LINE-1 Retrotransposon Activation in Mouse Fetal Oocytes
| dc.contributor.advisor | Kim, Yumi | |
| dc.contributor.committeeMember | Burns, Kathleen | |
| dc.contributor.committeeMember | Van Doren, Mark | |
| dc.contributor.committeeMember | Bortvin, Alex | |
| dc.creator | Tharp, Marla E | |
| dc.creator.orcid | 0000-0002-0653-1123 | |
| dc.date.accessioned | 2021-01-08T17:03:25Z | |
| dc.date.available | 2021-01-08T17:03:25Z | |
| dc.date.created | 2020-08 | |
| dc.date.issued | 2020-04-15 | |
| dc.date.submitted | August 2020 | |
| dc.date.updated | 2021-01-08T17:03:25Z | |
| dc.description.abstract | After her pivotal discovery of transposable elements or “jumping genes”, Barbara McClintock left future generations of scientists with the challenge of understanding how such elements control gene expression and development by rearranging the genome in response to genetic and environmental stress. In this work, we make strides toward understanding the impact of transposable element activity in mouse female germ cell development. Germ cells face an evolutionary conundrum: the remarkable responsibility of transmitting high quality genetic information to the subsequent generation while simultaneously providing windows of opportunity for the genome to diversify and adapt that are advantageous for the species fitness. This is an ideal task for transposons. Indeed, early in development oocytes encounter a gauntlet of stressors that together create a natural genomic shock and permit the release of active transposons. Specifically, DNA methylation, an elaborate epigenetic system that normally represses transposons, is surrendered for epigenetic reprogramming of germ cells while concurrent chromosome breakage and rearrangement are ongoing for meiotic prophase I, creating a permissive environment for transposon activity. The active L1 retrotransposon is expressed in this window of genome stress during development. This L1 burst correlates with death of up to 80% of fetal oocytes, a decades old observation and paradoxical phenomenon as female reproductive success relies on the size and quality of a finite ovarian reserve. A role for L1 in fetal oocyte attrition (FOA) has been characterized. L1-encoded protein ORF1p is heterogeneously expressed between fetal oocytes, and those with elevated ORF1p levels are preferentially killed. Using these findings as a foundation, I aimed to understand the mechanisms by which L1 activity triggers FOA and the biological significance of L1 expression that may outweigh the massive consequences to the oocyte supply. Here, I characterize the mechanisms of L1-mediated FOA that stem from two catalytic activities of L1 ORF2p required for retrotransposition: reverse transcriptase and endonuclease activities. I then successfully block FOA by inhibiting these mechanisms, specifically, by combined inhibition of L1 reverse transcriptase activity with the antiretroviral AZT and the DNA damage checkpoint activation through mutation of checkpoint kinase 2 (CHK2). Now, for the first time, we study the entire fetal oocyte population and understand the mechanisms of L1-mediated FOA, its impact on oogenesis and fertility, and the origin of L1 heterogeneity among oocytes that determines their fates. Surprisingly, I find that while FOA initially serves as quality control, when bypassed, oocytes are able to reduce genotoxic threats of L1 and differentiate, resulting in a maximized ovarian reserve at postnatal ages without compromising fertility. | |
| dc.format.mimetype | application/pdf | |
| dc.identifier.uri | http://jhir.library.jhu.edu/handle/1774.2/63437 | |
| dc.language.iso | en_US | |
| dc.publisher | Johns Hopkins University | |
| dc.publisher.country | USA | |
| dc.subject | LINE-1 retrotransposon | |
| dc.subject | Oocyte | |
| dc.subject | DNA damage checkpoint | |
| dc.subject | Meiosis | |
| dc.title | LINE-1 Retrotransposon Activation in Mouse Fetal Oocytes | |
| dc.type | Thesis | |
| dc.type.material | text | |
| thesis.degree.department | Biology | |
| thesis.degree.discipline | Biology | |
| thesis.degree.grantor | Johns Hopkins University | |
| thesis.degree.grantor | Krieger School of Arts and Sciences | |
| thesis.degree.level | Doctoral | |
| thesis.degree.name | Ph.D. |