Antagonism between MES-4 and Polycomb Repressive Complex 2 Promotes Appropriate Gene Expression in C. elegans Germ Cells

Establishment and maintenance of gene expression states is central to development and differentiation. Transcriptional and epigenetic mechanisms interconnect in poorly understood ways to determine these states. We explore these mechanisms through dissection of the regulation of Arabidopsis thaliana FLOWERING LOCUS C (FLC). FLC can be present in a transcriptionally active state marked by H3K36me3 or a silent state marked by H3K27me3. Here, we investigate the trans factors modifying these opposing histone states and find a physical coupling in vivo between the H3K36 methyltransferase, SDG8, and the H3K27me3 demethylase, ELF6. Previous modeling has predicted this coupling would exist as it facilitates bistability of opposing histone states. We also find association of SDG8 with the transcription machinery, namely RNA polymerase II and the PAF1 complex. Delivery of the active histone modifications is therefore likely to be through transcription at the locus. SDG8 and ELF6 were found to influence the localization of each other on FLC chromatin, showing the functional importance of the interaction. In addition, both influenced accumulation of the associated H3K27me3 and H3K36me3 histone modifications at FLC. We propose the physical coupling of activation and derepression activities coordinates transcriptional activity and prevents ectopic silencing.epigenetic regulation | histone modifications | histone methyltransferase | histone demethylase | FLOWERING LOCUS C C hromatin-based transcriptional activity is particularly important in multicellular organisms, where cells differentiate into very different developmental states. Transcriptional states are induced by internal developmental signals or triggered by environmental conditions and are then epigenetically maintained through many cell divisions. Considerable evidence suggests that opposing histone modifications mark different transcriptional states (1-6). However, there is still great debate as to how histone-based transcriptional states are initially established and maintained through development (7,8). We used Arabidopsis FLOWERING LOCUS C (FLC) as a model gene to explore histone-based transcriptional regulation and epigenetic memory. Local chromatin states are critical for quantitatively controlling FLC expression (9). Active FLC expression requires functional FRIGIDA (FRI) and a set of histone modifying Trithorax homologs, Complex Proteins Associated with Set1 (COMPASS), RNA polymerase II Associated Factor 1 complex (PAF1C), and SET DOMAIN GROUP 8 (SDG8), the major H3K36 methyltransferase (10-17). Repression of FLC requires either the autonomous pathway, which coordinately influences transcriptional initiation and elongation with associated chromatin modulation, or vernalization, the cold-induced Polycomb silencing (18-21). Both of these involve accumulation of high levels of H3K27me3 at FLC (20-22). A series of FLC antisense transcripts (COOLAIR) contribute to these repression pathways (18,(23)(24)(25)(26) Opposing H3K36me3 and H3K27me3 states are particularly ...

Section: Resultsmentioning

confidence: 49%

mentioning

confidence: 99%

Physical coupling of activation and derepression activities to maintain an active transcriptional state at FLC

Yang

Howard

Dean

2016

“…Gene categories were defined by using published microarray and SAGE datasets that profiled specific tissues or whole worms that contained or lacked a germ line, as described (3,48). Ubiquitous genes (1,895 genes) are genes that are expressed (tag > 0) in all SAGE datasets that profiled germ-line, muscle, neural, and gut tissue, but that are not in the germ-line-enriched category.…”

Section: Methodsmentioning

confidence: 99%

“…Maintaining the proper identity of these cell types is essential for propagation of species, and molecular barriers at both the transcriptional and translational levels have evolved to ensure the germ-soma distinction (1). Removal of these barriers in germ cells can lead to both expression of somatic factors and sterility (2)(3)(4), whereas removal of these barriers in somatic cells is associated with reentry into the cell cycle and cancer (5,6). Despite these barriers, it is unknown whether some cell types can tolerate partial fate switching and perhaps adopt traits of other cell types to benefit the organism.…”

mentioning

confidence: 99%

Reevaluation of whether a soma–to–germ-line transformation extends lifespan in Caenorhabditis elegans

