Indirect Effects of Impoundment on Migrating Fish: Temperature Gradients in Fish Ladders Slow Dam Passage by Adult Chinook Salmon and Steelhead

Thermal layering in reservoirs upstream from hydroelectric dams can create temperature gradients in fishways used by upstream migrating adults. In the Snake River, Washington, federally-protected adult salmonids (Oncorhynchus spp.) often encounter relatively cool water in dam tailraces and lower ladder sections and warmer water in the upstream portions of ladders. Using radiotelemetry, we examined relationships between fish passage behavior and the temperature difference between the top and bottom of ladders (∆T) at four dams over four years. Some spring Chinook salmon (O. tshawytscha) experienced ∆T ≥ 0.5 °C. Many summer and fall Chinook salmon and summer steelhead (O. mykiss) experienced ∆T ≥ 1.0 °C, and some individuals encountered ΔT > 4.0°C. As ΔT increased, migrants were consistently more likely to move down fish ladders and exit into dam tailraces, resulting in upstream passage delays that ranged from hours to days. Fish body temperatures equilibrated to ladder temperatures and often exceeded 20°C, indicating potential negative physiological and fitness effects. Collectively, the results suggest that gradients in fishway water temperatures present a migration obstacle to many anadromous migrants. Unfavorable temperature gradients may be common at reservoir-fed fish passage facilities, especially those with seasonal thermal layering or stratification. Understanding and managing thermal heterogeneity at such sites may be important for ensuring efficient upstream passage and minimizing stress for migratory, temperature-sensitive species.     

Human T-lymphotropic virus type 1 oncoprotein tax promotes unscheduled degradation of Pds1p/securin and Clb2p/cyclin B1 and causes chromosomal instability

Human T-lymphotropic virus type 1 (HTLV-1) is the causative agent of adult T-cell leukemia. The HTLV-1 transactivator, Tax, is implicated as the viral oncoprotein. Na?ve cells expressing Tax for the first time develop severe cell cycle abnormalities that include increased DNA synthesis, mitotic arrest, appearance of convoluted nuclei with decondensed DNA, and formation of multinucleated cells. Here we report that Tax causes a drastic reduction in Pds1p/securin and Clb2p/cyclin B levels in yeast, rodent, and human cells and a loss of cell viability. With a temperature-sensitive mutant of the CDC23 subunit of the anaphase-promoting complex (APC), cdc23(ts); a temperature-sensitive mutant of cdc20; and a cdh1-null mutant, we show that the diminution of Pds1p and Clb2p brought on by Tax is mediated via the Cdc20p-associated anaphase-promoting complex, APC(Cdc20p). This loss of Pds1p/securin and Clb2p/cyclin B1 occurred before cellular entry into mitosis, caused a G(2)/M cell cycle block, and was accompanied by severe chromosome aneuploidy in both Saccharomyces cerevisiae cells and human diploid fibroblasts. Our results support the notion that Tax aberrantly targets and activates APC(Cdc20p), leading to unscheduled degradation of Pds1p/securin and Clb2p/cyclin B1, a delay or failure in mitotic entry and progression, and faulty chromosome transmission. The chromosomal instability resulting from a Tax-induced deficiency in securin and cyclin B1 provides an explanation for the highly aneuploid nature of adult T-cell leukemia cells.     

Homologous and heterologous desensitization and synergy in pathways leading to the soybean oxidative burst

Because the H₂O₂ and O₂ ⁻ generated during a pathogen-triggered oxidative burst could either protect or destroy a besieged plant cell, their synthesis might be expected to be tightly regulated. We have examined the nature of this regulation as it is communicated between homologous and heterologous oxidative-burst pathways, using both chemical (oligogalacturonic acid, harpin, fensulfothion) and mechanical (osmotic stress) stimuli to induce the burst. We report here that the above three chemical elicitors attenuate a subsequent oxidative burst induced in cultured soybean (Glycine max L.) cells by either the same (homologous desensitization) or a different chemical elicitor (heterologous desensitization). Further, when the magnitude of the initial oxidative burst is maximal, the cells remain refractory to subsequent elicitation for at least 10 min and then revive their sensitivities to re-stimulation with a half-time of >20 min. Mechanical stimulation of the oxidative burst appears to be regulated by a different set of constraints. Although initiation of a mechanically induced burst leads to attenuation of a subsequent mechanically induced burst, the same mechanical stimulus is peculiarly unable to reduce a subsequent chemically induced burst. The converse is also true, suggesting that heterologous desensitization of the oxidative burst does not extend to mixed chemical and mechanical/osmotic stimuli. However, communication between these disparate forms of elicitation is still demonstrated to occur, since low-level chemical stimuli strongly synergize concurrent low-level osmotic stimuli and vice versa. Furthermore, the pattern of synergy changes dramatically if one stimulus is administered immediately prior to the other. Taken together, these data demonstrate that significant cross-talk occurs among the different signaling pathways of the oxidative burst and that the overall process is tightly regulated. Received: 10 January 2000 / Accepted: 22 February 2000     

