Browsing by Subject "Ovary"
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Item Gonadal dysgenesis(1968-09-26) UnknownItem Histone Demethylase LSD1 Restricts the Size of the Germline Stem Cell Niche in Drosophila Ovaries(2013-01-16) Eliazer, Susan; Buszczak, MichaelSpecialized microenvironments called niches keep stem cells in an undifferentiated and self-renewing state by producing a variety of factors. The size and signaling output of niches must be finely tuned to ensure proper tissue homeostasis. I use the Drosophila female germline as an excellent model system to study niche development and function. Five to seven somatic cap cells form the ovarian stem cell niche and produce dpp, a BMP homolog necessary for the maintenance of germline stem cells (GSCs). Mutations in Lsd1, a histone demethylase exhibit GSC-like tumor formation. Clonal analysis, cell-type specific knock down and rescue experiments demonstrate that Lsd1 functions within the escort cells that reside immediately adjacent to cap cells (niche). Loss of Lsd1 causes the escort cells to adopt an intermediate fate expressing both escort cell and cap cell markers and enables them to function as ectopic niches for the expanded stem cell population. Temporally restricted gene knock-down experiments suggest that Lsd1 functions both during development, to specify EC fate, and in adulthood, to prevent ECs from forming ectopic niches independent of changes in cell fate. Lsd1 specifically functions to repress dpp, the niche signal in the adult germaria. I have identified engrailed as a direct target of Lsd1 by performing Chromatin Immunoprecipitation (ChIP-seq) analysis in the escort cells of the Drosophila ovary. Engrailed is expressed in the cap cells of wild type germaria and in Lsd1 mutants engrailed transcripts are misexpressed in the escort cells. Knocking down engrailed expression in the escort cells suppresses the Lsd1 mutant phenotype. Moreover, ectopic expression of engrailed in the escort cells displays a GSC-tumor phenotype. Furthermore, I have shown that Engrailed functions upstream of dpp, and activates its expression in the cap cell niche.Item Investigations into the Role of Paf1 Complex Proteins in Drosophila Ovaries(2014-10-23) Chaturvedi, Dhananjay; Li, Bing; Olson, Eric N.; Jiang, Jin; Buszczak, MichaelOver the past decade considerable interest has grown in epigenetics and chromatin modifications. The ability of two cells with identical genomes to have entirely different transcriptomes and therefore cellular behaviors has piqued the curiosity of many researchers creating the whole field of Chromatin Biology. The difference in behavior of otherwise identical cells comes from an array of covalent modifications to protein spools wrapped by DNA in each cell. The complex of DNA and proteins is referred to as chromatin. Chromatin modifications influence the expression of regulatory proteins that control effectors of cellular physiology and metabolism. The outcome of protein function within a cell decides its fate from size, shape, function, the ability to divide or the lack thereof. The behavior of cells that can divide to give rise to themselves or progeny with a distinct specified function in an organism is of interest the biomedical community at large. These cells, called stem cells, hold promise in regenerative medicine to treat dystrophic diseases and injury. Work in cell culture systems shows that proteins modifying stem cell chromatin control their fate to a large extent. In this thesis I present to you, my efforts at understanding the role of a chromatin modifying complex: the Paf1 complex in the maintenance and differentiation of in vivo stem cell populations that control the maintenance of Drosophila ovaries.Item Polycystic ovarian syndrome: what is it and who's to blame?