Chronic amphetamine alters D-2 but not D-1 agonist-induced behavioral responses in rats

In two experiments, using different drug doses and periods of drug administration, rats were given amphetamine (AMPH) either continuously (via slow-release pellets), or intermittently (via injections). In both experiments, only the rats pretreated with intermittent AMPH subsequently showed heightened responsivity to the selective D-2 dopamine agonist LY171555 but not to SKF38393 (a D-1 agonist). This altered response to LY171555 was still present 30 days after the AMPH withdrawal, implying that D-2 dopamine receptors at least partially mediate AMPH inverse tolerance effects. The behavioral response to the D-2 agonist was clearly different in animals receiving high versus low doses of AMPH, suggesting that different drug-state learning may have occurred during pretreatment. In a third experiment, in which rats were given repeated daily injections of either the D-1 or the D-2 agonist, only rats pretreated with the D-2 agonist and subsequently injected with the D-2 agonist clearly showed heightened responsivity. These data imply an important role of D-2 receptors in the AMPH inverse tolerance effect.     

A chimeric ubiquitin conjugating enzyme that combines the cell cycle properties of CDC34 (UBC3) and the DNA repair properties of RAD6 (UBC2): implications for the structure, function and evolution of the E2s.

The CDC34 (UBC3) protein from Saccharomyces cerevisiae has a 125 residue tail that contains a polyacidic region flanked on either side by sequences of mixed composition. We show that although a catalytic domain is essential for CDC34 activity, a major cell cycle determinant of this enzyme is found within a 74 residue segment of the tail that does not include the polyacidic stretch or downstream sequences. Transposition of the CDC34 tail onto the catalytic domain of a functionally unrelated E2 such as RAD6 (UBC2) results in a chimeric E2 that combines RAD6 and CDC34 activities within the same polypeptide. In addition to the tail, the cell cycle function exhibited by the chimera and CDC34 is probably dependent on a conserved region of the catalytic domain that is shared by both RAD6 and CDC34. Despite this similarity, the CDC34 catalytic domain cannot substitute for the DNA repair and growth functions of the RAD6 catalytic domain, indicating that although these domains are structurally related, sufficient differences exist to maintain their functional individuality. Expression of the CDC34 catalytic domain and tail as separate polypeptides are capable of only partial function; thus, while the tail displays autonomous structural characteristics, there is considerable advantage gained when both domains coexist within the same polypeptide. The ability of these and other derivatives to restore partial function to a cdc34 temperature-sensitive mutant but not to a disruption mutant suggests that interaction between two CDC34 polypeptides is a requirement of CDC34 activity. Based on this idea we propose a model that accounts for the initiating steps leading to multi-ubiquitin chain synthesis.(ABSTRACT TRUNCATED AT 250 WORDS)     

Developmental changes in keratin patterns during epidermal maturation

The biochemical maturation of the epidermis of Xenopus laevis was examined through an identification of the keratins expressed at selected stages of development. The keratin patterns obtained were compared to those observed in the adult epidermis and two Xenopus non-epidermal, epithelial cell lines. The keratins expressed during development can be grouped into three classes: (1) keratins which are restricted to the embryonic epidermis (58 and 59 kDa); (2) keratins which are prominent during development, but become minor components of the adult epidermis (47, 48, and 60 kDa); and (3) keratins which accumulate during development to become the major keratins of the adult epidermis (49, 53, 56, and 63 kDa). The embryo-specific keratins are present at all developmental stages prior to metamorphosis which we have investigated, but disappear when the epidermis keratinizes during metamorphosis. Both class 1 and 2 keratins, while undetectable or minor components of the adult skin, are present in the two non-epidermal cell lines. In contrast, the class 3 keratins show little overlap with the keratins of these cell lines. All of the class 3 keratins appear after hatching with the exception of the 53-kDa keratin which is present at the earliest developmental stage which we have examined. All of the major keratins of the adult epidermis accumulate as metamorphosis proceeds, while the embryo-restricted keratins are gradually lost.     

