反义寡核苷酸片段可抑制鲫鱼视网膜电压依赖性钾离子通道的表达

爪蟾卵母细胞经注射鲫鱼视网总ＲＮＡ后,可表达大量电压依赖性钾离子通道。在此基础上,我们进一步发现,一个特定序列的寡核苷酸能专一地抑制该通道的表达。由于我们设计与合成的该片段与果蝇、小鼠中已克隆的钾通道中编码Ｎ端的一个多肽的ｍＲＮＡ完全互补,因此推测：鲫鱼视网膜中的Ｋ这个区域与其它物种的Ｋ通道有高度同源性,这为克隆该基因和研究它的功能提供了重要资料。     

The presence of inhibitors of the reproduction of Varroa jacobsoni Oud. (Gamasida: Varroidae) in infested cells

The mite Varroa jacobsoni was reared in artificial gelatin cells under laboratory conditions and the possible presence of factors inhibiting Varroa reproduction was studied. In cells infested with three mites, the mean offspring per female was reduced to 75% of that in singly infested cells. When gelatin cells were used for two successive rearing cycles, both the proportion of reproducing females and the offspring per reproducing female were significantly lower in cells that had contained an infested larva during the first rearing cycle than in those with an uninfested larva. The mean reduction of the offspring per female was 48%; this suggests that inhibitors of the reproduction are released into infested cells. Treatment of gelatin cells with the hexane extract of cells in which an infested bee pupa had developed caused a 21% reduction in the mean offspring per female, with a difference close to the significance level (p=0.07).     

Oxygen-dependent electron transport and protection from photoinhibition in leaves of tropical tree species

The roles of photorespiration and the Mehlerperoxidase pathway in sustaining electron transport and protection from photoinhibition were studied in outer canopy leaves of two species of tropical trees: the drought-deciduous Pseudobombax septenatum (Jacq.) Dug. and the evergreen Ficus insipida Willd. Ficus had a higher photosynthetic capacity than Pseudobombax and also a greater capacity for light-dependent electron transport under photorespiratory conditions (in the absence of CO₂). As a consequence, in the absence of CO₂, Ficus was able to maintain a largely oxidized electron-transport chain at higher photon flux densities than Pseudobombax. Under the same light conditions, photoinhibition (reduction in F_v/F_m) was always greater in Pseudobombax than Ficus, was increased when leaves were exposed to 2% O₂ in nitrogen compared to 21% O₂ in CO₂-free air, but was not increased by the absence of CO₂. Rates of electron transport due to the Mehler-peroxidase pathway (assessed in 2% O₂ in nitrogen) ranged between 16–40 mol · m^–2·s^–1 in both species. As the dry season approached and Pseudobombax neared leaf senescence there was a decline in the capacity for photorespiratory flux to maintain electron transport in Pseudobombax, but not in Ficus. Ratios of light-dependent electron transport to net CO₂ fixation for Pseudobombax, Ficus and two other species in the field, Luehea seemannii Tr. & Planch, and Didymopanax morototoni (Aubl.) Dec. & Planch., ranged from 6.2 (Ficus) to 16.7 (Pseudobombax). High in-situ rates of photorespiration combined with the decreased capacity of Pseudobombax for photorespiratory flux as the dry season approached indicates a decreased capacity to protect against photooxidative damage. This may contribute to the promotion of leaf senescence in Pseudobombax during the transition from wet to dry season.Abbreviations F_v/F_m ratio of variable to maximum chlorophyll a fluorescence - NPQ nonphotochemical fluorescence quenching - PFD photon flux density - Q_A primary electron acceptor of PSII This research was supported by a grant from the Mellon Foundation. We thank Monica Mejia and Juan Posada for assisting with the fluorescence measurements and Aurelio Virgo for assisting with the field CO₂-exchange measurements.     

Modulation of ion currents and regulation of transmitter release in short-term synaptic plasticity: The rise and fall of the action potential

Up and down-regulation of calcium and potassium conductances are associated with several forms of short-term synaptic modulation. Detailed investigation of synaptic plasticity in the marine gastropodAplysia, and in other mollusks, indicates that synaptic transmission can be influenced in a number of ways by modulatory neurotransmitters acting through several second-messenger cascades. Modulation at the synapse itself occurs by means of the regulation of calcium current as well as through effects on processes directly involved in transmitter mobilization and exocytosis. Modulation of potassium current plays a major role in controlling neuronal excitability and may contribute to a lesser extent to the regulation of transmitter release through actions on the resting potential and on action potential configuration.     

