Methylation of H3K4 Is Required for Inheritance of Active Transcriptional States

Division of Cell and Developmental Biology, College of Life Sciences, University of Dundee, Dundee DD1 5EH, Scotland, UK.
Current biology: CB (Impact Factor: 9.92). 02/2010; 20(5):397-406. DOI: 10.1016/j.cub.2010.01.017
Source: PubMed

ABSTRACT Maintenance of differentiation programs requires stability, when appropriate, of transcriptional states. However, the extent to which inheritance of active transcriptional states occurs from mother to daughter cells has not been directly addressed in unperturbed cell populations.
By live imaging of single-gene transcriptional events in individual cells, we have directly recorded the potential for mitotic inheritance of transcriptional states down cell lineages. Our data showed strong similarity in frequency of transcriptional firing between mother and daughter cells. This memory persisted for complete cell cycles. Both transcriptional pulse length and pulsing rate contributed to overall inheritance, and memory was determined by lineage, not cell environment. Analysis of transcription in chromatin mutants demonstrated that the histone H3K4 methylase Set1 and Ash2, a component of the methylase complex, are required for memory. The effects of Set1 methylation may be mediated directly by chromatin, because loss of memory also occurred when endogenous H3K4 was replaced by alanine. Although methylated H3K4 is usually associated with active transcriptional units, the modification was not required for gene activity but stabilized transcriptional frequency between generations.
Our data indicate that methylated H3K4 can act as a chromatin mark reflecting the original meaning of "epigenetic."

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    • "may be required to maintain fully active gene expression. Experiments in Dictyostelium and Xenopus have also provided evidence that H3K4me3 is required to maintain fully active transcription through cell division (Ng & Gurdon, 2008; Muramoto et al, 2010). "
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    • "In this context, various types of markers and biological functions have been used to evaluate the symmetry of cell divisions (Beckmann et al., 2007; Huang et al., 1999; Muramoto et al., 2010; Punzel et al., 2002; Suda et al., 1983; Wu et al., 2007; Zwaka and Thomson, 2005). Although each of these studies addressed a particular biological question (e.g., similarity levels of transcriptional oscillation of a few genes between Dictyostelium sister cells [Muramoto et al., 2010]) and provided important information to relevant fields, the overall level of similarity between sister cells has not been thoroughly addressed. Human ESCs, for example, are considered to divide and differentiate ''symmetrically'' regardless of the cultural condition, but this assumption is based on the distribution of the expression of a single gene POU5F1 measured through the signal of highly stable protein, eGFP (Zwaka and Thomson, 2005). "
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    • "Interaction between variants: K4A substitution on H3a results in loss of lysine 4-trimethylation on H3b Muramoto et al. (2010) previously reported that replacing the gene encoding H3a with a mutated version in which K4 is replaced with alanine (K4A) led to complete loss of K4me3 in Dictyostelium (25) which suggested that only H3a was trimethylated at K4. This previous analysis was performed by western blot but under gel conditions which did not separate the H3a and H3b variants. "
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    ABSTRACT: Dynamic acetylation of all lysine-4-trimethylated histone H3 is a complex phenomenon involved in Immediate-early gene induction in metazoan eukaryotes. Higher eukaryotes express repeated copies of three closely related H3 variants, inaccessible to genetic analysis. We demonstrate conservation of these phenomena in Dictyostelium which has three single-copy H3 variant genes. Although dynamic acetylation is targeted to two H3 variants which are K4-trimethylated, K9-acetylation is preferentially targeted to one. In cells lacking Set1 methyltransferase and any detectable K4-trimethylation, dynamic acetylation is lost demonstrating a direct link between the two. Gene replacement to express mutated H3 variants reveals a novel interaction between K4-trimethylation on different variants. Cells expressing only one variant show defects in growth, and in induction of a UV-inducible gene, demonstrating the functional importance of variant expression. These studies confirm that dynamic acetylation targeted to H3K4me3 arose early in evolution and reveal a very high level of specificity of histone variant utilization in a simple multicellular eukaryote.
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