紫胶虫的生物学研究

紫胶虫Laccifer lacca(Kerr)Targ.在云南自然分布区一年发生两代,各世代有涌散、固定、泌胶、泌蜡和排泄蜜露等活动。由于幼虫在饥饿状态下的存活期较短,迁移能力较差,必须及时实行人工放养和科学管理,才能获得紫胶高产。本文报道了紫胶虫各世代的泌胶量、生殖力和性比,并提出发展紫胶生产的建议。     

lac Operator nucleosomes. 2. lac Nucleosomes can change conformation to strengthen binding by lac repressor

We have shown previously that lac repressor binds specifically and quantitatively to lac operator restriction fragments which have been complexed with histones to form artificial nucleosomes (203 base pair restriction fragment) or core particles (144 base pair restriction fragment. We describe here a quantitative method for determining the equilibrium binding affinities of repressor for these lac reconstitutes. Quantitative analysis shows that the operator-histone reconstitutes may be grouped into two affinity classes: those with an affinity for repressor close to that of naked DNA and those with an affinity 2 or more orders of magnitude less than that of naked DNA. All particles in the lac nucleosome preparations bind repressor with high affinity, but the lac core particle preparations contain particles of both high and low affinities for repressor. Formaldehyde cross-linking causes all high-affinity species to suffer a 100-fold decrease in binding affinity. In contrast, there is no effect of cross-linking on species of low affinity. Therefore, the ability of a particle to be bound tightly by repressor depends on a property of the particle which is eliminated by cross-linking. Control experiments have shown that chemical damage to the operator does not accompany cross-linking. Therefore, the property sensitive to cross-linking must be the ability of the particle to change conformation. We infer that the particles of low native affinity, like cross-linked particles, are of low affinity because of an inability to facilitate repressor binding by means of this conformational change. Dimethyl suberimidate cross-linking experiments show that histone-histone cross-linking is sufficient to preclude high-affinity binding. Thus, the necessary conformational change involves a nucleosome histone core event. We find that the ability of a particle to undergo a repressor-induced facilitating conformational change appears to depend on the position of the operator along the DNA binding path of the nucleosome core. We present a general model which proposes that nucleosomes are divided into domains which function differentially to initiate conformational changes in response to physiological stimuli.     

Storage of marine fish erythrocytes in liquid nitrogen

The preservation of erythrocytes from cod ( Gadus morhua ), saithe ( Pollachius virens ) and mackerel ( Scomber scombrus ) at −196° C was studied using dimethyl sulphoxide (DMSO) as a cryoprotectant. Erythrocyte recoveries of greater than 90% were obtained from all species and cod erythrocytes were stored for eighteen months with insignificant lysis. Larger quantities of blood were stored by removal of plasma from citrated blood prior to the addition of DMSO solution, and by storage of pelleted frozen blood in aluminium canisters in liquid nitrogen. Maximum recoveries of washed intact erythrocytes required thawing of pellets in 125% DMSO solution and washing with buffer containing decreasing concentrations of DMSO. Washed erythrocytes kept at 4° for at least two days showed little haemolysis, were morphologically similar to fresh erythrocytes and equally susceptible to the δ-haemolysin of Staphylococcus aureus .     

An internal deletion in the cytoplasmic tail reverses the apical localization of human NGF receptor in transfected MDCK cells

A cDNA encoding the full-length 75-kD human nerve growth factor receptor was transfected into MDCK cells and its product was found to be expressed predominantly (80%) on the apical membrane, as a result of vectorial targeting from an intracellular site. Apical hNGFR bound NGF with low affinity and internalized it inefficiently (6% of surface bound NGF per hour). Several mutant hNGFRs were analyzed, after transfection in MDCK cells, for polarized surface expression, ligand binding, and endocytosis. Deletionof juxta-membrane attachment sites for a cluster of O-linked sugars did not alter apical localization. A mutant receptor lacking the entire cytoplasmic tail (except for the five proximal amino acids) was also expressed on the apical membrane, suggesting that information for apical sorting was contained in the ectoplasmic or transmembrane domains. However, a 58 amino acid deletion in the hNGFR tail that moved a cytoplasmic tyrosine (Tyr 308) closer to the membrane into a more charged environment resulted in a basolateral distribution of the mutant receptor and reversed vectorial (basolateral) targeting. The basolateral mutant receptor also internalized 125I-NGF rapidly (90% of surface bound NGF per hour), exhibited a larger intracellular fraction and displayed a considerably shortened half-life (approximately 3 h). We suggest that hNGFR with the internal cytoplasmic deletion expresses a basolateral targeting signal, related to endocytic signals, that is dominant over apical targeting information in the ecto/transmembrane domains. These results apparently contradict a current model that postulates that basolateral targeting is a default mechanism.     

Kininogen and Kinin in Experimental Spinal Cord Injury

Activation of the kallikrein-kinin system has been implicated in the pathogenesis of vasogenic brain edema and posttraumatic vascular injury. We determined the levels of kininogen and kinin in an experimental spinal cord injury model in the rat. Kininogen content in traumatized cord segments increased in a time-dependent manner. Western blot analysis showed that the kininogen in traumatized cord comigrates with 68K low-molecular-weight kininogen or T-kininogen. Trypsin treatment of the kininogen in traumatized cord released both bradykinin and T-kinin, which were separated by HPLC and quantified with a kinin radioimmunoassay. Endogenous kinin levels in the frozen spinal cord also increased up to 40-fold 2 h after injury as compared with controls. The results demonstrate an increased accumulation of kininogen and its conversion to vasoactive kinins in experimental spinal cord injury.     

青海犹伊螨属一新种（蜱螨亚纲：犹伊螨科）

本文绘图描述了根田鼠犹伊螨新种Eviphis oeconomus sp.nov.,并讨论了与喜马拉雅犹伊螨E.himalayaensis Ma et Piao,1981的鉴别特征。模式标本采自青海久治县的根田鼠Microtus oeconmus Pallas体上,存放在青海省地方病防治研究所。     

俗草蛉属的研究及三新种记述(脉翅目:草蛉科)

本文报道了发现于我国的俗草蛉属Suarius 3新种:海南俗草蛉S.hainanus sp.nov.,钩俗草蛉S.hamulasus sp.nov.及楔唇俗草蛉S.sphenochilus sp.nov.新种模式标本保存于北京农业大学昆虫标本室。     

中国草蛉科二新属记述（昆虫纲：脉翅目）

脉翅目(Neuroptera)草蛉科(Chrysopidae)作为一类重要天敌资源,在我国各地非常丰富,大量的标本有待鉴定。本文主要记述2新属及其所属种类,模式标本均保存于北京农业大学昆虫标本室。