Loss of stem cell self-renewal results in failure to maintain organs and can lead to degenerative disorders. In contrast, loss of differentiation can lead to cancers. Thus, the ability to prevent premature differentiation in degenerative diseases, or to induce differentiation in case of cancer, will have tremendous therapeutic impact. Our long-term goal is to determine key regulatory pathways that control the transition from stem cell self-renewal to differentiation, using Drosophila germline stem cells (GSCs) as a model system. The germ cells are the ultimate stem cells as they are both totipotent as well as immortal. Thus, paradigms established in the germ line can be extended to other stem cell systems. Drosophila is a superior model system to study questions about stem cell self-renewal and differentiation because of the availability of mutants, markers, RNAi technology and targeted expression methods. In Drosophila embryogenesis, the conserved process of global transcriptional silencing, mediated by the gene polar granule component (pgc), plays a pivotal role in germ cell specification. In absence of pgc, germ cells show precocious transcription that result in the transcription of somatic genes leading to their death. During oogenesis, an oocyte fate is being specified from a GSC fate during the process of differentiation. We have discovered that during oogenesis, Pgc is transiently expressed in the differentiating daughter of the GSC and loss of pgc results in differentiation defects. We propose that during oogenesis, Pgc mediated transcriptional silencing acts to suppress the response to self-renewal signaling from the surrounding niche cells and promotes differentiation in the GSC daughter. To test this hypothesis we will (1) Determine how the transcriptional silencer, Pgc, promotes GSC differentiation;(2) Identify Pgc targets and the mechanism of action during GSC differentiation;(3) Investigate how pgc is regulated during oogenesis. Our work will establish a role for transient transcriptional silencing in reprogramming stem cell fate by demonstrating that Pgc in the GSC daughter is expressed in a cell cycle dependent manner and determining a requirement for Pgc to promote efficient differentiation. We favor the idea that transcriptional silencing is needed to """"""""clear"""""""" residual stem cell factors, thereby reprogramming the GSC daughter prior to differentiation. Based on findings from this application, we posit that transcriptional silencing could be a potent target for increasing efficiency in deriving stem cells and also as a target in cancer treatment.

Public Health Relevance

The goal of this proposal is to determine how stem cells control their differentiation using the Drosophila germline stem cells as a model system. Loss of stem cell regulation can result in both degenerative diseases and cancer. The research proposed here will allow us to intervene in the correct cell type and block specific targets to promote or block differentiation for treating both cancers and degenerative diseases.

National Institute of Health (NIH)
National Institute of General Medical Sciences (NIGMS)
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Development - 2 Study Section (DEV2)
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Haynes, Susan R
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State University of New York at Albany
Schools of Arts and Sciences
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Upadhyay, Maitreyi; Kuna, Michael; Tudor, Sara et al. (2018) A switch in the mode of Wnt signaling orchestrates the formation of germline stem cell differentiation niche in Drosophila. PLoS Genet 14:e1007154
Flora, Pooja; Schowalter, Sean; Wong-Deyrup, SiuWah et al. (2018) Transient transcriptional silencing alters the cell cycle to promote germline stem cell differentiation in Drosophila. Dev Biol 434:84-95
McCarthy, Alicia; Deiulio, Aron; Martin, Elliot Todd et al. (2018) Tip60 complex promotes expression of a differentiation factor to regulate germline differentiation in female Drosophila. Mol Biol Cell 29:2933-2945
Flora, Pooja; McCarthy, Alicia; Upadhyay, Maitreyi et al. (2017) Role of Chromatin Modifications in Drosophila Germline Stem Cell Differentiation. Results Probl Cell Differ 59:1-30
Navarro-Costa, Paulo; McCarthy, Alicia; PrudĂȘncio, Pedro et al. (2016) Early programming of the oocyte epigenome temporally controls late prophase I transcription and chromatin remodelling. Nat Commun 7:12331
Upadhyay, Maitreyi; Martino Cortez, Yesenia; Wong-Deyrup, SiuWah et al. (2016) Transposon Dysregulation Modulates dWnt4 Signaling to Control Germline Stem Cell Differentiation in Drosophila. PLoS Genet 12:e1005918