PR-Set7-dependent lysine methylation ensures genome replication and stability through S phase

PR-Set7/SET8 is a histone H4–lysine 20 methyltransferase required for normal cell proliferation. However, the exact functions of this enzyme remain to be determined. In this study, we show that human PR-Set7 functions during S phase to regulate cellular proliferation. PR-Set7 associates with replication foci and maintains the bulk of H4-K20 mono- and trimethylation. Consistent with a function in chromosome dynamics during S phase, inhibition of PR-Set7 methyltransferase activity by small hairpin RNA causes a replicative stress characterized by alterations in replication fork velocity and origin firing. This stress is accompanied by massive induction of DNA strand breaks followed by a robust DNA damage response. The DNA damage response includes the activation of ataxia telangiectasia mutated and ataxia telangiectasia related kinase–mediated pathways, which, in turn, leads to p53-mediated growth arrest to avoid aberrant chromosome behavior after improper DNA replication. Collectively, these data indicate that PR-Set7–dependent lysine methylation during S phase is an essential posttranslational mechanism that ensures genome replication and stability.     

Co‐administration of betulinic acid and methamphetamine causes toxicity to dopaminergic and serotonergic nerve terminals in the striatum of late adolescent rats

Psychostimulant methamphetamine (METH) is toxic to striatal dopaminergic and serotonergic nerve terminals in adult, but not in the adolescent, brain. Betulinic acid (BA) and its derivatives are promising anti‐HIV agents with some toxic properties. Many METH users, particularly young men, are HIV‐positive; therefore, they might be treated with BA or its derivative for HIV infection. It is not known whether BA, or any of its derivatives, are neurotoxic in combination with METH in the adolescent brain. The present study investigated the effects of BA and binge METH in the striatum of late adolescent rats. BA or METH alone did not decrease the levels of dopaminergic or serotonergic markers in the striatum whereas BA and METH together decreased these markers in a BA dose‐dependent manner. BA+METH also caused decreases in the levels of mitochondrial complex I in the same manner; BA alone only slightly decreased the levels of this enzyme in striatal synaptosomes. BA or METH alone increased cytochrome c. METH alone decreased parkin, increased complex II and striatal BA levels. These results suggest that METH in combination with BA can be neurotoxic to striatal dopaminergic and serotonergic nerve terminals in the late adolescent brain via mitochondrial dysfunction and parkin deficit.

     

Nitrogen Utilization Efficiency in Canola Cultivars at Grain Harvest

Canola (Brassica napus L.) cultivars with improved nitrogen utilization efficiency (NUE) at grain harvest are of interest to growers to reduce fertilizer inputs. Our objective was to determine whether cultivar-specific responses in NUE (seed yield per N accumulated in the whole plant) could be related to the differences in dry matter and N partitioning among various plant parts. Four spring canola cultivars were grown in a glasshouse under the conditions of low and high N supply. When compared to high-N treatment, deficient N conditions resulted in a similar decrease in dry weight for all cultivars, averaging 46% for shoot, 47% for root, and 45% for dropped leaves. The reductions in N concentrations at low-N compared to high-N treatment were much smaller and averaged 15% for shoot, 16% for root and 10% for dropped leaves. Although significant variations occurred for dry weight, N concentration and N uptake in various plant sections, all cultivars accumulated a similar amount of N in total plant biomass at harvest. However, significant differences in plant biomass, seed yield and consequently, NUE existed because more N-efficient cultivars Eyre and Charlton produced larger seed yields than less N-efficient cultivars Pinnacle and Rainbow. No consistent variations in N concentration in various plant parts could be established among tested cultivars. Thus, cultivar-specific responses in NUE were mainly attributed to the differences in the root-to-shoot ratio and harvest index. N-efficient Eyre produced seed yield similar to the highest yielding Charlton, though it had the smallest plant dry weight of all cultivars. In contrast, N-inefficient Rainbow had the largest plant biomass, but produced the smallest seed yield because of its lowest harvest index and the highest root-to-shoot ratio. The absence of cultivar×N treatment interactions indicated that cultivars performed similarly for plant biomass, N uptake and seed yield across two contrasting N supplies. Canola cultivars significantly differed in NUE despite a similar amount of absorbed N in plant biomass; more N-efficient cultivars outyielded less N-efficient ones primarily because of cultivar-specific variations in the root-to-shoot ratio and harvest index.     

The effect of manganese supply on exudation of carboxylates by roots of lucerne (Medicago sativa)

Some low-molecular-weight carboxylates commonly found in plant root exudates have the potential to increase the availability of Mn in the rhizosphere. Release of various compounds into the rhizosphere by plant roots may also be a mechanism by which certain species and genotypes are able to tolerate conditions of low Mn availability better than others. Lucerne (Medicago sativa L.) plants of Salado, a genotype tolerant to Mn deficiency, and Sirosal, an intolerant genotype, were grown in solution culture with 0, 5 or 500 nM Mn (Mn-0, Mn-5 and Mn-500). Exudates of whole root systems were collected at 14, 24 and 36 d and analysed by HPLC. Oxalate, tartarate, L-malate, lactate, malonate, maleate, citrate and succinate were detected and quantified in exudates under all Mn treatments. Malonate, citrate and succinate accounted for the majority of carboxylates in the exudates. Exudation increased with plant age, but amounts of individual carboxylates remained constant in proportion to the total amount exuded. A significant increase in exudation of all carboxylates other than malonate and maleate resulted from omission of Mn from nutrient solutions. Salado exuded more oxalate, tartarate, L-malate, lactate, citrate and succinate than Sirosal at Mn-0, and more citrate and succinate than Sirosal at Mn-5. Genotypic differences in carboxylate exudation under Mn-0 were associated with production of roots with diameter <100 μm. Plant Mn concentrations and growth rates suggested carboxylate exudation differences were not the sole factor responsible for differential tolerance to Mn deficiency in the lucerne genotypes.     

