Salt tolerance requires cortical microtubule reorganization in Arabidopsis

Although the results of some studies indicate that salt stress affects the organization of microtubules, it remains an open question whether microtubules play an active role in the plant's ability to withstand salt stress. In the present study, we showed that salt stress-induced wild-type Arabidopsis seedling roots display right-handed skewed growth and depolymerization of the cortical microtubules. The results of a long-term observational study showed that cortical microtubules depolymerized then reorganized themselves under salt stress. Stabilization of microtubules with paclitaxel resulted in more seedling death under salt stress, while disruption of microtubules with oryzalin or propyzamide rescued seedlings from death. Seedlings in which the cortical microtubules were reorganized did not succumb to salt stress. These results suggest that both depolymerization and reorganization of the cortical microtubules are important for the plant's ability to withstand salt stress. Depolymerizing microtubules by drugs rescues seedlings from death under salt stress. This rescue effect was abolished by removing calcium from the medium or treatment with a calcium channel inhibitor. Depolymerization of the microtubules is followed by an increase in the free cytoplasmic calcium concentration. The addition of calcium to the growth medium increased the number of seedlings in which recovery of the cortical microtubules occurred, whereas the removal of calcium decreased the number of seedlings in which recovery occurred. Therefore, depolymerization of the cortical microtubules raises intracellular calcium concentrations, while reorganization of the cortical microtubules and seedling survival may be mediated by calcium influx in salt stress.     

人精子甘露糖受体参与诱导卵母细胞皮质颗粒反应

目的研究人精子甘露糖受体与卵母细胞皮质颗粒反应的关系。方法以亲和层析法纯化的人精子甘露糖受体(purified mannose receptor,pMR)作用去透明带金黄地鼠卵,继而用罗丹明偶联的兵豆凝集素(Tetramethylrhodam ine Isothiocyanate Labeled Lentil,TRITC-LCA)标记。通过荧光显微镜观察被标记的皮质颗粒及卵母细胞表面甘露糖基的变化情况。结果pMR作用卵母细胞后,卵母细胞内的皮质颗粒减少且细胞表面的甘露糖基数量增加。结论pMR作用于卵母细胞表面后,可触发皮质颗粒反应,并使皮质颗粒部分内容物转移到卵母细胞表面。     

Fusicoccin affects cortical microtubule orientation in the isolated epidermis of sunflower hypocotyls

Epidermal peels isolated from sunflower hypocotyls provide a convenient model to study the relationship between cortical microtubule orientation and strain rate. Extension of peels can be modulated using chemical treatment and mechanical stress, i.e., by adding a chemical to the incubation medium and applying a load exceeding the yield threshold for irreversible (plastic) strain. In this study, peels were pre-incubated for ca. 12 h (long-term pre-incubation) or for 1 h (short-term pre-incubation). In the long-term pre-incubated peels, fusicoccin applied to the medium neither enhanced the rate of longitudinal plastic strain of loaded peels, nor affected microtubule orientation. However, fusicoccin increased the strain rate of short-term, pre-incubated peels and affected microtubule orientation in both extending (loaded) and non-extending (unloaded) peels. Without fusicoccin, microtubule orientation was generally longitudinal or steep, whereas in fusicoccin-treated unloaded peels it was transverse and oblique microtubules in peel portions corresponding to the apical part of the hypocotyl. Although the frequency of transverse orientation was increased through loading, there was no strong correlation between the rate of fusicoccin-induced strain and microtubule orientation. It is hypothesized that the insensitivity of long-term pre-incubated peels to fusicoccin with respect to strain rate is due to a lack of active plasma membrane H(+) -ATPases. Thus, the sensitivity of short-term, pre-incubated, unloaded (non-extending) peels to fusicoccin, with respect to microtubule orientation, indicates that orientation might be affected by electric currents resulting from fusicoccin stimulation of H(+) -ATPases.     

In vivo photosystem I reduction in thermophilic and mesophilic cyanobacteria: the thermal resistance of the process is limited by factors other than the unfolding of the partners

Photosystem I reduction by plastocyanin and cytochrome c(6) in cyanobacteria has been extensively studied in vitro, but much less information is provided on this process inside the cell. Here, we report an analysis of the electron transfer from both plastocyanin and cytochrome c(6) to photosystem I in intact cells of several cyanobacterial species, including a comparative study of the temperature effect in mesophilic and thermophilic organisms. Our data show that cytochrome c(6) reduces photosystem I by following a reaction mechanism involving complex formation, whereas the copper-protein follows a simpler collisional mechanism. These results contrast with previous kinetic studies in vitro. The effect of temperature on photosystem I reduction leads us to conclude that the thermal resistance of this process is determined by factors other than the proper stability of the protein partners.     

