Oligodendrocytes regulate formation of nodes of Ranvier via the recognition molecule OMgp

The molecular mechanisms underlying the involvement of oligodendrocytes in formation of the nodes of Ranvier (NORs) remain poorly understood. Here we show that oligodendrocyte-myelin glycoprotein (OMgp) aggregates specifically at NORs. Nodal location of OMgp does not occur along demyelinated axons of either Shiverer or proteolipid protein (PLP) transgenic mice. Over-expression of OMgp in OLN-93 cells facilitates process outgrowth. In transgenic mice in which expression of OMgp is down-regulated, myelin thickness declines, and lateral oligodendrocyte loops at the node-paranode junction are less compacted and even join together with the opposite loops, which leads to shortened nodal gaps. Notably, each of these structural abnormalities plus modest down-regulation of expression of Na(+) channel alpha subunit result in reduced conduction velocity in the spinal cords of the mutant mice. Thus, OMgp that is derived from glia has distinct roles in regulating nodal formation and function during CNS myelination.     

Role of ICAM-1 in chronic hepatic allograft rejection in the rat

The pathogenesis of hepatic allograft rejection remains unclear. We aimed to clarify the early role of intercellular adhesion molecule-1 (ICAM-1)-mediated cell recruitment in chronic hepatic rejection. Liver transplantation was performed from Lewis to Lewis rats (isograft controls) and from Lewis to Brown Norway rats (allograft rejection group). The allografted rats were treated with either ICAM-1 antisense oligonucleotides (10 mg. kg(-1). day(-1) x 6 days ip) or a control preparation (either ICAM-1 missense oligonucleotide or normal saline). Hepatic leukocyte recruitment in vivo was studied on day 6 by using intravital microscopy. Liver histology, biochemistry, and survival rates were also examined. Leukocyte adhesion in terminal hepatic venules was significantly increased in the rejection group compared with isograft controls. Antisense ICAM-1 in the allografted group effectively reduced leukocyte adhesion. Histology and liver chemistry were less deranged in the antisense-treated groups compared with control-treated allografted rats. In the allograft groups, survival was significantly prolonged in the antisense-treated rats (42.3 +/- 1.2 days) compared with the controls (25.2 +/- 2.7 days). These results showed that early leukocyte recruitment in the hepatic microvasculature of rejecting allografts is ICAM-1 dependent and suggest that impacting on early cell recruitment can significantly ameliorate chronic rejection.     

Mitofusin 2 Protects Hepatocyte Mitochondrial Function from Damage Induced by GCDCA

Mitochondrial impairment is hypothesized to contribute to the pathogenesis of chronic cholestatic liver diseases. Mitofusin 2 (Mfn2) regulates mitochondrial morphology and signaling and is involved in the development of numerous mitochondrial-related diseases; however, a functional role for Mfn2 in chronic liver cholestasis which is characterized by increased levels of toxic bile acids remain unknown. Therefore, the aims of this study were to evaluate the expression levels of Mfn2 in liver samples from patients with extrahepatic cholestasis and to investigate the role Mfn2 during bile acid induced injury in vitro. Endogenous Mfn2 expression decreased in patients with extrahepatic cholestasis. Glycochenodeoxycholic acid (GCDCA) is the main toxic component of bile acid in patients with extrahepatic cholestasis. In human normal hepatocyte cells (L02), Mfn2 plays an important role in GCDCA-induced mitochondrial damage and changes in mitochondrial morphology. In line with the mitochondrial dysfunction, the expression of Mfn2 decreased significantly under GCDCA treatment conditions. Moreover, the overexpression of Mfn2 effectively attenuated mitochondrial fragmentation and reversed the mitochondrial damage observed in GCDCA-treated L02 cells. Notably, a truncated Mfn2 mutant that lacked the normal C-terminal domain lost the capacity to induce mitochondrial fusion. Increasing the expression of truncated Mfn2 also had a protective effect against the hepatotoxicity of GCDCA. Taken together, these findings indicate that the loss of Mfn2 may play a crucial role the pathogenesis of the liver damage that is observed in patients with extrahepatic cholestasis. The findings also indicate that Mfn2 may directly regulate mitochondrial metabolism independently of its primary fusion function. Therapeutic approaches that target Mfn2 may have protective effects against hepatotoxic of bile acids during cholestasis.     

