Genome Maintenance Mechanisms at the Chromatin Level

Diurnal control of H3K27me1 deposition shapes expression of a subset of cell cycle and DNA damage response genes

Rhythmic oscillation of biological processes helps organisms adapt their physiological responses to the most appropriate time of the day. Chromatin remodeling has been described as one of the molecular mechanisms controlling these oscillations. The importance of these changes in transcriptional activation as well as in the maintenance of heterochromatic regions has been widely demonstrated. However, little is still known on how diurnal changes can impact the global status of chromatin modifications and, hence, control gene expression. In plants, the repressive mark H3K27me1, deposited by ARABIDOPSIS TRITHORAX-RELATED PROTEIN 5 and 6 (ATXR5 and 6) methyltransferases, is largely associated with transposable elements but also covers lowly expressed genes. Here we show that this histone modification is preferentially deposited during the night. In euchromatic regions, it is found along the bodies of DNA damage response genes (DDR), where it is needed for their proper expression. The absence of H3K27me1 translates into an enhanced expression of DDR genes that follows a rhythmic oscillation pattern. This evidences a link between chromatin modifications and their synchronization with the diurnal cycle in order to accurately modulate the activation of biological processes to the most appropriate time of the day.

Boron: An intriguing factor in retarding Alzheimer's progression

Alzheimer's disease (AD) is a neurodegenerative disorder that is the fifth most common cause of mortality worldwide and the second most common cause of death in developed countries. The etiology of AD remains poorly understood; however, it is correlated with the accumulation of proteins in the brain, ultimately leading to cellular damage. Multiple factors, including genetic and environmental factors such as chemicals or food, have been linked to protein aggregation and cell death in AD. Boron is a vital micronutrient that is necessary for plant growth and is abundantly present in various fruits and nuts. Prior research has emphasized the importance of boron as a neuroprotective agent and necessary component for the preservation of brain health and function. However, the precise function of boron in the brain remains poorly understood. This review elucidates the molecular role of boron in the brain by examining existing information about its impact on neurodegenerative diseases and may provide a deeper understanding of the etiology of AD and, ultimately, lead to the development of novel approaches for its treatment.

At the Nexus between Cytoskeleton and Vacuole: How Plant Cytoskeletons Govern the Dynamics of Large Vacuoles

Large vacuoles are a predominant cell organelle throughout the plant body. They maximally account for over 90% of cell volume and generate turgor pressure that acts as a driving force of cell growth, which is essential for plant development. The plant vacuole also acts as a reservoir for sequestering waste products and apoptotic enzymes, thereby enabling plants to rapidly respond to fluctuating environments. Vacuoles undergo dynamic transformation through repeated enlargement, fusion, fragmentation, invagination, and constriction, eventually resulting in the typical 3-dimensional complex structure in each cell type. Previous studies have indicated that such dynamic transformations of plant vacuoles are governed by the plant cytoskeletons, which consist of F-actin and microtubules. However, the molecular mechanism of cytoskeleton-mediated vacuolar modifications remains largely unclear. Here we first review the behavior of cytoskeletons and vacuoles during plant development and in response to environmental stresses, and then introduce candidates that potentially play pivotal roles in the vacuole-cytoskeleton nexus. Finally, we discuss factors hampering the advances in this research field and their possible solutions using the currently available cutting-edge technologies.

DNA Damage Induction Alters the Expression of Ubiquitin and SUMO Regulators in Preimplantation Stage Pig Embryos

DNA damage in early-stage embryos impacts development and is a risk factor for segregation of altered genomes. DNA damage response (DDR) encompasses a sophisticated network of proteins involved in sensing, signaling, and repairing damage. DDR is regulated by reversible post-translational modifications including acetylation, methylation, phosphorylation, ubiquitylation, and SUMOylation. While important regulators of these processes have been characterized in somatic cells, their roles in early-stage embryos remain broadly unknown. The objective of this study was to explore how ubiquitylation and SUMOylation are involved in the regulation of early development in porcine embryos by assessing the mRNA profile of genes encoding ubiquitination (UBs), deubiquitination (DUBs), SUMOylation (SUMOs) or deSUMOylation (deSUMOs) enzymes in oocyte and embryos at different stages of development, and to evaluate if the induction of DNA damage at different stages of embryo development would alter the mRNA abundance of these genes. Pig embryos were produced by in vitro fertilization and DNA damage was induced by ultraviolet (UV) light exposure for 10 s on days 2, 4 or 7 of development. The relative mRNA abundance of most UBs, DUBs, SUMOs, and deSUMOs was higher in oocytes and early-stage embryos than in blastocysts. Transcript levels for UBs (RNF20, RNF40, RNF114, RNF169, CUL5, DCAF2, DECAF13, and DDB1), DUBs (USP16), and SUMOs (CBX4, UBA2 and UBC9), were upregulated in early-stage embryos (D2 and/or D4) compared to oocytes and blastocysts. In response to UV-induced DNA damage, transcript levels of several UBs, DUBs, SUMOs, and deSUMOs decreased in D2 and D4 embryos, but increased in blastocysts. These findings revealed that transcript levels of genes encoding for important UBs, DUBs, SUMOs, and deSUMOs are regulated during early embryo development and are modulated in response to induced DNA damage. This study has also identified candidate genes controlling post-translational modifications that may have relevant roles in the regulation of normal embryo development, repair of damaged DNA, and preservation of genome stability in the pig embryo.

GIP1 and GIP2 Contribute to the Maintenance of Genome Stability at the Nuclear Periphery

The maintenance of genetic information is important in eukaryotes notably through mechanisms occurring at the nuclear periphery where inner nuclear membrane proteins and nuclear pore-associated components are key factors regulating the DNA damage response (DDR). However, this aspect of DDR regulation is still poorly documented in plants. We addressed here how genomic stability is impaired in the gamma-tubulin complex component 3-interacting protein (gip1gip2) double mutants showing defective nuclear shaping. Using neutral comet assays for DNA double-strand breaks (DSBs) detection, we showed that GIP1 and GIP2 act redundantly to maintain genome stability. At the cellular level, γ-H2AX foci in gip1gip2 were more abundant and heterogeneous in their size compared to wild-type (WT) in root meristematic nuclei, indicative of constitutive DNA damage. This was linked to a constitutive activation of the DDR in the gip1gip2 mutant, with more emphasis on the homologous recombination (HR) repair pathway. In addition, we noticed the presence of numerous RAD51 foci which did not colocalize with γ-H2AX foci. The expression of GIP1-GFP in the double mutant rescued the cellular response to DNA damage, leading to the systematic colocalization of RAD51 and γ-H2AX foci. Interestingly, a significant proportion of RAD51 foci colocalized with GIP1-GFP at the nuclear periphery. Altogether, our data suggest that GIPs may partly contribute to the spatio-temporal recruitment of RAD51 at the nuclear periphery.