Chromatin regulation by Histone H4 acetylation at Lysine 16 during cell death and differentiation in the myeloid compartment

Histone H4 acetylation at Lysine 16 (H4K16ac) is a key epigenetic mark involved in gene regulation, DNA repair and chromatin remodeling, and though it is known to be essential for embryonic development, its role during adult life is still poorly understood. Here we show that this lysine is massively hyperacetylated in peripheral neutrophils. Genome-wide mapping of H4K16ac in terminally differentiated blood cells, along with functional experiments, supported a role for this histone post-translational modification in the regulation of cell differentiation and apoptosis in the hematopoietic system. Furthermore, in neutrophils, H4K16ac was enriched at specific DNA repeats. These DNA regions presented an accessible chromatin conformation and were associated with the cleavage sites that generate the 50 kb DNA fragments during the first stages of programmed cell death. Our results thus suggest that H4K16ac plays a dual role in myeloid cells as it not only regulates differentiation and apoptosis, but it also exhibits a non-canonical structural role in poising chromatin for cleavage at an early stage of neutrophil cell death

Is the interplay between epigenetic markers related to the acclimation of Cork oak plants to high temperatures?

Trees necessarily experience changes in temperature, requiring efficient short-term strategies that become crucial in environmental change adaptability. DNA methylation and histone posttranslational modifications have been shown to play a key role in both epigenetic control and plant functional status under stress by controlling the functional state of chromatin and gene expression. Cork oak (Quercus suber L.) is a key stone of the Mediterranean region, growing at temperatures of 45°C. This species was subjected to a cumulative temperature increase from 25°C to 55°C under laboratory conditions in order to test the hypothesis that epigenetic code is related to heat stress tolerance. Electrolyte leakage increased after 35°C, but all plants survived to 55°C. DNA methylation and acetylated histone H3 (AcH3) levels were monitored by HPCE (high performance capillary electrophoresis), MS-RAPD (methylation-sensitive random-amplified polymorphic DNA) and Protein Gel Blot analysis and the spatial distribution of the modifications was assessed using a confocal microscope. DNA methylation analysed by HPCE revealed an increase at 55°C, while MS-RAPD results pointed to dynamic methylation-demethylation patterns over stress. Protein Gel Blot showed the abundance index of AcH3 decreasing from 25°C to 45°C. The immunohistochemical detection of 5-mC (5-methyl-2'-deoxycytidine) and AcH3 came upon the previous results. These results indicate that epigenetic mechanisms such as DNA methylation and histone H3 acetylation have opposite and particular dynamics that can be crucial for the stepwise establishment of this species into such high stress (55°C), allowing its acclimation and survival. This is the first report that assesses epigenetic regulation in order to investigate heat tolerance in forest trees.This work is supported by FEDER through COMPETE (Programa Operacional Factores de Competitividade) and by the FCT project PTDC/AGR-CFL/ 112996/2009. G. Pinto is hired under the programme Cie ˆncia 2008 (FCT, Portugal), co-funded by the Human Potential Operational Programme (National Strategic Reference Framework 2007–2013) and European Social Fund (EU). FCT supported the fellowship of M.C. Dias (SFRH/BPD/41700/2007). L. Valledor fellow was supported by a Marie Curie Action of the European Union (FP7-PEOPLE-IEF). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.publishe

Global genomic DNA methylation percentages in leaves of cork oak plants exposed to heat stress.

<p>Data are means ± SD. Bars with different letters indicate significant differences between treatments (p<0.05).</p

<i>Quercus suber</i> plants used during the experience.

<p>a) Plants at 25°C; b) Plants after three days at 55°C with clear signals of stress (brown areas, black arrows).</p

Immunodetection of 5-mdC in sections of cork oak leaf in transversal axis using a confocal microscope.

<p>Differential Interference Contrast (DIC) of leaf section at (a) 25°C; (b) 35°C; (c) 45°C; (d) 55°C. 5-mdC labeling: DAPI (blue signals) superposition and 5-mdC (green signals) of leaf section at (e) 25°C; (f) 35°C; (g) 45°C; (h) 55°C.</p

Western blot analysis showing the quantification of AcH3 in leaves of cork oak plants exposed to temperature increase.

<p>Values represent relative abundance index calculated as: AcH3 band intensity/actin band intensity. Data are means ± SD. Bars with different letters indicate significant differences between treatments (p<0.05).</p

MS-RAPD profiles of cork oak leaves exposed to heat stress.

<p>Interpretation of MS-RAPD bands followed the representation of MSAP (methylation sensitive amplified polymorphisms) detected by <i>HpaII</i>/<i>MspI</i> endonuclease digestion according to Valledor et al. (2010). Appearance-disappearance of bands was used to study the variation of methylation between treatment steps (25°C to 35°C, 35°C to 45°C and 45°C to 55°C). Fragment analysis allowed the classification into two categories: <i>de novo</i> methylation and demethylation events.</p

Electrolyte leakage in leaves of cork oak plants exposed to heat stress.

<p>Data are means ± SD. Bars with different letters indicate significant differences between treatments (p<0.05).</p

Sequences of primers used in MS-RAPD protocol.

<p>Sequences of primers used in MS-RAPD protocol.</p