Loss of Llgl1 in retinal neuroepithelia reveals links between apical domain size, Notch activity and neurogenesis

To gain insights into the cellular mechanisms of neurogenesis, we analyzed retinal neuroepithelia deficient for Llgl1, a protein implicated in apicobasal cell polarity, asymmetric cell division, cell shape and cell cycle exit. We found that vertebrate retinal neuroepithelia deficient for Llgl1 retained overt apicobasal polarity, but had expanded apical domains. Llgl1 retinal progenitors also had increased Notch activity and reduced rates of neurogenesis. Blocking Notch function by depleting Rbpj restored normal neurogenesis. Experimental expansion of the apical domain, through inhibition of Shroom3, also increased Notch activity and reduced neurogenesis. Significantly, in wild-type retina, neurogenic retinal progenitors had smaller apical domains compared with proliferative neuroepithelia. As nuclear position during interkinetic nuclear migration (IKNM) has been previously linked with cell cycle exit, we analyzed this phenomenon in cells depleted of Llgl1. We found that although IKNM was normal, the relationship between nuclear position and neurogenesis was shifted away from the apical surface, consistent with increased pro-proliferative and/or anti-neurogenic signals associated with the apical domain. These data, in conjunction with other findings, suggest that, in retinal neuroepithelia, the size of the apical domain modulates the strength of polarized signals that influence neurogenesis.     

Zinc deficiency exacerbates diabetic down-regulation of Akt expression and function in the testis: essential roles of PTEN, PTP1B and TRB3

Since zinc (Zn) plays an important role in the spermatogenesis and Zn deficiency exacerbated diabetes-induced testicular apoptosis, the present study investigated the effect of Zn deficiency on diabetes-induced testicular Akt-mediated glucose metabolism changes and inflammation. Zn deficiency was induced by chronic treatment of normal and diabetic mice with the Zn chelator N,N,N',N', tetrakis (2-pyridylmethyl) ethylenediaminepentaethylene (TPEN). After diabetes onset induced by streptozotocin, both diabetic and age-matched control mice were given TPEN intraperitoneally for 4 months. Western blotting assay revealed that Akt-mediated glucose metabolism signaling was down-regulated in the diabetic testis and was further decreased in diabetic mice with Zn deficiency, reflected by reduced phosphorylation of both Akt and GSK-3β and increased phosphorylation of glycogen synthase along with a disarrangement of fatty acid metabolism (increased expression of PPAR-α and decreased adenosine-monophosphate-activated protein kinase phosphorylation). Testicular expressions of plasminogen activator inhibitor-1 and intracellular adhesion molecule-1 as inflammatory factors were increased in the TPEN or diabetes-alone group, but not additive in the group of diabetes with Zn deficiency. A mechanistic study showed that Akt negative regulators phosphatase and tensin homology deleted on chromosome 10 (PTEN), protein tyrosine phosphatases 1B and Tribbles 3 all increased in diabetic testis and further increased in the testis of diabetic mice with Zn deficiency. These studies suggest that Zn deficiency significantly exacerbated diabetic down-regulation of Akt expression and function, most likely by up-regulation of Akt negative regulators. Therefore, prevention of Zn deficiency for diabetic patients is important in order to avoid the exacerbation of diabetic inhibition of glucose metabolism in the testis.     

A SERS-based immunoassay with highly increased sensitivity using gold/silver core-shell nanorods

An integrated platform for a very sensitive detection of cocaine based on a refractometric biosensor is demonstrated. The system uses a waveguide grating biosensor functionalized with a cocaine multivalent antigen-carrier protein conjugate. The immunoassay scheme consists of the competitive binding of cocaine-specific antibodies to the immobilized conjugates. A 1000-fold enhancement of the sensor's sensitivity is achieved when using gold conjugated monoclonal antibodies instead of free antibodies. Together with the optimization of the assay conditions, the setup is designed for a quick identification of narcotics using automated sampling. The results show that the presence of cocaine in a liquid sample could be identified down to a concentration of 0.7 nM within one minute. This value can be reduced even further when longer binding time is allowed (0.2 nM after 15 min). Application of the system to detection of narcotics at airport security control points is discussed.     

