eIF4E promotes nuclear export of cyclin D1 mRNAs via an element in the 3'UTR

The eukaryotic translation initiation factor eIF4E is a critical modulator of cellular growth with functions in the nucleus and cytoplasm. In the cytoplasm, recognition of the 5' m(7)G cap moiety on all mRNAs is sufficient for their functional interaction with eIF4E. In contrast, we have shown that in the nucleus eIF4E associates and promotes the nuclear export of cyclin D1, but not GAPDH or actin mRNAs. We determined that the basis of this discriminatory interaction is an approximately 100-nt sequence in the 3' untranslated region (UTR) of cyclin D1 mRNA, we refer to as an eIF4E sensitivity element (4E-SE). We found that cyclin D1 mRNA is enriched at eIF4E nuclear bodies, suggesting these are functional sites for organization of specific ribonucleoproteins. The 4E-SE is required for eIF4E to efficiently transform cells, thereby linking recognition of this element to eIF4E mediated oncogenic transformation. Our studies demonstrate previously uncharacterized fundamental differences in eIF4E-mRNA recognition between the nuclear and cytoplasmic compartments and further a novel level of regulation of cellular proliferation.     

Molecular analysis of Arabidopsis endosperm and embryo promoter trap lines: reporter-gene expression can result from T-DNA insertions in antisense orientation, in introns and in intergenic regions, in addition to sense insertion at the 5' end of genes

Random insertions of promoterless reporter genes in genomes are a common tool for identifying marker lines with tissue-specific expression patterns. Such lines are assumed to reflect the activity of endogenous promoters and should facilitate the cloning of genes expressed in the corresponding tissues. To identify genes active in seed organs, plant DNA flanking T-DNA insertions (T-DNAs) have been cloned in 16 Arabidopsis thaliana GUS-reporter lines. T-DNAs were found in proximal promoter regions, 5' UTR or intron with GUS in the same (sense) orientation as the tagged gene, but contrary to expectations also in inverted orientation in the 5' end of genes or in intergenic regions. RT-PCR, northern analysis, and data on expression patterns of tagged genes, compared with the expression pattern of the reporter lines, suggest that the expression pattern of a reporter gene will reflect the pattern of a tagged gene when inserted in sense orientation in the 5' UTR or intron. When inserted in the promoter region, the reporter-gene expression patterns may be restricted compared with the endogenous gene. Among the trapped genes, the previously described nitrate transporter gene AtNRT1.1, the cyclophilin gene ROC3, and the histone deacetylase gene AtHD2C were found. Reporter-gene expression when positioned in antisense orientation, for example, in the SLEEPY1 gene, is indicative of antisense expression of the tagged gene. For T-DNAs found in intergenic regions, it is suggested that the reporter gene is transcribed from cryptic promoters or promoters of as yet unannotated genes.     

Adaptive phenotypic plasticity of gypsy moth digestive enzymes

The adaptiveness of plasticity of digestive enzyme responses to allelochemical stress was tested on 32 full-sib families of gypsy moth larvae from an oak forest population (the Quercus population) and 26 families from a locust-tree forest (the Robinia population), reared either on control diet, or on tannin-supplemented diet. Using the duration of larval development as an indirect measure of fitness, phenotypic selection analyses revealed that lower specific activities of total proteases and trypsin, and higher specific activity of leucine aminopeptidase were adaptive for both populations in the control environment. Plasticity was only shown to be costly for total proteases and trypsin activity in Quercus larvae. In a stressful environment, the most apparent adaptive response was a significant increase in lipase activity. There was no plasticity cost for lipase activity. The two populations differed in the direction of selection acting on α-glucosidase activity, which favoured decreased activity in Quercus larvae and increased activity in Robinia larvae in the control environment. α-glucosidase activity in Quercus larvae is characterized by cost of homeostasis, while cost of plasticity was shown for Robinia larvae. The results obtained on the plasticity of digestive enzyme activity indicate how this generalist species copes with variation in plant allelochemicals.     

Prior heat stress induces moderation of diabetic alterations in glycogen metabolism of rats

Adaptation to one environmental stressor sometimes provides protection against additional, more intensive type of stress, a phenomenon called cross-tolerance. We aimed to estimate theprotection provided by acute heat stress (AHS) over carbohydrate disturbances in streptozotocin-diabetic rats. We investigated changes in activity of some hepatic glycolitic and gluconeogenic enzymes, and concentration of some substrates in control and diabetic animals exposed to AHS (41±0.5°C / 1 h), with 1 h and 24 h recovery at room temperature before sacrifice or induction of streptozotocin (STZ)-diabetes, respectively. AHS with 1 h-recovery before sacrifice resulted in intensive glycogenolysis, directed to endogenous glucose production and further utilization of glucose by peripheral tissues, while 24 h recovery resulted in a slight tendency towards normalization of metabolic disturbances caused by AHS. Experimental diabetes caused a significant decrease of substrates and glycolytic enzymes, but an increase of gluconeogenic enzymes. In diabetic animals previously exposed to AHS we measured a less intensive decrease of liver glycogen and glucose-6-phosphate concentration and hexokinase activity, as well as less intensive increase of liver glucose concentration, glucose-6-phosphatase and fructose-1,6-bisphosphatase activity compared to control diabetic animals that had been maintained at room temperature. Prior AHS provided some protection over diabetes-induced alterations in carbohydrate-related parameters (see graphical apstract), indicating a possible development of cross-tolerance phenomenon between the two stressors, AHS and STZ-diabetes.     

Effects of iso-osmotic NaCl and mannitol on growth, proline content, and antioxidant defense in Mammillaria gracilis Pfeiff. in vitro-grown cultures

Effects of iso-osmotic concentrations of NaCl and mannitol were studied in Mammilaria gracilis (Cactaceae) in both calli and tumors grown in vitro. In both tissues, relative growth rates were reduced under osmotic stress, which were accompanied by a decrease in both tissue water and K⁺ content. However, growth was inhibited to a lesser extent after exposure to NaCl, when accumulation of Na⁺ ions was observed. In calli, only salinity increased proline content, whereas with tumors proline accumulated after both osmotic stresses. Osmotic stresses also induced oxidative damage in both cactus tissues, although higher oxidative injury was caused by mannitol in calli and by salt in tumors. Low iso-osmotic concentrations of NaCl (75 mM) and mannitol (150 mM) increased peroxidase, ascorbate peroxidase, and esterase activities, whereas elevated catalase activity was recorded only after mannitol treatment in both tissues. High osmotic stress generally decreased enzymatic activities. However, in calli, esterase activity increased in response to high salinity, whereas ascorbate peroxidase activity was enhanced after high mannitol stress. In conclusion, both in vitro-grown cactus tissues were found to be sensitive to osmotic stress caused by either mannitol or NaCl, but accumulation of Na⁺ ions in response to salt somewhat contributed to osmotic adjustment. However, more prominent oxidative damage induced by NaCl compared to mannitol in tumor could be related to ion toxicity. The mechanisms that mediate responses to salt- and mannitol-induced osmotic stresses differed and were dependent on tissue type.