Post-transcriptional Control of Gene Expression in «Drosophila Melanogaster»

Download or read book Post-transcriptional Control of Gene Expression in «Drosophila Melanogaster» written by Stephanie Yee and published by . This book was released on 2019 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: "Post-transcriptional control is a critical determinant of gene expression that acts at the level of the messenger RNA (mRNA), which includes processes such as translational control and RNA localization, and is the focus of this thesis. This regulation is in part dictated by the characteristics of the 5’ and 3’ untranslated regions (UTRs) of the mRNA and the cis-elements they harbour. Translational control can occur at the initiation step where the 5’ cap structure of the mRNA is recognized by the eIF4E, whose activity can be modulated by the eIF4E-binding protein (4E-BP), a repressor of translation. The target of rapamycin (TOR) pathway integrates a plethora of signals and impinges on protein synthesis through its action on 4E-BPs and S6 kinases (S6Ks), two well-characterized targets. The TOR/4E-BP/eIF4E axis is known to regulate the translation of subsets of mRNAs with distinct features in their 5’UTRs. In light of recent work that demonstrated dysregulated translation of specific mRNAs in the brains of mice lacking 4E-BP2 and engendering autism spectrum disorder-like phenotypes, we endeavoured to similarly identify mRNAs regulated by d4E-BP in Drosophila. In Chapter 2, we performed ribosome profiling to identify specific mRNAs that are translationally regulated downstream of d4E-BP in the adult fly head, used as a proxy for the brain. Gene ontology (GO) analysis revealed that the corresponding genes of some of the upregulated mRNAs are involved in innate immunity. We determined that upregulated mRNAs possess 5’UTRs that are shorter but more complex. In our effort to validate one of the targets, dS6K, we detected elevated levels of p-RPS6, a readout of dS6K activity, in d4E-BPnull flies. We conclude there are subsets of differentially ribosome-associated mRNAs with distinct 5’UTR features in the d4E-BPnull fly head.Subcellular localization of mRNAs in the Drosophila embryo establishes a molecular asymmetry of maternally-inherited determinants that is essential for its development. Of the hundreds of transcripts that localize to the primordial germ cells at the posterior of the early embryo, only 55 RNAs accumulate around posterior nuclei prior to the development of those cells, termed RNA islands. Many of the genes that encode these mRNAs have established functions in embryonic patterning and germline development. Despite their common destination to RNA islands, a shared localization element has yet to be identified. In Chapter 3, we mapped the localization elements within the 3’UTRs of two transcripts that localize to RNA islands, polar granule component (pgc) and germ cell-less (gcl). Based on deletion mutation analysis, we report that gcl has redundant localization elements, while pgc possesses a localization element in the distal region. We show that the localization of polar granule proteins, Oskar, Tudor and Vasa, and 11 RNAs have conserved posterior localization in Drosophilids. Using recent findings of a sequence motif that contributes to RNA island localization, we found that this motif is enriched in the 3’UTRs of the majority of transcripts that localize in this way. Our data suggests that the RNA island type of posterior localization is an important process for directing the localization of transcripts with key roles in germline development, as highlighted by the many aspects of this process that is conserved"--