Date of Award

5-1-2021

Language

English

Document Type

Master's Thesis

Degree Name

Master of Science (MS)

College/School/Department

Department of Biological Sciences

Content Description

1 online resource (iv, 22 pages) : illustrations (chiefly color)

Dissertation/Thesis Chair

Prashanth Rangan

Committee Members

Paolo Forni, Gabriele Fuchs

Keywords

drosophila, germline, inosine, oogenesis, purine, stem cell, Drosophila melanogaster, Drosophila, Oogenesis, RNA, Messenger RNA, Germ cells

Subject Categories

Biology | Developmental Biology

Abstract

Germline stem cells differentiate into mature egg or sperm cells that go through the process of fertilization which gives rise to all sexually reproducing organisms. During this process of differentiation, germ cells undergo a switch from mitosis to meiosis that allows for proper development and specification of the future gamete. The mechanisms that facilitate this shift from mitosis to meiosis, however, are not well understood. To gain insight into this process, we used Drosophila oogenesis as our model. To identify what RNA modifications are present during oogenesis we genetically enriched for each stage of development and performed mass spectrometry. We identified one modification to have a noticeable increase and subsequent decrease during the differentiation stage. This modification, inosine or I, is a modified version of adenosine monophosphate (AMP) in which the amino group on C6 of the nitrogenous base is converted into a carbonyl carbon. After carrying out a screen of enzymes involved in the synthesis and conversion of inosine monophosphate, we noticed that knockdown of the enzyme raspberry (ras) caused loss of germline and subsequent infertility. Raspberry is a homologue of human IMPDH1 and converts IMP into xanthosine monophosphate (XMP) during the rate limiting step of de novo purine synthesis, a three-step conversion of AMP into guanosine monophosphate (GMP). Here we propose a novel mechanism in which knockdown of ras leads to decreased expression of the meiosis-promoting mRNA binding protein Bruno1, causing a failure to enter meiosis that results in loss of germline and failure to produce egg chambers. Furthermore, we find that knockdown of ras downregulates cell-cycle transcription factors which causes a cell cycle arrest that can be rescued with knockdown of the tumor-suppressor protein p53, thereby restoring germline and later stages of development.

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