Effect of Mg2+ and Mn2+ on hydrolysis of calf thymus DNA by pancreatic deoxyribonuclease I

Divalent cations are activators for DNA hydrolysis by pancreatic deoxyribonuclease I. Apparent Vm and Km changes have been studied in presence of Mn2+ or Mg2+. The activation process modifies both Vm and Km, their relationship with Mg2+ or Mn2+ being a linear one. Deoxyribonucleotides inhibit the DNA hydrolysis, whether Mg2+ or Mn2+ is the activator; the purine deoxyribonucleotides are more effective as inhibitors than the pyrimidine ones. The effect of some derivatives of adenine has been studied: the inhibition is maximum with 5'-dAMP and minimum with adenine or adenosine. A kinetic mechanism of enzymatic activation by Mn2+ or Mg2+ is discussed.     

我国五个版本高中生物学教材《稳态与环境》内容的不一致

我国五个版本高中生物学教材《稳态与环境》中的内容在大体一致的前提下,在名称、外文注释、数据、时间以及反射弧的组成等方面存在着不一致,这些不一致对中学教师、教材编写和编辑人员都具有一定的启示。     

Conductimetric study of the binding of Mn2+ to bovine pancreatic deoxyribonuclease

The binding of Mn2+ on bovine pancreatic deoxyribonuclease has been studied by a conductimetric method. At low ionic strengths, a high-affinity single binding site is demonstrated. The association constant value (K = 1.2 x 10(5) M-1 at pH 8) is high enough to conclude that, in standard experimental conditions for DNA hydrolysis, the reacting species is the DNAase-cation complex. Competitive binding studies in presence of Mg++ and Ca++ show that these cations do not bind on the Mn++ site.     

心肌细胞发育过程中胞浆内钙稳态的调控

Ca^2＋信号是细胞和各器官生长发育、行使其生理功能的基础,维持心肌细胞的钙稳态是保持正常心脏功能的先决条件。作为在胚胎发育过程中最早出现并行使功能的器官,胚胎期心脏的形态结构发生了明显的变化,泵血功能不断增强,以适应不断增强的机体的生理需求。从胚胎到成年,心肌细胞的功能有非常大的改变,各钙离子通道的表达也发生明显变化。因此,发育早期心肌细胞的钙稳态调控与成熟心肌细胞有明显的不同,在发育过程中引起细胞收缩的Ca^2＋来源也有明显的变化。随着分子和细胞生物学研究的发展,以及胚胎干细胞体外分化模型的应用,人们对心肌细胞发育过程中钙稳态的调控有了进一步的认识。本文综述了早期心肌细胞发育过程中胞浆内钙稳态的变化,总结了早期心肌细胞钙稳态调控机制的最新研究进展。     

小胶质细胞在脑中的生理功能

小胶质细胞是脑中的巨噬细胞,也是脑实质中唯一的一种免疫细胞,因而被看作是中枢神经系统抵御病原入侵的第一道防线。在其他非感染病理状态下,如脑损伤及神经退行性疾病等,小胶质细胞也发挥着保护和毒性损伤的双重作用。相比较其病理功能,人们对小胶质细胞的生理功能长期以来很少关注。然而,近几年关于小胶质细胞生理功能的研究在多个方面都有突破。这些研究结果揭示,小胶质细胞在发育的神经系统中起着调控神经元存活和修饰突触的作用,并且在成熟的健康脑中具有探测和调控神经元活动的功能。将着重对近几年关于小胶质细胞生理功能的相关研究做一综述。     

基质Gla蛋白在大鼠附睾发育过程中的表达及定位

目的明确基质Gla蛋白(matrix Gla protein,MGP)在大鼠附睾发育过程中的表达特征。方法采用实时定量PCR和免疫荧光染色方法,对MGP在大鼠附睾不同发育阶段的表达及定位进行检测。结果实时定量PCR结果显示,MGP mRNA在6d、10d、3w、5w、7w、8w、10w和12w的大鼠附睾中均有表达,其表达量在3w达到最高峰,3w至8w表达量逐渐降低,成年大鼠(10～12w)MGP的表达量逐渐升高并稳定在较高水平。免疫荧光染色显示MGP在10d、3w的大鼠附睾各个节段均有表达,在7w、12w的表达主要集中于大鼠附睾体部和尾部,且MGP定位于附睾上皮主细胞和亮细胞。结论MGP在大鼠附睾发育的关键分化期高表达,成年后主要定位于附睾体部和尾部的主、亮细胞,可能对附睾的形态发育和管腔钙稳态的维持起重要作用。     

Calreticulin is an upstream regulator of calcineurin

Ca²⁺ is a signalling molecule involved in virtually every aspect of cell function. The endoplasmic reticulum (ER) is an important and dynamic organelle responsible for storage of the majority of intracellular Ca²⁺. Within the ER lumen are proteins that function as Ca²⁺ buffers and/or molecular chaperones including calreticulin, a multifunctional Ca²⁺-binding protein. Calreticulin-deficiency is lethal in utero due to impaired cardiac development. In the absence of calreticulin Ca²⁺ storage capacity in the ER and InsP₃ receptor mediated Ca²⁺ release from ER are compromised. Remarkably, over-expression of constitutively active calcineurin in the hearts of calreticulin deficient mice rescues them from embryonic lethality and produces live calreticulin deficient animals. These observations provide first evidence that calreticulin is a key upstream regulator of calcineurin in the Ca²⁺-signalling cascade and they highlight the importance of ER during early stages of cellular commitment and tissue development during organogenesis.     

