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Characterization of long non-coding RNAs in the Hox Complex of Drosophila
[Thesis]. Manchester, UK: The University of Manchester; 2016.
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Abstract
Long non-coding RNAs (lncRNAs) are often defined as transcripts >200nts that have no discernable protein-coding ability (Quinn and Chang, 2016). Although relatively little is understood about the molecular mechanisms of lncRNA function, they have established roles in regulation of gene expression during development, cell differentiation and pluripotency (Fatica and Bozzoni, 2014; Luo et al., 2016; Quinn and Chang, 2016; Rinn and Chang, 2012) across vastly diverse organisms ranging from plants to humans (Ulitsky and Bartel, 2013). LncRNAs have also been associated with numerous pathological conditions, such as cancers (Brunner et al., 2012), cardiovascular disease and neurodegeneration (Chen et al., 2013). Investigations into lncRNAs in wide ranging organisms, have revealed that many influence gene activity by forming ribonucleoprotein complexes that affect the conformational state of chromatin (Rinn and Chang, 2012). A genomic region that has revealed several functional lncRNAs in diverse organisms is the Hox complex (Pauli et al., 2011; Pettini, 2012; Rinn et al., 2007). The Hox complex encodes a set of transcription factors (TFs), physically clustered in the genome, which provide morphological identity along the anterior to posterior axis of developing embryos (Mallo and Alonso, 2013), throughout the majority of bilatarian animals (Moreno et al., 2011). Misexpression or mutation of Hox genes causes morphological and pathophysiological defects (Quinonez and Innis, 2014). We investigated clustering of lncRNAs throughout the D. melanogaster genome using available annotations and carried out RNA-seq in D. virilis to expand the repertoire of lncRNAs and identify clusters of lncRNAs. We found the Hox complex to be heavily enriched with lncRNAs in both organisms, and syntenic transcripts from D. melanogaster could be identified in D. pseudoobscura and D. virilis. Several lncRNAs aligned with polycomb response elements (PREs); transcription of PREs has previously been linked to a switch in their activity (Herzog et al., 2014). However, we found that transcribed PREs in D. melanogaster move positions relative to the protein-coding genes in other drosophilids, whilst the transcriptional units remain in the same syntenic region. Conservation of syntenic transcripts without evidence of remaining a PRE suggest that the transcription is not linked to PRE function, agreeing with recent findings that transcription of PREs does not affect their function (Kassis and Muller, 2015). We investigated functions of a novel lncRNA and adjacent PRE in the Hox complex by ectopic expression and utilization of other genetic manipulation tools. Overexpression of either the lncRNA or PRE and partial duplication of the lncRNA caused phenotypes such as missing halteres and/or T3 legs, misshaped T3 legs or malformed abdominal segments. The observations that ectopic expression of this lncRNA and an adjacent regulatory element from the Hox complex causes phenotypes that can be linked to adjacent Hox gene misregulation, Antp and Ubx, suggest that they are likely to have roles in the regulation of at least one of these Hox genes.