Mapping separase-mediated cleavage in situ.

Separase is a protease that performs critical functions in the maintenance of genetic homeostasis. Among them, the cleavage of the meiotic cohesin during meiosis is a key step in producing gametes in eukaryotes. However, the exact chromosomal localization of this proteolytic cleavage was not addressed due to the lack of experimental tools. To this end, we developed a method based on monoclonal antibodies capable of recognizing the predicted neo-epitopes produced by separase-mediated proteolysis in the RAD21 and REC8 cohesin subunits. To validate the epigenomic strategy of mapping cohesin proteolysis, anti-RAD21 neo-epitopes antibodies were used in ChIP-On-ChEPseq analysis of human cells undergoing mitotic anaphase. Second, a similar analysis applied for mapping of REC8 cleavage in germline cells in Macaque showed a correlation with a subset of alpha-satellites and other repeats, directly demonstrating that the site-specific mei-cohesin proteolysis hotspots are coincident but not identical with centromeres. The sequences for the corresponding immunoglobulin genes show a convergence of antibodies with close specificity. This approach could be potentially used to investigate cohesin ring opening events in other chromosomal locations, if applied to single cells.

Ectopic expression of meiotic cohesin generates chromosome instability in cancer cell line.

Many tumors express meiotic genes that could potentially drive somatic chromosome instability. While germline cohesin subunits SMC1B, STAG3, and REC8 are widely expressed in many cancers, messenger RNA and protein for RAD21L subunit are expressed at very low levels. To elucidate the potential of meiotic cohesins to contribute to genome instability, their expression was investigated in human cell lines, predominately in DLD-1. While the induction of the REC8 complex resulted in a mild mitotic phenotype, the expression of the RAD21L complex produced an arrested but viable cell pool, thus providing a source of DNA damage, mitotic chromosome missegregation, sporadic polyteny, and altered gene expression. We also found that genomic binding profiles of ectopically expressed meiotic cohesin complexes were reminiscent of their corresponding specific binding patterns in testis. Furthermore, meiotic cohesins were found to localize to the same sites as BORIS/CTCFL, rather than CTCF sites normally associated with the somatic cohesin complex. These findings highlight the existence of a germline epigenomic memory that is conserved in cells that normally do not express meiotic genes. Our results reveal a mechanism of action by unduly expressed meiotic cohesins that potentially links them to aneuploidy and chromosomal mutations in affected cells.

Bifunctional ultraviolet/ultrasound responsive composite TiO2/polyelectrolyte microcapsules.

Designing and fabricating multifunctional microcapsules are of considerable interest in both academic and industrial research aspects. This work reports an innovative approach to fabricate composite capsules with high UV and ultrasound responsive functionalities that can be used as external triggers for controlled release, yet with enhanced mechanical strength that can make them survive in a harsh environment. Needle-like TiO2 nanoparticles (NPs) were produced in situ into layer-by-layer (LbL) polyelectrolyte (PE) shells through the hydrolysis of titanium butoxide (TIBO). These rigid TiO2 NPs yielded the formed capsules with excellent mechanical strength, showing a free standing structure. A possible mechanism is proposed for the special morphology formation of the TiO2 NPs and their reinforcing effects. Synergistically, their response to UV and ultrasound was visualized via SEM, with the results showing an irreversible shell rapture upon exposure to either UV or ultrasound irradiation. As expected, the release studies revealed that the dextran release from the TiO2/PE capsules was both UV-dependent and ultrasound-dependent. Besides, the biocompatibility of the capsules with the incorporation of amorphous TiO2 NPs was confirmed by an MTT assay experiment. All these pieces of evidence suggested a considerable potential medicinal application of TiO2/PE capsules for controlled drug delivery.

Preparation, characterization and photocatalytic activities of boron- and cerium-codoped TiO2.

Boron- and cerium-codoped TiO2 photocatalysts were synthesized using modified sol-gel reaction process and characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), particle size distribution (PSD), diffuse reflectance spectra (DRS), and Brunauer-Emmett-Teller (BET). The photocatalytic activities were evaluated by monitoring the degradation of dye Acid Red B (ARB). The results showed that the prepared photocatalysts were mixed oxides mainly consisting of titania, ceria, and boron oxide. The structure of TiO2 could be transformed from amorphous to anatase and then to rutile by increasing calcination temperature; the transformation being accompanied by the growth of particle size without any obvious change in phase structure of CeO2. The XPS of B(1.6)Ce(1.0)-TiO2 prepared at 500 degrees C showed that a few boron atoms were incorporated into titania and ceria lattice, whereas others existed as B2O3. Cerium ions existed in two states, Ce3+ and Ce4+, and the atomic ratio of Ce3+/Ce4+ was 1.86. When boron and cerium were doped, the UV-Vis adsorption band wavelength showed an obvious shift toward the visible range (< or =526 nm). As the atomic ratio of Ce/Ti increased to 1.0, the absorbance edge wavelength increased to 481 nm. The absorbance edge wavelength decreased for higher cerium doping levels (Ce/Ti = 2.0). The particles size ranged from 122 to 255 nm with a domain at 168 nm (39.4%). The degradation of ARB dye indicated that the photocatalytic activities of boron- and cerium-codoped TiO2 were much higher than those of P25 (a standard TiO2 powder). The activities increased as the boron doping increased, whereas decreased when the Ce/Ti atomic ratio was greater than 0.5. The optimum atomic ratio of B/Ti and Ce/Ti was 1.6 and 0.5, respectively.

[Preparation and photocatalytic activity of boron doped CeO2/TiO2 mixed oxides].

Boron doped CeO2/TiO2 mixed oxides photocatalysts were prepared by adding boric acid and cerous nitrate during the hydrolyzation of titanium trichloride and tetrabutyl titanate. XRD, UV-Vis DRS and XPS techniques were used to characterize the crystalline structure, light absorbing ability and the chemical state of Boron element in the photocatalyst sample. The photocatalytic activities were evaluated by monitoring the degradation of acid red B under UV irradiation. These results indicate that the wavelengths at adsorbing edge are affected by the content of cerous nitrate and the maximum absorption wavelength is about 481 nm when the mole ratio of Ce/Ti is 1.0. For higher dosage of Cerium, the absorbance edge shifts to blue slightly. The prepared photocatalyst is composed of anatase TiO2 and cubic CeO2 when calcined at 500 degrees C. An increase in the calcination temperature transforms the crystalline structure of the titanium oxides from anatase to rutile, and has no obvious influence on crystalline structure of CeO2 but crystallites growth up. The absorbance edge decreases drastically with the increase of calcination temperature. With a view to the stability of photocatalyst and utilization of sun energy, 500 degrees C of calcination temperature is recommended. The XP spectrum for B1s exhibits that only a few boron ions dope into titania and ceria matrix, others exist in B2O3. The photocatalytic activity increases with increase of cerous nitrate dosage, and decreases drastically due to higher dosage (the mol ratio of Ce/Ti > 0.5). After 10 min UV irradiation, 96% of acid red B is degraded completely over photocatalyst under optimum reaction condition.