Human immunodeficiency virus protein gp120 interferes with β-adrenergic receptor-mediated protein phosphorylation in cultured rat cortical astrocytes

Summary 1. We have previously shown that acute exposure to the HIV coat protein gp120 interferes with the -adrenergic regulation of astroglial and microglial cells (Leviet al., 1993). In particular, exposure to 100 pM gp120 for 30 min depressed the phosphorylation of vimentin and glial fibrillary acidic protein (GFAP) induced by isoproterenol in rat cortical astrocyte cultures. In the present study we have extended our analysis on the effects of gp120 on astroglial protein phosphorylation.2. We found that chronic (3-day) treatment of the cells with 100 pM gp120 before exposure to isoproterenol was substantially more effective than acute treatment in depressing the stimulatory effect of the -adrenergic agonist on vimentin and GFAP phosphorylation.3. Even after chronic treatment with gp120, no differences were found in the levels and solubility of these proteins.4. Besides stimulating the phosphorylation of intermediate filament proteins, isoproterenol inhibited the incorporation of³²P into a soluble acidic protein of 80,000M _r , which was only minimally present in Triton X-100-insoluble extracts.5. Treatment of astrocytes with a phorbol ester or exposure to³H-myristic acid indicated that the acidic 80,000M _r protein is a substrate for protein kinase C (PKC) and is myristoylated, thus suggesting that it is related to the MARCKS family of PKC substrates.6. Acute (30-min) treatment with 100 pM gp120 totally prevented the inhibitory effect of isoproterenol on the phorphorylation of the 80,000M _r MARCKS-like protein.7. Our studies corroborate the hypothesis that viral components may contribute to the neuropathological changes observed in AIDS through the alteration of signal transduction systems in glial cells.     

Neurite Outgrowth Stimulated by the Tyrosine Kinase Inhibitor Herbimycin A Requires Activation of Tyrosine Kinases and Protein Kinase C

Abstract: Activation of tyrosine kinases is established as an important mechanism for controlling growth cone motility and neurite outgrowth. We have tested the effects of a range of tyrosine kinase inhibitors on neurite outgrowth from postnatal day 4 cerebellar granule cells cultured over confluent monolayers of 3T3 fibroblasts. The only agent that had any effect was herbimycin A, which stimulated neurite outgrowth. The response is shown to be attributable to a direct effect of this tyrosine kinase inhibitor on neurones. The neurite outgrowth response to herbimycin A was inhibited by two other tyrosine kinase inhibitors, which on their own did not affect neurite outgrowth. The data suggest that the response to herbimycin A reflects either a direct or indirect activation of one or more protein tyrosine kinases. Independent signalling events downstream from tyrosine kinase activation underlying the neurite outgrowth response to herbimycin A include increased activity of protein kinase C and calcium influx into neurones through both N-and L-type calcium channels.     

Vasoactive Intestinal Peptide and Forskolin Stimulate Interleukin 6 Production by Rat Cortical Astrocytes in Culture via a Cyclic AMP-Dependent, Prostaglandin-Independent Mechanism

Abstract: In this study we analyzed the involvement of the cyclic AMP (cAMP)-protein kinase A system in the regulation of interleukin 6 production by cultured cortical astrocytes. Vasoactive intestinal peptide strongly increased, in a dose-dependent manner, interleukin 6 production. This effect was reduced when protein kinase A was blocked by KT-5720; it was not affected by calphostin C, a protein kinase C inhibitor. Forskolin caused a concentration-dependent increase in interleukin 6 release that was also inhibited by KT-5720. Because prostaglandins are believed to play a role in interleukin 6 production, we tried to determine whether the stimulatory effects of vasoactive intestinal peptide and forskolin on cytokine release might be mediated by stimulation of prostaglandin production in cortical astrocytes. Vasoactive intestinal peptide did not increase the production of either prostaglandin E₂ or F_2α. Conversely, forskolin concentration-dependently stimulated the production of both prostaglandins, an effect that was blocked by indomethacin. Indomethacin did not affect either vasoactive intestinal peptide- or forskolin-stimulated interleukin 6 production. To exclude the possibility that prostaglandins participate in interleukin 6 production induced by forskolin, we tested prostaglandins E₂ and F_2α. The former was completely ineffective in eliciting the cytokine production, whereas prostaglandin F_2α slightly increased interleukin 6 production only at the highest concentrations. 8-Bromo-cAMP and dibutyryl-cAMP stimulated interleukin 6 production to a lesser extent than vasoactive intestinal peptide and forskolin. In conclusion, we provide evidence that vasoactive intestinal peptide increases interleukin 6 production by astrocytes through the stimulation of the cAMP-protein kinase A pathway, an effect that is reproduced by cAMP analogues. In addition, we point out that prostaglandins are not involved in vasoactive intestinal peptide- and forskolin-mediated induction of interleukin 6 production in cultured astrocytes.     

Phosphorylation of pollen proteins in relation to self-incompatibility in rye (Secale cereale L.)

The gametophytic two-locus self-incompatibility (SI) system in rye was investigated in view of a possible involvement of protein phosphorylation and Ca²⁺ as constituents of a signal transduction mechanism. Phosphorylation kinetics in pollen grains was found to be significantly different after in vitro treatment of pollen with either cross or self stigma proteins, with a pronounced phosphorylation activity in self-treated pollen grains. Loss of SI in self-compatible (SC) mutants was associated with a significantly decreased basic phosphorylation activity in untreated pollen grains as compared to SI genotypes. Separation of phosphorylated pollen proteins by SDS-PAGE reveals four major proteins in the MW range of 43–82 kDa which were differently phosphorylated in SI vs SC genotypes as well as in cross vs self-treated pollen grains. Application of different protein kinase inhibitors and the Ca²⁺ antagonists verapamil and La³⁺ to isolated stigmas resulted in an inhibition of the SI response in in vitro self-pollination. The role of protein kinases and Ca²⁺ as constituents of a putative SI-specific signal transduction mechanism is discussed.