Inlaid Nd-substituted bismuth titanate nanoplates for protein immobilization and Nd-controlled electrochemical properties

Neodymium (Nd) substituted bismuth titanate (Bi(4-x)Nd(x)Ti(3)O(12), BNTO-x) nanoplates inlaid one another were prepared by sol-gel hydrothermal method, which was explored for protein immobilization and biosensor fabrication. Comparative experiments witnessed that Bi(3+) ions in bismuth titanate (Bi(4)Ti(3)O(12), BTO) were successfully substituted with Nd(3+) ions, and the electrochemical properties of the Hb-Chi-BNTO biosensors closely depended on the Nd(3+) ion content. With increasing the Nd(3+) doping content, the electrochemical performance of the Hb-Chi-BNTO-x biosensors showed regularly variable. Moreover, compared with the Hb-Chi-BTO and other Hb-Chi-BNTO-x biosensors, the Hb-Chi-BNTO-0.85 biosensor had more excellent electrochemical and electrocatalytic properties such as stronger redox peak currents (approximately three-fold), smaller peak-to-peak separation (50 mV), larger heterogeneous electron transfer rate (14.1 ± 3.8s(-1)), higher surface concentration of electroactive redox protein (about 8.16 × 10(-11)mol/cm(2)), and better reproducibility and stability. The Nd-depended electrochemical properties of the Hb-Chi-BNTO biosensors may open up a new idea for designing third-generation electrochemical biosensors, and the BNTO-0.85-based biosensor is also expected to find potential applications in many areas such as biomedical, food, and environmental detection.     

Amplified detection of nucleic acid by G-quadruplex based hybridization chain reaction

A protein-free, isothermal, self-amplified nucleic acid sensing system which was a G-quadruplex integrated hybridization chain reaction (GQ-HCR) system was developed. The G-quadruplex was closed two-thirds in the loop and one-third in the stem of one of the GQ-HCR hairpin probes. In the absence of the target molecule, the GQ-HCR probes stayed as inactive meta-stable hairpin structures and the G-quadruplex was inert. Reversely, the GQ-HCR probes could be cross-opened to start a hybridization chain reaction and the closed G-quadruplex could be released to be free when the GQ-HCR probes came across the target molecule. The GQ-HCR nucleic acid sensing system could detect as low as 7.5nM ssDNA or RNA by the colorimetric method and 4nM ssDNA by the fluorometric method. Less than 10 copies of dsDNA template could also be detected when PCR was combined with the GQ-HCR system (PCR+GQ-HCR). Because of these advantages, the GQ-HCR system was also studied for application in visual chip detection to obtain a satisfactory repeatable and specific result.     

Elongator complex is critical for cell cycle progression and leaf patterning in Arabidopsis

The mitotic cell cycle in higher eukaryotes is of pivotal importance for organ growth and development. Here, we report that Elongator, an evolutionarily conserved histone acetyltransferase complex, acts as an important regulator of mitotic cell cycle to promote leaf patterning in Arabidopsis. Mutations in genes encoding Elongator subunits resulted in aberrant cell cycle progression, and the altered cell division affects leaf polarity formation. The defective cell cycle progression is caused by aberrant DNA replication and increased DNA damage, which activate the DNA replication checkpoint to arrest the cell cycle. Elongator interacts with proliferating cell nuclear antigen (PCNA) and is required for efficient histone 3 (H3) and H4 acetylation coupled with DNA replication. Levels of chromatin-bound H3K56Ac and H4K5Ac known to associate with replicons during DNA replication were reduced in the mutants of both Elongator and chromatin assembly factor 1 (CAF-1), another protein complex that physically interacts with PCNA for DNA replication-coupled chromatin assembly. Disruptions of CAF-1 also led to severe leaf polarity defects, which indicated that Elongator and CAF-1 act, at least partially, in the same pathway to promote cell cycle progression. Collectively, our results demonstrate that Elongator is an important regulator of mitotic cell cycle, and the Elongator pathway plays critical roles in promoting leaf polarity formation.     

