In situ hydrothermal syntheses, crystal structures and luminescent properties of two novel zinc(II) coordination polymers based on tetrapyridyl ligand

Two novel Zn(II) coordination polymers, [Zn(2-pytpy)(fum)]_n·nH₂O (1) and [Zn₆(4-pytpy)₃(mal)₄]_n·5n(H₂O) (2), (2-pytpy = 4′-(4-pyridyl)-2,2′:6′,2″-terpyridine, 4-pytpy = 4′-(4-pyridyl)-4,2′:6′,4″-terpyridine, H₂fum = fumaric acid and H₂mal = malic acid) have been hydrothermally synthesized and structurally characterized. Notably, in situ ligand reactions occur in the formation of complexes 1 and 2, in which maleic acid is converted into fumaric acid and malic acid, respectively. Complex 1 is a 1D infinite chain structure, which is extended into a supramolecular layer by intermolecular π…π stacking interactions. Complex 2 is a 3D network structure, in which the bidentate-bridging 4-pytpy ligands link the layers based on the tetranuclear Zn(II) subunits to form the (4,10)-connected network. The luminescent properties of 1 and 2 have been investigated with emission spectra and UV-Vis diffuse reflectance spectra in the solid state. Additionally, these two complexes possess great thermal stabilities.     

Difference in tree growth responses to climate at the upper treeline: Qilian Juniper in the Anyemaqen Mountains

Three ring-width chronologies were developed from Qilian Juniper (Sabina przewalskii Kom.) at the upper treeline along a west-east gradient in the Anyemaqen Mountains.Most chronological statistics,except for mean sensitivity (MS),decreased from west to east.The first principal component (PC1) Ioadings indicated that stands in a similar climate condition were most important to the variability of radial growth.PC2 Ioadings decreased from west to east,suggesting the difference of tree-growth between eastern and western Anyemaqen Mountains.Correlations between standard chronologies and climatic factors revealed different climatic influences on radial growth along a west-east gradient in the study area.Temperature of warm season (July-August) was important to the radial growth at the upper treeline in the whole study area.Precipitation of current May was an important limiting factor of tree growth only in the western (drier) upper treeline,whereas precipitation of current September limited tree growth in the eastern (wetter) upper treeline.Response function analysis results showed that there were regional differences between tree growth and climatic factors in various sampling sites of the whole study area.Temperature and precipitation were the important factors influencing tree growth in western (drier) upper treeline.However,tree growth was greatly limited by temperature at the upper treeline in the middle area,and was more limited by precipitation than temperature in the eastern (wetter) upper treeline.     

Angiopoietins assemble distinct Tie2 signalling complexes in endothelial cell-cell and cell-matrix contacts

The receptor tyrosine kinase Tie2, and its activating ligand Angiopoietin-1 (Ang1), are required for vascular remodelling and vessel integrity, whereas Ang2 may counteract these functions. However, it is not known how Tie2 transduces these different signals. Here, we show that Ang1 induces unique Tie2 complexes in mobile and confluent endothelial cells. Matrix-bound Ang1 induced cell adhesion, motility and Tie2 activation in cell-matrix contacts that became translocated to the trailing edge in migrating endothelial cells. In contrast, in contacting cells Ang1 induced Tie2 translocation to cell-cell contacts and the formation of homotypic Tie2-Tie2 trans-associated complexes that included the vascular endothelial phosphotyrosine phosphatase, leading to inhibition of paracellular permeability. Distinct signalling proteins were preferentially activated by Tie2 in the cell-matrix and cell-cell contacts, where Ang2 inhibited Ang1-induced Tie2 activation. This novel type of cellular microenvironment-dependent receptor tyrosine kinase activation may explain some of the effects of angiopoietins in angiogenesis and vessel stabilization.     

Pnas4 is a novel regulator for convergence and extension during vertebrate gastrulation

Recent studies show that human Pnas4 might be tumor associated, while its function remains unknown. Here, we investigate the developmental function of Pnas4 using zebrafish as a model system. Knocking down Pnas4 causes gastrulation defects with a shorter and broader axis, as well as a posteriorly mis-positioned prechordal plate, due to the defective convergence and extension movement. Conversely, over-expression of Pnas4 mRNA leads to an elongated body axis. We further demonstrate that Pnas4 is required cell-autonomously for dorsal convergence but not for anterior migration. In addition, genetic interaction assays indicate that Pnas4 might act in parallel with non-canonical Wnt signal in the regulation of cell movement. Our data suggest that Pnas4 is a key regulator of cell movement during gastrulation.     