Fatty Acid Transport and Utilization for the Developing Brain

Abstract: To determine the transport and utilization of dietary saturated, monounsaturated, and n-6 and n-3 polyunsaturated fatty acids for the developing brain and other organs, artificially reared rat pups were fed a rat milk substitute containing the perdeuterated (each 97 atom% deuterium) fatty acids, i.e., palmitic, stearic, oleic, linoleic, and linolenic, from day 7 after birth to day 14 as previously described. Fatty acids in lipid extracts of the liver, lung, kidney, and brain were analyzed by gas chromatography-mass spectrometry to determine their content of each of the deuterated fatty acids. The uptake and metabolism of perdeuterated fatty acid lead to the appearance of three distinct groups of isotopomers: the intact perdeuterated, the newly synthesized (with recycled deuterium), and the natural unlabeled fatty acid. The quantification of these isotopomers permits the estimation of uptake and de novo synthesis of these fatty acids. Intact perdeuterated palmitic, stearic, and oleic acids from the diet were found in liver, lung, and kidney, but not in brain. By contrast, perdeuterated linoleic acid was found in all these organs. Isotopomers of fatty acid from de novo synthesis were observed in palmitic, oleic, and stearic acids in all tissues. The highest enrichment of isotopomers with recycled deuterium was found in the brain. The data indicate that, during the brain growth spurt and the prelude to myelination, the major saturated and monounsaturated fatty acids in brain lipids are exclusively produced locally by de novo biosynthesis. Consequently, the n-6 and n-3 polyunsaturated fatty acids must be transported and delivered to the brain by highly specific mechanisms.     

Synthesis and SAR of 2,3-diarylpyrrole inhibitors of parasite cGMP-dependent protein kinase as novel anticoccidial agents

Several analogs of 2,3-diaryl pyrroles were synthesized and evaluated as inhibitors of Eimeria tenella cGMP-dependent protein kinase and in in vivo anticoccidial assays. A 4-fluorophenyl group enhances both in vitro and in vivo activities. The most potent analogs are the 5-(N-methyl, N-ethyl, and N-methylazetidine methyl) piperidyl derivatives 12, 23, and 34. These compounds have a broad spectrum of activity. Based on the in vivo efficacy and cost of synthesis, the N-ethyl analog 23 was chosen as a novel anticoccidial agent for a field trial.     

RNA silencing of mycotoxin production in Aspergillus and Fusarium species

Mycotoxins are natural fungal products that are defined by their harmful effects on humans and animals. Aflatoxin contamination of maize by Aspergillus species and trichothecene contamination of small grains by Fusarium species are two of the most severe mycotoxin problems in the United States. We are investigating RNA silencing in an effort to identify novel ways to control mycotoxin contamination of crops. Transformation of two Aspergilli (A. flavus and A. parasiticus) and a Fusarium (F. graminearum) with inverted repeat transgenes (IRT) containing sequences of mycotoxin-specific regulatory genes suppressed mycotoxin production in all three plant-pathogenic fungi. This atoxigenic phenotype was stable during infection on corn and wheat, and importantly, F. graminearum IRT strains were less virulent on wheat than were wild type. The IRT did not alter physiological characteristics of the fungi, such as spore production and growth rate on solid media. These results indicate that RNA silencing exists in Aspergillus and Fusarium plant pathogens and suggest that RNA silencing technology may be a useful tool for eliminating mycotoxin contamination of agricultural products.