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Dissertation
Defining the roles of prostaglandin signaling and Fascin in controlling nucleolar function and morphology during Drosophila oogenesis
University of Iowa
Doctor of Philosophy (PhD), University of Iowa
Spring 2025
DOI: 10.25820/etd.007951
Abstract
Reproduction is one of the most critical yet complicated biological processes. For reproduction to occur properly, it requires the creation of high-quality haploid gametes that must come together, fuse, and develop to form viable offspring. If these gametes fail to be created, fuse, or develop into viable offspring, it can lead to infertility. Many diseases, including infertilities, are a result of dysfunction on the cellular level. In oogenesis, the process for producing female gametes, there are many cellular factors, hormonal signals, and other stimuli that must integrated overtime and throughout the body to create viable eggs and support growing embryos. My thesis project focuses on uncovering these cellular factors that are essential for high quality oocyte production and the maintenance of fertility.
Specifically, my thesis focuses on three cellular factors that have been previously implicated in oocyte development and fertility. These factors are the nucleolus, prostaglandin signaling, and nuclear actin. The nucleolus is an organelle located within the nucleus that has many functions, most notably synthesizing ribosomal RNA to make ribosomes. Nucleolar dysfunction can lead to several diseases and disorders. There are many pathways that converge on the nucleolus to modulate its function. One of these pathways is prostaglandin signaling. Prostaglandins are small lipid signaling molecules that have a wide variety of roles in many biological processes, including of female fertility. It has been well established that prostaglandins are required for many different aspects of female fertility, however the identity of the cellular targets of prostaglandin signaling and the mechanisms underlying prostaglandin control of female fertility are less understood. One of the cellular targets of prostaglandin signaling that has been shown to be important in fertility is nuclear actin. Actin, best known for its roles as a cytoskeletal protein, also localizes and functions in the nucleus. Here actin has numerous roles in transcription, chromatin movements, and nuclear architecture. Nuclear actin has also been demonstrated to have critical roles in the oocytes of many different species including mammals. Each of these factors have been separately shown to be important for some facet of female reproduction including oogenesis, ovulation, maintenance of pregnancy, embryonic development, or the onset of labor. While each of these factors, the nucleolus, prostaglandin signaling, and nuclear actin, have been separately implicated as critical regulators of fertility, this thesis aims to investigate how these factors interact to control oogenesis and promote female fertility.
To investigate the relationship between these cellular factors, our lab utilizes the powerful, in vivo model of Drosophila melanogaster oogenesis. Drosophila have two ovaries comprised of 15-20 long chains of sequentially developing follicles (aka eggs) termed ovarioles. These developing follicles are broken up into 14 distinct developmental stages, beginning at the germarium and ending at Stage 14, the mature egg. Although initially it may seem like Drosophila oogenesis is far removed from mammalian oogenesis there are several conserved features between the two species. Given the ethical and technical limitations that are associated with studying mammalian oogenesis, Drosophila oogenesis is a suitable alternative model that can be used to investigate the basic cellular mechanisms that govern oogenesis and female fertility.
In Chapter 2, I present data revealing that prostaglandins limit nuclear actin to control nucleolar functions and morphology during Drosophila oogenesis. Here using a prostaglandin synthesis mutant, I find that loss of all prostaglandin signaling results in a rounded nucleolar morphology, increased nucleolar transcription, and increased protein translation. I also find that loss of prostaglandin signaling results in increased nuclear actin. Further experiments revealed it is this increase in nuclear actin that is driving the increased nucleolar functions. These data lead to a model where prostaglandins and nuclear actin are novel regulators of nucleolar function and morphology. Next, in Chapter 3, I asked how nuclear actin is regulated to control nucleolar functions, which lead me to investigate the role of an actin binding protein, Fascin, during oogenesis. Previous work determined Fascin is a novel regulator of nucleolar morphology during Drosophila oogenesis, but it was not clear what this change in nucleolar morphology meant about the underlying nucleolar function. In Chapter 3, I find that loss of Fascin results in decreased nucleolar transcription and decreased global protein translation. I also find that loss of Fascin results in decreased nuclear actin accumulation, and I propose a model where Fascin is promoting nuclear actin accumulation to support nucleolar transcription and morphology.