Knutson

Rechtsteiner

Strome

2016

Self Cite

The germ lineage is considered to be immortal. In the quest to extend lifespan, a possible strategy is to drive germ-line traits in somatic cells, to try to confer some of the germ lineage's immortality on the somatic body. Notably, a study in Caenorhabditis elegans suggested that expression of germ-line genes in the somatic cells of long-lived daf-2 mutants confers some of daf-2's long lifespan. Specifically, mRNAs encoding components of C. elegans germ granules (P granules) were up-regulated in daf-2 mutant worms, and knockdown of individual P-granule and other germ-line genes in daf-2 young adults modestly reduced their lifespan. We investigated the contribution of a germ-line program to daf-2's long lifespan and also tested whether other mutants known to express germ-line genes in their somatic cells are long-lived. Our key findings are as follows. (i) We could not detect P-granule proteins in the somatic cells of daf-2 mutants by immunostaining or by expression of a P-granule transgene. (ii) Whole-genome transcript profiling of animals lacking a germ line revealed that germ-line transcripts are not up-regulated in the soma of daf-2 worms compared with the soma of control worms. (iii) Simultaneous removal of multiple P-granule proteins or the entire germ-line program from daf-2 worms did not reduce their lifespan. (iv) Several mutants that robustly express a broad spectrum of germ-line genes in their somatic cells are not long-lived. Together, our findings argue against the hypothesis that acquisition of a germ-cell program in somatic cells increases lifespan and contributes to daf-2's long lifespan.germ line | aging | C. elegans | daf-2 | P granules G erm and soma are the two most fundamentally different cell types found in multicellular organisms (1). Germ cells are totipotent and constitute the only immortal lineage, capable of generating entire new organisms generation after generation, whereas somatic cells differentiate into specialized cell types and are mortal, senescing and dying each generation. Maintaining the proper identity of these cell types is essential for propagation of species, and molecular barriers at both the transcriptional and translational levels have evolved to ensure the germ-soma distinction (1). Removal of these barriers in germ cells can lead to both expression of somatic factors and sterility (2-4), whereas removal of these barriers in somatic cells is associated with reentry into the cell cycle and cancer (5, 6). Despite these barriers, it is unknown whether some cell types can tolerate partial fate switching and perhaps adopt traits of other cell types to benefit the organism.An attractive possibility is that acquisition of a germ-cell program by the somatic body can capture some of the immortality of the germ lineage and extend lifespan (7,8). Indeed, a study in Caenorhabditis elegans supports that possibility (9). In C. elegans, inhibition of the insulin-like signaling pathway by a mutation in daf-2 doubles lifespan through activation of the FOXO transcription factor DAF-16...

“…In Caenorhabditis elegans, spreading of H3K27me3 into adjacent chromatin is prevented by H3K36 methylation (68,69). We therefore asked if methylation of other H3 tail residues affects the distribution of H3K27 methylation in Neurospora.…”

Section: H3k9me3 H3k27me3mentioning

confidence: 99%

Genome-wide redistribution of H3K27me3 is linked to genotoxic stress and defective growth

Basenko

Sasaki

et al. 2015

H3K9 methylation directs heterochromatin formation by recruiting multiple heterochromatin protein 1 (HP1)-containing complexes that deacetylate histones and methylate cytosine bases in DNA. In Neurospora crassa, a single H3K9 methyltransferase complex, called the DIM-5,-7,-9, CUL4, DDB1 Complex (DCDC), is required for normal growth and development. DCDC-deficient mutants are hypersensitive to the genotoxic agent methyl methanesulfonate (MMS), but the molecular basis of genotoxic stress is unclear. We found that both the MMS sensitivity and growth phenotypes of DCDC-deficient strains are suppressed by mutation of embryonic ectoderm development or Su-(var)3-9; E(z); Trithorax (set)-7, encoding components of the H3K27 methyltransferase Polycomb repressive complex-2 (PRC2). Trimethylated histone H3K27 (H3K27me3) undergoes genome-wide redistribution to constitutive heterochromatin in DCDC- or HP1-deficient mutants, and introduction of an H3K27 missense mutation is sufficient to rescue phenotypes of DCDC-deficient strains. Accumulation of H3K27me3 in heterochromatin does not compensate for silencing; rather, strains deficient for both DCDC and PRC2 exhibit synthetic sensitivity to the topoisomerase I inhibitor Camptothecin and accumulate γH2A at heterochromatin. Together, these data suggest that PRC2 modulates the response to genotoxic stress.