(2007-05-11) Hammes, Stephen R.Item Rbfox1 Regulates mRNA Translation to Promote Germ Cell Differentiation(2016-07-12) Carreira-Rosario, Arnaldo; Zinn, Andrew R.; Buszczak, Michael; Conrad, Nicholas; Olson, Eric N.; Rothenfluh, AdrianGerm cells are the only cells that can give rise to an embryo. During differentiation, female germ cells that will give rise to oocytes form a syncytium called a germline cyst. The mechanisms that regulate germline cyst development remain poorly understood. In Drosophila, germline stem cells (GSCs) undergo an asymmetric division, giving rise to a stem cell and a cystoblast that then divides four times to produce a 16-cell germline cyst. This 16-cell cyst will then continue differentiation until it forms a mature oocyte. Drosophila RNA-binding Fox-1 (Rbfox1), also known as Ataxin-2 Binding Protein 1 (A2BP1), mutant females exhibit a germ cell differentiation defect that results in germline cystic tumors. The Rbfox genes encode several isoforms, many of which contain a highly conserved RNA recognition motif (RRM). Disruption of human RBFOX homologs have been linked with a number of different neurological disorders and cancers. Some of these isoforms localize to the nucleus while others localize to the cytoplasm. Nuclear forms have well-established roles in regulating alternative splicing. However the function of Rbfox in the cytoplasm remains unclear. Here, we demonstrate that cytoplasmic Drosophila Rbfox1 regulates germline cyst development. We further show that Rbfox1 represses the translation of mRNAs that contain (U)GCAUG elements within their 3’ UTRs. We have identified pumilio (pum) as a critical Rbfox1 target gene. Pum is an RNA-binding protein essential for germline maintenance across species. During germline cyst differentiation, Rbfox1 silences pum mRNA translation thereby promoting germ cell development. Mis-expression of pum results in the formation of germline cystic tumors that resemble Rbfox1 mutant phenotype. In addition, these cysts breakdown and dedifferentiate back to single, mitotically active cells. Together these results reveal that cytoplasmic Rbfox family members regulate the translation of specific target mRNAs to promote differentiation. In the Drosophila ovary, this activity provides a genetic barrier that prevents germ cells from reverting back to an earlier developmental state. These findings have thus advanced our understanding of germline development and the molecular function of Rbfox proteins, with implications in cellular differentiation and Rbfox-related disorders.Item The Role of EGFR Signaling in Gonadotropin-Induced Steroidogenesis(2010-11-02) Carbajal, Liliana; Hammes, Stephen R.Recent evidence has demonstrated that cross talk between G protein-coupled receptors and Epidermal Growth Factor Receptor (EGFR) is critical for steroidogenesis in all three major steroid-producing tissues. We have recently characterized the intracellular signals regulating Luteinizing Hormone (LH) -induced steroid production in Leydig cells, demonstrating a linear pathway whereby LH receptor activation stimulates cAMP production and PKA signaling. Protein Kinase A (PKA) signaling then triggers EGF receptor activation, which activates the Mitogen Activated Protein Kinase (MAPK) cascade to promote steroidogenic acute regulatory (StAR) phosphorylation and translocation to the mitochondria. Interesting, PKA-mediated transactivation of the EGF receptor occurs via both intracellular, ligand-independent signaling, as well as extracellular, ligand-dependent activation that requires Matrix Metalloproteinase (MMP)-mediated release of membrane-bound EGF receptor ligands. However, only intracellular signaling is required for LH-induced steroid production. Furthermore, the LH-EGFR pathway appears to be important only for early steroidogenesis in Leydig cells, as LHinduced steroidogenesis beyond 60 minutes no longer requires EGFR or MAPK signaling. Here we characterize the LH-induced signals that regulate steroidogenesis in the ovary. We demonstrate that, similar to Leydig cells, activation of the EGF receptor is important for gonadotropin-induced steroid production in the ovary. Trans-activation of the EGFR is mediated by an increase of cAMP and PKA signaling. However, steroidogenesis in the ovary is dependent on an extracellular ligandindependent mechanism, as MMPs were shown to be crucial for the cleavage and activation of membrane bound EGFR upon LH stimulation. EGFR signaling was shown to activate the MAPK cascade and lead to subsequent phosphorylation of the steroidogenic acute regulatory protein (StAR). Interestingly, EGFR and MAPK signaling, unlike that in Leydig cells, as necessary for short and long term gonadotropininduced steroid production in the ovary. In vivo studies further demonstrate the importance of EGFR signaling since serum progesterone levels were significantly reduced when EGFR was inhibited. These findings demonstrate physiologic importance and potential treatment options since women with endocrine disorder such as PCOS can be treated with EGFR antagonist to reduce excess steroid production in the ovary.