期刊论文详细信息
Epigenetics & Chromatin
Distinct roles of KAP1, HP1 and G9a/GLP in silencing of the two-cell-specific retrotransposon MERVL in mouse ES cells
Matthew C Lorincz3  Mohammad M Karimi2  Prim B Singh1  Steven JM Jones2  Preeti Goyal3  Peter J Thompson3  Irina A Maksakova3 
[1] Fächereverbund Anatomie, Institut für Zell and Neurobiologie, Charite - Universitätsmedizin, Charitéplatz 1, 10117, Berlin, Germany;British Columbia Cancer Agency, Genome Sciences Centre, 675 West 10th Avenue, Vancouver, British Columbia V5Z 4S6, Canada;Department of Medical Genetics, Life Sciences Institute, 2350 Health Sciences Mall, University of British Columbia, Vancouver, British Columbia V6T 1Z3, Canada
关键词: mESC;    H3K9me2;    Preimplantation;    Chimeric transcripts;    ERV;    MERVL;    KAP1;    HP1;    GLP;    G9a;   
Others  :  810195
DOI  :  10.1186/1756-8935-6-15
 received in 2012-12-14, accepted in 2013-05-08,  发布年份 2013
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【 摘 要 】

Background

In mouse embryonic stem cells (mESCs), transcriptional silencing of numerous class I and II endogenous retroviruses (ERVs), including IAP, ETn and MMERVK10C, is dependent upon the H3K9 methyltransferase (KMTase) SETDB1/ESET and its binding partner KAP1/TRIM28. In contrast, the H3K9 KMTases G9a and GLP and HP1 proteins are dispensable for this process. Intriguingly, MERVL retroelements are actively transcribed exclusively in the two-cell (2C) embryo, but the molecular basis of silencing of these class III ERVs at later developmental stages has not been systematically addressed.

Results

Here, we characterized the roles of these chromatin factors in MERVL silencing in mESCs. While MMERVK10C and IAP ERVs are bound by SETDB1 and KAP1 and are induced following their deletion, MERVL ERVs show relatively low levels of SETDB1 and KAP1 binding and are upregulated exclusively following KAP1 depletion, indicating that KAP1 influences MERVL expression independent of SETDB1. In contrast to class I and class II ERVs, MERVL and MERVL LTR-driven genic transcripts are also upregulated following depletion of G9a or GLP, and G9a binds directly to these ERVs. Consistent with a direct role for H3K9me2 in MERVL repression, these elements are highly enriched for G9a-dependent H3K9me2, and catalytically active G9a is required for silencing of MERVL LTR-driven transcripts. MERVL is also derepressed in HP1α and HP1β KO ESCs. However, like KAP1, HP1α and HP1β are only modestly enriched at MERVL relative to IAP LTRs. Intriguingly, as recently shown for KAP1, RYBP, LSD1 and G9a-deficient mESCs, many genes normally expressed in the 2C embryo are also induced in HP1 KO mESCs, revealing that aberrant expression of a subset of 2C-specific genes is a common feature in each of these KO lines.

Conclusions

Our results indicate that G9a and GLP, which are not required for silencing of class I and II ERVs, are recruited to MERVL elements and play a direct role in silencing of these class III ERVs, dependent upon G9a catalytic activity. In contrast, induction of MERVL expression in KAP1, HP1α and HP1β KO ESCs may occur predominantly as a consequence of indirect effects, in association with activation of a subset of 2C-specific genes.

【 授权许可】

   
2013 Maksakova et al.; licensee BioMed Central Ltd.

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