Foraminifera and meiofauna on an intertidal mudflat,Cornwall, England: Populations; respiration and secondary production; and energy budget

A rich and varied meiofauna inhabits a Cornish mudflat near the mouth of the Tamar River in southwestern England. Population densities range from 117 to 943 individuals · g^–1 (wet) sediment (1.4–11.4 × 10⁶ individuals · m^–2), with foraminifera, harpacticoid copepods and nematodes appearing in nearly equal numbers and comprising most of the meiofauna. Seasonally, meiofaunal numbers rise and fall with solar radiation and vary inversely with river discharge. Two species, the atestate allogromiid A and the calcareous Haynesina germanica (Ehrenberg), far outnumber other foraminifera; their population densities and growth rates reach maxima in spring and summer.Monthly rates of sediment respiration are locally variable, but clearly increase from winter (4.13 ml O₂ · m^–2 · h^–1 in December) to spring (38.87 ml O₂ · m^–2 · h^–1 in April). Experiments and calculations ascribe approximately 30% of this total to the meiofauna (including microfauna and microflora), 50% to bacteria and less than 20% to chemical oxidation. A tentative energy budget for the mudflat suggests that secondary production by meiofauna is small as compared with coastal environments elsewhere, and that meiofaunal production (426 Kcal · m^–2 · y^–1) is nearly twice meiofaunal respiration (252 Kcal · m^–2 · yr^–1).     

Transmission of Megatrypanum Trypanosomes to Cervus dama by Tabanidae1

Four fallow deer, Cervus dama, became infected with Trypanosoma (Megatrypanum) sp. by oral application of triturated guts from tabanids collected in an area with deer but without any cattle; four control calves remained negative. Upon challenge with triturated guts from tabanids from an area with pastured cattle, the four calves became infected with Trypanosoma (M.) theileri. The prepatent period in deer was five days or less. Haematopota spp. and Tabanus spp. were identified as vectors of the deer trypanosomes. It is concluded that the trypanosomes of C. dama belong to a Megatrypanum species that is not identical with T. theileri.     

The assembly of an H2A2,H2B2,H3,H4 hexamer onto DNA under conditions of physiological ionic strength

A novel nucleohistone particle is generated in high yield when a complex of DNA with the four core histones formed under conditions that are close to physiological (0.15 M NaCl, pH 8) is treated with micrococcal nuclease. The particle was found to contain 102 base pairs of DNA in association with six molecules of histones in the ratio 2H2A:2H2B:1H3:1H4 after relatively brief nuclease treatment. Prolonged nuclease digestion resulted in a reduction in the DNA length to a sharply defined 92-base pair fragment that was resistant to further degradation. Apparently normal nucleosome core particles containing two molecules each of the four core histones in association with 145 base pairs of DNA and a particle containing one molecule each of histones H2A and H2B in association with approximately 40 base pairs of DNA were also generated during nuclease treatment of the histone-DNA complexes formed under physiological ionic strength conditions. Kinetic studies have shown that the hexamer particle is not a subnucleosomal fragment produced by the degradation of nucleosome core particles. Furthermore, the hexamer particle was not found among the products of nuclease digestion when histones and DNA were previously assembled in 0.6 M NaCl. The high sedimentation coefficient of the hexameric complex (8 S) suggests that the DNA component of the particle has a folded conformation.     

Elevated CO2 alters anatomy,physiology, growth,and reproduction of red mangrove (Rhizophora mangle L.)

