哺乳动物中的DNA主动去甲基化

DNA甲基化是一种相对稳定且可遗传的表观遗传标记,在植物和动物细胞中均发现有DNA主动去甲基化现象,其机制在植物中已基本得到阐释,但在哺乳动物中尚未鉴定出一种有效的DNA去甲基化酶,并且DNA主动去甲基化途径也存在争议。文章综合分析了近期的文献资料,阐述了哺乳动物中发生DNA主动去甲基化的时空特异性,并从细胞和组织特异性角度介绍DNA主动去甲基化的可能通路和机制,即5-甲基胞嘧啶的氧化作用、5-甲基胞嘧啶脱氨基以及DNA修复等,旨在为破译表观遗传重编程过程提供理论依据。     

Comparative proteomic analysis of virulent Korean Mycobacterium tuberculosis K-strain with other mycobacteria strain following infection of U-937 macrophage

In Korea, the Mycobacterium tuberculosis K-strain is the most prevalent clinical isolates and belongs to the Beijing family. In this study, we conducted comparative porteomics of expressed proteins of clinical isolates of the K-strain with H37Rv, H37Ra as well as the vaccine strain of Mycobacterium bovis BCG following phagocytosis by the human monocytic cell line U-937. Proteins were analyzed by 2-D PAGE and MALDITOF-MS. Two proteins, Mb1363 (probable glycogen phosphorylase GlgP) and MT2656 (Haloalkane dehalogenase LinB) were most abundant after phagocytosis of M. tuberculosis K-strain. This approach provides a method to determine specific proteins that may have critical roles in tuberculosis pathogenesis.     

Sphingomyelin synthase as a potential target for D609-induced apoptosis in U937 human monocytic leukemia cells

Tricyclodecan-9-yl-xanthogenate (D609) is a selective tumor cytotoxic agent. However, the mechanisms of action of D609 against tumor cells have not been well established. Using U937 human monocytic leukemia cells, we examined the ability of D609 to inhibit sphingomyelin synthase (SMS), since inhibition of SMS may contribute to D609-induced tumor cell cytotoxicity via modulating the cellular levels of ceramide and diacylglycerol (DAG). The results showed that D609 is capable of inducing U937 cell death by apoptosis in a dose- and time-dependent manner. The induction of U937 cell apoptosis was associated with an inhibition of SMS activity and a significant increase in the intracellular level of ceramide and decrease in that of sphingomyelin (SM) and DAG, which resulted in an elevation of the ratio between ceramide and DAG favoring the induction of apoptosis. In addition, incubation of U937 cells with C(6)-ceramide and/or H7 (a selective PKC inhibitor) reduced U937 cell viability; whereas pretreatment of the cells with a PKC activator, PMA or 1-oleoyl-2-acetylglycerol (OAG), attenuated D609-induced U937 cell apoptosis. These results suggest that SMS is a potential target of D609 and inhibition of SMS may contribute to D609-induced tumor cell death via modulation of the cellular levels of ceramide and DAG.     

充气和搅动对球形棕囊藻生长及囊体形成的影响

球形棕囊藻生活史中包含游离单细胞和球形囊体两种生活形态,但是实验室中培养的球形棕囊藻经常无法形成囊体。研究通过向培养基中泵入过滤空气,以及给培养基提供不同程度的搅动,研究了充气和搅动对球形棕囊藻生长及囊体形成的影响。充气和搅动均显著提高了囊体的数量,并且提高了囊体内细胞的生长速率。但是充气对于囊体直径及囊体内细胞密度并无显著影响。搅动则明显的提高了囊体直径和囊体内细胞数量。然而,尽管充气以及搅动有利于球形棕囊藻囊体的形成,但是培养的囊体直径依然小于自然海区中囊体的大小。     

Cdk5在可卡因诱导的药物成瘾中的作用

细胞周期素依赖性蛋白激酶5(cyclin dependent kinase-5,Cdk5)是细胞周期素蛋白激酶之一,具有很多磷酸化底物,其激动剂p35和p39特异存在于神经系统(CNS)。因此,Cdk5在神经系统中的功能尤为突出,成为神经科学研究热点。目前研究较多的是Cdk5在可卡因诱导的药物成瘾中的作用。在可卡因所致药物成瘾过程中,多巴胺系统,ΔFosB,神经元突触可塑性等发挥重要作用。Cdk5与这些分子相互作用,所以,Cdk5与可卡因诱导所致药物成瘾密切相关。阐明其与药物成瘾的联系,探索新的以Cdk5为靶向的药物,将可能成为成瘾治疗的有效手段。综述了在可卡因诱导的药物成瘾中Cdk5作用,以及Cdk5与相关的信号转导分子之间的相互调节。     

