Roles of histone post-translational modifications in meiosis†.

Histone post-translational modifications, such as phosphorylation, methylation, acetylation, and ubiquitination, play vital roles in various chromatin-based cellular processes. Meiosis is crucial for organisms that depend on sexual reproduction to produce haploid gametes, during which chromatin undergoes intricate conformational changes. An increasing body of evidence is clarifying the essential roles of histone post-translational modifications during meiotic divisions. In this review, we concentrate on the post-translational modifications of H2A, H2B, H3, and H4, as well as the linker histone H1, that are required for meiosis, and summarize recent progress in understanding how these modifications influence diverse meiotic events. Finally, challenges and exciting open questions for future research in this field are discussed. Summary Sentence  Diverse histone post-translational modifications exert important effects on the meiotic cell cycle and these "histone codes" in meiosis might lead to the development of novel therapeutic strategies against reproductive diseases.

Per-nucleus crossover covariation is regulated by chromosome organization.

Meiotic crossover (CO) recombination between homologous chromosomes regulates chromosome segregation and promotes genetic diversity. Human females have different CO patterns than males, and some of these features contribute to the high frequency of chromosome segregation errors. In this study, we show that CO covariation is transmitted to progenies without detectable selection in both human males and females. Further investigations show that chromosome pairs with longer axes tend to have stronger axis length covariation and a stronger correlation between axis length and CO number, and the consequence of these two effects would be the stronger CO covariation as observed in females. These findings reveal a previously unsuspected feature for chromosome organization: long chromosome axes are more coordinately regulated than short ones. Additionally, the stronger CO covariation may work with human female-specific CO maturation inefficiency to confer female germlines the ability to adapt to changing environments on evolution.

Meiotic chromosome organization and crossover patterns†.

Meiosis is the foundation of sexual reproduction, and crossover recombination is one hallmark of meiosis. Crossovers establish the physical connections between homolog chromosomes (homologs) for their proper segregation and exchange DNA between homologs to promote genetic diversity in gametes and thus progenies. Aberrant crossover patterns, e.g., absence of the obligatory crossover, are the leading cause of infertility, miscarriage, and congenital disease. Therefore, crossover patterns have to be tightly controlled. During meiosis, loop/axis organized chromosomes provide the structural basis and regulatory machinery for crossover patterning. Accumulating evidence shows that chromosome axis length regulates the numbers and the positions of crossovers. In addition, recent studies suggest that alterations in axis length and the resultant alterations in crossover frequency may contribute to evolutionary adaptation. Here, current advances regarding these issues are reviewed, the possible mechanisms for axis length regulating crossover frequency are discussed, and important issues that need further investigations are suggested.

HDAC6 regulates antibody-dependent intracellular neutralization of viruses via deacetylation of TRIM21.

Tripartite motif-containing protein 21 (TRIM21) is a cytosolic antibody receptor that targets the internalized virus-antibody complex to the proteasome for degradation. However, the precise mechanism regulating TRIM21 activity is unknown. Here we show that TRIM21 is a substrate of histone deacetylase 6 (HDAC6) and that its function is regulated by acetylation. HDAC6 interacts with TRIM21 through its PRYSPRY motif and deacetylates TRIM21 at lysine 385 and lysine 387, thus promoting its homodimerization. Inhibiting HDAC6 activity increases TRIM21 acetylation, and hyperacetylation blocks TRIM21 dimerization and ubiquitination, preventing its binding to the virus-antibody complex and its degradation via the ubiquitin-proteasome pathway. HDAC6 depletion or inhibition increases virus accumulation in cells, indicative of an impaired capacity for antibody-dependent intracellular neutralization of viruses, whereas TRIM21 acetylation-deficient K385/387R mutant rescues HDAC6 depletion-caused ADIN impairment. These findings provide evidence for HDAC6 as a novel regulator of TRIM21-mediated intracellular innate immunity.

Genetic mechanisms of salt stress responses in halophytes.

Abiotic stress is a major threat to plant growth and development, resulting in extensive crop loss worldwide. Plants react to abiotic stresses through physiological, biochemical, molecular, and genetic adaptations that promote survival. Exploring the molecular mechanisms involved in abiotic stress responses across various plant species is essential for improving crop yields in unfavorable environments. Halophytes are characterized as plants that survive to reproduce in soils containing high salt concentrations, and thus act as an ideal model to comprehend complicated genetic and physiological mechanisms of salinity stress tolerance. Plant ecologists classify halophytes into three main groups: euhalophytes, recretohalophytes, and pseudo-halophytes. Recent genetic and molecular research has showed complicated regulatory networks by which halophytes coordinate stress adaptation and tolerance. Furthermore, investigation of natural variations in these stress responses has supplied new perspectives on the evolution of mechanisms that regulate tolerance and adaptation. This review discusses the current understanding of the genetic mechanisms that contribute to salt-stress tolerance among different classes of halophytes.

Embryonic Lethality and Host Immunity of RelA-Deficient Mice Are Mediated by Both Apoptosis and Necroptosis.

In mammalian cells, signaling pathways triggered by TNF can be switched from NF-κB activation to apoptosis and/or necroptosis. The in vivo mechanisms underlying the mutual regulation of these three signaling pathways are poorly understood. In this article, we report that the embryonic lethality of RelA-deficient mice is partially prevented by the deletion of Rip3 or Mlkl, but it is fully rescued by the combined ablation of Fadd and Rip3 or Mlkl or by blocking RIP1 kinase activity (RIP1K45A). RelA-/-Fadd-/-Rip3-/- triple-knockout (TKO) and RelA-/-Rip1K45A/K45A mice displayed bacterial pneumonia leading to death ∼2 wk after birth. Moreover, RelA-/-Rip1K45A/K45A mice, but not TKO mice, developed severe inflammation associated with inflammatory skin lesion. Antibiotic treatment improved bacterial pneumonia, extended the lifespan of TKO and RelA-/-Rip1K45A/K45A mice, and alleviated skin inflammation in RelA-/-Rip1K45A/K45A mice. These results show the mechanisms underlying the in vivo mutual regulation between NF-κB activation and the cell death pathway and provide new insights into this interplay in embryonic development and host immune homeostasis.