Uptake of zinc from chelate-buffered nutrient solutions by wheat genotypes differing in zinc efficiency

Zinc-efficient Triticum aestivum (cv. Warigal) and Zn-inefficientTriticum turgidum conv. durum (cv. Durati) were grown in chelate-buffered,complete nutrient solutions providing either deficient or sufficientZn supply. When transferred to fresh chelatebuffered nutrientsolutions containing a wide range of Zn supplies (0–1.28µmol m^–3 Zn²⁺ activity) for 24–48 h, bothgenotypes increased net Zn uptake linearly with an increasein solution Zn²⁺ activities. Zincefficient Warigal accumulatedZn at a greater rate than Zn-inefficient Durati. The greaterrate of net Zn uptake was observed by plants of both genotypeswhen pretreated at deficient Zn supply. Net loss of Zn to thesolution was higher in plants pretreated with sufficient Znand was inversely related to Zn²⁺ activity in the external solution.When continuously supplied with 40 nmol m^–3 Zn²⁺, netZn uptake by Zn-efficient Warigal was significantly greaterthan that of Zn-inefficient Durati, but the difference diminishedwith plant age. Shoot concentrations of Fe, Mn and Cu were higherwhen plants were grown at deficient than at sufficient Zn supply.The Zn-efficient genotype transported less Zn and Fe to shootsand had higher Fe concentrations in roots than the Zn-inefficientgenotype, supporting the hypothesis that Zn efficiency may beconnected with inefficient transport of Fe from roots to shootsand thus initiation of the Fe-deficiency response resultingin increased release of Zn- and Fe-binding phytosiderophores.It is concluded that differential Zn efficiency of wheat genotypesis at least partly due to a greater ability of efficient genotypesto accumulate Zn. Key words: Chelate-buffering, genotypes, micronutrients, Triticum spp., uptake, zinc efficiency     

Effects of 4-hydroxy-4-androstene-3,17-dione and 10-propargylestr-4-ene-3,17-dione on the metabolism of androstenedione in human breast carcinoma and breast adipose tissues

The effects of 4-hydroxy-4-androstene-3,17-dione (4-OH-A) and 10-propargylestr-4-ene-3,17-dione (PED) on the aromatization of androstenedione (A) and the conversion of A to testosterone (T) were studied in incubations with breast carcinoma and breast adipose tissues. Parallel studies were carried out to determine the effects of 4-OH-A and PED on A metabolism in tissue from 5 patients with breast carcinoma. At 11 μM, both compounds fully inhibited aromatization, whereas the conversion of A to T was decreased in only 2 incubations.Studies with varying concentrations of 4-OH-A and PED demonstrated that both compounds inhibited estrone (E₁) formation by 80% at a concentration of 0.085 μM, with maximum effect at 0.34 μM. 90% inhibition of estradiol (E₂) formation was observed at inhibitor concentrations of 0.17 μM or greater. T formation was slightly affected at 0.67 μM, but was progressively inhibited with increasing 4-OH-A or PED concentrations, reaching 70% at 11 μM.Similar experiments with 4-OH-A in breast adipose tissue homogenates showed that a concentration of 0.1 μM was sufficient to inhibit aromatization while T inhibition required 11 μM.4-OH-A and PED are selective inhibitors of aromatization in human breast tissues and may provide a mechanism for controlling estrogen responsive processes.     

The analogs of oxytocin and D-homoarginine vasopressin with bulky substituted phenylalanine in position 2

Summary Solid phase technique on p-methylbenzhydrylamine resin was used for the synthesis of eight analogs of oxytocin and 8-D-homoarginine vasopressin with the non-coded amino acids L- or D-2,3,4,5,6-pentamethylphenylalanine and L- or D-4-phenylphenylalanine in position 2. The preparation of the above mentioned non-coded amino acids is described as well. All eight analogs were found to be potent inhibitors of oxytocin activity in the uterotonicin vitro test in the absence of Mg²⁺ ions. In the uterotonic testin vitro in the presence of Mg²⁺ and in the testin vivo, their potency is strongly decreased or completely abolished. The substances are also weak pressor inhibitors. The L or D configuration does not seem to influence the activity significantly. Abbreviations: All the chiral amino acids unless otherwise stated are of the L-series. Phe(4-Ph) denotes the 4-phenylphenylalanine, Phe(pentaMe) the 2,3,4,5,6-pentamethylphenylalanine, Har the homoarginine, DMF dimethylformamide, OHBT 1-hydroxybenzotriazole and DCC dicylohexyl-carbodiimitz. The Nomenclature and symbols of the amino acids and peptides obey the published recommendations: IUPAC-IUB Joint Commission on Biochemical Nomenclature: Eur. J. Biochem., 138 (1984) 9.