Biochemical characterization of a novel beta-1--3, 1--4 glucan 4-glucanohydrolase from Thermomonospora sp. having a single active site for lichenan and xylan

A bifunctional high molecular weight (Mr, 64,500 Da) beta-1-3, 1-4 glucan 4-glucanohydrolase was purified to homogeneity from Thermomonospora sp., exhibiting activity towards lichenan and xylan. A kinetic method was used to analyze the active site that hydrolyzes lichenan and xylan. The experimental data was in agreement with the theoretical values calculated for a single active site. Probing the conformation and microenvironment at active site of the enzyme by fluorescent chemo-affinity label, OPTA resulted in the formation of an isoindole derivative with complete inactivation of the enzyme to hydrolyse both lichenan and xylan confirmed the results of kinetic method. OPTA forms an isoindole derivative by cross-linking the proximal thiol and amino groups. The modification of cysteine and lysine residues by DTNB and TNBS respectively abolished the ability of the enzyme to form an isoindole derivative with OPTA, indicating the participation of cysteine and lysine in the formation of isoindole complex.     

Heterodimerization of yLAT-1 and 4F2hc visualized by acceptor photobleaching FRET microscopy

y⁺LAT-1 and 4F2hc are the subunits of a transporter complex for cationic amino acids, located mainly in the basolateral plasma membrane of epithelial cells in the small intestine and renal tubules. Mutations in y⁺LAT-1 impair the transport function of this complex and cause a selective aminoaciduria, lysinuric protein intolerance (LPI, OMIM #222700), associated with severe, complex clinical symptoms. The subunits of an active transporter co-localize in the plasma membrane, but the exact process of dimerization is unclear since direct evidence for the assembly of this transporter in intact human cells has not been available. In this study, we used fluorescence resonance energy transfer (FRET) microscopy to investigate the interactions of y⁺LAT-1 and 4F2hc in HEK293 cells expressing y⁺LAT-1 and 4F2hc fused with ECFP or EYFP. FRET was quantified by measuring fluorescence intensity changes in the donor fluorophore (ECFP) after the photobleaching of the acceptor (EYFP). Increased donor fluorescence could be detected throughout the cell, from the endoplasmic reticulum and Golgi complex to the plasma membrane. Therefore, our data prove the interaction of y⁺LAT-1 and 4F2hc prior to the plasma membrane and thus provide evidence for 4F2hc functioning as a chaperone in assisting the transport of y⁺LAT-1 to the plasma membrane.     

Robustness of neural codes and its implication on natural image processing

In this study, based on the view of statistical inference, we investigate the robustness of neural codes, i.e., the sensitivity of neural responses to noise, and its implication on the construction of neural coding. We first identify the key factors that influence the sensitivity of neural responses, and find that the overlap between neural receptive fields plays a critical role. We then construct a robust coding scheme, which enforces the neural responses not only to encode external inputs well, but also to have small variability. Based on this scheme, we find that the optimal basis functions for encoding natural images resemble the receptive fields of simple cells in the striate cortex. We also apply this scheme to identify the important features in the representation of face images and Chinese characters.

分化抑制因子-1在大肠癌中的表达及临床意义

目的:研究分化抑制因子-1(Id-1)在人大肠癌组织中的表达及其与临床病理特征的关系。方法:应用免疫组织化学方法(SP法)检测Id-1在56例大肠癌组织及56例远癌肠黏膜中的表达水平,并分析其与临床病理特征的关系。结果:在大肠癌组织中Id-1的过表达率为80.4%,在远癌肠粘膜中过表达率为12.5%,两组比较差异有统计学意义(P0.01)。Id-1过表达与大肠癌Dukes分期及淋巴结转移有关(P0.05),而与患者年龄、性别、肿瘤组织分化程度无关(P0.05)。结论:Id-1过表达可能参与大肠癌演进,Id-1可作为判断大肠癌恶性程度和预后的指标。     

