Table 2 Selected factors silencing ERVs in embryonic stem cells
From: Transposable elements in the mammalian embryo: pioneers surviving through stealth and service
Factor | Relevant function in ESCs | Interacting proteins | Reference(s) |
|---|---|---|---|
Zfp809 | KRAB zinc finger protein, recognizes PBS Pro and recruits Trim28 | Trim28 | [85] |
YY1 | Yin-Yang 1 (YY1) is a zinc finger protein, initially binds to mouse ERV LTRs (U3 region) and helps assemble Trim28/Eset silencing complex | Trim28 | [92] |
SHIN | Short heterochromatin inducing sequence initiates heterochromatin and transcriptional repression | KRABZfps (likely) | [93] |
Trim28 (Kap1, Tif1-β) | Transcriptional co-repressor, acts as a bridge between KRAB-Zfps and other transcriptional repressors, mediates H3K9me3 recruitment | KRABZfps, Eset, NuRD deacetylase complex, HP1 | |
Eset (Setdb1, Kmt1e) | Histone methyltransferase, trimethylates H3K9 and H4K20, crucial for HP1 binding | Trim28, HP1 | [73] |
Sumo2 | Sumoylation factor, post-translational sumoylation of Trim28 enhances recruitment of Trim28 to proviral DNA | Trim28 | [72] |
HP1 | Heterochromatin protein 1, binding to Trim28 might be important for repression of transcription | Trim28, Eset, Atrx | |
Chaf1a | Histone chaperone, deposits histone H3/H4 which marks proviral DNA for silencing, might execute different silencing mechanisms on different classes of ERVs | Eset, Kdm1a, Hdac1/2, Asf1a/b | [72] |
Asf1a/b | Histone chaperones, components of the Chaf1a interactome | Chaf1a | [72] |
Atrx | ATP-dependent helicase, establishes and maintains heterochromatin | Eset, Trim28 (both likely) | [93] |
Daxx | H3.3-specific chaperone, may facilitate H3.3-deposition on ERV sequences, possible role in SHIN-silencing | Atrx |