[Reciprocity between active transcription and histone methylation]

Comprehensive analysis of nonsurrounded nucleolus and surrounded nucleolus oocytes on chromatin accessibility using ATAC-seq

Mouse germinal vesicle (GV) oocytes are divided into surrounded nucleolus (SN) and nonsurrounded nucleolus (NSN) oocytes based on chromatin morphology. NSN oocytes spontaneously transform into SN oocytes after accumulating enough maternal transcripts. SN oocytes show transcriptional silencing. When oocyte maturation is abnormal or takes place in vitro, NSN oocytes do not go through SN stage before proceeding to MII. Nontransitive oocytes show developmental retardation, a low fertilization rate, and arrest at the two-cell embryo stage in mice. Here, chromatin-binding ribonucleic acid polymerase II (RNAP II) activity, newly synthesized RNA, and chromatin accessibility in GV oocytes were examined. In SN oocytes, RNAP II did not bind to DNA, neo-RNA was not generated in nuclei, and the phosphorylation state of RNAP II did not affect the chromatin-binding activity. The number of accessible genes in SN oocytes was remarkably lower than that in NSN oocytes. The accessibility of different functional genes was also different between the two types of oocytes. Thus, low chromatin accessibility leads to transcriptional silencing in SN oocytes.

Arabidopsis SDG8 Potentiates the Sustainable Transcriptional Induction of the Pathogenesis-Related Genes PR1 and PR2 During Plant Defense Response

Post-translational covalent modifications of histones play important roles in modulating chromatin structure and are involved in the control of multiple developmental processes in plants. Here we provide insight into the contribution of the histone lysine methyltransferase SET DOMAIN GROUP 8 (SDG8), implicated in histone H3 lysine 36 trimethylation (H3K36me3), in connection with RNA polymerase II (RNAPII) to enhance Arabidopsis immunity. We showed that even if the sdg8-1 loss-of-function mutant, defective in H3K36 methylation, displayed a higher sensitivity to different strains of the bacterial pathogen Pseudomonas syringae, effector-triggered immunity (ETI) still operated, but less efficiently than in the wild-type (WT) plants. In sdg8-1, the level of the plant defense hormone salicylic acid (SA) was abnormally high under resting conditions and was accumulated similarly to WT at the early stage of pathogen infection but quickly dropped down at later stages. Concomitantly, the transcription of several defense-related genes along the SA signaling pathway was inefficiently induced in the mutant. Remarkably, albeit the defense genes PATHOGENESIS-RELATED1 (PR1) and PR2 have retained responsiveness to exogenous SA, their inductions fade more rapidly in sdg8-1 than in WT. At chromatin, while global levels of histone methylations were found to be stable, local increases of H3K4 and H3K36 methylations as well as RNAPII loading were observed at some defense genes following SA-treatments in WT. In sdg8-1, the H3K36me3 increase was largely attenuated and also the increases of H3K4me3 and RNAPII were frequently compromised. Lastly, we demonstrated that SDG8 could physically interact with the RNAPII C-terminal Domain, providing a possible link between RNAPII loading and H3K36me3 deposition. Collectively, our results indicate that SDG8, through its histone methyltransferase activity and its physical coupling with RNAPII, participates in the strong transcriptional induction of some defense-related genes, in particular PR1 and PR2, to potentiate sustainable immunity during plant defense response to bacterial pathogen.

Epigenetics and bone diseases

Owing to the development of new technologies, the epigenome, a second dimensional method for genome analysis has emerged. Epigenetic mechanisms, including DNA methylation, histone modifications and noncoding RNAs, regulate gene expression without changing the genetic sequence. These epigenetic mechanisms normally modulate gene expression, trans-generational effects and inherited expression states in various biological processes. Abnormal epigenetic patterns typically cause pathological conditions, including cancers, age-related diseases, and specific cartilage and bone diseases. Facing the rapidly developing epigenetic field, we reviewed epigenetic mechanisms and their involvement with the skeletal system and their role in skeletal development, homeostasis and degeneration. Finally, we discuss the prospects for the future of epigenetics.