregation. The centromere is specified by epigenetic mechanisms and centromere specific histone CENP-A acts as a key epigenetic marker. However, it is still unclear how kinetochore is formed following CENP-A incorporation into centromeres. To address this question we developed a unique chromosome-engineering method with DT40 cells and created artificial kinetochores. Through analysis of these artificial kinetochores, we propose a model how the CCAN (Constitutive Centromere-Associated Network) proteins are assembled to form functional kinetochores. In addition, we demonstrate a centromere-specific histone modification that enables to assemble kinetochore proteins. Combing these results, we would like to discuss about the current model of molecular mechanisms for kinetochore formation.