Nuclear envelope disassembly and nuclear lamina depolymerization during germinal vesicle breakdown in starfish

During germinal vesicle breakdown (GVBD) in starfish, the nuclear envelope disassembles before the nuclear lamina completely depolymerizes, judging from correlative ultrastructural, immunolabeling, and light microscopic analyses. At 13 degrees C, prophase-arrested oocytes of Pisaster ochraceus begin GVBD and rapidly undergo nuclear envelope disassembly about 50 min after addition of the maturation-inducing hormone 1-methyladenine (1-MA). The nuclear lamina of these oocytes, however, remains present for 10-20 min following the vesiculation of the nuclear envelope. Completion of GVBD, as evidenced by a blending of the nuclear contents with the surrounding cytoplasm, occurs within about 15 min after the nuclear lamina has fully depolymerized. Immunofluorescence studies also indicate that a marked increase in the phosphorylations of nuclear proteins precedes the structural reorganizations of the nuclear envelope and nuclear lamina during GVBD.     

5,6,7,8-Tetrahydromethanopterin-dependent enzymes involved in methanogenesis

Abstract In the process of methanogenesis, 5,6,7,8-tetrahydromethanopterin (H₄MPT) is the carrier of the C₁ unit at the formyl through methyl state of reduction. By the transfer of a formyl group from formylmethanofuran, 5-formyl- and 10-formyl-H₄MPT are formed in hydrogenotrophic and methylotrophic organisms, respectively. Cyclohydrolysis of the 5- and 10-formyl derivatives then yields 5,10-methenyl-H₄MPT, which is reduced in two subsequent coenzyme F₄₂₀-dependent reactions to 5-methyl-H₄MPT. Following the transfer of the methyl group to coenzyme M, the substrate of the terminal step in methanogenesis, methylcoenzyme M, is produced. In this paper properties of the enzymes catalyzing the individual H₄MPT-dependent reactions are discussed.     

Species-specific effects of bombesin on gastric emptying and neurohypophyseal secretion

Previous reports have demonstrated that systemic injection of cholecystokinin (CCK) in rats produces dose-related decreases in food intake, increases in neurohypophyseal secretion of oxytocin (OT), and decreases in gastric emptying. The present studies determined whether systemic injection of bombesin (BBS), another peptide that potently reduces food intake in rats, had similar effects on OT secretion and gastric emptying. Although BBS produces a dose-dependent inhibition of food intake, even very high doses did not significantly affect plasma OT levels and only slightly decreased rates of gastric emptying. Consequently, despite their similar inhibitory effects on food intake, BBS does not appear to activate the same network of central nervous system pathways as does CCK in rats. However, parallel studies in monkeys demonstrated that systemic injection of BBS was effective in stimulating neurohypophyseal secretion of vasopressin rather than OT, in a pattern both qualitatively and quantitatively analogous to the effects of CCK in this species. Together with previous findings that BBS more potently inhibits gastric emptying in primates than in rats, these results therefore also suggest the presence of significant species differences in the central mechanisms by which BBS acts to reduce food intake.     

Transformation with a mutant Arabidopsis acetolactate synthase gene renders tobacco resistant to sulfonylurea herbicides

Summary A gene encoding acetolactate synthase was cloned from a chlorsulfuron-resistant mutant of Arabidopsis. The DNA sequence of the mutant gene differed from that of the wild type by a single base pair substitution. When introduced into tobacco by Ti plasmid-mediated transformation the gene conferred a high level of herbicide resistance. These results suggest that the cloned gene may confer agronomically useful levels of herbicide resistnace in other crop species, and that it may be useful as a selectable marker for plant transformation experiments.     

