Browsing by Subject "mRNA"
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Item Genome-wide pharmacological modulation of cap-dependent translational control(2013-12) Braziunas, Jeffrey JosephThe first step of cap-dependent translation is mediated by the mRNA cap-binding protein eukaryotic initiation factor 4E (eIF4E). Although involved in translating nearly all cellular transcripts, mRNAs vary widely in their translational response to eIF4E activity changes. Prior studies of mRNA structure revealed several features governing eIF4E responsiveness; however, most of this knowledge is based on comparison of two levels of eIF4E activity with unclear physiological relevance. To identify mRNA structural features that govern genome-wide ribosome recruitment across a full range of physiological eIF4E activities, we precisely modulated eIF4E activity using an eIF4E-inducible system together with 4Ei-1, an inhibitor of the eIF4E-5'mRNA cap association. We identified genes that were more (4E hypersensitive) or less (4E hyposensitive) responsive to eIF4E activity changes than average. Distinct characteristics associated with each class: 4E hypersensitive genes had longer 5'UTRs with higher GC content, longer 3'UTRs with lower GC content; more AU-rich elements and a higher density of unique microRNA targets sites than typical genes. Importantly, these structural characteristics predicted the translational response across the dose range of 4Ei-1. Gene ontology analysis showed an association between 4E hypersensitive genes and proliferation; and cell cycle experiments with 4Ei-1 validated this result. A search for the outcome and mechanism of this proliferative gene activation in a physiological setting revealed that abrupt gain of eIF4E function in quiescent cells first triggers G0 exit and then cell cycle transit at least partially by increasing ribosome recruitment to cyclins C and D1. Whereas cyclin C is not necessary for this effect; cyclin D1 is indispensable, although not sufficient. Our findings provide important insights into mRNA properties of eIF4E-modulated translational control.Item Micronutrient interactions affecting the developing rat brain(2013-06) Bastian, Thomas WilliamMicronutrient deficiencies affect billions of people worldwide and often coexist in developing countries due to consumption of diets lacking nutrient diversity. Thus, it is important to consider how micronutrients such as copper (Cu), iron (Fe), and iodine interact physiologically. Cu, Fe, and iodine/thyroid hormone (TH) deficiencies lead to similar brain development deficits, suggesting these micronutrient deficiencies share a common mechanism contributing to the observed derangements. Previous studies in rodents and humans indicate that Cu and Fe deficiencies during adolescence or adulthood lead to impaired TH status. However, prior to this thesis research, relationships between Fe or Cu deficiencies and thyroidal status had not been assessed in the most vulnerable population, the developing fetus/neonate. My first two studies showed that Fe deficiency lowers newborn rat circulating and brain TH concentrations and alters TH-regulated brain gene expression. In a third study, Fe deficiency exacerbated the effect of mild TH insufficiency on neonatal thyroidal status and brain TH-responsive gene expression. Together, these novel findings suggest that impaired neonatal thyroidal status may contribute to some of the brain developmental abnormalities associated with fetal/neonatal Fe deficiency. Fe deficiency also has significant impacts on the developing brain independent of effects on thyroid function. In humans, Fe deficiency often results in anemia, reduced blood oxygen carrying capacity. Decreased oxygen delivery to the brain can induce a compensatory increase in blood vessel outgrowth. My final study demonstrated, for the first time, that Fe deficiency anemia increases blood vessel growth in the neonatal rat brain. The functional contribution of increased vasculature to the developing Fe-deficient brain is unknown but could be adaptive, maladaptive, or both. In summary, my thesis research exploring micronutrient interactions during brain development has identified two novel potential contributors to the brain developmental derangements associated with Fe deficiency: impaired neonatal thyroid function and increased neonatal brain vasculature.