RIP1 kinase activity-dependent roles in embryonic development of Fadd-deficient mice.

RIP1 is an essential regulator of TNF-induced signaling complexes mediating NF-κB activation, apoptosis and necroptosis. Loss of Rip1 rescues the embryonic lethality of Fadd or Caspase-8-deficient mice, even though the double knockout mice die shortly after birth like Rip1-deficient mice. Recent studies demonstrated that mice expressing RIP1 kinase-dead mutants developed normally and resisted necroptotic stimuli in vitro and in vivo. However, the impact of RIP1 kinase activity on Fadd-/- embryonic development remains unknown. Here, we engineered two RIP1 kinase inactive mutant mouse lines, a Rip1K45A/K45A mouse line as previously reported and a novel Rip1Δ/Δ mouse line with an altered P-loop in the kinase domain. While RIP1K45A could not rescue the embryonic lethality of Fadd-deficient mice at E11.5, RIP1Δ rescued lethality of Fadd-/- mice at E11.5 and Fadd-/-Rip1Δ/Δ mice eventually died at E16.5 due to excessive death of fetal liver cells and unregulated inflammation. Under necropotosis-inducing conditions, comparing to Rip1K45A/K45A cells, Rip1Δ/Δcells displayed reduced phosphorylation and oligomerization of RIP3 and MLKL, which lead to increased cell viability. Thus, our study provides genetic evidence that different kinase inactive mutations have distinct impacts on the embryogenesis of Fadd-deficient mice, which might attribute to their extents of protection on necroptosis signaling.

MLKL and FADD Are Critical for Suppressing Progressive Lymphoproliferative Disease and Activating the NLRP3 Inflammasome.

MLKL, a key component downstream of RIPK3, is suggested to be a terminal executor of necroptosis. Genetic studies have revealed that Ripk3 ablation rescues embryonic lethality in Fadd- or Caspase-8-deficient mice. Given that RIPK3 has also been implicated in non-necroptotic pathways including apoptosis and inflammatory signaling, it remains unclear whether the lethality in Fadd(-/-) mice is indeed caused by necropotosis. Here, we show that genetic deletion of Mlkl rescues the developmental defect in Fadd-deficient mice and that Fadd(-/-)Mlkl(-/-) mice are viable and fertile. Mlkl(-/-)Fadd(-/-) mice display significantly accelerated lymphoproliferative disease characterized by lymphadenopathy and splenomegaly when compared to Ripk3(-/-)Fadd(-/-) mice. Mlkl(-/-)Fadd(-/-) bone-marrow-derived macrophages and dendritic cells have impaired NLRP3 inflammasome activation associated with defects in ASC speck formation and NF-κB-dependent NLRP3 transcription. Our findings reveal that MLKL and FADD play critical roles in preventing lymphoproliferative disease and activating the NLRP3 inflammasome.

Gambogenic acid inhibits LPS-simulated inflammatory response by suppressing NF-κB and MAPK in macrophages.

Inflammation is a response of body tissues to injury and infection. Compounds that can inhibit inflammation have been shown to have potential therapeutic clinical application. Gambogenic acid (GEA) has potent antitumor and anti-inflammatory activities. Herein, the molecular mechanisms of GEA's anti-inflammatory effect were investigated in lipopolysaccharide (LPS)-stimulated macrophage cells. The results showed that pretreatment with GEA could markedly inhibit interleukin (IL)-1α, IL-1ß, tumor necrosis factor-α, IFN-ß, IL-12b, and IL-23a production in a dose-dependent manner in LPS-induced model. Furthermore, this drug significantly reduced the release of nitric oxide (NO), and impaired the protein level of inducible NO synthase and the cyclooxygenase 2. The finding also showed that the effect of GEA may be related to the suppression of the nuclear factor-κB (NF-κB) and mitogen-activated protein kinase (MAPK) signaling pathway. These results indicate that GEA could suppress LPS-simulated inflammatory response partially by attenuating NO synthesis and NF-κB and MAPK activation, suggesting that it may become a potent therapeutic agent for the treatment of inflammatory diseases.

A novel sgRNA selection system for CRISPR-Cas9 in mammalian cells.

CRISPR-Cas9 mediated genome editing system has been developed as a powerful tool for elucidating the function of genes through genetic engineering in multiple cells and organisms. This system takes advantage of a single guide RNA (sgRNA) to direct the Cas9 endonuclease to a specific DNA site to generate mutant alleles. Since the targeting efficiency of sgRNAs to distinct DNA loci can vary widely, there remains a need for a rapid, simple and efficient sgRNA selection method to overcome this limitation of the CRISPR-Cas9 system. Here we report a novel system to select sgRNA with high efficacy for DNA sequence modification by a luciferase assay. Using this sgRNAs selection system, we further demonstrated successful examples of one sgRNA for generating one gene knockout cell lines where the targeted genes are shown to be functionally defective. This system provides a potential application to optimize the sgRNAs in different species and to generate a powerful CRISPR-Cas9 genome-wide screening system with minimum amounts of sgRNAs.