Herein, we report on the preparation, purification, and preliminary characterization of multicolor fluorescent carbon nanoparticles (CNPs) obtained from the combustion soot of candles. The CNPs are small (< 2 nm) and water soluble. Different CNPs fluoresce with different colors under a single-wavelength UV excitation.Carbon-based nanomaterials, which include carbon nanotubes, fullerenes, and nanofibers, have promising applications in nanotechnology, biosensing, and drug delivery. [1][2][3] Recently, CNPs-a new class of carbon-based nanomaterials with interesting photoluminescence properties-were isolated. [4][5][6][7][8][9][10] These nanoparticles are either nanodiamonds or materials derived from carbon nanotubes and the laser ablation of graphite. Unlike fluorescent semiconductor nanocrystals (so-called quantum dots or Qdots), the fluorescent CNPs have only been poorly studied up to now because of the lack of preparative methods and separation techniques. Herein, we report a method for efficiently preparing and isolating fluorescent CNPs from a common carbon source, namely, candle soot.Our approach includes: 1) The preparation of fluorescent CNPs from the combustion soot of candles by means of an oxidative acid treatment and 2) the purification of the fluorescent CNPs by using polyacrylamide gel electrophoresis (PAGE). Incomplete combustion produces CNPs with diameters of 20-800 nm. [11,12] These particles strongly interact with each other to form agglomerates of several micrometers. To break down such inherent interactions and produce welldispersed, individual CNPs, we adopted an oxidative acid treatment, which is commonly used for the purification of carbon nanotubes.[13] This method is known to introduce OH and CO 2 H groups to the CNP surfaces, [14] thus making the particles become negatively charged and hydrophilic.The candle soot was collected by sitting a glass plate on top of smoldering candles. The soot contained mainly elemental carbon (elemental analysis: C 91.69 %, H 1.75 %, N 0.12 %, O (calculated) 4.36 %) and was hydrophobic and insoluble in common solvents. After refluxing the candle soot with 5 m HNO 3 , it turned into a homogeneous, black aqueous suspension. Upon centrifugation, the suspension separated into a black carbon precipitate and a light-brown supernatant, which exhibited yellow fluorescence when irradiated with UV light (312 nm). The black precipitate also contained fluorescent material (even after washing it several times). For maximum recovery of this fluorescent material, both the supernatant and the precipitate were neutralized and then extensively dialyzed against water. The neutralized candle soot exhibited an excellent dispersibility in water, which lasted several months.The same procedure failed to generate visible fluorescence if an oxidant, such as HNO 3 , was not present (this happened both in the presence and in the absence of surfactants, SDS). Another oxidant (30 % H 2 O 2 /AcOH = 2:1) resulted in blue fluorescence. The oxidative acid treatment might have three functions:...

DNA is renowned for its double helix structure and the base pairing that enables the recognition and highly selective binding of complementary DNA strands. These features, and the ability to create DNA strands with any desired sequence of bases, have led to the use of DNA rationally to design various nanostructures and even execute molecular computations. Of the wide range of self-assembled DNA nanostructures reported, most are one- or two-dimensional. Examples of three-dimensional DNA structures include cubes, truncated octahedra, octohedra and tetrahedra, which are all comprised of many different DNA strands with unique sequences. When aiming for large structures, the need to synthesize large numbers (hundreds) of unique DNA strands poses a challenging design problem. Here, we demonstrate a simple solution to this problem: the design of basic DNA building units in such a way that many copies of identical units assemble into larger three-dimensional structures. We test this hierarchical self-assembly concept with DNA molecules that form three-point-star motifs, or tiles. By controlling the flexibility and concentration of the tiles, the one-pot assembly yields tetrahedra, dodecahedra or buckyballs that are tens of nanometres in size and comprised of four, twenty or sixty individual tiles, respectively. We expect that our assembly strategy can be adapted to allow the fabrication of a range of relatively complex three-dimensional structures.

No abstract

Alterations of symbiosis between microbiota and intestinal epithelial cells (IEC) are associated with intestinal and systemic pathologies. Interactions between bacterial products (MAMPs) and Toll-like receptors (TLRs) are known to be mandatory for IEC homeostasis, but how TLRs may time homeostatic functions with circadian changes is unknown. Our functional and molecular dissections of the IEC circadian clock demonstrate that its integrity is required for microbiota-IEC dialog. In IEC, the antiphasic expression of the RORα activator and RevErbα repressor clock output regulators generates a circadian rhythmic TLR expression that converts the temporally arrhythmic microbiota signaling into circadian rhythmic JNK and IKKβ activities, which prevents RevErbα activation by PPARα that would disrupt the circadian clock. Moreover, through activation of AP1 and NF-κB, these activities, together with RORα and RevErbα, enable timing homeostatic functions of numerous genes with IEC circadian events. Interestingly, microbiota signaling deficiencies induce a prediabetic syndrome due to ileal corticosterone overproduction consequent to clock disruption.

