Single-Cell Profiling of Epigenetic Modifiers Identifies PRDM14 as an Inducer of Cell Fate in the Mammalian Embryo

SummaryCell plasticity or potency is necessary for the formation of multiple cell types. The mechanisms underlying this plasticity are largely unknown. Preimplantation mouse embryos undergo drastic changes in cellular potency, starting with the totipotent zygote through to the formation of the pluripotent inner cell mass (ICM) and differentiated trophectoderm in the blastocyst. Here, we set out to identify and functionally characterize chromatin modifiers that define the transitions of potency and cell fate in the mouse embryo. Using a quantitative microfluidics approach in single cells, we show that developmental transitions are marked by distinctive combinatorial profiles of epigenetic modifiers. Pluripotent cells of the ICM are distinct from their differentiated trophectoderm counterparts. We show that PRDM14 is heterogeneously expressed in 4-cell-stage embryos. Forced expression of PRDM14 at the 2-cell stage leads to increased H3R26me2 and can induce a pluripotent ICM fate. Our results shed light on the epigenetic networks that govern cellular potency and identity in vivo.Video Abstrac

Identification of Histone Demethylases in Saccharomyces Cerevisiae

Based on the prediction that histone lysine demethylases may contain the JmjC domain, we examined the methylation patterns of five knock-out strains (ecm5 Delta, gis1 Delta, rph1 Delta, jhd1 Delta, and jhd2 Delta ( yjr119c Delta)) of Saccharomyces cerevisiae. Mass spectrometry (MS) analyses of histone H3 showed increased modifications in all mutants except ecm5 Delta. High-resolution MS was used to unequivocally differentiate trimethylation from acetylation in various tryptic fragments . The relative abundance of specific fragments indicated that histones K36 me3 and K4me3 accumulate in rph1 Delta and jhd2 Delta strains, respectively, whereas both histone K36me2 and K36me accumulate in gis1 Delta and jhd1 Delta strains. Analyses performed with strains overexpressing the JmjC proteins yielded changes in methylation patterns that were the reverse of those obtained in the complementary knock-out strains. In vitro enzymatic assays confirmed that the JmjC domain of Rph1 specifically demethylates K36me3 primarily and K36me2 secondarily. Overexpression of RPH1 generated a growth defect in response to UV irradiation. The demethylase activity of Rph1 is responsible for the phenotype. Collectively, in addition to Jhd1, our results identified three novel JmjC domain-containing histone demethylases and their sites of action in budding yeast S. cerevisiae. Furthermore, the methodology described here will be useful for identifying histone demethylases and their target sites in other organisms

Molecular signals of epigenetic states.

Epigenetic signals are responsible for the establishment, maintenance, and reversal of metastable transcriptional states that are fundamental for the cell's ability to "remember" past events, such as changes in the external environment or developmental cues. Complex epigenetic states are orchestrated by several converging and reinforcing signals, including transcription factors, noncoding RNAs, DNA methylation, and histone modifications. Although all of these pathways modulate transcription from chromatin in vivo, the mechanisms by which epigenetic information is transmitted through cell division remain unclear. Because epigenetic states are metastable and change in response to the appropriate signals, a deeper understanding of their molecular framework will allow us to tackle the dysregulation of epigenetics in disease

Chromatin Starts to Come Clean

In an effort to identify a chromatin-associated pluripotent network, Rafiee et al., (2016) developed a powerful ChIP-MS technique and discovered a novel protein, TRIM24, enriched on OCT4-, SOX2-, and NANOG-associated chromatin, paving the way for future proteomic studies on chromatin