Complementary roles for dynein and kinesins in the Xenopus egg cortical rotation

Aligned vegetal subcortical microtubules in fertilized Xenopus eggs mediate the "cortical rotation", a translocation of the vegetal cortex and of dorsalizing factors toward the egg equator. Kinesin-related protein (KRP) function is essential for the cortical rotation, and dynein has been implicated indirectly; however, the role of neither microtubule motor protein family is understood. We examined the consequence of inhibiting dynein--dynactin-based transport by microinjection of excess dynamitin beneath the vegetal egg surface. Dynamitin introduced before the cortical rotation prevented formation of the subcortical array, blocking microtubule incorporation from deeper regions. In contrast, dynamitin injected after the microtubule array was fully established did not block cortical translocation, unlike inhibitory-KRP antibodies. During an early phase of cortical rotation, when microtubules showed a distinctive wavy organization, dynamitin disrupted microtubule alignment and perturbed cortical movement. These findings indicate that dynein is required for formation and early maintenance of the vegetal microtubule array, while KRPs are largely responsible for displacing the cortex once the microtubule tracks are established. Consistent with this model for the cortical rotation, photobleach analysis revealed both microtubules that translocated with the vegetal cytoplasm relative to the cortex, and ones that moved with the cortex relative to the cytoplasm.     

A C-type lectin associated and translocated with cortical granules during oocyte maturation and egg fertilization in fish

Oocyte maturation and egg fertilization in both vertebrates and invertebrates are marked by orchestrated cytoplasmic translocation of secretory vesicles known as cortical granules. It is thought that such redistribution of cellular content is critical for asymmetrical cell division during early development, but the mechanism and regulation of the process is poorly understood. Here we report the identification, purification and cDNA cloning of a C-type lectin from oocytes of a freshwater fish species gibel carp (Carassius auratus gibelio). The purified protein has been demonstrated to have lectin activity and to be a Ca(2+)-dependent C-type lectin by hemagglutination activity assay. Immunocytochemistry revealed that the lectin is associated with cortical granules, gradually translocated to the cell surface during oocyte maturation, and discharged to the egg envelope upon fertilization. Interestingly, the lectin becomes phosphorylated on threonine residues upon induction of exocytosis by fertilization and returns to its original state after morula stage of embryonic development, suggesting that this posttranslational modification may represent a critical molecular switch for early embryonic development.     

Increased seizure susceptibility and cortical malformation in beta-catenin mutant mice

Beta-catenin has been implicated in epilepsy because of its altered post seizure expression and the role of Wnt2 signaling in autism. To determine beta-catenin's role in seizure susceptibility, we injected penetylenetetrazol intraperitoneally in beta-catenin cerebral cortex- and hippocampus-specific knockout mice. We then analyzed the latency, number, and duration of four phases of seizure behaviors: (I) non-seizure activity, (II) myoclonic jerks, (III) generalized clonic seizures, and (IV) tonic seizures. The latencies to both death and Phase IV were significantly reduced in mutant mice. Mutant mice also spent significantly more time in Phases III and IV and showed significantly less time in the non-convulsive state (Phase I). Nissl and gold chloride staining indicated that the knockout mice had underdeveloped cortices, lacked a corpus callosum, and were missing hippocampal structures. This suggests that dysfunction of beta-catenin-mediated signaling pathways in mice leads to cortical malformation and increased seizure susceptibility.     

Dipyridamole is neuroprotective for cultured rat embryonic cortical neurons

The effects of a clinically useful cardiovascular agent, dipyridamole, were examined in a rodent tissue culture model of neuroprotection. Dipyridamole effectively protected rat embryonic day 18 (E18) cortical neurons from either 48 h trophic deprivation or 48 h exposure to the glutathione synthesis inhibitor, L-buthionine (R,S) sulfoximine. The neuron sparing actions of dipyridamole were time- and concentration-dependent and mimicked the actions of exogenously applied glutathione. These results demonstrate that dipyridamole protects primary neuronal cultures against either trophic or chemically mediated insults, and suggest that dipyridamole has a potent antioxidant ability that compensates for glutathione depletion in neuronal cultures.