Support for a trans-acting repression mechanism has recently been found by identification of the transcription factor Snail, binding directly to E2 boxes in the E-cadherin promoter and potently repressing its transcription [ 48, 49].
Seminal reviews on miRNAs have discussed about miRNAs as multi-facet regulators acting beyond simple repression of gene expression: buffering noise in the expression of their targets or setting a threshold-linear response (Bartel, 2009; Hausser and Zavolan, 2014).
"I think there's a tradition in English acting of emotional repression," said the British director, who won an Oscar for "The King's Speech".
Hence, these divergent observations have led to hypothesize that in stem cells PcG proteins target both genes poised for later activation and genes poised for later repression, acting as a common platform that clearly requires additional gene- and lineage-specific signals when differentiation unfolds [6], [9].
miRNAs are key regulators of eukaryotic gene expression, acting via translational repression and mRNA decay (Friedman and Jones, 2009).
The receptor-like CLAVATA2 (CLV2) is involved in WUS repression acting within the CLV3 signaling path-way [ 8].
They are typically loaded into the Ago1-RISC complex, where they trigger the silencing of complementary mRNA targets, acting through translational repression and mRNA cleavage.
In these contexts, Prdm1 has been shown to mediate transcriptional repression, acting as a scaffold that recruits co-repressors and chromatin-modifying enzymes to specific target genes (Yu et al, 2000; Gyory et al, 2004).
It thus seems that on repressed promoters (mostly bivalent in mESCs), Tet1 might recruit the Sin3a complex (directly) and the Ezh2 complex (indirectly), enabling these complexes in turn to maintain histones H3 in a deacetylated and K27 trimethylated form, therefore acting on gene repression.
If, as our data indicate, transcriptional activity of these elements is commonplace and widespread, the lack of insertional activity and genome expansion in contemporary hybrids is intriguing and suggests mechanisms of transposable element repression acting posttranscriptionally, such as RNAi (Slotkin and Martienssen 2007; Lisch 2009).
However, our data highlight that different degrees of carbon catabolite repression are acting on individual MUT genes; for example DAS1/2 are less de-repressed than AOX1/2.
