RNA localisation is essential for the establishment of body axes in the developing Drosophila embryo. Transcripts of certain maternal genes are transported along microtubules and translated in restricted regions of the oocyte to define these axes. RNA from one such gene, gurken (grk) is first localised to the oocyte posterior, where translated Grk signals to the soma to specify the follicle cells in this region to adopt a posterior fate. Subsequently these posterior follicle cells signal back to the oocyte triggering cytoskeletal reorganisation. The nucleus and grk RNA are then transported to the dorsal-anterior region of the oocyte, where Grk signals to specify the surrounding cells to become dorsal. This two-stage grk localisation thereby determines both the anterior-posterior and dorsal-ventral axes. This thesis describes a random mutagenesis screen designed to identify novel genes on chromosome arm 3R that are involved in grk RNA localisation in the oocyte. We observed the distribution of endogenous grk RNA in vivo using a fluorescent construct. From 4943 mutagenised lines scored, I recovered 38 with reproducible grk mislocalisation and 78 lines with other defects in oogenesis. After phenotypic analyses and complementation testing, these mutants were grouped and the affected genes identified using whole genome sequencing and recombinational mapping. I focus on three groups of mutants from the screen that showed a grk mislocalisation phenotype. Mutations in karyopherin-beta3, a nuclear import factor gene, and in CG9925, encoding a TUDOR-domain containing protein, cause reduced Grk translation and axis misspecification. In two new mutant alleles of CG5508/minotaur, which encodes a protein involved in phospholipid biosynthesis, Grk translation is reduced and transposon expression levels are elevated, a typical phenotype of mutants for piRNA pathway genes. Mutants of these three genes, despite diverse predicted gene functions, share many phenotypes. I describe detailed characterisation of these novel mutants and suggest how they may all be affecting grk mRNA localisation due to disruptions in the mechanisms of piRNA biogenesis and the protection of genome integrity.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:626713 |
| Date | January 2014 |
| Creators | Liddell, S. J. |
| Publisher | University College London (University of London) |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://discovery.ucl.ac.uk/1421417/ |
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