基于16S rDNA的系统发育分析在微生物进化关系中的应用

系统发育树的构建是现代生命科学研究中的重要技术,是分析未知菌种与其他菌种的亲缘关系,为进一步了解生物的进化关系的重要依据。对系统发育树的构建进行了详细的介绍。并对其在微生物进化研究中的具体应用进行了阐述。     

利用肠激酶加工融合蛋白的方法制备重组人甲状旁腺素（1—34）肽

采用全基因分段合成和补丁连接相结合的方法构建了人甲状旁腺素 (hPTH) (1～ 34)肽基因 ,并利用GST融合表达系统 ,在大肠杆菌中克隆和可溶性表达了hPTH(1～ 34)肽基因。融合蛋白表达量占菌体总蛋白质的 2 5 %以上 ,经高密度发酵、亲和纯化后 ,在每升发酵液中得到了 10 g融合蛋白。融合蛋白经肠激酶一步加工并亲合纯化和反相脱盐后 ,最终可以得到约 0 .6g /L人甲状旁腺素 (1～ 34)肽纯品 ,样品的理论回收值达到了4 8.75 %。产物的纯度和性质经HPLC、毛细管电泳、质谱分析、N端测序等得到证明 ,并与化学合成产物的结果相吻合。兔肾皮质细胞测活表明 ,重组产物与化学合成人甲状旁腺素 (1～ 34)肽具有相近的腺苷酸环化酶激活活性。     

Chaperone-mediated refolding of recombinant prochymosin

It has been verified that prochymosin is characterized by a two-stage refolding: dilution of unfolded protein into pH 11 buffer followed by neutralization at pH 8; the high-pH step is indispensable. Here we demonstrate that one-stage refolding around pH 8 can be achieved when GroE or 10-fold molar excess (rather than catalytic concentration) of protein disulfide isomerase (PDI) over prochymosin is present. The helping effect varies with the oxidation states of prochymosin. GroE and PDI increase the reactivation of the unfolded, partially reduced and the unfolded, oxidized prochymosin from 5% to 40% and from 50% to 100%, respectively. For the unfolded and fully reduced prochymosin, GroE does not have a positive effect, whereas PDI promotes renaturation from 2% to 28%. Based on our previous and present observations, we propose that at pH 8 there may be two kinds of incorrect interactions within and between prochymosin polypeptides leading to unproductive pathways: one prevents disulfide rearrangement, which can be avoided by high pH; the other interferes with acquisition of native conformation, which can be relieved by GroE and PDI.     

Avian pluripotent stem cells

Pluripotent embryonic stem cells are undifferentiated cells capable of proliferation and self-renewal and have the capacity to differentiate into all somatic cell types and the germ line. They provide an in vitro model of early embryonic differentiation and are a useful means for targeted manipulation of the genome. Pluripotent stem cells in the chick have been derived from stage X blastoderms and 5.5 day gonadal primordial germ cells (PGCs). Blastoderm-derived embryonic stem cells (ESCs) have the capacity for in vitro differentiation into embryoid bodies and derivatives of the three primary germ layers. When grafted onto the chorioallantoic membrane, the ESCs formed a variety of differentiated cell types and attempted to organize into complex structures. In addition, when injected into the unincubated stage X blastoderm, the ESCs can be found in numerous somatic tissues and the germ line. The potential give rise to somatic and germ line chimeras is highly dependent upon the culture conditions and decreases with passage. Likewise, PGC-derived embryonic germ cells (EGCs) can give rise to simple embryoid bodies and can undergo some differentiation in vitro. Interestingly, chicken EG cells contribute to somatic lineages when injected into the stage X blastoderm, but only germ line chimeras have resulted from EGCs injected into the vasculature of the stage 16 embryo. To date, no lines of transgenic chickens have been generated using ESCs or EGCs. Nevertheless, progress towards the culture of avian pluripotent stem cells has been significant. In the future, the answers to fundamental questions regarding segregation of the avian germ line and the molecular basis of pluripotency should foster the full use of avian pluripotent stem cells.