In summary, this thesis demonstrates that prostaglandin signaling and Fascin tightly regulate nuclear actin to control the nucleolus during oogenesis. This thesis shows that normally prostaglandins limit nuclear actin to limit nucleolar functions. Conversely, Fascin normally promotes nucleolar transcription and nuclear actin accumulation. In this case, I hypothesize that it is Fascin-dependent nuclear actin accumulation that controls the nucleolus but further experiments are needed to fully test this hypothesis. These studies reveal that Drosophila oogenesis is an ideal model to uncover cellular factors that are critical for oocyte development and the maintenance of female fertility. Moreover, the cellular components discussed here are highly conserved in many cell types and have roles in numerous basic cellular processes. Thus, the findings and relationships defined in this thesis are broadly applicable to many biological contexts and provide further insight into how prostaglandins and Fascin regulate nuclear actin to control the nucleolus to maintain nucleolar and cellular functions.
Details
- Title: Subtitle
- Defining the roles of prostaglandin signaling and Fascin in controlling nucleolar function and morphology during Drosophila oogenesis
- Creators
- Danielle Elizabeth Talbot
- Contributors
- Tina L. Tootle (Advisor)Thomas Rutkowski (Committee Member)Sarit Smolikove (Committee Member)Daniel Weeks (Committee Member)Charles Yeaman (Committee Member)
- Resource Type
- Dissertation
- Degree Awarded
- Doctor of Philosophy (PhD), University of Iowa
- Degree in
- Biomedical Science (Cell and Developmental Biology)
- Date degree season
- Spring 2025
- DOI
- 10.25820/etd.007951
- Publisher
- University of Iowa
- Number of pages
- xviii, 164 pages
- Copyright
- Copyright 2025 Danielle Elizabeth Talbot
- Grant note
- This project was supported by National Institutes of Health (NIH) R01 GM116885 (TT), and National Science Foundation MCB2017797 (TT). MG was supported by NIH T32 CA078586 Free Radical and Radiation Biology, University of Iowa.
- Language
- English
- Date submitted
- 03/05/2025
- Description illustrations
- Illustrations, tables, graphs, charts
- Description bibliographic
- Includes bibliographical references (pages 128-146).
- Public Abstract (ETD)
All living things have the capacity to reproduce. For reproduction to be successful, it requires specialized cells, sperm and egg, to fuse to make an embryo. Any issues with the sperm or egg, or embryo will result in infertility. Many diseases often occur because of problems that arise within individual cells. In infertilities, these problems prevent the creation of good eggs or oocytes. My thesis project is focused on understanding why the cellular components of the nucleolus, prostaglandins, and nuclear actin are important for the development of good oocytes, and how these components become altered to contribute to infertility. To answer these questions, I use Drosophila oogenesis as a model, as many of the basic processes of oogenesis are the same between Drosophila and mammals. Using this model, I find that normally prostaglandins limit nuclear actin to limit nucleolar function. This limitation of nucleolar function is important for fertility, as increased nucleolar function impairs oocyte quality and development. I also find that an actin binding protein, Fascin, has a role in promoting nucleolar functions and nuclear actin accumulation. I hypothesize this Fascin-dependent nuclear actin accumulation is necessary to support nucleolar function. Decreasing nucleolar function also has negative impacts on oocytes and can impair their development and later function. Overall, these data lead to a model where prostaglandins and Fascin tightly control nuclear actin levels to control the nucleolus during oogenesis. This project shows the importance of studying these cellular components and understanding their roles in creating good eggs.
- Academic Unit
- Anatomy and Cell Biology
- Record Identifier
- 9984831023802771
Metrics
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