Jurnal : The Assembly and Maintenance of Heterochromatin Initiated byTransgene Repeats Are Independent of the RNA InterferencePathway in Mammalian Cells - Skripsi Teknik Informatika

Jurnal : The Assembly and Maintenance of Heterochromatin Initiated byTransgene Repeats Are Independent of the RNA InterferencePathway in Mammalian Cells

(Jurnal Teknik Informatika)

ABSTRACT

A role for the RNA interference (RNAi) pathway in the establishment of heterochromatin is now wellaccepted for various organisms. Less is known about its relevance and precise role in mammalian cells. Wepreviously showed that tandem insertion of a 1,000-copy inducible transgene into the genome of baby hamsterkidney (BHK) cells initiated the formation of an extremely condensed chromatin locus. Here, we characterizedthe inactive transgenic locus as heterochromatin, since it was associated with heterochromatin protein 1(HP1), histone H3 trimethylated at lysine 9, and cytosine methylation in CpG dinucleotides. Northern blotanalysis did not detect any transgene-derived small RNAs. RNAi-mediated Dicer knockdown did not disruptthe heterochromatic transgenic locus or up-regulate transgene expression. Moreover, neither Dicer knockdownnor overexpression of transgene-directed small interfering RNAs altered the bidirectional transition of thetransgenic locus between the heterochromatic and euchromatic states. Interestingly, tethering of HP1 to thetransgenic locus effectively induced transgene silencing and chromatin condensation in a Dicer-independentmanner, suggesting a role for HP1 in maintaining the heterochromatic locus. Our results suggest that theRNAi pathway is not required for the assembly and maintenance of noncentromeric heterochromatin initiatedby tandem transgene repeats in mammalian cells.

1.INTRODUCTION

In  eukaryotic  cells,  DNA  is  packaged  with  chromosomalproteins into chromatin and higher-order chromosome struc-tures.  Chromosomes  are  composed  of  two  types  of  domains,euchromatin and heterochromatin. While euchromatin is gen-erally considered to be the transcriptionally active portion ofthe  genome,  heterochromatin  was  originally  defined  throughcytological studies as genomic regions that remain visibly con-densed and deeply stained throughout the cell cycle (42). Fromthe biochemical aspect, DNA methylation, histone H3 meth-ylated  at  lysine  9  (H3K9me),  and  heterochromatin  protein  1(HP1) have been identified as important markers for hetero-chromatic  domains  (42).  Heterochromatin  mediates  variousfunctions in the nucleus, including centromere function, genesilencing,  and  nuclear  organization  (14).  In  large  blocks  ofheterochromatin  surrounding  functional  chromosome  struc-tures, such as centromeres and telomeres, heterochromatin isalso thought to stabilize repetitive DNA sequences and trans-posable elements (13, 29)

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Kata Kunci : Jurnal Maintenance of Heterochromatin Initiated, sistem pendukung keputusan, SPK, Jurnal Teknik Informatika, Jurnal Skripsi, Jurnal, Contoh Jurnal, Skripsi Teknik Informatika, Contoh Skripsi Teknik Informatika ,Contoh Skripsi, Skripsi.