Date Thesis Awarded

5-2017

Document Type

Honors Thesis

Degree Name

Bachelors of Science (BS)

Department

Neuroscience

Advisor

Matthew Wawersik

Committee Member

Cheryl Dickter

Committee Member

Margaret Saha

Abstract

Stem cells are vital for organogenesis, tissue regeneration, and tissue homeostasis. These cells reside within a stem cell niche, where they divide to provide the functional cell types necessary for organ function while also retaining a stem cell population. Given the critical role of stem cells in tissue maintenance, it is important to understand how these cells first form. To better understand the mechanisms regulating stem cell development, we are examining testis stem cell niche formation in Drosophila melanogaster. In adult testes, the stem cell niche is comprised of a tightly clustered group of hub cells that act as a signaling center to regulate sperm-producing germline stem cells (GSCs) as well as somatic cyst stem cells (CySCs). One signaling pathway that has been shown to regulate GSC maintenance in the larval and adult gonads is the evolutionarily conserved Bone Morphogenetic Protein (BMP) signaling pathway (Leatherman and DiNardo, 2010; see also Chang et al, 2013). In this thesis, we explore the functional significance of BMP activation during late embryonic and larval stages of testis development. Specifically, we characterize the activation pattern of BMP in the testis during stem cell niche formation, provide supporting evidence for the role of BMP signaling in the maintenance of GSCs in larval testis after testis stem cell niche formation, assess the role of BMP activation prior to stem cell niche formation, and examine the role of BMP signaling in developing cyst cells produced by CySCs. We find that BMP signaling shows a dynamic activation pattern in developing germ cells prior to and during testis stem cell niche formation. Additionally, we find that the BMP signaling pathway is necessary and sufficient for GSC maintenance after stem cell niche formation and that it functions to repress premature spermatogenic differentiation prior to stem cell niche formation. Our results support the current model of BMP signaling from CySCs to promote GSC maintenance; demonstrating the importance of soma-germline communication in proper spermatogonial differentiation. Furthermore, our data suggests the existence of a novel population of somatic gonadal precursor (SGPs) cells at the testis posterior that regulate PGC behavior during the process of niche formation. As GSCs are required for continuous gamete production in the adult, these studies have implications for organogenesis, fertility, and cancer.

Comments

Please italicize the word Drosophila in the title of the thesis.

Available for download on Saturday, May 07, 2022

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