Correction of chlorophyll-defective male-sterile winter oilseed rape (Brassica napus) through organelle exchange: Characterization of the chlorophyll deficiency

Jarl, C. I., Ljungberg, U. K. and Bornman, C. H. 1988. Correction of chlorophyll-defective male-sterile winter oilseed rape ( Brassica napus ) through organelle exchange: Characterization of the chlorophyll deficiency. - Physiol. Plant. 72: 505–510.
As is known, the introduction of male-sterile Raphanus sativus L. cytoplasm into Brassica napus L. results in male-sterile oilseed rape plants, which display a temperature-related chlorophyll defect. The influences of temperature and irradiance on this defect were investigated. Compared to a line of normal (green phenotype) male-fertile oilseed rape, the male-sterile line had reduced chlorophyll content, fewer chloroplasts per cell, an altered ultrastructure of the chloroplasts and reduced activities of both photosystems, although the relative amounts of the photosystems and the chlorophyll a/b ratio were similar. The lower activity of the photosystems is explained by a decreased functional antennae size and a reduced efficiency in the interactions between the nuclear-encoded light-harvesting proteins and the reaction centres coded for by the plastome. Some thylakoid polypeptides differed in proportion between the male-fertile line with green phenotype and the male-sterile line with chlorotic phenotype. Characters, in which the two lines exhibited differences, are ascribed to difficulties in molecular communication between the oilseed rape nucleus and the radish cytoplasm, which are combined in the deficient male-sterile line.     

Constitutive and transport-related endocytotic pathways in turtle bladder epithelium

Summary Proton secretion in the urinary bladder of the fresh-water turtle is mediated by a proton pump located in the apical membrane of a population of cells characteristically rich in carbonic anhydrase. Earlier studies have demonstrated that these cells exhibit apical-membrane endocytotic and exocytotic processes which are thought to be involved in the regulation of the rate of proton transport via alterations in the number of pumps within the apical membrane. In this study, we sought to characterize these processes using two different methods. Analysis of transepithelial impedance yielded estimates of membrane capacitance which could be related to membrane area, thereby allowing one to monitor net changes in apical-membrane area resulting from changes in the net rates of endo-and exocytosis. Uptake of the fluid-phase marker FITC-dextran provided a measure of net extracellular volume uptake which was related to net rates of endocytosis. Our major conclusions are summarized as follows. The bladder cells exhibit a high baseline rate of endocytosis which appears to be a constitutive process similar to pinocytosis. This process is completely inhibited when ambient temperature is reduced to 15°C. In addition, serosal application of 0.5mm acetazolamide causes a transient increase in the rate of endocytosis, concomitant with a decrease in the rate of transport. Reduction of ambient temperature to 15°C reduces the rate of acetazolamide-induced endocytosis, but does not abolish it. Addition of 1mm serosal azide not only prevents the acetazolamide-induced increase in endocytosis, but also prevents the decrease in transport caused by acetazolamide. Azide has no effect on the baseline rate of endocytosis, nor does it prevent inhibition of carbonic anhydrase by acetazolamide. The specificity of azide, coupled with the different temperature sensitivities, demonstrate that the constitutive and transport-dependent endocytotic pathways are distinct processes. The observation that azide prevents both the acetazolamide-induced increase in endocytosis and the decrease in transport strongly supports the notion that endocytosis of proton-pump-containing membrane is requisite for the inhibition of transport by acetazolamide. Finally, the results also demonstrate that acetazolamide does not inhibit proton secretion simply by inhibiting carbonic anhydrase.     

