Contents of Volume 53

Plant Molecular Biology -     

The Stress Hormone Corticosterone Increases Synaptic ��-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid (AMPA) Receptors via Serum- and Glucocorticoid-inducible Kinase (SGK) Regulation of the GDI-Rab4 Complex

Corticosterone, the major stress hormone, plays an important role in regulating neuronal functions of the limbic system, although the cellular targets and molecular mechanisms of corticosteroid signaling are largely unknown. Here we show that a short treatment of corticosterone significantly increases α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR)-mediated synaptic transmission and AMPAR membrane trafficking in pyramidal neurons of prefrontal cortex, a key region involved in cognition and emotion. This enhancing effect of corticosterone is through a mechanism dependent on Rab4, the small GTPase-controlling receptor recycling between early endosome and plasma membrane. Guanosine nucleotide dissociation inhibitor (GDI), which regulates the cycle of Rab proteins between membrane and cytosol, forms an increased complex with Rab4 after corticosterone treatment. Corticosterone also triggers an increased GDI phosphorylation at Ser-213 by the serum- and glucocorticoid-inducible kinase (SGK). Moreover, AMPAR synaptic currents and surface expression and their regulation by corticosterone are altered by mutating Ser-213 on GDI. These results suggest that corticosterone, via SGK phosphorylation of GDI at Ser-213, increases the formation of GDI-Rab4 complex, facilitating the functional cycle of Rab4 and Rab4-mediated recycling of AMPARs to the synaptic membrane. It provides a potential mechanism underlying the role of corticosteroid stress hormone in up-regulating excitatory synaptic efficacy in cortical neurons.     

Size-dependent mortality in a Neotropical savanna tree: the role of height-related adjustments in hydraulic architecture and carbon allocation

Size-related changes in hydraulic architecture, carbon allocation and gas exchange of Sclerolobium paniculatum (Leguminosae), a dominant tree species in Neotropical savannas of central Brazil (Cerrado), were investigated to assess their potential role in the dieback of tall individuals. Trees greater than ∼6-m-tall exhibited more branch damage, larger numbers of dead individuals, higher wood density, greater leaf mass per area, lower leaf area to sapwood area ratio (LA/SA), lower stomatal conductance and lower net CO₂ assimilation than small trees. Stem-specific hydraulic conductivity decreased, while leaf-specific hydraulic conductivity remained nearly constant, with increasing tree size because of lower LA/SA in larger trees. Leaves were substantially more vulnerable to embolism than stems. Large trees had lower maximum leaf hydraulic conductance ( K _leaf) than small trees and all tree sizes exhibited lower K _leaf at midday than at dawn. These size-related adjustments in hydraulic architecture and carbon allocation apparently incurred a large physiological cost: large trees received a lower return in carbon gain from their investment in stem and leaf biomass compared with small trees. Additionally, large trees may experience more severe water deficits in dry years due to lower capacity for buffering the effects of hydraulic path-length and soil water deficits.     

数种昆虫5S rRNA结构特点的比较

比较已知结构的昆虫5S rRNA的核苷酸顺序,发现同科、同目的昆虫比不同科、不同目的昆虫有较少的核苷酸差别.根据Kimura和Ohta(1972)提出的经验公式,绘制了数种昆虫的系统发育图.结果表明,从分子进化得到的结论和经典分类基本上是一致的.根据DeWachter等(1982)提出的二级结构模型,归纳分析这些昆虫5S rRNA,发现保守位点与半保守位点(同一位点仅出现二种核苷酸残基)之和几乎占整个5S rRNA分子的100%.     

陕西省棘蝇属一新种(双翅目:蝇科)

整理近年来采自我国秦岭山区的蝇科标本中,发现棘蝇属Phaonia R.-D.一新种。模式标本保存于沈阳师范学院生物系。     

桑蚕促前胸腺激素的作用与前胸腺分泌活动的某些特点

本工作以前胸腺的体外器官培养技术和蜕皮激素的放射免疫分析法(MH-RIA)相结合,研究了桑蚕(Bombyx mori)促前胸腺激素(PTTH)的作用与前胸腺分泌的某些特点。结果表明,被PTTH激活后的前胸腺,在一定的时相过程内合成并分泌脱皮甾类激素;前胸腺本体不积累蜕皮甾类激素;PTTH对前胸腺的作用是积累性的;五龄不同天数的前胸腺合成分泌脱皮甾类激素的能力不同,并有不同的剂量反应。     

B7-2胚胎性癌细胞诱导分化过程中的表型转变

胚胎性癌细胞(简称EC细胞)作为一类肿瘤(畸胎瘤)的干细胞近年受到广泛的重视,从胚胎学、肿瘤学和分子生物学等许多学科领域都应用它作为实验材料,离体诱导分化研究是其中的一个方面。B 7-2 EC细胞是我们从129品系小鼠的自发睾丸畸胎瘤中分离克隆得到的一株多能EC细胞,它在同种同基因小鼠     

体外分化的人体巨噬细胞抑制天然杀伤(NK)细胞的研究

本文继先前工作后,进一步应用正常健康人外周血单个核细胞(PBMNC)经塑料培皿粘附技术把单核细胞分离出来,经培养进一步纯化,随后动态观察培养0,2,4,6和8天的单核-巨噬细胞的形态变化和对新鲜分离同种异基因个体PBMNC中NK活性的影响。实验表明,体外分化6天和8天的巨噬细胞质/核比例和胞浆内空泡显著增加,细胞直径约为0天时的2倍。这些细胞和PBMNC之比为0.5:1时,引起了NK细胞活性的50%以上抑制(4小时~(51)Cr标记K 562肿瘤的同位素释放试验)。这种抑制效应不为过氧化氢酶(Catalase 4000单位/毫升)和前列腺素合成酶的抑制剂(Indom 1×10~(-5)M)所阻断。实验证明,同种异基因个体的NK细胞不能识别巨噬细胞表面抗原,从而排除了巨噬细胞和K562肿瘤抗原竞争的可能性。实验还表明,巨噬细胞对NK活性的抑制是不受HLA约束的。应用高频超声振荡破碎巨噬细胞膜方法和免疫调变技术进一步提示,人体巨噬细胞对NK活性的抑制与巨噬细胞体积无关,而与体外分化所赋有的固有特性和它们分泌的免疫调节分子有关。