Mangroves, woody halophytes restricted to protected tropical coasts, form some of the most productive ecosystems in the world, but their capacity to act as a carbon source or sink under climate change is unknown. Their ability to adjust growth or to function as potential carbon sinks under conditions of rising atmospheric CO₂ during global change may affect global carbon cycling, but as yet has not been investigated experimentally. Halophyte responses to CO₂ doubling may be constrained by the need to use carbon conservatively under water-limited conditions, but data are lacking to issue general predictions. We describe the growth, architecture, biomass allocation, anatomy, and photosynthetic physiology of the predominant neotropical mangrove tree, Rhizophora mangle L., grown solitarily in ambient (350 ll^–1) and double-ambient (700 ll^–1) CO₂ concentrations for over 1 year. Mangrove seedlings exhibited significantly increased biomass, total stem length, branching activity, and total leaf area in elevated CO₂. Enhanced total plant biomass under high CO₂ was associated with higher root:shoot ratios, relative growth rates, and net assimilation rates, but few allometric shifts were attributable to CO₂ treatment independent of plant size. Maximal photosynthetic rates were enhanced among high-CO₂ plants while stomatal conductances were lower, but the magnitude of the treatment difference declined over time, and high-CO₂ seedlings showed a lower P_max at 700 ll^–1 CO₂ than low-CO₂ plants transferred to 700 ll^–1 CO₂: possible evidence of downregulation. The relative thicknesses of leaf cell layers were not affected by treatment. Stomatal density decreased as epidermal cells enlarged in elevated CO₂. Foliar chlorophyll, nitrogen, and sodium concentrations were lower in high CO₂. Mangroves grown in high CO₂ were reproductive after only 1 year of growth (fully 2 years before they typically reproduce in the field), produced aerial roots, and showed extensive lignification of the main stem; hence, elevated CO₂ appeared to accelerate maturation as well as growth. Data from this long-term study suggest that certain mangrove growth characters will change flexibly as atmospheric CO₂ increases, and accord with responses previously shown in Rhizophora apiculata. Such results must be integrated with data from sea-level rise studies to yield predictions of mangrove performance under changing climate.     

Physical mapping of three fruit ripening genes：Endopolygalacturonase,ACC oxidase and ACC synthase from apple（Malus x domestica） in an apple rootstock A106（Malus sieboldii

The apple rootstock,A106(Malus sieboldii),had 17 bivalents in pollen mother cells at meiotic metaphase 1,and 17 chromosomes in a haploid pollen cell.Karyotypes were prepared from root-tip cells with 2n=34 chromosomes,Seven out of 82 karyotypes(8.5%) showed one pari of satellites at the end of the short arm of chromosome 3.C-bands were shown on 6 pairs of chromosomes 2,4,6,8,14,and 16 near the telomeric regions of short arms.Probes for three ripening-related genes from Malus x domestica:endopolygalacturonase(EPG,0.6kb),ACC oxidase(1.2kb),and ACC synthase(2kb)were hybridized in situ to metaphase chromosomes of A106.Hybridization sites for the EPG gene were observed on the long arm of chromosome 14 in 15 out of 16 replicate spreads and proximal to the centromere of chromosomes 6 and 11.For the ACC oxidase gene,hylridization sites were observed in the telomeric region of the short arm of chromosomes 5 and 11 in 87% and 81% of 16 spreads respectively,proxiaml to the centromere of chromosome 1 in 81% of the spreads,and on the long arm of chromosome 13 in 50% of the spreads. Physical mapping of three fruit ripening genes in an apple rootstock A106.Twenty five spreads were studied for the ACC synthase gene and hybridization sites were observed in the telomeric region of the short arm of chromosome 12 in 96% of the spreads.chromosomes 9 and 10 in 76% of the spreads,and chromosome 17 in 56% of the spreads.     

Stress resistance in Saccharomyces cerevisiae is strongly correlated with assembly of a novel type of multiubiquitin chain.

The covalent attachment of ubiquitin (Ub) to short-lived or damaged proteins is believed to be the signal that initiates their selective degradation. In several cases, it has been shown that the proteolytic signal takes the form of a multi-Ub chain in which successive Ub molecules are linked tandemly at lysine 48 (K-48). Here we show that Ub molecules can be linked together in vivo at two other lysine positions, lysine 29 (K-29) and lysine 63 (K-63). The formation of these alternative linkages is strongly dependent on the presence of the stress-related Ub conjugating enzymes UBC4 and UBC5. Furthermore, expression of Ub carrying a K-63 to arginine 63 substitution in a strain of Saccharomyces cerevisiae that is missing the poly-Ub gene, UBI4, fails to compensate for the stress defects associated with these cells. Taken together, these results suggest that the formation of multi-Ub chains involving K-63 linkages plays an important role in the yeast stress response. In broader terms, these results also suggest that Ub is a versatile signal in which different Ub chain configurations are used for different functions.