Dexamethasone downregulates the expression of parathyroid hormone-related protein (PTHrP) in mesenchymal stem cells

Parathyroid hormone-related protein (PTHrP) has been shown to have anabolic effects in women with postmenopausal osteoporosis. PTHrP promotes the recruitment of osteogenic cells and prevents apoptotic death of osteoblasts and osteocytes. The receptor responsible for the effects of PTHrP is the common PTH/PTHrP receptor (PTH1R). Glucocorticoids (GC) are commonly used as drugs to treat inflammatory diseases. Long-term GC treatments are often associated with bone loss which can lead to GC-induced osteoporosis. The aim of this work was to study the effects of the glucocorticoid dexamethasone (Dex) on the expression of PTHrP and PTH1R in adult human mesenchymal stem cells, the progenitor cells of osteoblasts.Adult human mesenchymal stem cells (hMSC) were cultured and differentiated by standard methods. The expression of PTHrP and PTH1R mRNA was assayed by real-time qPCR. The PTHrP release into the culture media was measured by an immunoradiometric assay.Treatment with Dex (10 nM) resulted in an 80% drop in the PTHrP release within 6 h. A 24 h Dex treatment also reduced the expression of PTHrP mRNA by up to 90%. The expression of PTH1R receptor mRNA was simultaneously increased up to 20-fold by 10 nM Dex. The effects of Dex on PTHrP and PTH1R were dose-dependent and experiments with the GC-receptor antagonist mifepristone showed an involvement of GC-receptors in these effects. In addition to the Dex-induced effects on PTHrP and PTH1R, Dex also increased mineralization and the expression of the osteoblast markers Runx2 and alkaline phosphatase. In our studies, we show that dexamethasone decreases the expression of PTHrP and increases the expression of the PTH1R receptor. This could have an impact on PTHrP-mediated anabolic actions on bone and could also affect the responsiveness of circulating PTH. The results indicate that glucocorticoids affect the signalling pathway of PTHrP by regulating both PTHrP and PTH1R expression and these mechanisms could be involved in glucocorticoid-induced osteoporosis.     

Negative regulating factors of notch signaling may be a key factor for the teeth root formation

It is still an open question that how the teeth root development is initiated at the molecular level. But what we know is that the teeth root development begins after the crown part is completely formed, and then the terminal cervical loop structure faces two developmental fate options when the crown development is quite advanced: it can remain as a ‘crown’ pattern, and continue enamel production, or it can adopt the ‘root’ fate, and begins teeth root development. Epithelial notch and mesenchymal fgf10 signaling are thought to be the key switches of root or crown development pattern. But, for a rodent's molars and incisors, it is very interesting that after a similar teeth crown developmental process, the late development for the molars and incisors is quite different: the molar germ forms a multi-rooted pattern, while the incisor germ forms a single-rooted analogue and without a really root development process. In a recent study, one of the negative regulating factors for notch signaling, sel1l was found strongly related to the molar root development. So we hypotheses that the negative regulating factors of notch signaling, may be the key signals to determine the tooth root developmental onset, and the quantity or function's abnormal of that factors, may lead to hypoplasia of the teeth root.     

子宫内膜癌组织中PTEN和MTA1蛋白的表达及其相关性

目的：探讨子宫内膜癌组织中PTEN和MTA1表达及其与子宫内膜癌生物学行为之间的关系。方法：采用免疫组化SP法检测130例子宫内膜癌和40例正常宫内膜组织中PTEN和MTAl1的表达水平,并分析两者在子宫内膜癌中的相关性。结果：子宫内膜癌组织中PTEN、MTA1阳性表达均显著高于正常子宫内膜组织（P〈0．01）;PTEN与MTAI在子宫内膜癌组织中的表达呈负相关（r=0．35,P〈0．05）。结论：PTEN和MTA1表达与子宫内膜癌的发生、发展及生物行为密切相关,且两者表达存在负相关性。