Compositional characterization and imaging of “wall-bound” acylesters of Populus trichocarpa reveal differential accumulation of acyl molecules in normal and reactive woods

Acylesterification is one of the common modifications of cell wall non-cellulosic polysaccharides and/or lignin primarily in monocot plants. We analyzed the cell-wall acylesters of black cottonwood (Populus trichocarpa Torr. & Gray) with liquid chromatography-mass spectrometry (LC-MS), Fourier transform-infrared (FT-IR) microspectroscopy, and synchrotron infrared (IR) imaging facility. The results revealed that the cell wall of dicotyledonous poplar, as the walls of many monocot grasses, contains a considerable amount of acylesters, primarily acetyl and p-hydroxycinnamoyl molecules. The "wall-bound" acetate and phenolics display a distinct tissue specific-, bending stress responsible- and developmental-accumulation pattern. The "wall-bound" p-coumarate predominantly accumulated in young leaves and decreased in mature leaves, whereas acetate and ferulate mostly amassed in the cell wall of stems. Along the development of stem, the level of the "wall-bound" ferulate gradually increased, while the basal level of p-coumarate further decreased. Induction of tension wood decreased the accumulation of the "wall-bound" phenolics while the level of acetate remained constant. Synchrotron IR-mediated chemical compositional imaging revealed a close spatial distribution of acylesters with cell wall polysaccharides in poplar stem. These results indicate that different "wall-bound" acylesters play distinct roles in poplar cell wall structural construction and/or metabolism of cell wall matrix components.     

Bak Foong protects dopaminergic neurons against MPTP-induced neurotoxicity by its anti-apoptotic activity

Bak Foong pill (BFP) is a well-known traditional Chinese medicine used for treatment of various gynaecological disorders. In addition, it exerts beneficial effects on other functional systems including the central nervous system. In the present study, we have investigated the possible neuroprotective action of BFP upon the nigrostriatal dopaminergic system by examining its effect on the expression patterns of tyrosine hydroxylase (TH) and dopamine transporter (DAT) in the 1-methyl-4-phenyl-1,2,3,6-tetrahyrdropyridine (MPTP)-induced Parkinson's disease (PD) mouse model. MPTP significantly decreased TH and DAT mRNA levels in the striatum and midbrain of both female and male C57BL/6 mice. However, with BFP pre-treatment mice showed a reduced neurotoxicity, with TH and DAT mRNA levels either not affected by MPTP or affected to a lesser extent in the midbrain and striatum when compared to vehicle treated animals. Possible anti-apoptotic activity of BFP was further studied in a dopamine-secreting neuroendocrine cell line, PC12. In this assay, MPTP elevated the expression of a pro-apoptotic gene, Bax, while this expression was reduced by BFP pre-treatment. Flow cytometry results also revealed that the effect of MPTP-induced apoptosis in PC12 cell lines was significantly reduced by BFP. The present results suggest that BFP is able to protect dopaminergic neurons from neurotoxin-induced neuronal injury with anti-apoptotic activity being one of the possible mechanisms.     

The spatiotemporal development of adipose tissue

Adipose tissue is a structure highly specialized in energy storage. The adipocyte is the parenchymal component of adipose tissue and is known to be mesoderm or neuroectoderm in origin; however, adipocyte development remains poorly understood. Here, we investigated the development of adipose tissue by analyzing postnatal epididymal adipose tissue (EAT) in mouse. EAT was found to be generated from non-adipose structure during the first 14 postnatal days. From postnatal day 1 (P1) to P4, EAT is composed of multipotent progenitor cells that lack adipogenic differentiation capacity in vitro, and can be regarded as being in the 'undetermined' state. However, the progenitor cells isolated from P4 EAT obtain their adipogenic differentiation capacity by physical interaction generated by cell-to-matrix and cell-to-cell contact both in vitro and in vivo. In addition, we show that impaired angiogenesis caused by either VEGFA blockade or macrophage depletion in postnatal mice interferes with adipose tissue development. We conclude that appropriate interaction between the cellular and matrix components along with proper angiogenesis are mandatory for the development of adipose tissue.     