Cell dynamics and gene expression control in tissue homeostasis and development

During tissue and organ development and maintenance, the dynamic regulation of cellular proliferation and differentiation allows cells to build highly elaborate structures. The development of the vertebrate retina or the maintenance of adult intestinal crypts, for instance, involves the arrangement of newly created cells with different phenotypes, the proportions of which need to be tightly controlled. While some of the basic principles underlying these processes developing and maintaining these organs are known, much remains to be learnt from how cells encode the necessary information and use it to attain those complex but reproducible arrangements. Here, we review the current knowledge on the principles underlying cell population dynamics during tissue development and homeostasis. In particular, we discuss how stochastic fate assignment, cell division, feedback control and cellular transition states interact during organ and tissue development and maintenance in multicellular organisms. We propose a framework, involving the existence of a transition state in which cells are more susceptible to signals that can affect their gene expression state and influence their cell fate decisions. This framework, which also applies to systems much more amenable to quantitative analysis like differentiating embryonic stem cells, links gene expression programmes with cell population dynamics.     

Effects of SH group reagents on creatine kinase interaction with the mitochondrial membrane

Solubilization of the specific mitochondrial isoenzyme of creatine kinase (CKm) from rabbit heart mitochondria by treatment with SH group reagents has been studied. From the various compounds tested only the negatively charged organomercurials are able to induce an extensive solubilization of the enzyme. This effect is fully reversible since the solubilized enzyme readily reassociates with the membrane when the bound organomercurial is removed by treatment of the homogenate by an excess of dithiothreitol. Solubilization by negatively charged organomercurials can be partly prevented by pretreatment of mitochondria with either disulfide or uncharged organomercurials. No clear-cut relationship has been pointed out when the amount of SH titrated by various reagents has been compared with the extent of CKm solubilization. More detailed studies with para-chloromercuribenzoate (pCMB) show that extensive CKm solubilization (about 75%) occurs for pCMB concentration as low as 25 microM, whereas pronounced inhibition of the enzyme is observed only for concentrations greater than 200 microM. By cross-reassociation of enzyme solubilized either by para-hydroxymercuribenzoate (pHMB) or by 20 mM sodium phosphate (NaPi) with mitochondria depleted of CKm by pHMB or by NaPi treatment, SH groups whose titration impedes CKm reassociation with the mitochondrial membrane have been tentatively located on the enzyme. Thus, negatively charged organomercurials, could induce a reversible conformational modification of the enzyme which is no longer able to bind on the inner mitochondrial membrane. Furthermore, our results show that the binding of an excess of mitochondrial CK, which has been previously reported, could reflect unspecific binding since it occurs only on mitoplasts incubated in very hypotonic medium, but not in isotonic medium.     

黄土高原退耕还草地C、N、P生态化学计量特征对植物多样性的影响

为探讨退耕还草地生态化学计量特征随恢复年限的变化以及其对植物多样性的影响,选取黄土高原不同恢复年限退耕还草地为研究对象,分别为农田(对照)、恢复8 a、15 a、25 a和35 a,测定了植物地上部分和土壤C、N、P含量,并分析了其C∶N∶P化学计量特征与植物多样性之间的关系。结果表明:(1)总体上,随着恢复年限的增加,植物地上部分C、N、P含量呈现增长趋势,而其C∶N、C∶P以及N∶P呈现降低趋势,其中C含量在恢复35 a时达到最大值(434.95 g/kg);N含量在农田阶段最高(2.29 g/kg),P含量在恢复25 a时达到最高(1.23 g/kg)。(2)土壤C、N、P含量及N∶P随恢复年限的增加总体上呈现增加趋势,C∶N呈现降低趋势,而C∶P基本保持不变;土壤C、N、P含量的最大值均出现在恢复35 a,其值分别为10.94 g/kg、0.07 g/kg、0.06 g/kg。(3)随着植物地上部分C含量和C∶N的增加,Shannon-Weiner指数降低;植物地上部分C含量和土壤P含量是影响Simpson指数的主要因子,其与植物地上部分C含量负相关,而与土壤P含量显著正相关;Pielou均匀度指数与土壤N含量、N∶P、C∶P以及植物地上部分C含量等因子正相关;Margalef指数与植物地上部分N含量、P含量等因子正相关。研究表明草地恢复中植物和土壤C∶N∶P化学计量特征对植物多样性具有重要的影响。