X-chromosome inactivation (XCI) results in the differential marking of the active and inactive X with epigenetic modifications including DNA methylation.
Using a genome-wide approach, we examined the distribution of H4K5ac, a mark of active chromatin implicated in transcriptional re-activation of post-mitotic cells through gene bookmarking [ 26], and its role in regulating transcriptional activity following the establishment of contextual fear memory in the adult mouse [ 4, 13].
In general, one parental allele is modified with DNA methylation and histone modifications associated with silenced heterochromatin, while the other allele is modified with marks of active chromatin, such as H3K4me3, associated with promoter activity on this parental allele.
Furthermore, the bivalent promoters are associated with promoters "poised" for transcription [ 27] while the p300 marks of active enhancers are expected to co-occur with actively transcribed target genes [ 38], so they are unlikely to co-occur in the same tissue/stage for a given gene.
As a result, it is believed that histone acetylation primarily results in a more "open" chromatin configuration, serving as a "mark" of active gene transcription.
Wouldn't such evaluative attitudes manifest themselves in the kind of practical action that Brady thinks is the mark of active evaluative attitudes?
Here we used epigenomic profiling for H3K27ac, a mark of active enhancers, coupled to transgenic mouse assays to examine the genome-wide utilization of enhancers in three different mouse tissues across seven developmental stages.
Together, these data show that part of the FLC and FT chromatin simultaneously possesses the bivalent chromatin marks of active H3K4me3 and repressive H3K27me3.
Through its associated repressor complexes NRS F/RESTbinding is speculated to erase histone marks of active transcription (H3K4me2 and H3K9Ac), establish the repressive histone mark (H3K9me2), and repress transcription [27].
The A. thaliana NORs in root-tip cells of 15 day old plants do not overlap with signals for H3K4me3, a mark of active euchromatin (Figure 2B, second row from top).