The proteasome is responsible for caspase-3-like activity during xylem development

Xylem development is a process of xylem cell terminal differentiation that includes initial cell division, cell expansion, secondary cell wall formation and programmed cell death (PCD). PCD in plants and apoptosis in animals share many common characteristics. Caspase-3, which displays Asp-Glu-Val-Asp (DEVD) specificity, is a crucial executioner during animal cells apoptosis. Although a gene orthologous to caspase-3 is absent in plants, caspase-3-like activity is involved in many cases of PCD and developmental processes. However, there is no direct evidence that caspase-3-like activity exists in xylem cell death. In this study, we showed that caspase-3-like activity is present and is associated with secondary xylem development in Populus tomentosa. The protease responsible for the caspase-3-like activity was purified from poplar secondary xylem using hydrophobic interaction chromatography (HIC), Q anion exchange chromatography and gel filtration chromatography. After identification by liquid chromatography-tandem mass spectrometry (LC-MS/MS), it was revealed that the 20S proteasome (20SP) was responsible for the caspase-3-like activity in secondary xylem development. In poplar 20SP, there are seven α subunits encoded by 12 genes and seven β subunits encoded by 12 genes. Pharmacological assays showed that Ac-DEVD-CHO, a caspase-3 inhibitor, suppressed xylem differentiation in the veins of Arabidopsis cotyledons. Furthermore, clasto-lactacystin β-lactone, a proteasome inhibitor, inhibited PCD of tracheary element in a VND6-induced Arabidopsis xylogenic culture. In conclusion, the 20S proteasome is responsible for caspase-3-like activity and is involved in xylem development.     

Rice RNA-dependent RNA polymerase 6 acts in small RNA biogenesis and spikelet development

Higher plants have evolved multiple RNA-dependent RNA polymerases (RDRs), which work with Dicer-like (DCL) proteins to produce different classes of small RNAs with specialized molecular functions. Here we report that OsRDR6, the rice (Oryza sativa L.) homolog of Arabidopsis RDR6, acts in the biogenesis of various types and sizes of small RNAs. We isolated a rice osrdr6-1 mutant, which was temperature sensitive and showed spikelet defects. This mutant displays reduced accumulation of tasiR-ARFs, the conserved trans-acting siRNAs (tasiRNAs) derived from the TAS3 locus, and ectopic expression of tasiR-ARF target genes, the Auxin Response Factors (including ARF2 and ARF3/ETTIN). The loss of tasiR-mediated repression of ARFs in osrdr6-1 can explain its morphological defects, as expression of two non-targeted ARF3 gene constructs (ARF3muts) in a wild-type background mimics the osrdr6 and osdcl4-1 mutant phenotypes. Small RNA high-throughput sequencing also reveals that besides tasiRNAs, 21-nucleotide (nt) phased small RNAs are also largely dependent on OsRDR6. Unexpectedly, we found that osrdr6-1 has a strong impact on the accumulation of 24-nt phased small RNAs, but not on unphased ones. Our work uncovers the key roles of OsRDR6 in small RNA biogenesis and directly illustrates the crucial functions of tasiR-ARFs in rice development.     

Facile synthesis of triterpenoid saponins bearing β-Glu/Gal-(1→3)-β-GluA methyl ester and their cytotoxic activities

Convenient synthetic strategy toward spinasaponin A methyl ester 1 and calenduloside G methyl ester 2, two natural oleanane-type triterpenoid saponins bearing an unique β-D-glucosyl/galactosyl-(1→3)-β-D-glucuronic acid methyl ester disaccharide moiety, was established. Based on this facile approach, four structurally modified congeners 3-6 with ursolic acid and glycyrrhetinic acid as aglycones were efficiently synthesized. MTT assay revealed the cytotoxicities against cancer cells of the synthesized saponins were varied with the change of aglycones and sugar units. Saponin 2 possessing the most potent cytotoxic effects could induce apoptosis of MCF-7 cells, which was detected by confocal micrographs using DAPI staining and flow cytometry using Annexin V and PI double staining. Furthermore, 2-induced apoptosis in MCF-7 cells was associated with ROS generation and loss of the mitochondria membrane potential (Δψ(m)).     

Synthesis and spectral studies of 2-[(N-ethyl carbazole)-3-sulfonyl ethylenediamine]-1-N,N-2-(2-methypyridy) as a fluorescence probe for Zn²⁺

A novel Zn(2+) fluorescence probe, 2-[(N-ethyl carbazole)-3-sulfonyl ethylenediamine]-1-N,N-bis(2-methypyrbidy), was designed and synthesized via simple steps, and its structure was confirmed by IR and (1)H NMR. The probe gives significant fluorescence enhancement immediately following Zn(2+) addition at neutral pH and exhibits improved selectivity for Zn(2+) compared to the other metal ions in aqueous solution. The spectra and fluorescence quantum yield of the synthesized compound were carefully investigated by UV-vis absorption and fluorescence spectra in various solvents.