Mapping of QTLs prolonging the latent period of Puccinia triticina infection in wheat

Slow rusting is considered a crucial component of durable resistance to wheat leaf rust caused by Puccinia triticina and is often expressed in the form of a prolonged latent period. Selection for a longer latent period is considered an effective approach to developing wheat cultivars with improved durable resistance to leaf rust. A recombinant inbred line (RIL) population derived from CI 13227 (long latent period) × Suwon 92 (short latent period) was phenotyped for latent period in two greenhouse experiments in separate years, and amplified fragment length polymorphism (AFLP) and simple sequence repeat (SSR) markers were analyzed in the same population. Among the RILs, the frequency distribution for latent period was continuous, and latent period was highly correlated between years (r=0.94, P<0.0001). A quantitative trait locus (QTL) prolonging the latent period of P. triticina, designated as QLrlp.osu-2DS, explained 42.8% and 54.5% of the phenotypic and genetic variance in the two experiments, respectively. QLrlp.osu-2DS was mapped on the distal region of chromosome 2DS. Two other QTLs for latent period, QLrlp.osu-2B and QLrlp.osu-7BL, were localized on chromosome 2B and the long arm of chromosome 7B, respectively. Multiple regression analysis showed that these three QTLs collectively explained 58.0% and 73.8% of the phenotypic and genetic variance over two experiments, respectively. Fourteen RILs that carried all three alleles for long latent period at three AFLP loci flanking QLrlp.osu-2DS, QLrlp.osu-2B, and QLrlp.osu-7BL had a mean latent period of 12.5 days, whereas 13 RILs without any long-latent-period alleles at the corresponding loci had a mean latent period of 7.4 days. Three SSR markers closely linked to these QTLs have potential to be applied in marker-assisted selection for prolonged latent period in wheat.     

Mechanism and rate constants of the Cdc42 GTPase binding with intrinsically disordered effectors

Intrinsically disordered proteins (IDPs) are often involved in signaling and regulatory functions, through binding to cellular targets. Many IDPs undergo disorder‐to‐order transitions upon binding. Both the binding mechanisms and the magnitudes of the binding rate constants can have functional importance. Previously we have found that the coupled binding and folding of any IDP generally follows a sequential mechanism that we term dock‐and‐coalesce, whereby one segment of the IDP first docks to its subsite on the target surface and the remaining segments subsequently coalesce around their respective subsites. Here we applied our TransComp method within the framework of the dock‐and‐coalesce mechanism to dissect the binding kinetics of two Rho‐family GTPases, Cdc42 and TC10, with two intrinsically disordered effectors, WASP and Pak1. TransComp calculations identified the basic regions preceding the GTPase binding domains (GBDs) of the effectors as the docking segment. For Cdc42 binding with both WASP and Pak1, the calculated docking rate constants are close to the observed overall binding rate constants, suggesting that basic‐region docking is the rate‐limiting step and subsequent conformational coalescence of the GBDs on the Cdc42 surface is fast. The possibility that conformational coalescence of the WASP GBD on the TC10 surface is slow warrants further experimental investigation. The account for the differences in binding rate constants among the three GTPase‐effector systems and mutational effects therein yields deep physical and mechanistic insight into the binding processes. Our approach may guide the selection of mutations that lead to redesigned binding pathways. Proteins 2016; 84:674–685. © 2016 Wiley Periodicals, Inc.     

Scale specific determinants of tree diversity in an old growth temperate forest in China

The major processes generating pattern in plant community composition depend upon the spatial scale and resolution of observation, therefore understanding the role played by spatial scale on species patterns is of major concern. In this study, we investigate how well environmental (topography and soil variables) and spatial variables explain variation in species composition in a 25-ha temperate forest in northeastern China. We used new variation partitioning approaches to discover the spatial scale (using multi-scale spatial PCNM variables) at which environmental heterogeneity and other spatially structured processes influence tree community composition. We also test the effect of changing grain of the study (i.e. quadrat size) on the variation partitioning results. Our results indicate that (1) species composition in the Changbai mixed broadleaf-conifer forest was controlled mainly by spatially structured soil variation at broad scales, while at finer scales most of the explained variation was of a spatial nature, pointing to the importance of biotic processes. (2) These results held at all sampling grains. However, reducing quadrat size progressively reduced both spatially and environmentally explained variance. This probably partly reflects increasing stochasticity in species abundances, and the smaller proportion of quadrats occupied by each species, when quadrat size is reduced. The results suggest that environmental heterogeneity (i.e. niche processes) and other biotic processes such as dispersal work together, but at different spatial scales, to build up diversity patterns.