Over the past years, a large number of histone posttranslational modifications have been described, some of which function to attain a repressed chromatin structure, while others facilitate activation by allowing access of regulators to DNA. Histone H2B monoubiquitination is a mark associated with transcriptional activity. Using a highly reconstituted chromatin-transcription system incorporating the inducible RARbeta2 promoter, we find that the establishment of H2B monoubiquitination by RNF20/40 and UbcH6 is dependent on the transcription elongation regulator complex PAF, the histone chaperone FACT, and transcription. H2B monoubiquitination facilitates FACT function, thereby stimulating transcript elongation and the generation of longer transcripts. These in vitro analyses and corroborating in vivo experiments demonstrate that elongation by RNA polymerase II through the nucleosomal barrier is minimally dependent upon (1) FACT and (2) the recruitment of PAF and the H2B monoubiquitination machinery.

Designed oligonucleotides can self-assemble into DNA nanostructures with well-defined structures and uniform sizes, which provide unprecedented opportunities for biosensing, molecular imaging, and drug delivery. In this work, we have developed functional, multivalent DNA nanostructures by appending unmethylated CpG motifs to three-dimensional DNA tetrahedra. These small-sized functional nanostructures are compact, mechanically stable, and noncytotoxic. We have demonstrated that DNA nanostructures are resistant to nuclease degradation and remain substantially intact in fetal bovine serum and in cells for at least several hours. Significantly, these functional nanostructures can noninvasively and efficiently enter macrophage-like RAW264.7 cells without the aid of transfection agents. After they are uptaken by cells, CpG motifs are recognized by the Toll-like receptor 9 (TLR9) that activates downstream pathways to induce immunostimulatory effects, producing high-level secretion of various pro-inflammatory cytokines including tumor necrosis factor (TNF)-α, interleukin (IL)-6, and IL-12. We also show that multivalent CpG motifs greatly enhance the immunostimulatory effect of the nanostructures. Given the high efficacy of these functional nanostructures and their noncytotoxic nature, we expect that DNA nanostructures will become a promising tool for targeted drug delivery.

H3K27 methylation mediated by the histone methyltransferase complex PRC2 is critical for transcriptional regulation, Polycomb silencing, Drosophila segmentation, mammalian X chromosome inactivation, and cancer. PRC2-mediated H3K27 methylation can spread along the chromatin and propagate the repressive chromatin environment; thus, chromatin components that antagonize the activity of PRC2 are important for restraining Polycomb silencing. Here we report that in HeLa cells, H3 histones unmethylated at Lys-36 are mostly methylated at Lys-27, with the exception of newly synthesized H3. In addition, K27me3 rarely co-exists with K36me2 or K36me3 on the same histone H3 polypeptide. Moreover, PRC2 activity is greatly inhibited on nucleosomal substrates with preinstalled H3K36 methylation. These findings collectively identify H3K36 methylation as a chromatin component that restricts the PRC2-mediated spread of H3K27 methylation. Finally, we provide evidence that the controversial histone lysine methyltransferase Ash1, a known Trithorax group protein that antagonizes Polycomb silencing in vivo, is an H3K36-specific dimethylase, not an H3K4 methylase, further supporting the role of H3K36 methylation in antagonizing PRC2-mediated H3K27 methylation.

Mutations in triggering receptor expressed on myeloid cells 2 (TREM2) have been linked to increased Alzheimer's disease (AD) risk. Neurobiological functions of TREM2 and its pathophysiological ligands remain elusive. Here we found that TREM2 directly binds to β-amyloid (Aβ) oligomers with nanomolar affinity, whereas AD-associated TREM2 mutations reduce Aβ binding. TREM2 deficiency impairs Aβ degradation in primary microglial culture and mouse brain. Aβ-induced microglial depolarization, K inward current induction, cytokine expression and secretion, migration, proliferation, apoptosis, and morphological changes are dependent on TREM2. In addition, TREM2 interaction with its signaling adaptor DAP12 is enhanced by Aβ, regulating downstream phosphorylation of SYK and GSK3β. Our data demonstrate TREM2 as a microglial Aβ receptor transducing physiological and AD-related pathological effects associated with Aβ.