Competition shapes the landscape of X-chromosome-linked genetic diversity.

X chromosome inactivation (XCI) generates clonal heterogeneity within XX individuals. Combined with sequence variation between human X chromosomes, XCI gives rise to intra-individual clonal diversity, whereby two sets of clones express mutually exclusive sequence variants present on one or the other X chromosome. Here we ask whether such clones merely co-exist or potentially interact with each other to modulate the contribution of X-linked diversity to organismal development. Focusing on X-linked coding variation in the human STAG2 gene, we show that Stag2variant clones contribute to most tissues at the expected frequencies but fail to form lymphocytes in Stag2WT Stag2variant mouse models. Unexpectedly, the absence of Stag2variant clones from the lymphoid compartment is due not solely to cell-intrinsic defects but requires continuous competition by Stag2WT clones. These findings show that interactions between epigenetically diverse clones can operate in an XX individual to shape the contribution of X-linked genetic diversity in a cell-type-specific manner.

Structural basis of centromeric cohesion protection.

In the early stages of mitosis, cohesin is released from chromosome arms but not from centromeres. The protection of centromeric cohesin by SGO1 maintains the sister chromatid cohesion that resists the pulling forces of microtubules until all chromosomes are attached in a bipolar manner to the mitotic spindle. Here we present the X-ray crystal structure of a segment of human SGO1 bound to a conserved surface of the cohesin complex. SGO1 binds to a composite interface formed by the SA2 and SCC1RAD21 subunits of cohesin. SGO1 shares this binding interface with CTCF, indicating that these distinct chromosomal regulators control cohesin through a universal principle. This interaction is essential for the localization of SGO1 to centromeres and protects centromeric cohesin against WAPL-mediated cohesin release. SGO1-cohesin binding is maintained until the formation of microtubule-kinetochore attachments and is required for faithful chromosome segregation and the maintenance of a stable karyotype.

Discovery of MurA Inhibitors as Novel Antimicrobials through an Integrated Computational and Experimental Approach.

The bacterial cell wall is essential for protecting bacteria from the surrounding environment and maintaining the integrity of bacteria cells. The MurA enzyme, which is an essential enzyme involved in bacterial cell wall synthesis, could be a good drug target for antibiotics. Although fosfomycin is used clinically as a MurA inhibitor, resistance to this antibiotic is a concern. Here we used molecular docking-based virtual screening approaches to identify potential MurA inhibitors from 1.412 million compounds from three databases. Thirty-three top compounds from virtual screening were experimentally tested in Listeria innocua (Gram-positive bacterium) and Escherichia coli (Gram-negative bacterium). Compound 2-Amino-5-bromobenzimidazole (S17) showed growth inhibition effect in both L. innocua and E. coli, with the same Minimum Inhibitory Concentration (MIC) value of 0.5 mg/mL. Compound 2-[4-(dimethylamino)benzylidene]-n-nitrohydrazinecarboximidamide (C1) had growth inhibition effect only in L. innocua, with a MIC value of 0.5 mg/mL. Two FDA-approved drugs, albendazole (S4) and diflunisal (S8), had a growth inhibition effect only in E. coli, with a MIC value of 0.0625 mg/mL. The identified MurA inhibitors could be potential novel antibiotics. Furthermore, they could be potential fosfomycin substitutes for the fosfomycin-resistant strains.

Deactivation-free ethanol steam reforming at nickel-tipped carbon filaments.

Ni based catalysts have been widely studied for H2 production due to the ability of Ni to break C-C and C-H bonds. In this work, we study inverse catalysts prepared by well-controlled sub-monolayer deposition of CeO2 nanocubes onto Ni thin films for ethanol steam reforming (ESR). Results show that controlling the coverage of CeO2 nanocubes on Ni enhances H2 production by more than an order of magnitude compared to pure Ni. Contrary to the idea that C deposits must be continuously oxidized for sustained H2 production, the surface of the most active catalysts show significant C deposition, yet no deactivation is observed. HAADF-STEM analysis reveals the formation of carbon filaments (CFILs), which propel Ni particles upward at the filament tips via a catalytic tip growth mechanism, resulting in a Ni@CFIL active phase for ESR. Near-ambient pressure XPS indicates that the Ni@CFIL active phase forms as a result of C gradients at the interface between regions of pure Ni metal and domains of closely packed CeO2 nanocubes. These results show that the mesoscale morphology of deposited CeO2 nanocubes is responsible for templating the formation of a Ni@CFIL catalyst, which resists deactivation leading to highly active and stable H2 production from ethanol.

Ni-Catalyzed Reductive Cyanation of Aryl Halides and Phenol Derivatives via Transnitrilation.

Herein, we report a Ni-catalyzed reductive coupling for the synthesis of benzonitriles from aryl (pseudo)halides and an electrophilic cyanating reagent, 2-methyl-2-phenyl malononitrile (MPMN). MPMN is a bench-stable, carbon-bound electrophilic CN reagent that does not release cyanide under the reaction conditions. A variety of medicinally relevant benzonitriles can be made in good yields. Addition of NaBr to the reaction mixture allows for the use of more challenging aryl electrophiles such as aryl chlorides, tosylates, and triflates. Mechanistic investigations suggest that NaBr plays a role in facilitating oxidative addition with these substrates.

The p38α Stress Kinase Suppresses Aneuploidy Tolerance by Inhibiting Hif-1α.

Deviating from the normal karyotype dramatically changes gene dosage, in turn decreasing the robustness of biological networks. Consequently, aneuploidy is poorly tolerated by normal somatic cells and acts as a barrier to transformation. Paradoxically, however, karyotype heterogeneity drives tumor evolution and the emergence of therapeutic drug resistance. To better understand how cancer cells tolerate aneuploidy, we focused on the p38 stress response kinase. We show here that p38-deficient cells upregulate glycolysis and avoid post-mitotic apoptosis, leading to the emergence of aneuploid subclones. We also show that p38 deficiency upregulates the hypoxia-inducible transcription factor Hif-1α and that inhibiting Hif-1α restores apoptosis in p38-deficent cells. Because hypoxia and aneuploidy are both barriers to tumor progression, the ability of Hif-1α to promote cell survival following chromosome missegregation raises the possibility that aneuploidy tolerance coevolves with adaptation to hypoxia.