The glucocorticoid (GC) receptor (GR), when liganded to GC, activates transcription through direct binding to simple (+)GRE DNA binding sequences (DBS). GC-induced direct repression via GR binding to complex "negative" GREs (nGREs) has been reported. However, GR-mediated transrepression was generally ascribed to indirect "tethered" interaction with other DNA-bound factors. We report that GC-induces direct transrepression via the binding of GR to simple DBS (IR nGREs) unrelated to (+)GRE. These DBS act on agonist-liganded GR, promoting the assembly of cis-acting GR-SMRT/NCoR repressing complexes. IR nGREs are present in over 1000 mouse/human ortholog genes, which are repressed by GC in vivo. Thus variations in the levels of a single ligand can coordinately turn genes on or off depending in their response element DBS, allowing an additional level of regulation in GR signaling. This mechanism suits GR signaling remarkably well, given that adrenal secretion of GC fluctuates in a circadian and stress-related fashion.

The CUL4-DDB1-ROC1 ubiquitin E3 ligase regulates cell-cycle progression, replication and DNA damage response. However, the substrate-specific adaptors of this ligase remain uncharacterized. Here, we show that CUL4-DDB1 complexes interact with multiple WD40-repeat proteins (WDRs) including TLE1-3, WDR5, L2DTL (also known as CDT2) and the Polycomb-group protein EED (also known as ESC). WDR5 and EED are core components of histone methylation complexes that are essential for histone H3 methylation and epigenetic control at K4 or K9 and K27, respectively, whereas L2DTL regulates CDT1 proteolysis after DNA damage through CUL4-DDB1 (ref. 8). We found that CUL4A-DDB1 interacts with H3 methylated mononucleosomes and peptides. Inactivation of either CUL4 or DDB1 impairs these histone modifications. However, loss of WDR5 specifically affects histone H3 methylation at K4 but not CDT1 degradation, whereas inactivation of L2DTL prevents CDT1 degradation but not histone methylation. Our studies suggest that CUL4-DDB1 ligases use WDR proteins as molecular adaptors for substrate recognition, and modulate multiple biological processes through ubiquitin-dependent proteolysis.

Cellular senescence is a tumour suppressor mechanism that is triggered by cancer-initiating or promoting events in mammalian cells. The molecular underpinnings for this stable arrest involve transcriptional repression of proliferation-promoting genes regulated by the retinoblastoma (Rb)/E2F repressor complex. Here, we demonstrate that AGO2, Rb and microRNAs (miRs), as exemplified here by let-7, physically and functionally interact to repress Rb/E2F target genes in senescence, a process that we refer to as senescence-associated transcriptional gene silencing (SA-TGS). Herein, AGO2 acts as the effector protein for miR-let7-directed implementation of silent state chromatin modifications at target promoters and inhibition of the let-7-AGO2 effector complex perturbs the timely execution of senescence. Thus, we identify cellular senescence as the an endogenous signal of miR-AGO2-mediated TGS in human cells. Our results suggest that miR-AGO2-mediated SA-TGS may contribute to tumour suppression by stably repressing proliferation-promoting genes in pre-malignant cancer cells.

Herein, we report on the preparation, purification, and preliminary characterization of multicolor fluorescent carbon nanoparticles (CNPs) obtained from the combustion soot of candles. The CNPs are small (< 2 nm) and water soluble. Different CNPs fluoresce with different colors under a single-wavelength UV excitation.Carbon-based nanomaterials, which include carbon nanotubes, fullerenes, and nanofibers, have promising applications in nanotechnology, biosensing, and drug delivery. [1][2][3] Recently, CNPs-a new class of carbon-based nanomaterials with interesting photoluminescence properties-were isolated. [4][5][6][7][8][9][10] These nanoparticles are either nanodiamonds or materials derived from carbon nanotubes and the laser ablation of graphite. Unlike fluorescent semiconductor nanocrystals (so-called quantum dots or Qdots), the fluorescent CNPs have only been poorly studied up to now because of the lack of preparative methods and separation techniques. Herein, we report a method for efficiently preparing and isolating fluorescent CNPs from a common carbon source, namely, candle soot.Our approach includes: 1) The preparation of fluorescent CNPs from the combustion soot of candles by means of an oxidative acid treatment and 2) the purification of the fluorescent CNPs by using polyacrylamide gel electrophoresis (PAGE). Incomplete combustion produces CNPs with diameters of 20-800 nm. [11,12] These particles strongly interact with each other to form agglomerates of several micrometers. To break down such inherent interactions and produce welldispersed, individual CNPs, we adopted an oxidative acid treatment, which is commonly used for the purification of carbon nanotubes.[13] This method is known to introduce OH and CO 2 H groups to the CNP surfaces, [14] thus making the particles become negatively charged and hydrophilic.The candle soot was collected by sitting a glass plate on top of smoldering candles. The soot contained mainly elemental carbon (elemental analysis: C 91.69 %, H 1.75 %, N 0.12 %, O (calculated) 4.36 %) and was hydrophobic and insoluble in common solvents. After refluxing the candle soot with 5 m HNO 3 , it turned into a homogeneous, black aqueous suspension. Upon centrifugation, the suspension separated into a black carbon precipitate and a light-brown supernatant, which exhibited yellow fluorescence when irradiated with UV light (312 nm). The black precipitate also contained fluorescent material (even after washing it several times). For maximum recovery of this fluorescent material, both the supernatant and the precipitate were neutralized and then extensively dialyzed against water. The neutralized candle soot exhibited an excellent dispersibility in water, which lasted several months.The same procedure failed to generate visible fluorescence if an oxidant, such as HNO 3 , was not present (this happened both in the presence and in the absence of surfactants, SDS). Another oxidant (30 % H 2 O 2 /AcOH = 2:1) resulted in blue fluorescence. The oxidative acid treatment might have three functions:...