Date of Degree

2-2017

Document Type

Dissertation

Degree Name

Ph.D.

Program

Biology

Advisor

Diana Bratu

Committee Members

Eric Lai

Amanda Norvell

Diego Loayza

Frida Kleiman

Subject Categories

Biology | Developmental Biology | Genetics

Keywords

mRNA, translational control, oogenesis, genetics, developmental biology

Abstract

In a wide variety of biological contexts, messenger RNA (mRNA) is known to have a complex and dynamic life cycle. In particular, the localization and translational control of mRNA are essential for proper development in eukaryotes. The fly Drosophila melanogaster is an excellent model for studying these processes. During D. melanogaster oogenesis, several mRNAs are trafficked and localized within the developing egg chamber, and regulated at the translational level to enable embryo patterning. One such mRNA, bicoid, is localized at the anterior of the oocyte and translated in the early embryo, where its encoded protein directs formation of the fly's head and thoracic segments.

In this thesis, we investigated several aspects of bicoid's post-transcriptional regulation that may impact its stability and translational timing. First, we demonstrate that bicoid mRNA is present in Processing Bodies (P-bodies), cytoplasmic organelles implicated in mRNA storage and decay. Perturbing P-body formation/structure, via manipulation of the mRNA decay pathway, affects the levels of bicoid and additional maternal transcripts. We next explored the possibility that the microRNA (miRNA) pathway regulates the translational timing of bicoid. We find that in cell culture experiments, a bicoid reporter gene is translationally repressed by miR-305; we also demonstrate that miR-305 is expressed in ovaries. However, loss of miR-305 is not sufficient to alter ectopic bicoid mRNA translation in the egg chamber. To determine if any genes are singly required for bicoid translational repression in the egg chamber, we used GFP-tagged transgenes to express bicoid mRNA in vivo. Although we do not yet identity any candidate genes in this small screen, we show that overexpression of bicoid mRNA results in its translation in the egg chamber, suggesting that one or more factors normally act in its translational repression.

Overall, our work points to several plausible avenues of investigation into processes that regulate the translational timing of bicoid mRNA during oogenesis. Moreover, our findings are also relevant to a general understanding of the complex, multifaceted problems surrounding mRNA post-transcriptional regulation.

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