Development of methods to decrease aneuploidy in mammalian oocytes
by Gerrit Altmeppen
Date of Examination:2022-03-31
Date of issue:2022-05-24
Advisor:Dr. Melina Schuh
Referee:Dr. Melina Schuh
Referee:Prof. Dr. Ernst A. Wimmer
Files in this item
Name:Final thesis - with Cover.pdf
This file will be freely accessible after 2023-03-30.
EnglishMaternal mRNAs accompany and control all processes from the onset of meiosis until the blastocyst stage when the maternal pool of mRNAs is fully replaced by the emryonic mRNA set. The successful development of blastocysts relies on the stability of maternal mRNAs before and during meiosis. Numerous maternal mRNA controlling proteins have been identified in the oocytes of Drosophila melanogaster, Xenopus laevis and Mus musculus. Although the function of many mRNA binding proteins is known, the exact mechanisms that regulate translation and mRNA stability remain unclear. A better understanding of this topic would be very important both from a fundamental research as well as from a medical perspective, because the orchestrated translation and decay of maternal mRNAs is crucial for the successful development of early embryo. In addition, alterations in the sequence of translation and decay affect the process of meiosis and impair the developmental capacity of oocytes. Delayed maturation and aneuploidy are consequences of imbalanced maternal mRNA pools. Aneuploidy in eggs is the main cause of infertility and miscarriages in women. The aim of my thesis was to identify new mRNA regulatory pathways that support the healthy development of oocytes and early embryos, and to develop methods that can be used to decrease aneuploidy. In the first part of my thesis, I investigated a maternal mRNA controlling protein that we termed maternal mRNA-Sequestering Protein (MMSP). We found that MMSP organizes a novel mRNA storage domain in oocytes, and characterized the dynamics, composition and physical properties of this domain. In addition, I studied how depletion of MMSP in a knockout mouse model affects the functionality of the oocyte and progression through meiosis. In the second part of my thesis, I used specific dyes and single molecule RNA-FISH (smRNA-FISH) to study a specific gene whose mRNA is sequestered by MMSP. We showed that the pre-mature loss of the mRNA in MMSP knockout oocytes causes severe defects in the lipid metabolism and mitochondrial activity in immature oocytes. We further provide evidence that altered lipid metabolism and mitochondrial activity cause oxidative stress. Oxidative stress is known to contribute to age-related damage in oocytes that eventually can lead to aneuploidy. In the third part of my thesis, I aimed to develop tools to correct chromosome segregation errors by artificially moving chromosomes inside living oocytes. I used different types of magnetic tweezers and glass needles to reposition chromosomes within oocytes, or to remove chromosomes from oocytes. This work provides a proof-of-concept that chromosomes can be modified inside oocytes, and also be removed from oocytes without affecting oocyte viability. However, substantial further development will be required to apply related methods to the reduction of aneuploidy in fertility treatments.
Keywords: RNA storage; Maternal mRNAs; Meiosis; Mammalian oocytes; MARDO; Mitochondria; Lipid metabolism; Lipid droplets; Transcriptional regulation; Aneuploidy; Magnetic tweezers; Chromosome missegregation