Lymphokine production by human melanoma tumor-infiltrating lymphocytes

Summary Lymphokine production by human melanoma tumor-infiltrating lymphocytes (TIL) was studied. Uncultured TIL produced interferon (IFN), but not interleukin-2 (IL-2) or IL-4, in response to anti-CD3 mAb or IL-2. In bulk cultures, IL-2-activated TIL displaying autologous tumor-specific cytotoxicity (CTL-TIL) produced IFN in culture with medium alone, whereas IL-2-activated noncytotoxic TIL did not. Addition of anti-CD3 mAb or autologous tumor cells up-regulated IFN production in IL-2-activated TIL from 10 of 12 or 6 of 12 cases respectively. Those from 4 of 12 cases (2 CTL-TIL and 2 noncytotoxic TIL) produced IL-2 in culture with medium alone. At the clonal level, 5 (4 CD4⁺ and 1 CD8⁺) of 7 autologous tumor-specific CTL clones derived from TIL and 3 (2 CD4⁺ and 1 CD8⁺) of 7 noncytotoxic TIL clones produced IFN in culture with medium alone, which was up-regulated by adding anti-CD3 mAb. Two IFN-producing CTL clones tested produced IL-2 in 4 ×-concentrated supernatants from a 3.5-h culture with medium alone. Furthermore, 2 IFN-producing CTL clones tested expressed mRNA for both IFN and IL-2. IL-2 production and its mRNA expression were up- or down-regulated, respectively, by adding anti-CD3 mAb or autologous tumor cells. IL-4 production was not observed in culture either with medium alone or with IL-2 in any of the cells described above. Anti-CD3 mAb was required for IL-4 production in 3 of 12 IL-2-activated TIL, 2 of 6 CTL clones, and none of 5 noncytotoxic TIL clones. In summary, IFN production was characteristic of melanoma TIL. Some autologous tumor-specific CTL in TIL are suggested to be productive of IL-2 and IFN under unstimulated conditions, both being required for self-activation in an autocrine loop.This work was supported in part by grant CA-47891 from the National Cancer Institute     

Measurement and effects of gel matric potential and expressibility on production of morphogenic callus by cultured sugarbeet leaf discs

During studies to optimize production of morphogenic callus from cultured leaf discs of sugarbeet (Beta vulgaris L.) large differences were observed associated with the gelling agent employed. Water availability, as determined mainly by gel matric potential, was found to be the dominant factor. A simple method was devised to measure the relative matric potential of different gels. A precisely moistened filter-paper disc was placed on the gel surface, allowed to equilibrate, removed and weighed. The relative gain or loss of water from the paper disc was a measure of the matric potential of the gel and varied with both gel type and concentration. Leaf disc expansion and production of callus-derived embryos and shoots were shown to be directly proportional to gel matric potential. Water availability may also be affected by the ease with which liquid is expressed from gels in response to localized pressure caused by explant expansion and contortion. This property, called gel expressibility, was easily measured with a weight and capillary pipette and shown also to vary with gel type and concentration. Validity of the technique for measuring relative matric potential was verified physiologically by culturing leaf discs on filter-paper overlays to eliminate expressibility differences among gels. Additionally, comparison of leaf disc growth on uncovered gel surfaces versus filter-paper overlays demonstrated the contribution of liquid expression to overall water availability. Expression of liquid by explants on uncovered gel surfaces greatly enhanced the production of morphogenic callus.     

Oxytocin and an oxytocin agonist administered centrally decrease food intake in rats.

Intracerebroventricular administration of oxytocin (OT) and an OT agonist significantly decreased food intake in a dose-related manner in fasted rats. Central administration of an OT antagonist by itself (up to doses of 8 nmol) did not potentiate deprivation-induced food intake, but pretreatment with the OT receptor antagonist prevented the expected inhibition of food intake produced by OT and the OT agonist. Once-daily ICV injections of OT led to the development of tolerance to the inhibitory effects on food intake by the third day of treatment, but daily pretreatment with the OT antagonist prevented the development of this tolerance. In addition to causing decreased food intake, ICV administration of OT significantly increased grooming behavior but produced no dyskinesias. The inhibitory effect of OT on food intake was characterized by decreased amounts of food intake but a normal pattern of ingestion. The anorexia produced was central in nature and was not associated with altered plasma levels of hormones involved in caloric homeostasis or with changes in blood glucose. The OT agonist had relatively little effect on water intake when given in doses that significantly inhibited food intake. These results support the hypothesis that specific OT receptors within the central nervous system participate in the inhibition of feeding under certain conditions in rats.