A deletion in a cis element of Foxe3 causes cataracts and microphthalmia in rct mice

The Rinshoken cataract (rct) mutation, which causes congenital cataracts, is a recessive mutation found in SJL/J mice. All mutants present with opacity in the lens by 2?months of age. The rct locus was mapped to a 1.6-Mb region in Chr 4 that contains the Foxe3 gene. This gene is responsible for cataracts in humans and mice, and it plays a crucial role in the development of the lens. Furthermore, mutation of Foxe3 causes various ocular defects. We sequenced the genomic region of Foxe3, including the coding exons and UTRs; however, no mutations were discovered in these regions. Because there were no differences in Foxe3 sequences between the rct/rct and wild-type mice, we inferred that a mutation was located in the regulatory regions of the Foxe3 gene. To test this possibility, we sequenced a 5' noncoding region that is highly conserved among vertebrates and is predicted to be the major enhancer of Foxe3. This analysis revealed a deletion of 22-bp located approximately 3.2-kb upstream of the start codon of Foxe3 in rct mice. Moreover, we demonstrated by RT-PCR and in situ hybridization that the rct mutant has reduced expression of Foxe3 in the lens during development. We therefore suggest that cataracts in rct mice are caused by reduced Foxe3 expression in the lens and that this decreased expression is a result of a deletion in a cis-acting regulatory element.     

Functional reconstitution of purified chloroquine resistance membrane transporter expressed in yeast

Malaria is one of the major parasitic diseases. Current treatment of malaria is seriously hampered by the emergence of drug resistant cases. A once-effective drug chloroquine (CQ) has been rendered almost useless. The mechanism of CQ resistance is complicated and largely unknown. Recently, a novel transmembrane protein, Plasmodium falciparum chloroquine resistance transporter (PfCRT), has fulfilled all the requirements of being the CQ resistance gene. In order to elucidate the mechanism how PfCRT mediates CQ resistance, we have cloned the cDNA from a CQ sensitive parasite (3D7) and tried to express it in Pichia pastoris (P. pastoris) but with unsuccessful results due to AT-rich sequences in the malaria genome. We have therefore, based on the codon usage in P. pastoris, chemically synthesized a codon-modified pfcrt with an overall 55% AT content. This codon-modified pfcrt has now been successfully expressed in P. pastoris. The expressed PfCRT has been purified with immuno metal affinity chromatography (IMAC) and then reconstituted into proteoliposome. It was found that proteoliposomes have a saturable, concentration and time-dependent CQ transport activity. In addition, we found that proteoliposomes with resistant PfCRT(r) (K76T or K76I) showed an increased CQ transport activity compared to liposomes with lipid alone, or proteoliposomes reconstituted with sensitive PfCRT(s) (K76) protein. This activity could be inhibited by nigericin and decreased with the removal of Cl(-). This work suggests that PfCRT is mediating CQR in P. falciparum by virtue of its changes in CQ transport activity depending on pH gradient and chloride ion in the food vacuole.     

Shear stress activates Tie2 receptor tyrosine kinase in human endothelial cells

The receptor tyrosine kinase (RTK) Tie2 is expressed predominantly on endothelial cells. Tie2 is critical for vasculogenesis during development and could be important for maintaining endothelial cell survival and integrity in adult blood vessels. Although most RTKs are activated by shear stress in the absence of ligand activation, the effect of shear stress on Tie2 is unknown. Therefore, we examined the effect of shear stress on Tie2 phosphorylation in primary cultured endothelial cells. Interestingly, shear stress (20 dyne/cm(2)) produced a rapid, marked, and sustained Tie2 phosphorylation, while it produced a rapid but slight and transient phosphorylation of insulin receptor and VEGF receptor 2 (Flk1). In addition, Tie2 phosphorylation in response to shear stress was velocity-dependent, while phosphorylation of insulin receptor and Flk1 was not. Shear stress also produced Akt phosphorylation in a time-, velocity-, and PI 3-kinase-dependent manner. Accordingly, shear stress suppressed serum deprivation-induced endothelial cell apoptosis. Taken together, our results indicated that activation of Tie2/PI 3-kinase/Akt in response to shear stress could be an important signaling cascade for maintaining endothelial survival and integrity in blood vessels.